Description:FIELD OF THE INVENTION

The present disclosure resides in the field of cryogenic systems and material analysis, specifically focusing on advancements in the measurement of matrix conductivity ratio and conduction degradation factor within regenerator matrix materials. This innovation finds application in experimental setups designed for cryogenic testing, utilizing a combination of pressure supply, stabilization, and cryogenic cooling mechanisms, along with sophisticated data acquisition systems. The field encompasses the exploration and enhancement of material performance at extremely low temperatures, catering to diverse applications such as cryogenic engineering, superconductivity research, and the development of efficient cooling technologies. The apparatus is tailored to investigate the thermal and electrical characteristics of regenerator matrix materials under cryogenic conditions, providing valuable insights for the optimization of materials in cryogenic applications and the advancement of related scientific and technological domains.

BACKGROUND OF THE INVENTION

Cryocoolers, compact cryogenic refrigerators crucial for achieving temperatures below 123 K, serve diverse applications in industrial, military, space, and medical fields. Categorized as regenerative and recuperative, regenerative cryocoolers, including Stirling, Gifford-McMahon (GM), Vullieumer, and pulse tubes, are structurally simple and widely employed. The regenerator, a hollow tube of SS304 in pulse tube cryocoolers and Hylam/Micarta in GM/Stirling cryocoolers, filled with materials like SS meshes, phosphor bronze, or lead spheres, enhances heat transfer.
However, challenges arise below 30 K due to helium's unique behavior, prompting the development of rare-earth magnetic materials as temporary heat storage for cryogenic regenerators. This invention addresses the need for enhanced efficiency in cryocooler design, particularly for high-frequency miniature space cryocoolers. The trend towards miniaturization necessitates additional considerations for regenerator design, crucial for applications like cooling IR sensors and satellites.
In one prior art solution, the researcher developed experimental setups (both steady state test rig and dynamic testing test rig) and evaluated the heat transfer and flow characteristics of regenerator meshes consisting of SS and phosphor bronze.
In another prior art solution, the researcher developed an experimental apparatus to measure the performance of a regenerator in the temperature range of 298 to 40 K. However, the reasearcher tested the effectiveness of the regenerator between 298 to 80 K (using liquid nitrogen) and 80 to 20 K (using liquid hydrogen). Additionally, the researcher developed an experimental test rig to measure the longitudinal conduction of a matrix subjected to different filling pressures.
In one prior art solution, the researcher developed an experimental test rig to measure the conduction degradation factor of regenerator screen meshes and spheres of SS, lead, and copper at different filling pressures.
International space agencies, including NASA, ESA, and ISRO, are actively pursuing high-frequency miniature cryocoolers. ISRO collaborates with the Centre for Cryogenic Technology at the Indian Institute of Science, Bangalore, to develop micro-cryocoolers. In this context, the invention introduces a novel apparatus designed to evaluate matrix conductivity ratio and conduction degradation factor at varying temperatures. The apparatus accommodates both dry and wet cryogenic cooling mediums, employing cryocoolers and cryogenic liquids like LN2 and LHe. The versatility of the apparatus, whether dry or wet, caters to laboratory space, funding, and resource availability, providing a comprehensive solution for advanced cryogenic testing.
In view of the foregoing discussion, it is portrayed that there is a need to have an apparatus for the measurement of matrix conductivity ratio and conduction degradation factor of regenerator matrix materials in cryogenic temperature limits.

SUMMARY OF THE INVENTION

The present disclosure seeks to provide an apparatus for the measurement of the matrix conductivity ratio and conduction degradation factor of regenerator matrix materials in cryogenic temperature limits. The apparatus has been designed to evaluate the matrix conductivity ratio and conduction degradation factor of regenerator meshes at different levels of temperature. The normal architecture of the apparatus adopts both dry and wet approaches to provide cryogenic cooling. In a dry cryogenic cooling medium, a cryocooler (a two-stage GM cryocooler, a single-stage GM cryocooler, and a single-stage GM cryocooler is adopted with a heat pipe) generates the cooling temperature that is required to be maintained while conducting experiments. This is also noted that pulse tube, Stirling and Vullieumer cryocoolers can be used in place of GM cryocoolers to maintain the temperature of the cold end of matrix housing. In the wet cryogenic cooling medium, LN2 and LHe are used to maintain the temperature of the cold end of matrix housing down to 77 K and 4.2 K respectively. Thus, depending upon the dry cryogenic cooling medium or wet cryogenic cooling medium, the apparatus may be called a dry cryogenic testing apparatus and a wet cryogenic testing apparatus respectively. The use of any apparatus (either dry or wet type) depends on the availability of laboratory space, funding, availability of LN2, LHe, cryocoolers, etc. Because of the availability of excellent facilities, both types of testing apparatus are focused.

In an embodiment, an apparatus for the measurement of the matrix conductivity ratio and conduction degradation factor of regenerator matrix materials in cryogenic temperature limits is disclosed. The system includes a. a pressure supply unit configured with a high-pressure pure gas cylinder, a flow meter, a needle valve, and a cut-off valve, adapted to supply pure gases, including helium and nitrogen.
The system further includes a pressure stabilization unit comprising a buffer tank, a pressure regulator for controlling the release of helium gas from the cylinder, a sample holder connector, a pressure gauge, and a relief valve, wherein the pressure stabilization unit stabilizes pressure throughout a sample holder and a regenerator matrix housing to enable testing at different charging pressures.
The system further includes a regenerator matrix sample holder comprising a long tube connected to a regenerator matrix housing, the matrix housing containing matrix material such as screen meshes, spheres, and rare-earth magnetic materials, wherein the regenerator matrix sample holder is connected to the pressure stabilization unit and a vacuum pumping system for pre-experiment evacuation.
The system further includes a cryogenic cooling unit for providing cooling effects to one end of the regenerator matrix, the cooling unit being a cryocooler or a cryogenic fluid, wherein the cryogenic cooling unit creates a temperature gradient inside the matrix to facilitate the measurement of matrix conductivity ratio and conduction degradation factor, wherein the cryogenic cooling unit may be a GM cryocooler or any other cryocooler such as Stirling, Vullieumer, or pulse tube, wherein for cooling below 77 K and up to 20 K, hydrogen or liquid nitrogen is used, and for cooling from 80 to 4.2 K, liquid helium is preferred.
The system further includes a plurality of data acquisition systems for reading and storing measured values of temperature, resistance, and heat flow thereby computing the matrix conductivity ratio and conduction degradation factor by computing the measured values using a control unit.
The system further includes a controllable cold end temperature regulation system, wherein the cold end temperature is monitored using either the cryocooler or a suitable cryogenic fluid, and the apparatus is selectively designated as either a dry matrix conductivity testing apparatus or a wet matrix conductivity testing apparatus.

An object of the present disclosure is to serve as an experimental apparatus for evaluating the matrix conductivity ratio and conduction degradation factor of various regenerator materials. This assessment spans the temperature range from ambient temperature to 4.2 K, addressing a diverse range of cryogenic applications.
Another object of the present disclosure is to incorporate an inbuilt programmable controller, empowering users to precisely control the high and low-temperature values. This feature facilitates the variation of temperatures at the hot and cold ends, allowing a comprehensive examination of their impacts on matrix conductivity ratio and conduction degradation factor.
Another object of the present disclosure is to evaluate the conduction degradation factor of meshes across different materials and filling pressures. This expands the scope of analysis, providing insights into the performance characteristics of regenerator components.
Another object of the present disclosure is to assess the thermal conductivity of materials and insulators. This feature enhances its utility by allowing users to study the broader thermal properties of substances under varying conditions.
Yet another object of the present invention is to deliver an expeditious and cost-effective apparatus for the measurement of the matrix conductivity ratio and conduction degradation factor of regenerator matrix materials in cryogenic temperature limits.

To further clarify the advantages and features of the present disclosure, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail in the accompanying drawings.

BRIEF DESCRIPTION OF FIGURES

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read concerning the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1 illustrates a block diagram of a generalized anatomy of the regenerator matrix conductivity ratio and conduction degradation factor test apparatus in accordance with an embodiment of the present disclosure;
Figure 2 illustrates a schematic of a two-stage cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for a single sample;
Figure 3 illustrates a schematic of a two-stage cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for multiple samples with a single buffer;
Figure 4 illustrates a schematic of a two-stage cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for multiple samples with multiple buffers;
Figure 5 illustrates a schematic of a single-stage cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for the single sample;
Figure 6 illustrates a schematic of a single-stage cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for multiple samples with the single buffer;
Figure 7 illustrates a schematic of a single-stage cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for multiple samples with multiple buffers;
Figure 8 illustrates a schematic of a single-stage cryocooler and heat pipe-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for the single sample;
Figure 9 illustrates a schematic of a single-stage cryocooler and heat pipe-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for multiple samples with the single buffer;
Figure 10 illustrates a schematic of a single-stage cryocooler and heat pipe-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for multiple samples with multiple buffers;
Figure 11 illustrates a schematic of a liquid nitrogen-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus;
Figure 12 illustrates a schematic of a liquid helium-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus (immersion cooling);
Figure 13 illustrates a schematic of a liquid helium-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus (spray cooling);
Figure 14 illustrates a schematic of a two-stage twin cold finger GM cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus;
Figure 15 illustrates a schematic of a single-stage twin cold finger GM cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus;
Figure 16 illustrates a schematic of a single-stage twin cold finger GM cryocooler and heat pipe-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus;
Figure 17 illustrates a schematic of a typical architectural model of a GM cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus: (a) Exterior view, (b) interior view;
Figure 18 illustrates a schematic of a typical architectural model of a sample holder and its connection with regenerator matrix housing;
Figure 19 illustrates a schematic of a typical architectural model of a twin cold finger GM cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor testing apparatus;
Figure 20 illustrates a schematic of a typical architectural model of a liquid nitrogen-cooled regenerator matrix conductivity ratio and conduction degradation factor test apparatus; and
Figure 21 illustrates a schematic of a typical architectural model of a liquid helium-cooled regenerator matrix conductivity ratio and conduction degradation factor test apparatus.

Further, skilled artisans will appreciate those elements in the drawings are illustrated for simplicity and may not have necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the present disclosure. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

DETAILED DESCRIPTION:

To promote an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.

Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase “in an embodiment”, “in another embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises...a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

Embodiments of the present disclosure will be described below in detail concerning the accompanying drawings.

Referring to Figure 1, a block diagram of a generalized anatomy of the regenerator matrix conductivity ratio and conduction degradation factor test apparatus is illustrated in accordance with an embodiment of the present disclosure. The system 100 includes a. a pressure supply unit (101) configured with a high-pressure pure gas cylinder, a flow meter, a needle valve, and a cut-off valve, adapted to supply pure gases, including helium and nitrogen.
In an embodiment, a pressure stabilization unit (102) comprising a buffer tank, a pressure regulator for controlling the release of helium gas from the cylinder, a sample holder connector, a pressure gauge, and a relief valve, wherein the pressure stabilization unit stabilizes pressure throughout a sample holder and a regenerator matrix housing to enable testing at different charging pressures.
In an embodiment, a regenerator matrix sample holder (103) comprising a long tube connected to a regenerator matrix housing, the matrix housing containing matrix material such as screen meshes, spheres, and rare-earth magnetic materials, wherein the regenerator matrix sample holder (103) is connected to the pressure stabilization unit and a vacuum pumping system for pre-experiment evacuation.
In an embodiment, a cryogenic cooling unit (104A/104B) is used for providing cooling effects to one end of the regenerator matrix, the cooling unit being a cryocooler or a cryogenic fluid, wherein the cryogenic cooling unit creates a temperature gradient inside the matrix to facilitate the measurement of matrix conductivity ratio and conduction degradation factor, wherein the cryogenic cooling unit may be a GM cryocooler or any other cryocooler such as Stirling, Vullieumer, or pulse tube, wherein for cooling below 77 K and up to 20 K, hydrogen or liquid nitrogen is used, and for cooling from 80 to 4.2 K, liquid helium is preferred.
In an embodiment, a plurality of data acquisition systems (105) for reading and storing measured values of temperature, resistance, and heat flow thereby computing the matrix conductivity ratio and conduction degradation factor by computing the measured values using a control unit.
In an embodiment, a controllable cold end temperature regulation system, wherein the cold end temperature is monitored using either the cryocooler or a suitable cryogenic fluid, and the apparatus is selectively designated as either a dry matrix conductivity testing apparatus or a wet matrix conductivity testing apparatus.

In another embodiment, the regenerator matrix sample holder is configured to accommodate different regenerator matrix materials, allowing testing of various matrix compositions, wherein the cryogenic cooling unit can be adjusted to provide cooling effects within specific temperature ranges, thereby accommodating different cryogenic testing requirements, wherein the pressure stabilization unit is designed to maintain pressure within the sample holder and regenerator matrix housing, enabling precise testing conditions and facilitating the measurement of matrix conductivity ratio and conduction degradation factor at different charging pressures, wherein the data acquisition systems include sensors for temperature, resistance, and heat flow measurements, ensuring accurate data collection for the calculation of matrix conductivity ratio and conduction degradation factor.

In another embodiment, the pure helium cylinder (1) is configured to supply pure helium gas, wherein the flow meter (3) is configured to measure the flow of helium gas, wherein the needle valve (4) is configured to control gas flow, wherein the cut-off valve (5) is configured to shut off the gas supply, wherein the buffer tank (6) is configured to stabilize gas pressure and is connected to the sample holder (7), wherein the sample holder (7), a long hollow tube connected at one end to the regenerator matrix housing (8) filled with meshes for evaluation, wherein the regenerator matrix housing (8) is equipped with temperature sensors and heating wires for temperature and heat load measurements, respectively.

In another embodiment, the system further comprises one or more PID controllers configured for setting and maintaining desired temperature limits, wherein the PID and temperature control arrangements at designated locations (24 and 25), wherein the PID controllers and temperature control arrangements allow precise control over the testing conditions, facilitating accurate measurements and evaluations.
In one embodiment, a vacuum pump (22) is connected to the sample holder through KF-25 clamp (23).
In one embodiment, a second-stage cold heat exchanger (9) is connected to one end of the regenerator matrix housing for providing the desired cooling effect, maintaining a temperature of 4.2 K or as required, wherein the regenerator matrix housing is configured to accommodate various regenerator matrix materials, enabling the evaluation of different matrix compositions.
In one embodiment, a radiation shield (18) inside the vacuum chamber is used to reduce radiation heat load, wherein the vacuum chamber is equipped with a radiation shield and multiple layers of MLI to enhance thermal insulation and reduce heat load during testing.
In one embodiment, one or more multiple layers of Multi-Layer Insulation (MLI) wound over the radiation shield.
In one embodiment, an additional dummy connector flange (21) is attached to the sample holder for suitable connections, wherein the additional dummy connector flange provides flexibility for connecting and integrating various components, enhancing the adaptability of the apparatus for different testing scenarios.

In another embodiment, the GM cryocooler comprising a room temperature portion (13) with valve and drive mechanisms, a first-stage cylinder (12), a first-stage heat exchanger (11), a second-stage cylinder (10), and a second-stage heat exchanger (9), wherein the room temperature portion (13) connected to a helium compressor (14) via flexible pipes for gas supply and recovery, wherein the helium compressor (14) cooled by water from a water chiller (15), wherein the cold end of the GM cryocooler is positioned inside a vacuum chamber (19) connected to a vacuum pump (20) through KF-25 clamp (23).

In another embodiment, the single sample holder (7) comprises a portion 7a connected with regenerator matrix housing 8a and a portion 7b connected with regenerator matrix housing 8b, wherein both regenerator matrix housings (8a and 8b) may have similar or dissimilar dimensions and may be filled with uniform materials or materials in different proportions, wherein the arrangement of connecting portions 7a and 7b to regenerator matrix housings 8a and 8b facilitates simultaneous testing of more than one combination of materials, allowing for accelerated testing approaches, wherein an extra material of high thermal conductivity, such as copper, is attached over the second-stage heat exchanger (9) to increase the heat transfer surface area for improved heat exchange between cryocooler tip (9) and individual regenerator housings (8a and 8b), wherein more than two regenerator matrix housings can be accommodated by branching the sample holder appropriately to enhance the rate of testing, provided that careful heat load calculations are carried out to determine the cooling capacity at the second stage of the cryocooler, wherein a cryocooler of matching capacity is selected to accelerate the testing process when more than two regenerator matrix housings are placed, ensuring efficient cooling and accurate evaluation of matrix conductivity ratio and conduction degradation factor for various combinations of materials.

In another embodiment, two different pressure stabilization units, i.e., buffer volumes (6a and 6b), and separate sample holders (7a and 7b) with regenerator matrix housings (8a and 8b) to simultaneously test two different configurations with distinct filling pressures, wherein the gas, after passing from helium cylinders (1) through (2), (3), (4), and (5), is divided into two streams, with one stream connected to buffer volume 6a and the other to buffer volume 6b, wherein buffer volume 6a is connected to sample holder 7a, regenerator matrix housing 8a, and vacuum pump 22a, and buffer volume 6b is connected to sample holder 7b, regenerator matrix housing 8b, and vacuum pump 22b, wherein the filling pressure values of buffer volumes 6a and 6b can be adjusted independently by valves 27a and 27b, respectively, allowing for testing multiple combinations of samples simultaneously with different filling pressures, wherein more than two sample holders and corresponding buffers can be arranged for testing multiple combinations of samples simultaneously, and the filling pressure for each sample holder can be varied independently according to the requirements for individual sample holders due to the presence of different buffer volumes and valves, wherein the simultaneous testing of different configurations with varied filling pressures accelerates the testing process, providing flexibility in evaluating matrix conductivity ratio and conduction degradation factor under diverse experimental conditions.

In another embodiment, a heat pipe (28) with a heat exchanger (29) as the cooling medium is used to cool the cold end of the regenerator matrix housing (8) attached to the sample holder (7), wherein the heat pipe (28) is attached to the first-stage heat exchanger (11) at one end and another heat exchanger (29) at the other end, with the heat exchanger (29) cooling one end of the regenerator matrix housing (8) and creating a temperature gradient during the testing of the matrix conductivity ratio and conduction degradation factor, wherein the gas from the helium cylinder (1) reaches the buffer (6) through the regulating valve (2), with buffer volume (6) attached to a relief valve (202) and a pressure gauge (203), wherein the gas flows from buffer volume (6) to the regenerator matrix housing (8) attached to the cold end of the sample holder (7), and the sample holder (7) is further connected to a vacuum pump (22) through a vacuum fitting KF-25 clamp (23).

In another embodiment, a PID controller is employed to maintain the temperature value (Tc) at the cold end, and heat load is provided by a heater to fix the temperature value of the hot end (Th), allowing for accurate estimation of matrix conductivity ratio and conduction degradation factor values, wherein the heat exchanger (29) is cooled from the first-stage heat exchanger (11) of the cryocooler through the heat pipe (28), and the cryocooler is a mechanical/pneumatic drive GM cryocooler generating a cooling effect through adiabatic expansion of the gas parcel, wherein the oscillating pressure wave is generated by the rotary valve and helium compressor (14), with the compressor being a scroll-type water-cooled helium compressor and the cooling water being provided from a water chiller (15), although the compressor may be of an air-cooling arrangement without limiting the scope of the invention.

In another embodiment, the buffer volume (6) is attached to a pressure gauge (203), a relief valve (202), and two connecting pipes, one connected to the gas cylinder and the other to the sample holder (7), wherein the gas from the buffer volume (6) flows to the sample holder (7), which is connected to the regenerator matrix housing (8) at its opposite end, wherein the sample holder (7) is further connected to a vacuum pump (22) via a KF-25 quick dismantled coupling (23), wherein the sample holder and regenerator matrix housing are placed inside a sample mounting vessel (32), and the cold end of the regenerator matrix touches a heat-conducting thermal mass (35) that is cooled by LN2, wherein the sample mounting vessel (32) has an opening (36) through which evacuation and purging occur before the start of experimental investigations, wherein the LN2 storage vessel comprises an outer Dewar (31) providing support to an inner Dewar (30), and the interspace between both outer Dewar (31) and inner Dewar (30) has high vacuum with Multi-Layer Insulation (MLI) layers to reduce heat load, wherein the inner Dewar (30) is connected with LN2 entry port (33), LN2 exit port (34), and also connected with a vacuum pump (20) via a clamp (23), wherein the thermal mass (35) is thermally connected with the regenerator matrix housing cold end and helps to maintain its cold end temperature (Tc), wherein a PID controller is attached between the thermal mass (35) and the cold end of the matrix housing (8) to set the cold end temperature (Tc), wherein another PID controller is applied to the opposite end of the matrix housing (8) to set the hot end temperature value (Th) at its desired value by applying the required heat load, wherein the matrix conductivity ratio and conduction degradation factor can be evaluated mathematically based on the value of the applied heat load.
In another embodiment, in the dry matrix conductivity testing apparatus, the cold end temperature is set to a desired value using a cryocooler, with specific applications including a single-stage cryocooler for 80 K, a 20 K cryocooler for single-stage and heat pipe applications, and a 4.2 K cryocooler for two-stage applications, in combination with a PID controller, wherein the cold end temperature is set to the desired value using a suitable cryogenic fluid, including liquid nitrogen (LN2) for temperatures of 80 K and above, and liquid helium (LHe) for temperatures of 4.2 K and above, wherein the cooling effect in the wet matrix conductivity testing apparatus can be achieved using any other cryogenic fluid, selected based on the boiling point of the cryogenic fluid, while recognizing the extensive use of liquid nitrogen and liquid helium in cryogenic testing due to their advantages over other cryogenic fluids.

In another embodiment, the wet-type testing apparatus for regenerator matrix conductivity, utilizing liquid nitrogen (LN2) as a cooling medium instead of a cryocooler, comprising a pure helium gas cylinder (1) to supply helium gas to a buffer volume (6) through a flow meter (3), needle valve (4), and cut-off valve (5), with the buffer volume equipped with a pressure gauge (203), relief valve (202), and two connecting pipes for gas supply to the sample holder and the gas cylinder.
In one embodiment, a sample holder (7) is connected to the regenerator matrix housing (8) at its opposite end, with gas flow facilitated by a vacuum pump (22) through a KF-25 quick dismantled coupling (23), wherein the sample holder and regenerator matrix housing placed within a sample mounting vessel (32), with the cold end of the regenerator matrix in contact with a heat-conducting thermal mass (35) cooled by LN2, wherein the sample mounting vessel having an opening (36) for evacuation and purging before experimental investigations, wherein the LN2 storage vessel features a double-container configuration comprising an outer Dewar (31) supporting an inner Dewar (30) storing LN2, with high vacuum and multiple layers of multi-layer insulation (MLI) in the interspace to reduce heat load, wherein the LN2 storage vessel further comprising an LN2 entry port (33) and LN2 exit port (34), with connections to a vacuum pump (20) via a clamp (23), enabling efficient cooling of the thermal mass (35) connected to the regenerator matrix housing cold end, wherein the PID controller is interposed between the thermal mass (35) and the cold end of the matrix housing (8) to regulate and set the cold end temperature (Tc).
Figure 1 illustrates the simple anatomy of a regenerator matrix conductivity test apparatus as per the objectives of the present invention. It consists of a pressure supply unit (101), a pressure stabilization unit (102), a regenerator matrix sample holder (which holds the regenerator matrix that need to be tested 103), a cryogenic cooling unit (104A/ 104B), and associated data acquisition systems (105). However, the anatomy described here is for one embodiment and can be modified for many other embodiments without affecting any change in overall architecture. The pressure supply unit consists of a high pressure pure gas cylinder (or an equivalent arrangement to produce pure gas, purify, and supply it), a regular, flow meter, a needle valve, and a cut-off valve. Since in most applications the testing will happen up to 4.2 K, and it is difficult to obtain such temperature with other gases, it will be always preferred to use helium gas. However, for testing using liquid nitrogen, pure nitrogen gas may be produced from compressed air by adopting suitable coalescing filters, adsorbers, membrane filters, water filters, oil filters, drains, etc. The pressure stabilization unit stabilizes the pressure up to certain mean value throughout the sample holder and regenerator matrix housing, which helps for the testing of matrix conductivity ratio and conduction degradation factor at different charging pressures. The pressure stabilization unit in the current apparatus consists of a buffer tank with four openings connected to the helium cylinder, a pressure regulator, a sample holder connector, a pressure gauge, and a relief valve. The regenerator sample holder consists of a long tube which at its one end is attached to regenerator matrix housing. The matrix housing contains the matrix material (screen meshes, spheres, rare-earth magnetic materials, etc.). The other end of the sample holder is connected with a pressure stabilization unit and a vacuum pumping system. The vacuum pumping system evacuates the system (buffer tank, sample holder, and matrix housing together) before the experiment. The cryogenic cooling unit provides the desired cooling effect to cool one end of the regenerator to create a temperature gradient inside the matrix. The cryogenic cooling unit may be a cryocooler or a cryogenic fluid. In the current invention, we have utilized GM cryocoolers; however, any other cryocooler e.g. Stilring, Vullieumer, or pulse tube can be used to create the cooling effect at one end of the sample holder. The choice of individual cooling medium depends upon several factors and the availability of desired facilities. Also, for cooling up to 77 K, it is preferred to use liquid nitrogen, which is comparatively less expensive. For cooling below 77 K and up to 20 K hydrogen can be used, but the use of hydrogen needs additional safety requirements, highly skilled technical personnel, etc. Thus, it is preferred to use liquid helium for 80 to 4.2 K applications. Data acquisition systems read and store the measured values of temperature, resistance and heat flow, and the values are used to compute the matrix conductivity ratio and conduction degradation factor. The value of matrix conductivity ratio and thermal conduction degradation factor can be calculated based on the mathematical expressions available in references [Panda et al. (2022). Influence of gas axial conduction enhancement factor on the oscillating flow behavior of an inertance pulse tube cryocooler. Cryogenics, 122, 103437; Lewis, M. A., & Radebaugh, R. (2001). “Measurement of heat conduction through metal spheres”, Cryocoolers 11 (pp. 419-425). Boston, MA: Springer US]. Based on the aforementioned anatomy several configurations of regenerator matrix conductivity test apparatus (both dry and wet configurations) have been proposed and some of the important embodiments are mentioned below. It may be noted that the following does not reflect the limitations of the invention and can be extended to more using the anatomy disclosed earlier.

Figure 2 illustrates a schematic of a two-stage cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for a single sample. This consists of a pure helium cylinder 1 which supplies pure helium gas. The gas is allowed to pass to buffer volume 6 from the cylinder by opening pressure regulator 2 through flow mater 3, needle valve 4, and cut-off valve 5. The buffer stabilizes the pressure and is connected with the sample holder 7. The sample holder is a long hollow tube, which at its other end is connected with a regenerator matrix housing 8 that is filled with meshes, whose performance needs to be evaluated. The regenerator matrix housing is connected with temperature sensors and heating wires to measure the temperature, and heat load respectively. PID controllers are also opted to set the temperature in its desired limit. The sample holder is connected with vacuum pump 22 through KF-25 clamp 23. It may be noted that several KF-25 clamps have been used in all schematics of the current invention and all are designated by 23 for easy of illustration. One end of the regenerator matrix housing is connected with the second-stage cold heat exchanger 9 of the cryocooler, which provides the desired cooling effect to cool this end and maintain its temperature of 4.2 K (or its desired value upon requirement). The GM cryocooler provides the necessary cooling effect that is required to cool at one end of the regenerator matrix housing. The GM cryocooler consists of its room temperature portion 13 (which contains valve mechanism and drive mechanism), first-stage cylinder 12, first-stage heat exchanger 11, second-stage cylinder 10, and second-stage heat exchanger 9. The room temperature portion 13 is connected with helium compressor 14 by two flexible pipes. One pipe supplies gas to the cold end and the other recovers the gas from the cold end. Helium gas which behaves like a refrigerant is charged into the helium compressor through regulator 17 from ultra-pure helium cylinder 16. The helium compressor is cooled with water that is supplied from water chiller 15. The cold end of the GM cryocooler is kept inside the vacuum chamber 19, which is connected to vacuum pump 20201 through KF-25 clamp 23. Radiation shield 18 is provided inside the vacuum chamber to reduce the radiation heat load. Several layers of MLI are also wounded over the radiation shield. Additional dummy connector flange 21 is attached in sample holder for providing suitable connections. 24 and 25 are locations for PID and temperature control arrangements.

Figure 3 illustrates a schematic of a two-stage cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for multiple samples with a single buffer. This is similar to the apparatus disclosed in Figure 2, but sample holder 7 at its regenerator matrix housing end is branched into two pieces as indicated by 7a and 7b. The portion 7a of the sample holder is connected with regenerator matrix housing 8a and portion 7b is connected with regenerator matrix housing 8b. Both regenerator matrix housing may be of similar dimensions or may not be of similar dimensions, may be filled with uniform materials, and may be filled with materials in some different proportions. This arrangement is only to accelerate the testing approach, thus, more than one combination of materials can be tested simultaneously. An extra material of high thermal conductivity like copper may be attached over the second-stage heat exchanger 9 to increase the heat transfer surface area for better heat exchange between cryocooler tip 9 and individual regenerator housings i.e. 8a and 8b. This can also be stated that more than two such regenerator matrix housings can be placed by branching the sample holder appropriately to enhance the rate of testing. However, careful heat load calculation needs to be carried out to determine the cooling capacity at the second stage of the cryocooler and a cryocooler of matching capacity can be selected to accelerate the testing process.

Figure 4 illustrates a schematic of a two-stage cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for multiple samples with multiple buffers. Figure 4 shows structurally similar to Figure 2 but contains two different pressure stabilization units (i.e., buffer volumes 6a and 6b) and separate sample holders including regenerator matrix housings to test two different configurations at the same time with different filing pressures. The gas after passing from helium cylinders 1 through 2, 3, 4, and 5 divided into two streams. One stream is connected with buffer 6a and the other stream is connected with buffer 6b. Buffer 6a is connected with sample holder 7a, regenerator matrix housing 8a, and vacuum pump 22a. Whereas, buffer 6b is connected with sample holder 7b, regenerator matrix housing 8b, and vacuum pump 22b. Therefore, more than one specimen can be tested simultaneously with different filling pressures to accelerate the testing process. The filling pressure values of buffer volumes 6a and 6b can be adjusted by valves 27a and 27b respectively. In this manner, more than two sample holders, and buffers can be arranged for testing multiple combinations of samples at the same time. The difference between the invention disclosed in Figure 4 and Figure 3 involves the filling pressure. In Figure 3 filling pressure is fixed for both sample holders and regenerator matrix housings, on the other hand, it can be varied in this apparatus according to requirements for individual sample holders because of different buffer volumes and valves.

Figure 5 illustrates a schematic of a single-stage cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for the single sample. Figure 5 shows structurally similar to Figure 2, but a difference arises in cryogenic cooling requirements. Here, a single-stage GM cryocooler provides the desired cooling effect to cool the cold end of the regenerator matrix housing attached to the sample holder. Therefore, in this apparatus, it may not be possible to test the properties up to 4.2 K, but with this arrangement, it is possible to test in the range of 30 K to 50 K or more than this cold end temperature. The single-stage GM cryocooler is either a mechanical drive arrangement or a pneumatic drive arrangement.

Figure 6 illustrates a schematic of a single-stage cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for multiple samples with the single buffer. Figure 6 shows similar to Figure 3 and Figure 5. In this arrangement, a single-stage GM cryocooler provides the necessary cooling effect for cooling two sample holders (connected with individual regenerator matrix housings 8a and 8b) at a fixed filling pressure for both sample holders 7a and 7b. As, the cryocooler is a single-stage configuration, it is possible to test in the range of 30 K to 50 K or more than this cold end temperature. On the other hand, the apparatus shown in Figure 5 is also capable of testing from 30 K to 50 K cold end temperature by enhancing the heating load through the PID controller connected at the cold end plate with a cryocooler tip.

Figure 7 illustrates a schematic of a single-stage cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for multiple samples with multiple buffers. Figure 7 shows structurally similar to that disclosed in Figure 4, but here, a single-stage GM cryocooler is used to provide the desired cooling effect. In a similar manner, single-stage Stirling, pulse tube cryocoolers can also be used in place of single-stage GM cryocoolers to provide the desired cooling effect.

Figure 8 illustrates a schematic of a single-stage cryocooler and heat pipe-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for the single sample. Figure 8 shows structurally similar to the apparatus disclosed in Figure 2, but it contains a single-stage GM cryocooler and a heat pipe (28) with a heat exchanger (29) as the cooling medium to cool the cold end of the regenerator matrix housing 8 attaches with the sample holder 7. Heat pipe 28 is attached with the first-stage heat exchanger 11 at its one end and another heat exchanger 29 at its other end. The heat exchanger 29 cools one end of the regenerator matrix housing 8 and the other end of the regenerator matrix housing 8 is heated to create a temperature gradient while testing the matrix conductivity ratio and conduction degradation factor. The gas reaches buffer 6 from the helium cylinder 1 through 3, 4, and 5 after the opening of regulating valve 2. Buffer volume 6 is attached with a relief valve 202 and a pressure gauge 203. From buffer volume 6, the gas flows to the regenerator matrix housing 8, which is attached to the cold end of the sample holder 7. The sample holder 7 is further attached with vacuum pump 22 through vacuum fitting KF-25 clamp 23. The regenerator matrix housing 8 is located at the cold end of the sample holder, and its one end is cooled by attaching it to heat exchanger 29. A PID controller is used to maintain the temperature value Tc at the cold end and heat load is provided by the heater to fix the temperature value of the hot end (Th). Based on this, the matrix conductivity ratio and conduction degradation factor values can be estimated. The heat exchanger 29 gets cooled from the first-stage heat exchanger 11 of the cryocooler through heat pipe 28. The cryocooler is a mechanical / pneumatic drive GM cryocooler that generates a cooling effect by adiabatic expansion of the gas parcel through a mechanical expander inside the first-stage cylinder of cryocooler 12. The oscillating pressure wave is generated by the rotary valve and helium compressor 14. The compressor is a scroll-type water-cooled helium compressor and the cooling water is provided from water chiller 15. The compressor may be of air-cooling arrangement and this does not limit the scope of the invention.

Figure 9 illustrates a schematic of a single-stage cryocooler and heat pipe-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for multiple samples with the single buffer. Figure 9 shows a modification of invention disclosed in Fig. 8. Here, two regenerator matrix housings (8a and 8b) are attached with two branched ends (7a and 7b) of a common sample holder with a common pressure stabilization unit 6. Therefore, this configuration is capable of testing more possible combinations of samples by utilizing the same cooling power. A thermal anchor plate 26 is attached in between the heat exchanger 29 and the cold end of the regenerator matrix housing 8a and 8b to enhance the heat exchange area. The cold end of the cryocooler, heat pipe, heat exchanger, sample holder cold end, etc. are placed inside the vacuum chamber 19, and the vacuum pump 20 continuously generates a vacuum during its operation. The radiation shield 18 reduces the radiation heat load.

Figure 10 illustrates a schematic of a single-stage cryocooler and heat pipe-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus for multiple samples with multiple buffers. Figure 10 shows cooling effect is generated by a combination of a single-stage cryocooler, heat pipe, and heat exchanger to cool the cold end of the regenerator matrix housing. Two different matrix housings 8a and 8b are placed over the thermal anchoring plate with different filling pressures to measure the matrix conductivity ratio and conduction degradation factor at the same time. This will allow rapid testing of samples at the same time. The remaining cooling mechanism and gas flow mechanisms with the pressure stabilization unit are similar to those of Figure 4 and Figure 8.

Figure 11 illustrates a schematic of a liquid nitrogen-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus. Figure 11 shows another embodiment of the matrix conductivity ratio testing apparatus using LN2 as a cooling fluid. This is a wet-type testing apparatus because LN2 is used in place of the cryocooler to generate the necessary cooling effect required to cool one end of the regenerator matrix housing to maintain cooling temperature (Tc). The construction and operation features of this regenerator matrix conductivity testing apparatus are discussed as follows. Pure helium gas cylinder 1 will supply helium gas to buffer volume 6 via flow meter 3, needle valve 4, and cut-off valve 5 after opening regulator 2. The buffer volume 6 is attached with a pressure gauge 203, relief valve 202, and two connecting pipes (one with the gas cylinder and the other with the sample holder). The gas from the buffer volume 6 flows to the sample holder 7, which is connected with the regenerator matrix housing 8 at its opposite end. The sample holder 7 is also connected with a vacuum pump 22 via the KF-25 quick dismantled coupling 23. The sample holder and regenerator matrix housing are placed inside the sample mounting vessel 32, and the cold end of the regenerator matrix touches the heat-conducting thermal mass 35, which gets cooled by LN2. The sample mounting vessel 35 further has an opening 36 through which evacuation and purging happen before the starting of experimental investigations. The LN2 storage vessel is of double container configuration as shown in Figure 11. Here, the outer Dewar 31 provides support to the inner Dewar, whereas, the inner Dewar 30 stores the cryogenic fluid (i.e. LN2). The interspace between both outer Dewar 31 and inner Dewar 30 has high vacuum with MLI layers to reduce heat load. The inner Dewar is also connected with LN2 entry port 33, LN2 exit port 34, and also connected with vacuum pump 20 via clamp 23. When LN2 is filled inside the inner Dewar 30 of the LN2 storage vessel, the thermal mass 35 gets cooled. This thermal mass 35 is thermally connected with the regenerator matrix housing cold end and helps to maintain its cold end temperature (Tc). PID controller is attached in between thermal mass 35 and cold end of matrix housing 8 and this sets the cold end temperature (Tc). The hot end temperature value (Th) at the opposite end of the matrix housing (i.e., at the hot end) has been set to its desired value by another PID controller by applying required heat load. By using the value of this heat load, the matrix conductivity ratio and conduction degradation factor can be evaluated mathematically.

Figure 12 illustrates a schematic of a liquid helium-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus (immersion cooling). Figure 12 shows regenerator matrix conductivity testing apparatus using liquid helium (LHe) as a cooling fluid. The major disadvantage of the invention disclosed in Figure 11 is that it is not capable of maintaining a temperature below 77 K, which is the boiling point of LN2. On the other hand, the present apparatus uses LHe as the cooling fluid, hence the cold end temperature (Tc) can attain a temperature value from room temperature to 4.2 K. Additionally; the apparatus is capable of attaining a temperature below 4.2 K by continuous evacuation and pumping on LHe. More details on this feature are not disclosed here, but are within the scope of this invention. Figure 12 shows only one embodiment of a helium storage container, which adopts a detachable tail extension, however, any type of LHe cryostat can be utilized for storage of LHe to generate the desired cooling effect necessary for the cooling of thermal mass 35. Helium cylinder 1 stores pure helium gas at high pressure and gas flows from the helium cylinder to the pressure stabilization unit (which is buffer 6) through flow meter 3, needle valve 4, cut-off valve 5 by adjusting the opening of regulator 2. Gas flows to the sample holder 7 from buffer 6 and then to the regenerator matrix housing 8, which is attached at the cold end of the sample holder 7. The regenerator materials that need to be tested are placed inside the regenerator matrix housing 8. The warm end of the sample holder is also connected to an evacuation line and a vacuum pump 22 by clamp 23. An additional safety precaution is also provided in the sample holder to measure the value of charging pressure and a relief valve for the release of gas. One end of the regenerator matrix housing is connected with thermal mass 35 for cooling up to the cooling temperature (Tc) and a PID controller maintain the value of Tc constant throughout the experiment. On the other hand, at the opposite end of the regenerator matrix housing 8, sensor and PID controller are provided. The sensor displays the temperature, and heat load is provided to increase the value of temperature to the desired value of hot temperature (Th). From the heat load value, the matrix conductivity ratio and conduction degradation factor have been computed by using mathematical expressions. Here, cooling to the thermal mass 35 has been provided by LHe. The cryostat consists of an external vacuum chamber 37, which further contains nitrogen storage container 38, and the interspace between 37 and 38 is maintain high vacuum with MLI and radiation shields. The external vacuum chamber 37 is connected with vacuum pump 47 via vacuum clamp 23. The nitrogen container 38 is connected with two lines, 42 for the supply of LN2 and 43 for the vent of GN2 (nitrogen gas) as shown in the figure. Before the supply of LN2, the LN2 chamber is evacuated with a vacuum pump. Another vacuum space is made interior to the LN2 chamber, and the interspace between 39 and 40 is thermally insulated with MLI and radiation shield. A vacuum pump 46 is connected through clamp 23. Vacuum pump 22 is also connected with 41 for evacuation and duration of evacuation is controlled by a ball valve, which is not shown in the figure. Interior to the vacuum enclosure 39, the liquid helium chamber 40 is placed, which contains LHe filling line 44 and LHe recovery line 45 (sum of boil-off gas comes from LHe storage chamber 40 and sample tube 41). The recovery line should be connected to the LHe gas storage system, so that the liquid helium that cools the sample will be boiled off, and helium gas will be collected. The collected/recovered gas is further liquefied and used. Inside the helium Dewar, the sample mounting chamber 41 is placed, which is isolated from the helium container by suitable means. The sample holder containing the regenerator matrix housing is kept inside the regenerator sample mounting vessel 41. In this embodiment, the tail of the helium storage container 40 has been extended in its bottom. It may be noted that this is not the limitation of the current invention as this extension can be removed. In extension, the section 37, 39, and 40 has been extended. Thus, LHe flows and touches the sample mounting vessel 41 and cools the thermal mass 35. A PID controller maintains the desired temperature value Tc in between the thermal mass 35 and the regenerator matrix housing 8 at its bottom end (i.e. cold end). The calculation process is similar to that discussed above.

Figure 13 illustrates a schematic of a liquid helium-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus (spray cooling). Figure 13 shows another embodiment of the current invention, in which LHe is used to cool the thermal mass 35. The construction features of the current cryostat are similar to that of Figure 12. The only difference lies in the mode of LHe cooling. Here, a capillary tube 48 is connected to the LHe Dewar 40, and the flow rate through the capillary tube is controlled by orifice valve 50 whose opening (kept outside of the cryostat at room temperature) can be controlled by the user through a long stainless steel stick. By adjusting the opening area of the orifice, controlled amount of LHe is allowed to flow through the capillary tube and helium is then allowed to vaporize through vaporizer/heat exchanger 49. This vapor of LHe is allowed to cool the thermal mass 35. The thermal mass 35 cools one end of the regenerator matrix housing 8 to temperature value Tc and its value is maintained by the PID controller. Whereas, the temperature value at the opposite end of regenerator matrix housing 8 will be fixed to Th by attaching a heater with suitable heat load. From the heat load value, the matrix conductivity ratio and conduction enhancement factor values can be calculated. The remaining process including the charging of gas to the regenerator matrix housing, maintaining its filling pressure is similar to that of earlier descriptions. An isolation membrane has been used between 41 and 40 to reduce the boil-off rate of LHe stored in chamber 40. Boil-off liquid helium from both 40 and 41 is transported to the central recovery lines by 45.

Figure 14 illustrates a schematic of a two-stage twin cold finger GM cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus. Figure 14 shows another embodiment of the current invention. In this invention, a two-stage twin cold finger GM cryocooler is used to generate the cooling effect that is required to cool the cold end of the regenerator matrix housing. The twin cold finger GM cryocooler consists of a common warm end portion 13 (which contains the drive mechanism and the pressure generation unit), a bottom cold finger, and a top cold finger. The bottom cold finger consists of a bottom first-stage cylinder 12b, bottom first-stage heat exchanger 11b, bottom second-stage cylinder 10b, and bottom second-stage heat exchanger 9b. The bottom first-stage cylinder and bottom second-stage cylinder contain the bottom-first-stage displacer and bottom second-stage displacer respectively. They undergo reciprocating motion within the respective cylinders to expand the gas to generate the cooling effect. The top cold finger also contains similar components such as the top first-stage cylinder 12t, top first-stage heat exchanger 11t, and top second-stage cylinder 10t, and top second-stage heat exchanger 9t. The top second-stage cylinder and top first-stage cylinder contain the top second-stage displacer and top first-stage displacer respectively. These displacers upon its motion inside the cylinders generate cooling effects inside the expansion chambers. A common helium compressor 14 provides the compressed gas to the twin cold-finger GM cryocooler and the compressor 14 is water cooled. The cooling water is circulated from water chiller 15. When the twin cold finger GM cryocooler is operated, a cooling effect is generated in the cold ends of both first and second-stage cold fingers. This cooling effect is used to cool the cold ends of the regenerator matrix housings. The gas supply unit is similar to that of earlier inventions. The gas supply unit consists of a helium cylinder 1, a regular 2, a flow meter 3, a needle valve 4, and a cut-off valve 5. As two cold fingers are present, the compressed gas can be supplied to two sample holders. After valve 5, a T-joint may be used to split the gas for two different sample holders, but here the gas from one buffer volume (i.e., 6t) is supplied to another buffer volume. The gas from cut-off valve 5 flows to buffer volume 6t, which is also connected with a relief valve 202, a pressure gauge 203, and two openings, one for the sample holder 7t and another opening for second buffer 6b. The gas flows from buffer 6t to sample holder 7t, which is further attached to the regenerator matrix housing 8t. In this manner, the filling pressure value of 8t can be maintained to its desired value. One end of 8t is connected with the top second-stage cold heat exchanger 9t to maintain the cold temperature. Here, a PID controller is used to set the temperature value Tc with a suitable heat load. At the hot end of 8t, a heater is placed to apply heat load to maintain the temperature value Th. From the heat load value, the matrix conductivity factor, and conduction degradation factor values can be calculated. A fraction of gas flows from 6t to 6b, and its flow rate can be adjusted by adjusting valve 51. Then from 6b, it flows to another sample holder 7b which is also attached with a regenerator matrix housing 8b. In the absence of valve 51, temperature values of both buffer 6t and 6b are uniform values, but with valve 51, it is possible to vary the pressure values of both buffers and it becomes possible to test at different filling pressure values. Gas flows from 6b to sample holder 7b and then to regenerator matrix housing 8b. The cold end temperature is set to Tc by connecting one end with the second-stage bottom heat exchanger 9b and applying heat load through the PID controller, whereas, the temperature Th can be controlled by connecting the other end with the heater and PID controller. From the heat load values, the matrix conductivity ratio and conduction degradation factor can be easily computed. The top sample holder 7t is connected with vacuum pump 22t via clamp 23, and the bottom sample holder 7b is connected with vacuum pump 22b via clamp 23 as shown in Figure 14. The bottom cold finger (consisting of 12b, 11b, 10b, 9b), bottom regenerator matrix housing 8b, and bottom sample holder cold end 7b are placed inside a vacuum chamber 19b which is connected to a vacuum pump 20b via KF 25 clamp 23. The radiation shield 18b is placed inside the bottom vacuum chamber 19b to reduce the radiation heat load. Similarly, the top cold finger (consisting of 12t, 11t, 10t, and 9t), top regenerator matrix housing 8t, and top sample holder cold end 7t are placed inside a vacuum chamber 19t which is connected with a vacuum pump 20t via clamp 23. The radiation shield 18t is placed inside the bottom vacuum chamber 19t to reduce the radiation heat load. The invention disclosed in Fig. 14 can be modified to use multiple regenerator matrix housings as disclosed in Figs. 3 and 4 by making branches to accelerate the testing phase, and details are not illustrated here.

Figure 15 illustrates a schematic of a single-stage twin cold finger GM cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus. Figure 15 is another embodiment of the current invention, which uses a single-stage twin cold finger GM cryocooler to provide the cooling effect to the regenerator matrix housing and sample holders. The constructional features and gas charging principles are similar to that of the invention disclosed in Figure 14, but as it is a single-stage twin cold finger GM cryocooler it does not contain the second-stage bottom cylinder, second-stage bottom heat exchanger, second-stage top cylinder, second-stage top heat exchanger. The cold end of the top and bottom regenerator matrix housing are directly in contact with the top first-stage heat exchanger and top second-stage heat exchanger to get the desired cooling temperature. The remaining procedures are similar to that of earlier descriptions. The cooling mechanism arrangements can be modified in this invention as discussed earlier in Figs. 6 and 7 to test more than one regenerator configurations simultaneously.

Figure 16 illustrates a schematic of a single-stage twin cold finger GM cryocooler and heat pipe-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus. Figure 16 is another embodiment of the present invention. This is similar to that of the invention disclosed in Figure 15, but it adopts heat pipes 28t and 28b at the first-stage cold heat exchangers 11t and 11b for both top and bottom cold fingers to transfer the cooling load. As a result of this, the temperature can decrease up to a certain extent, and at the end of both heat pipes, two additional heat exchangers 29t and 29b are attached to transfer the cooling load. The cold end of the regenerator matrix housings 8t and 8b are attached with heat exchangers 29t and 29b respectively to transfer the cooling load, and the PID controller is used to maintain the temperature Tc. On the opposite side, the PID controller and heater is used to maintain temperature Th. From these heating load values, the matrix conductivity ratio and conduction degradation factor values can be calculated.

Figure 17 illustrates a schematic of a typical architectural model of a GM cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor test apparatus: (a) Exterior view, (b) interior view. Figure 17 shows an architectural model of a single sample holder single cold finger GM cryocooler cooled regenerator matrix conductivity test rig. The helium compressor and water chiller parts of the cryocooler are omitted. Buffer volume 6 has four openings connected with helium charging cylinder 1 by pipe 201, relief valve 202, pressure gauge 203, and sample holder connector 204. The pipe that is connected with the sample holder is rigid and at its end, it is connected with a flexible pipe 205 thus, it can be easily connected and disconnected during experimental investigation. Figure 17 shows two images, one in the assembled view (17.a), and the interior view (17.b). Flexible pipe 205 is connected with sample holder 7 via T-flange 206 and a reducer 207. The T-joint flange on the other side is connected with another T-joint flange 208 and a straight tube, which is open for its connection with vacuum pump 22 (not shown in the image). The sample holder 7 is brazed with a number of radiation baffles (made up of copper) to reduce the radiation heat load. At the cold end of the sample holder regenerator matrix housing 8 is connected. An expanded architectural view of the sample holder is drawn in Fig. 18. The sample holder can easily be connected and disconnected from the test rig to accelerate the experimental phase. Figure 17 (i.e., Fig.17.b) second view shows the connection of the regenerator matrix housing with the second-stage cold heat exchanger of the cryocooler. The GM cryocooler is kept in the vertical direction, where the second stage heat exchanger 9 touches the cold end of 8 to provide the cooling effect. The room temperature end of cryocooler is connected with a helium compressor through hose pipes, which is not shown in the Figure. The helium compressor is further connected to the water chiller for efficient cooling, which is also not shown in the figure. A supporting table 209 is used to hold the cryocooler, buffer volume, and other accessories to make the apparatus robust and reliable.

Figure 18 illustrates a schematic of a typical architectural model of a sample holder and its connection with regenerator matrix housing.

Figure 19 illustrates a schematic of a typical architectural model of a twin cold finger GM cryocooler-based regenerator matrix conductivity ratio and conduction degradation factor testing apparatus. Figure 19 shows an architectural model of a twin cold finger GM cryocooler-operated regenerator matrix conductivity test rig. It contains two buffer volumes (6t and 6b), two vacuum chambers (19t and 19b), vacuum ports, pressure gauges, safety valves, sample holders (7t and 7b), twin cold finger GM cryocooler, and related supporting connections, couplings, etc. The constructional features of this apparatus are explained in Figure 14, but the architectural model does not contain a helium compressor and water chiller, and is of different in physical appearance. However, constructional features are almost similar. Also, here the gas needs to be supplied to both buffer volumes separately after cut-off valve 5 through T-joint flanges, as a five-opening approach has not been made in buffer volume 6t (as discussed in Figure 14). The apparatus is kept in a horizontal orientation to make it easier to use both cold fingers' cooling power during experimentation. Both top and bottom vacuum chambers are supported by some supporting structures 210 as shown in Fig. 19.

Figure 20 illustrates a schematic of a typical architectural model of a liquid nitrogen-cooled regenerator matrix conductivity ratio and conduction degradation factor test apparatus. Figure 20 illustrates the architectural model of an LN2-cooled cryostat-based wet-type regenerator matrix thermal conductivity testing apparatus. This apparatus contains buffer 6 (which acts like a pressure stabilization unit) with four openings that are connected to helium charging cylinder 1 by pipe 201, relief valve 202, pressure gauge 203, and sample holder connector 204. The sample holder connector consists of a rigid section 204 and a flexible section 205, thus, it can be easily assembled and disassembled while conducting experimental studies. The flexible section 205 is connected with reducer 207, T-joint flange 206, another T-joint flange 208 and a straight tube, which is open for its connection with a vacuum pump 22 (not shown in the image). The sample holder 7 is brazed with a number of radiation shields (made up of copper) to reduce the radiation heat load. At the cold end of the sample holder, regenerator matrix housing 8 is connected. The sample holder 7 and regenerator matrix holder are of similar configuration as illustrated in Fig. 18. The regenerator matrix housing 8 cold sides gets cooled by absorbing the cooling effect from the thermal mass 35 which is continuously cooled with LN2. The LN2 is supported with supporting table 209 through an extended flange 211 at its middle on the external periphery of the outer vacuum jacket. It contains an outer container and an inner LN2 storage tank, and the intermediate space between them maintained at high vacuum with MLI and radiation shields. At the top of the cryostat, an opening 212 is made for the charging of LN2, another opening 213 is made for venting of LN2/GN2, and another opening for feed-through 214 is made for measuring instruments. The LN2 is filled into the LN2 container through 212 and via 213 the boil-off gas is vented to the outside of the storage tank.

Figure 21 illustrates a schematic of a typical architectural model of a liquid helium-cooled regenerator matrix conductivity ratio and conduction degradation factor test apparatus. Figure 21 shows an architectural model of a LHe cooled wet type regenerator matrix conductivity testing apparatus. Its constructional features are almost identical to that discussed earlier in Figure 12. However, it does not adopt the extended tail structural features as it is not essential in our case. This apparatus contains buffer 6 with four openings that are connected with helium charging cylinder 1 by pipe 201, relief valve 202, pressure gauge 203, and sample holder connector 204. The sample holder connector consists of a rigid section 204 and a flexible section 205, thus, it can be easily assembled and disassembled while conducting experimental studies. The flexible pipe 205 is connected with T-joint flange 206 through reducer 207; another T-joint flange 208 is connected with 206 and a straight tube is joined with 208, which is open for its connection with a vacuum pump 22 (not shown in Figure 21). The sample holder 7 is brazed with a number of radiation shields (made up of copper) to reduce the radiation heat load. At the cold end of the sample holder, the regenerator matrix housing 8 is connected. The sample holder 7 and regenerator matrix holder 8 are of similar configuration as illustrated in Fig. 18. The liquid helium cryostat is of double-walled coaxial configuration. The outer vacuum jacket is attached with a supporting flange 211 so that it can be easily fitted with the supporting table 209. At the center of the cryostat, the regenerator sample mounting vessel and regenerator matrix housing are inserted into the cryostat. The regenerator matrix cold end touches the thermal mass 35 to get cooled. Liquid helium is kept within the liquid helium chamber that is connected with LHe charging line 215. Also, helium gas vent line 216 (not visible in the image) and provision for measuring the liquid level, temperature and vacuum level is incorporated in the helium chamber by 217 and 218. Liquid helium is charged into the helium Dewar by the helium charging line and the vent line is connected to the helium gas recovery system. LN2 is kept in an outer container in an annular Dewar so that heat loss can be reduced, and in between the LN2 Dewar and LHe Dewar, an MLI insulation and radiation shield insulation has been provided to reduce the radiation heat loss. The nitrogen Dewar is connected with an LN2 charging line 219 and a vent line 220 (not visible in the image). An opening 221 is provided for instrumentation. At the external periphery of LN2, and outer vacuum jacket, MLI and radiation shields have been provided to reduce radiation heat loss. Vacuum ports 222 and 223 have been provided for outer vacuum space and inner vacuum space respectively. The gas filling and other construction features are similar to those of discussed earlier.

• Development of an experimental apparatus for evaluation of the matrix conductivity ratio and conduction degradation factor of various regenerator materials in the temperature range from ambient temperature to 4.2 K.
• The high and low-temperature values of the apparatus can be controlled using an inbuilt programmable controller. Thus, users can vary the temperature at hot and cold end to check their influences on matrix conductivity ratio and conduction degradation factor.
• The cold end temperature of the apparatus can be monitored either by cryocooler or by suitable cryogenic fluid. Based on the mode of cryogenic cooling, the apparatus may be named as a dry matrix conductivity testing apparatus or wet matrix conductivity testing apparatus. In a dry matrix conductivity testing apparatus, the temperature of the cold end is fixed to the desired value by using a cryocooler (single-stage for 80 K application, 20 K for single-stage and heat pipe, and 4.2 K for two-stage application) and PID controller. In a wet matrix conductivity testing apparatus, the temperature of the cold end is fixed to the desired value by using suitable cryogenic fluid (LN2 for 80 K and above, LHe for 4.2 K and above). However, any other cryogenic fluid can be used to provide the cooling effect based on the boiling point of the cryogenic fluid, but liquid nitrogen and liquid helium are extensively used in cryogenic testing because of their merits over other cryogenic fluids.
• The apparatus is also capable of evaluating the conduction degradation factor of meshes for different materials and different filling pressures.
• The apparatus is also capable of evaluating the thermal conductivity of materials and insulators.

The current invention is related to the construction of an apparatus for testing of matrix conductivity ratio and conduction degradation factor for cryogenic regenerators. Regenerators are essential components of all regenerative cryocoolers, and these are used in a wide variety of space, military, medical, locomotive, and industrial applications.
• Stirling cryocoolers and Stirling pulse tube cryocoolers are used for the cooling of sensors in space satellites, cooling of IR sensors in fighter jets and missiles, and night vision cameras for tactical military applications.
• GM cryocoolers and GM-Type pulse tube cryocoolers are used in cooling superconducting magnets in MRI, NMR, SQUIDS, and construction of small-scale helium, hydrogen, nitrogen, neon liquefiers, etc.
• GM cryocoolers are also used in the cooling of superconducting magnets adopted in superconducting motors, superconducting generators, superconducting transformers, nuclear-powered submarines, magnets in MagLev vehicles, etc.
• The disclosed apparatus can also be used for the measurement of the thermal conductivity of materials from room temperature to cryogenic temperature range by removing the pressurization unit.
• The disclosed apparatus can also be used for the measurement of thermal conductivity of insulating materials for different pressures (vacuum pressure to higher pressure range) for cryogenic insulation applications for cryogenic transfer lines.

The apparatus design for evaluation of matrix conductivity ratio and conduction degradation factor, which consists of: a gas supply unit to supply pure gas; a pressure stabilization unit that stabilizes the filling pressure; a sample holder that is attached with regenerator matrix housing at its cold end and a cooling unit. The gas supply unit of the apparatus consists of a high pressure pure helium gas cylinder, a pressure regulator, a flow meter, a needle valve, a cut-off valve, and connecting pipes (both rigid and flex pipes). The pressure stabilization unit of the apparatus consists of a buffer volume, which can stabilize the pressure and is fitted with a relief valve and pressure gauge to display the pressure. The buffer also contains two openings, through which gas is communicated from the gas supply unit to the buffer and buffer to the sample holder. The connecting pipe that carries gas from the buffer to the sample holder consists of a rigid pipe and a flexible pipe. Thus, the flexible pipe can be easily connected and disconnected during experimental studies. The sample holder consists of a hollow pipe that is brazed with a series of radiation shields at its exterior surface to reduce the radiation heat loss. One end (may be called a warm end) of the sample holder is connected to a pressure stabilization unit and an evacuation line, whereas, the other end (may be called the cold end) is connected with the regenerator matrix housing. The regenerator matrix housing holds the regenerator materials that need to be tested, and the filling pressure value needs to be decided by the pressurization unit. The cold end of the regenerator matrix holder needs to be cooled to the desired cooling temperature Tc, and this value can be maintained by a PID controller. At the hot end of the regenerator matrix holder, a heat load is supplied to maintain the hot end temperature. From the heat load and temperature values, the matrix conductivity ratio and conduction degradation factor values can be calculated. The apparatus further contains several vacuum flanges, and KF-25 quick dismantled coupling, which facilitates the assemble and disassemble processes quicker to run the experiments. Pressure gauges, temperature sensors, flow meters, PID controllers, heating wires, and associated instrumentation facilities have been provided in the apparatus. A relief valve, needle valve, and cut-off valve are provided to maintain safety and regulate the flow rates of the gas. The cooling unit may be a single-stage GM cryocooler, two-stage GM cryocooler, single-stage GM cryocooler with heat pipe attached at its cold end; twin cold finger GM cryocooler, or cryostat containing cryogenic fluid (liquid nitrogen or liquid helium). If the cooling effect is provided by a cryocooler, then the apparatus may be called dry matrix conductivity test apparatus. However, if the cooling effect is provided by cryogenic fluid, then the apparatus may be called wet matrix conductivity test apparatus. Here, a GM cryocooler has been adopted for providing the cooling effect necessary to cool the cold end of the regenerator matrix housing, however, in place of GM cryocooler other cryocoolers like pulse tube cryocooler, Stirling cryocooler, Vullieumer cryocooler, JT cryocooler, Brayton cryocooler, etc. can be used to produce the desired cooling effect. This is not the limitation of the current invention. The sample holder may be branched into two small pieces by T-joints at its cooled end, thus two different regenerator matrix housings can be fitted simultaneously. This will permit the user to test more than one combination of samples simultaneously. A supporting thermal conducting plate needs to be placed in between the cold end of the cryocooler and two matrix housings to effectively transfer the cooling load to the cold end of the cryocooler. The apparatus can also be modified by using two pressurization units in place of a single pressurization unit; thus, more than one configuration can be tested simultaneously. In this manner, more than one pressurization units can be connected to make more than one sample simultaneously with different filling pressure. The GM cryocooler can be replaced by a twin cold-finger GM cryocooler, thus, more than one sample holder, pressurization units can be connected at the same time for testing more than one samples. This configuration can be modified using a single-stage twin cold finger GM cryocooler, single-stage twin cold finger GM cryocooler with heat pipe and heat exchangers, or two-stage twin cold finger GM cryocooler. The wet cooling regenerator test apparatus may use LN2 as a cooling medium to test the matrix conductivity up to the boiling point of liquid nitrogen (i.e., 77 K). Also, it may use other cryogenic fluids like neon, hydrogen, and helium for testing matrix conductivity up to 27.1 K, 20.3 K, and 4.2 K respectively. However, it is recommended to adopt liquid helium as it is an inert gas. Based on the choice of cryogenic fluid, the constructional features of the storage cryostat can be varied. For liquid nitrogen, the Dewar is of two Dewar configurations, LN2 will be kept in the inner Dewar, and the outer one will provide support. The interspace between both is filled with MLI and radiation shields with high vacuum. The liquid helium Dewar is of a four-channel configuration. Liquid helium is stored in the inner Dewar, liquid nitrogen is placed in an intermediate Dewar, in between LN2 and LHe is vacuum insulation, MLI materials is provided to reduce the heat loss. To the exterior of LN2 Dewar, another MLI and vacuum insulation is provided to reduce the heat loss. This arrangement is the most ideal arrangement to reduce the loss of helium. The helium Dewar contains opening for charging and venting, and liquid nitrogen Dewar contains openings for charging and venting.

The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

Benefits, other advantages, and solutions to problems have been described above about specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims. , Claims:
1. An apparatus for the measurement of matrix conductivity ratio and conduction degradation factor of regenerator matrix materials in cryogenic temperature limits, the apparatus comprises:

a. a pressure supply unit (101) configured with a high-pressure pure gas cylinder, a flow meter, a needle valve, and a cut-off valve, adapted to supply pure gases, including helium and nitrogen;
b. a pressure stabilization unit (102) comprising a buffer tank, a pressure regulator for controlling the release of helium gas from the cylinder, a sample holder connector, a pressure gauge, and a relief valve, wherein the pressure stabilization unit stabilizes pressure throughout a sample holder and a regenerator matrix housing to enable testing at different charging pressures;
c. a regenerator matrix sample holder (103) comprising a long tube connected to a regenerator matrix housing, said matrix housing containing matrix material such as screen meshes, spheres, and rare-earth magnetic materials, wherein the regenerator matrix sample holder (103) is connected to the pressure stabilization unit and a vacuum pumping system for pre-experiment evacuation;
d. a cryogenic cooling unit (104A/104B) for providing cooling effects to one end of the regenerator matrix, said cooling unit being a cryocooler or a cryogenic fluid, wherein the cryogenic cooling unit creates a temperature gradient inside the matrix to facilitate the measurement of matrix conductivity ratio and conduction degradation factor, wherein the cryogenic cooling unit may be a GM cryocooler or any other cryocooler such as Stirling, Vullieumer, or pulse tube, wherein for cooling below 77 K and up to 20 K, hydrogen or liquid nitrogen is used, and for cooling from 80 to 4.2 K, liquid helium is preferred;
e. a plurality of data acquisition systems (105) for reading and storing measured values of temperature, resistance, and heat flow thereby computing the matrix conductivity ratio and conduction degradation factor by computing said measured values using a control unit; and
f. a controllable cold end temperature regulation system, wherein the cold end temperature is monitored using either the cryocooler or a suitable cryogenic fluid, and the apparatus is selectively designated as either a dry matrix conductivity testing apparatus or a wet matrix conductivity testing apparatus.

2. The apparatus as claimed in claim 1, wherein the regenerator matrix sample holder is configured to accommodate different regenerator matrix materials, allowing testing of various matrix compositions, wherein the cryogenic cooling unit can be adjusted to provide cooling effects within specific temperature ranges, thereby accommodating different cryogenic testing requirements, wherein the pressure stabilization unit is designed to maintain pressure within the sample holder and regenerator matrix housing, enabling precise testing conditions and facilitating the measurement of matrix conductivity ratio and conduction degradation factor at different charging pressures, wherein the data acquisition systems include sensors for temperature, resistance, and heat flow measurements, ensuring accurate data collection for the calculation of matrix conductivity ratio and conduction degradation factor.

3. The apparatus as claimed in claim 1, wherein the pure helium cylinder (1) is configured to supply pure helium gas, and the flow meter (3) is configured to measure the flow of helium gas;
wherein the needle valve (4) is configured to control gas flow and the cut-off valve (5) is configured to shut off the gas supply;
wherein the buffer tank (6) is configured to stabilize gas pressure and is connected to the sample holder (7), wherein the sample holder (7), a long hollow tube connected at one end to the regenerator matrix housing (8) filled with meshes for evaluation; and
wherein the regenerator matrix housing (8) is equipped with temperature sensors and heating wires for temperature and heat load measurements, respectively.

4. The apparatus as claimed in claim 1, further comprises:
one or more PID controllers configured for setting and maintaining desired temperature limits, wherein the PID and temperature control arrangements at designated locations (24 and 25), wherein the PID controllers and temperature control arrangements allow precise control over the testing conditions, facilitating accurate measurements and evaluations;
a vacuum pump (22) connected to the sample holder through KF-25 clamp (23);
a second-stage cold heat exchanger (9) connected to one end of the regenerator matrix housing for providing the desired cooling effect, maintaining a temperature of 4.2 K or as required, wherein the regenerator matrix housing is configured to accommodate various regenerator matrix materials, enabling the evaluation of different matrix compositions;
a radiation shield (18) inside the vacuum chamber to reduce radiation heat load, wherein the vacuum chamber is equipped with a radiation shield and multiple layers of MLI to enhance thermal insulation and reduce heat load during testing;
one or more multiple layers of Multi-Layer Insulation (MLI) wound over the radiation shield; and
an additional dummy connector flange (21) attached to the sample holder for suitable connections, wherein the additional dummy connector flange provides flexibility for connecting and integrating various components, enhancing the adaptability of the apparatus for different testing scenarios.

5. The apparatus as claimed in claim 1, wherein the GM cryocooler comprising a room temperature portion (13) with valve and drive mechanisms, a first-stage cylinder (12), a first-stage heat exchanger (11), a second-stage cylinder (10), and a second-stage heat exchanger (9), wherein the room temperature portion (13) connected to a helium compressor (14) via flexible pipes for gas supply and recovery, wherein the helium compressor (14) cooled by water from a water chiller (15), wherein the cold end of the GM cryocooler is positioned inside a vacuum chamber (19) connected to a vacuum pump (20) through KF-25 clamp (23), wherein the single sample holder (7) comprises a portion 7a connected with regenerator matrix housing 8a and a portion 7b connected with regenerator matrix housing 8b, wherein both regenerator matrix housings (8a and 8b) may have similar or dissimilar dimensions and may be filled with uniform materials or materials in different proportions, wherein the arrangement of connecting portions 7a and 7b to regenerator matrix housings 8a and 8b facilitates simultaneous testing of more than one combination of materials, allowing for accelerated testing approaches, wherein an extra material of high thermal conductivity, such as copper, is attached over the second-stage heat exchanger (9) to increase the heat transfer surface area for improved heat exchange between cryocooler tip (9) and individual regenerator housings (8a and 8b), wherein more than two regenerator matrix housings can be accommodated by branching the sample holder appropriately to enhance the rate of testing, provided that careful heat load calculations are carried out to determine the cooling capacity at the second stage of the cryocooler, wherein a cryocooler of matching capacity is selected to accelerate the testing process when more than two regenerator matrix housings are placed, ensuring efficient cooling and accurate evaluation of matrix conductivity ratio and conduction degradation factor for various combinations of materials.

6. The apparatus as claimed in claim 1, further comprises two different pressure stabilization units, i.e., buffer volumes (6a and 6b), and separate sample holders (7a and 7b) with regenerator matrix housings (8a and 8b) to simultaneously test two different configurations with distinct filling pressures, wherein the gas, after passing from helium cylinders (1) through (2), (3), (4), and (5), is divided into two streams, with one stream connected to buffer volume 6a and the other to buffer volume 6b, wherein buffer volume 6a is connected to sample holder 7a, regenerator matrix housing 8a, and vacuum pump 22a, and buffer volume 6b is connected to sample holder 7b, regenerator matrix housing 8b, and vacuum pump 22b, wherein the filling pressure values of buffer volumes 6a and 6b can be adjusted independently by valves 27a and 27b, respectively, allowing for testing multiple combinations of samples simultaneously with different filling pressures, wherein more than two sample holders and corresponding buffers can be arranged for testing multiple combinations of samples simultaneously, and the filling pressure for each sample holder can be varied independently according to the requirements for individual sample holders due to the presence of different buffer volumes and valves, wherein the simultaneous testing of different configurations with varied filling pressures accelerates the testing process, providing flexibility in evaluating matrix conductivity ratio and conduction degradation factor under diverse experimental conditions.

7. The apparatus as claimed in claim 1, further comprises a heat pipe (28) with a heat exchanger (29) as the cooling medium to cool the cold end of the regenerator matrix housing (8) attached to the sample holder (7), wherein the heat pipe (28) is attached to the first-stage heat exchanger (11) at one end and another heat exchanger (29) at the other end, with the heat exchanger (29) cooling one end of the regenerator matrix housing (8) and creating a temperature gradient during the testing of the matrix conductivity ratio and conduction degradation factor, wherein the gas from the helium cylinder (1) reaches the buffer (6) through the regulating valve (2), with buffer volume (6) attached to a relief valve (202) and a pressure gauge (203), wherein the gas flows from buffer volume (6) to the regenerator matrix housing (8) attached to the cold end of the sample holder (7), and the sample holder (7) is further connected to a vacuum pump (22) through a vacuum fitting KF-25 clamp (23).

8. The apparatus as claimed in claim 1, wherein a PID controller is employed to maintain the temperature value (Tc) at the cold end, and heat load is provided by a heater to fix the temperature value of the hot end (Th), allowing for accurate estimation of matrix conductivity ratio and conduction degradation factor values, wherein the heat exchanger (29) is cooled from the first-stage heat exchanger (11) of the cryocooler through the heat pipe (28), and the cryocooler is a mechanical/pneumatic drive GM cryocooler generating a cooling effect through adiabatic expansion of the gas parcel, wherein the oscillating pressure wave is generated by the rotary valve and helium compressor (14), with the compressor being a scroll-type water-cooled helium compressor and the cooling water being provided from a water chiller (15), although the compressor may be of an air-cooling arrangement without limiting the scope of the invention.

9. The apparatus as claimed in claim 1, wherein in the dry matrix conductivity testing apparatus, the cold end temperature is set to a desired value using a cryocooler, with specific applications including a single-stage cryocooler for 80 K, a 20 K cryocooler for single-stage and heat pipe applications, and a 4.2 K cryocooler for two-stage applications, in combination with a PID controller, wherein the cold end temperature is set to the desired value using a suitable cryogenic fluid, including liquid nitrogen (LN2) for temperatures of 80 K and above, and liquid helium (LHe) for temperatures of 4.2 K and above, wherein the cooling effect in the wet matrix conductivity testing apparatus can be achieved using any other cryogenic fluid, selected based on the boiling point of the cryogenic fluid, while recognizing the extensive use of liquid nitrogen and liquid helium in cryogenic testing due to their advantages over other cryogenic fluids.

10. The apparatus as claimed in claim 1, wherein the wet-type testing apparatus for regenerator matrix conductivity, utilizing liquid nitrogen (LN2) as a cooling medium instead of a cryocooler, comprising:
a pure helium gas cylinder (1) to supply helium gas to a buffer volume (6) through a flow meter (3), needle valve (4), and cut-off valve (5), with the buffer volume equipped with a pressure gauge (203), relief valve (202), and two connecting pipes for gas supply to the sample holder and the gas cylinder;
a sample holder (7) connected to the regenerator matrix housing (8) at its opposite end, with gas flow facilitated by a vacuum pump (22) through a KF-25 quick dismantled coupling (23);
wherein the sample holder and regenerator matrix housing placed within a sample mounting vessel (32), with the cold end of the regenerator matrix in contact with a heat-conducting thermal mass (35) cooled by LN2, wherein the sample mounting vessel having an opening (36) for evacuation and purging before experimental investigations;
wherein the LN2 storage vessel features a double-container configuration comprising an outer Dewar (31) supporting an inner Dewar (30) storing LN2, with high vacuum and multiple layers of multi-layer insulation (MLI) in the interspace to reduce heat load, wherein the LN2 storage vessel further comprising an LN2 entry port (33) and LN2 exit port (34), with connections to a vacuum pump (20) via a clamp (23), enabling efficient cooling of the thermal mass (35) connected to the regenerator matrix housing cold end; and
wherein the PID controller is interposed between the thermal mass (35) and the cold end of the matrix housing (8) to regulate and set the cold end temperature (Tc).