FIELD OF INVENTION
The present invention relates to an apparatus and method for prediction of transient metal temperatures in multiple axes of periodic heat exchanger elements. It relates to periodic heat exchangers in general and the Ljungstrom configuration of Regenerative Air Preheaters in particular. The method and apparatus developed can be extended for demonstration of thermal and flow phenomena in periodic heat exchangers. The apparatus in the invention describes the entry, exit and flow path of heating and cooling fluid media. The method in the invention describes operation of the equipment and means to achieve a coupled heating and cooling in the same apparatus. Finally, the method details an experimental arrangement and the apparatus provides basis for validation of heat transfer characteristics of metallic elements in the periodic heat exchanger by capturing thermal parameters. This helps in design of air preheater elements to withstand low temperature corrosion, before actual bulk fabrication of equipment.
BACKGROUND OF INVENTION
A heat exchanger is a device used to transfer heat between two or more fluids. They are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power stations, chemical plants,

petrochemical plants, petroleum refineries, natural-gas processing and sewage treatment. In a periodic heat exchanger, a matrix of metal elements is present in a systematic arrangement. During the heat exchange process, this matrix rotates and the cold and hot side change their position, but the fluid flow direction remains same. Due to this the hot side becomes cool by the cold fluid and cold side gains heat by the hot fluid. This process continuously repeated.
Conventionally, correlations and programs have been developed for prediction of hot and cold stream thermal properties and performance for Heat exchanger design. Methodology to compute the metal temperatures of the Heat exchanger elements was absent. Further, the accurate establishment of these computed temperatures, experimentally, was not available for lack of suitable apparatus. The present invention seeks to meet these two shortcomings. Metal temperature prediction enhances heat exchanger design capability vis-a-vis the selection of material, thickness and arrangement. It further assists in design of profiles with better thermal performance and desirable geometrical configurations.
In abstract, the invention disclosed in US 2011/0303135 Al, is on an air damper assembly that partially restricts an air inlet and a flue gas damper assembly that partially restricts flue gas inlet during periods of reduced boiler load. Restricting the air inlet reduces the effective heat transfer surface area of the air preheater, which raises the gas temperature in the cold end of the air preheater and thereby reduces acid condensation and fouling.

In abstract, the invention disclosed in US 4548186 A, is on method and device for Preheating an Engine or an internal combustion Engine intake air. The method provides an engine intake air preheating device having an intake air preheater for preheating air to be fed into an engine, the preheater including a first metal hydride and being disposed within an intake air feeding tube for heat exchange with the intake air, a hydrogen storage container including hydrogen or a second metal hydride, and a pipe having a valve and connecting the intake air preheater to the hydrogen storage container so that hydrogen can move between them.
In abstract, the invention disclosed in US 5950707 A, is on an improved sealing element, for a regenerative heat exchanging apparatus, such as a Ljungstrom TM -type or a Rothemuhle TM -type Preheater. The sealing element is mounted to a radial wall to provide a secure seal between the radial wall and an outer housing of the heat exchanging apparatus and prevent leakage between the hot gas conduit and cool air conduit. In a preferred embodiment, the sealing element includes a reinforced mounting strip that is used to mount the sealing element to the radial wall.
In abstract, the invention disclosed in US 2018/0010792 A1, is on a method to improve effectiveness of a steam generator system includes providing air to an air preheater in excess of that required for combustion of fuel and providing the air at a mass flow such that the air preheater has a cold end metal temperature that is no less than a water dew point temperature in the air preheater and such that the cold end metal temperature is less than a sulfuric acid dew point temperature. The method includes

mitigating SO3 in the flue gas which is discharged directly from the air preheater to a particulate removal system and then directly into a flue gas desulfurization system.
In abstract, the invention disclosed in US 2002/0110507 A1, is an apparatus and method for a preheated micro-reformer system, comprising a reformer and a micro-reformer in fluid communication with the reformer. The micro-reformer being electrically preheatable. An apparatus comprising a micro-reformer including a first zone and a second zone, the first zone being preheatable to a first temperature and the second zone being preheatable to a second temperature, the second temperature being higher than the first temperature. The preheated micro-reformer system, includes a preheater comprising a catalytic material for reforming a fuel.
In abstract, the invention disclosed in US 5581574 A relates to a method and apparatus for conditioning and using furnace off-gases in a Scrap Preheating Apparatus. It describes a preheat system for a furnace comprising a preheat vessel on a rotating turret and a receiving chamber for conditioning furnace off-gases prior to use in preheating.
In abstract, the invention disclosed in CN2011242815U 20110221 relates to a dredge type air leakage control device with sealing brushes for a Junker type air preheater, which comprises a mechanical sealing device, an air leakage dredging device and an automatic control device. The dredge type air leakage control device is suitable for the air preheaters of boilers for large and medium-sized power plants for preventing the air from leaking and has the advantages of simple structure, accuracy in control, favorable sealing and dredging effect and electricity economization.

The proposed specifications of this invention are a method and an apparatus for prediction of transient metal temperatures in multiple axes and for different profiles of periodic heat exchanger elements, unlike as compared to the invention discussed in US 2011/0303135 A1, which is about an actual air preheater and damper assembly that reduces air inlet at reduced boiler loads and not about metal temperature of elements; or the invention discussed in US 4548186 A, which is a preheating device for only an internal combustion engine with hydrogen storage and where heat exchange with engine is involved; or the invention discussed in US 5950707 A, which only describes a sealing element for a regenerative heat exchanging apparatus and a set of bellows positioned on the sealing element to provide flexibility to sealing element; or the invention discussed in US 2018/0010792 A1, which describes a method for improving effectiveness of a steam generator system by ensuring that the air preheater has a cold end metal temperature that is no less than water dew point temperature; or the invention discussed in US 2002/0110507 A1, which is about preheated micro-reformer system and a vaporizer which comprises a micro-reformer and it includes a catalyst, which is electrically preheatable; or the invention discussed in US 5581574 A, which is particularly suitable for a closable top opening for receiving material and a closable bottom opening for discharging material into the furnace and is only for preheating of scrap in a furnace; or the invention discussed in CN2011242815U 20110221, which only describes a mechanical sealing device for a heat end sector plate, a cold head section plate and an axial sealing plate as well as a radial sealing element and an axial sealing element which are fixed on a rotor separation board, without any mention of heating and cooling of metal plates for temperature distribution.

OBJECTS OF THE INVENTION
Therefore it is an object of the invention to propose an apparatus and method for determination of transient metal temperature distribution in periodic heat exchangers which is capable of directing sequentially the flow media to achieve an integrated heating and cooling phenomena from hot to cold medium.
Another object of the invention to propose an apparatus and method for determination of transient metal temperature distribution in periodic heat exchangers which is able to elaborate flow path of medium to obtain thermal data and temperature distribution of the heat exchanger elements in multiple axis.
SUMMARY OF THE INVENTION
The present invention relates to a method and novel apparatus to measure the multi-axes transient metal temperatures of periodic heat exchanger elements. This is required to design the heat exchanger in an economic manner, avoiding trial and error practice for design of new element profiles. Present design tools predict heat exchanger sizing based purely on fluid behavior and thermal properties. However, certain unconventional heat exchangers require the prediction of metal temperatures to arrive at the thermo-hydraulic design. In this particular case, this prediction is essential to prevent the formation of Ammonium Bi-Sulfate and fouling of Air Preheater elements. The elements of the periodic heat exchanger are stacked in a particular fashion in the

apparatus prior to experimentation. The present invention relates to transient temperature prediction in multiple axes viz axial, radial and circumferential directions, for such periodic heat exchanger elements. This is essential as the element geometry is anisotropic and has different metal temperature values in different flow directions. The elements are heated and cooled systematically for different flow and temperature distributions. The elements are instrumented with temperature sensors and signals are connected to a data logging device and time variation in flows, pressures and temperatures are captured. The apparatus provides experimental results, which would then be utilized for validating an analytical program developed. Multiple experimentations are done on different profiles of the periodic heat exchanger to make the program robust. Upon validation, the program can henceforth be employed to generate results for all new profiles of the same periodic heat exchanger. This shall be repeated for any new periodic heat exchanger configuration.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The drawings refer to embodiments of the invention in which:
Figure 1 illustrates a stack of a particular configuration of periodic heat exchanger elements.
Figure 2 illustrates an apparatus for experimentation of periodic heat exchanger elements to determine temperature distribution.

Figure 3 illustrates top orientation of the experimental apparatus arrangement with indicative flow directions.
Figure 4 illustrates a representational temperature chart showing the transient temperature with respect to axial distance variation for a test condition of heat exchanger elements.
Figure 5 illustrates arrangement method for thermocouples to be fixed onto the stacked heat exchanger elements.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The present invention, now be described more specifically with reference to the following specifications:
Certain unconventional periodic heat exchangers require the prediction of metal temperatures to arrive at the thermo-hydraulic design. Present thermal programs do not provide entire metal temperature distributions as that data is not directly related to the overall design of a heat exchanger. The present invention caters to those heat exchangers for which metal temperature distributions, both transient and steady state, are essential for design sizing and parameter validation. In the present case, it is to handle flue gas down stream of Selective Catalytic Reduction (SCR) equipment, containing traces of ammonia and to avoid formation of Ammonium Bi-Sulfate (ABS) in the cold end of Air Preheater. In the apparatus, sample elements of the heat exchanger are stacked in a particular fashion prior to experimentation. The invention relates to transient temperature

prediction in multiple axes viz axial, radial and circumferential directions, for such periodic heat exchanger elements. This is essential as the element geometry is complex and anisotropic and has different metal temperature values in different axes. A set of sample element pairs are stacked and placed in a chamber. This chamber is placed in an air duct that has dampers, louvers and bypass plates. A heating system is located at the suction of the air duct. A blower system is provided for air supply. The elements are first heated and then cooled systematically for different flow and temperature distribution combinations. Heating is achieved by pre-heating air to desired temperature and is then allowed to flow over the stacked elements in chamber. The temperature of the metal elements in the stack are monitored and recorded by data logging system during heating stage at transient and steady state conditions. The hot air flow is then stopped. To purge the apparatus of the hot air in the duct, bypass dampers are activated and the main flow circuit is cut off. Cold air flow is then sent into the duct and the metal elements are allowed to cool down. The temperature of the metal elements in the stack are monitored and recorded by data logging system during cooling stage, at transient and steady state conditions. The purpose of the bypass duct is to isolate the heat exchanger elements during heating and cooling phases of the experimentation.
Fig.l shows a schematic of stacked heat exchanger elements (207) with elemental contour and indentations.
The apparatus (100) shown in Fig.2 is having a heating system (201). The heating system (201), enclosed in enclosure (102) is having heaters and controls and air suction grid (101). Air is sucked through enclosure (102). The heaters of required capacity

is disposed to heat the air obtained through air suction guide (101). A blower system (203) with motor (204) sucks air. A flow dumper system (202) with multiple settings to regulate hot air flow, is disposed in the apparatus. The hot air is obtained through duct (103) by suction of blower system (203) over the heating system (201). The apparatus has a plurality of ducts (103, 104, 105) for enabling flow of entry air and also has an exit air duct (108), a bypass exit air duct (106) for enabling flow of exit air. A test chamber (107) for holding stacked heat exchanger elements for experimentation is configured in the system. Also the apparatus includes a main duct by pass plate (206) and bypass duct bypass plate (205) for bypass of air in test chamber (107) and a bypass exit air duct (106). The apparatus also includes an instrumentation cables (208) for connecting the stacked heat exchanger elements (207) to a data logging computer system (208) to capture multiple thermal, pressure and flow data, in a structured numbering format at radial (301) and axial (302) locations for case of data storage and interpretation. The apparatus also includes a systematic arrangement of thermocouples in radial (301) and axial (302) directions for capturing transient and steady state metal temperatures. The ducts are insulated with multitude of insulation layers (210) to prevent heat loss from ducts and optimize heater power.
The test chamber (107) consisting of stacked heat exchanger elements (207) is flexible for removal and can be replaced with another chamber as required during maintenance.

The apparatus has main duct bypass plate (206) for allowing flow of air into bypass exit air duct (106) and bypass duct bypass plate (205) for allowing flow of air into test chamber (107) and subsequently into main exit air duct (108).
The instrumentation cable is connected to flow and pressure sensors in the test chamber (107).
Figure 3 shows details of the apparatus (100), focusing on the air flow path via the ducts (103,104,105), main exit air duct (108) and bypass exit air duct (106) from top view. It also schematically depicts the insulation layers (210) that cover the entire flow path as indicated.
Figure 4 illustrates an outcome from the experimentation; a transient temperature distribution chart for different axial (302) locations of stacked heat exchanger elements (207).
Figure 5 illustrates an arrangement scheme for thermocouples to be fixed onto stacked heat exchanger elements (207) at radial (301) and axial (302) locations.
The method of obtain integrated heating and cooling consists of the following steps.
For heating stage of the stacked heat exchanger elements (207), the data logging computer system (209) is turned ON. The motor (204) is turned ON, which powers the blower system (203) to suck in cold air from the air suction grid (101) and flowing over heating system (201). The heating system (201) is turned ON. Desired temperature is set in the control system for the heaters. The uniform distribution during heating is ensured in enclosure (102). The temperature of air is maintained high by low setting in

flow damper system (202) and vice-versa. The hot air then flows through plurality of ducts (103,104,105) and enters the test chamber (107) and flows over the stacked heat exchanger elements (207), leaving the apparatus (100) from the main exit air duct (108). During this stage, the bypass duct bypass plate (205) is closed and main duct bypass plate (206) is opened. The hot air starts heating the stacked heat exchanger elements (207) gradually. Transient data is captured by the data logging computer system (209) from the instrumentation cables (208) connected to the stacked heat exchanger elements (207), at desired locations. The stacked heat exchanger elements (207) reach steady state condition, of which data is captured for computation in data logging computer system (209).
For cooling stage of the stacked heat exchanger elements (207), the data logging computer system (209) continues to remain ON. The heating system (201) is turned OFF. During this stage, the bypass duct bypass plate (205) is opened and main duct bypass plate (206) is closed. The hot air in the plurality of ducts (103,104,105) is purged out of apparatus (100) through bypass exit air duct (106). The test chamber (107) and stacked heat exchanger elements (207) are isolated. On complete purging of hot air in the plurality of ducts (103,104,105), the bypass duct bypass plate (205) is closed and main duct bypass plate (206) is re-opened. This initiates the cooling stage of the experimentation. Transient and steady state data for cooling is captured by the data logging computer system (209) from the instrumentation cables (208) connected to the entire stacked heat exchanger elements (207), at desired radial (301) and axial (302) locations.

WE CLAIM
1. An apparatus (100) for determination of transient metal temperature distribution in periodic heat exchangers, the said apparatus (100) comprising;
a heating system (201) having heaters, controls, enclosure (102) for air suction, an air suction grid (101);
a blower system (203) with motor (204) for air suction;
a flow damper system (202) with multiple settings for variation in air flow;
a plurality of ducts (103,104,105) for enabling flow of entry air and main exit air duct (108), bypass exit air duct (106) for enabling flow of exit air; wherein
a test chamber (107) is disposed for holding stacked heat exchanger elements (207) for experimentation; when
a main duct bypass plate (206) and bypass duct bypass plate (205) are configured for bypass of air in test chamber (107) and bypass exit air duct (106) respectively; wherein
a data logging computer system (209), along with instrumentation cables (208) are disposed for capturing multiple thermal, pressure and flow data; wherein
a systematic arrangement of thermocouples, is provided in radial (301) and axial (302) directions for capturing transient and steady state metal temperatures; when
a multitude of insulation layers (210) are provided on ducts for preventing heat loss from ducts.

2. The apparatus (100) as claimed in claim 1, wherein the test chamber consisting of
stacked heat exchanger elements (207) is flexible and removable for replacing with another chamber as required during maintenance.
3. The apparatus as claimed in claim 1, wherein the heating system (201) with heaters is
disposed to heat the air obtained through air suction grid (101) and via duct (103) by suction of blower system (203).
4. The apparatus as claimed in claim 1, wherein the flow dumper system (202) with
multiple settings is configured to regulate hot air flow flowing through duct (103).
5. The apparatus as claimed in claim 1, wherein ducts are provided throughout with insulation layers (210) for preventive heat loss from hot air flowing through plurality of ducts (103, 104, 105) and optimize heater power.
6. The apparatus as claimed in claim 1, wherein main duct bypass plate (206) is disposed
for allowing flow of air into bypass exit air duct (106) and bypass duct bypass plate (205) is disposed for allowing flow of air into test chamber (107) and subsequently into main exit air duct (108).
7. The apparatus as claimed in claim 1, wherein the data logging computer system (209)
connected to different axial, radial and circumferential locations of stacked heat

exchanger elements (207) through instrumentation cables (208) wherein the said cables (208) are connected to flow and pressure sensors in the test chamber (107).
8. A method for determination of transient metal temperature distribution in periodic heat exchangers by an apparatus claimed in claim 1, comprising the steps of;
starting the data logging computer system (209);
turning a motor (204) ON to provide power to the blower system (203) to suck in cold air from the air suction grid (101);
starting the heating system (201);
setting the desired temperature in the control system for the heaters ensuring uniform distribution during heating in enclosure;
maintaining the temperature of air high by low setting in flow damper system (202) and vice-versa;
allowing the hot air to flow through plurality of duct (103, 104, 105) and then to test chamber )207) to flow over the stacked heat exchanger elements (207) and leaving the apparatus (100) from the main exit air duct (108); wherein the bypass duct bypass plate (205) is kept closed and main duct bypass plate (206) is kept opened, when the hot air heats the stack exchanger elements (207) gradually, the transient data is captured by the data logging computer system (209) through the instrumentation cables (208) connected to the said stacked heat exchanger elements (207) at the desired locations, wherein the stacked heat exchanger elements (207) reach steady state condition when the corresponding data is captured for computation

in data logging computer system (209), wherein for cooling stage of the stacked heat exchanger elements (207), the data logging computer system continues to remains ON and the heating system being turned OFF, the bypass duct bypass plate (205) being opened and main duct bypass plate (206) being close, the hot air in the plurality of ducts (103,104,105) being purged out of the apparatus (100) through bypass exit air duct (106), the test chamber (107) and stacked heat exchanger elements (207) are isolated, wherein after complete purging of hot air in the plurality of ducts (103, 104, 105), the bypass duct bass plate (205) is closed and main duct bypass plate (206) is reopened to initiate the cooling stage of the experimentation when transient and steady state data for cooling is captured by the data logging computer system (209) through instrumentation cables (208) connected to the entire stacked heat exchanger elements (207) at desired radial (301) and axial (302) locations.