Description:1
A)
TECHNICAL FIELD 5
[0001] The present invention relates to a system for dynamically adjusting the radial clearance between the rotor and the casing. More particularly, the present invention employs Shape Memory Alloys (SMAs) embedded within the casing to enable temperature-responsive deformation, thereby regulating the clearance during compressor operation.
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B)
BACKGROUND OF THE INVENTION
[0002] Screw compressors are positive displacement machines widely employed across industries such as HVAC (Heating, Ventilation, and Air Conditioning), refrigeration, oil and gas, and process manufacturing for compressing gases or air. These machines rely on a pair of 15 intermeshing rotors enclosed within a casing to achieve compression. A critical design parameter in screw compressors is the radial clearance between the rotor surfaces and the inner casing wall. This clearance ensures that there is no direct contact between the rotating elements and the casing, which is essential for avoiding mechanical damage and accommodating thermal expansion. 20
[0003] However, fixed radial clearance is a fundamental limitation in conventional screw compressors. During operation, temperature and pressure within the compressor fluctuate based on load and environmental conditions. These variations affect the dimensions of both the rotor and the casing due to thermal expansion, potentially leading to suboptimal 25 clearances. If the clearance becomes too large, leakage losses increase, thereby reducing volumetric efficiency and increasing energy consumption. On the other hand, excessively tight clearances under high-temperature conditions may lead to rotor-casing interference, resulting in wear, frictional losses, or even mechanical failure.
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[0004] To address these performance issues, conventional designs often integrate external control mechanisms such as Variable Frequency Drives (VFDs), slide valves, or mechanical actuators. VFDs allow variable speed operation to match the compressor’s output to demand, but they do not address leakage losses due to fixed clearances. Slide valves partially regulate
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the compressor’s capacity but require additional control and feedback systems, making the 5 design more complex. Mechanical actuators or hydraulically controlled mechanisms have also been proposed for adjusting rotor position or internal geometry, but these introduce more moving parts, increasing the risk of failure and the cost of maintenance.
[0005] Some advanced technologies such as magnetic bearings or thermally expanding casing 10 materials have been investigated to address clearance issues. However, magnetic bearings are expensive and require continuous power and complex electronics, while passive thermal expansion relies on bulk material properties and lacks precision or control.
[0006] Therefore, there exists a strong need for a simplified, integrated, and passive system capable of dynamically adjusting the radial clearance between the rotor and the casing in 15 response to changing thermal and operational conditions—without requiring external power, control systems, or mechanical actuators. The present invention addresses this unmet need through the novel use of Shape Memory Alloys (SMAs) embedded within the casing to achieve temperature-responsive radial clearance control, thereby enhancing compressor efficiency, reliability, and adaptability. 20
C)
OBJECT OF THE INVENTION
[0007] The primary object of the present invention is to provide a screw compressor with an adaptive radial clearance control system that dynamically adjusts the clearance between the 25 rotor and the casing during in operation.
[0008] Another object of the present invention is to utilize shape memory alloys (SMAs) embedded within the compressor casing to effect clearance adjustment based on temperature-induced material deformation, thus eliminating the need for external 30 mechanical or electronic control systems.
[0009] Yet another object of the present invention is to reduce losses due to leakage and wear and tear during friction in screw compressors by maintaining optimal radial clearance under constantly or intermittently varying load, pressure, and thermal conditions. 35
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[0010] Yet another object of the present invention is to enhance energy efficiency and 5 lifespan of the compressor by providing a self-regulating mechanism that responds passively to internal operating conditions.
[0011] Yet another object of the present invention is to simplify compressor design by minimizing moving parts and external actuators, thus reducing system complexity, 10 maintenance requirements, and cost.
[0012] Yet another object of the present invention is to teach about a scalable and retrofittable adaptive radial clearance control system to a wide range of screw compressor configurations and industrial use cases. 15
[0013] These and other objects of the present invention teach about providing an adaptive, temperature-responsive radial clearance control system for screw compressors using shape memory alloys (SMAs), enabling dynamic clearance adjustment without external controls.
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D)
SUMMARY OF THE INVENTION
[0014] Various embodiments of the present invention provide for an adaptive radial clearance control system for screw compressors, wherein shape memory alloys (SMAs) are embedded within the compressor casing to dynamically adjust the clearance between the 25 rotor and the casing in response to operational temperature variations.
[0015] The primary embodiment of the present invention the SMA elements are strategically positioned in the compressor casing such that their thermally induced shape changes cause the casing to expand or contract radially, thereby modifying the rotor-to-casing clearance in 30 real-time.
[0016] Another embodiment of the present invention provides for the SMA material to be selected to activate at specific temperature thresholds corresponding to typical operational ranges of the compressor, ensuring precise and passive clearance regulation based on 35 thermal conditions.
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[0017] In yet another embodiment of the present invention, the SMAs are selectively placed 5 to achieve precise and localized deformation in the casing, ensuring real-time adjustment of the radial clearance even during variations of compressor load and speed of the compressor.
[0018] In yet another embodiment of the present invention, the system eliminates the need for external actuators, Variable Frequency Drives (VFDs), or control electronics by utilizing the 10 intrinsic material behaviour of SMAs, resulting in a simplified, energy-efficient, and low-maintenance design.
[0019] In yet another embodiment of the present invention, the system can be implemented in various types of screw compressors such as oil-injected or oil-free systems and the system 15 can be scaled up or scaled down and even retrofitted for different industrial applications.
[0020] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, 20 while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
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E)
BRIEF DESCRIPTION OF DRAWINGS
[0021] Fig.1 illustrates a cross-sectional view of the rotor casing in a screw compressor. It shows a cross-sectional view of the rotor casing, highlighting the interior surface where the rotor operates. The sections where the SMA is to be embedded are located along the inner 30 circumference of the casing wall, close to the rotor. These SMA elements will allow for dynamic radial clearance adjustments as temperature varies.
[0022] Fig.2 illustrates a longitudinal sectional view of the Rotor Casing. It provides a longitudinal view, showing the internal flow path of the rotor within the casing. The SMA 35 embedding regions are positioned along the casing walls that interact directly with the rotor.
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These SMA elements will contract or expand based on the thermal environment to optimize 5 the clearance between the rotor and casing.
[0023] Fig. 3 illustrates an isometric view of the Screw Compressor Assembly with the rotor casing fully enclosed.
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[0024] Fig. 4 illustrates a cross-sectional view of rotor casing with embedded shape memory alloy (SMA) elements on the inner surface for adaptive radial clearance control.
[0025] Fig. 5 illustrates a flowchart of SMA based adaptive radial clearance control in screw compressor. 15
F)
DETAILED DESCRIPTION OF THE INVENTION
[0026] In the following detailed description, a reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. The embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that 20 the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0027] The present invention relates to an adaptive clearance control system for screw 25 compressors, employing Shape Memory Alloys (SMAs) integrated within the compressor casing to regulate the radial clearance between the rotor and the casing in real time. The invention is particularly beneficial for rotary screw compressors operating under variable load and speed conditions, where traditional fixed-clearance systems result in performance inefficiencies, increased wear, and energy losses. 30
[0028] Screw compressors are widely used in industrial applications such as HVAC systems, refrigeration, oil and gas, and manufacturing. They operate by trapping and compressing air or gas between meshing helical rotors. A critical parameter influencing compressor efficiency is the radial clearance between the rotor and the surrounding casing. Excessive clearance 35
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leads to leakage losses, while insufficient clearance results in increased friction, wear, and 5 mechanical failure.
[0029] Conventional compressors maintain a fixed radial clearance, which must be conservatively large enough to accommodate thermal expansion and mechanical tolerances under the highest load and temperature conditions. However, under lower load or 10 temperature conditions, the oversized clearance reduces compression efficiency. Some existing solutions, such as Variable Frequency Drives (VFDs), mechanical actuators, or hydraulic systems, address performance variability but do not dynamically adapt the radial clearance during operation.
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[0030] The present invention proposes a novel approach to dynamically adjust the radial clearance by embedding thermally responsive SMA elements within the casing structure. SMAs are materials that exhibit the ability to return to a pre-defined shape when exposed to specific temperatures. Upon heating, SMAs undergo a phase transformation (from martensite to austenite), causing contraction or expansion, depending on the design. This property is 20 harnessed to induce controlled deformation in the casing wall adjacent to the rotor.
[0031] By strategically embedding SMA elements in specific sections of the casing, the invention allows localized expansion or contraction of the casing, thereby increasing or decreasing the radial clearance relative to the rotor. This deformation occurs passively during 25 compressor operation as internal temperatures rise, eliminating the need for active monitoring or external actuation.
[0032] In one embodiment, the SMA elements are configured as embedded wires, coils, or strips placed circumferentially within grooves in the inner wall of the rotor casing. The SMAs 30 are selected based on their transformation temperature, mechanical properties, and compatibility with the casing material.
[0033] The casing may include a layered or composite structure, with the SMA layer bonded between an inner thermal-conductive casing surface and an outer structural layer. As the 35 compressor operates and internal temperatures rise due to rotor motion and gas
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compression, the SMA is heated to its transformation temperature. This causes it to contract, 5 pulling the casing slightly inward to reduce the clearance.
[0034] Conversely, during cooling or low-load operation, the SMA returns to its martensitic phase and relaxes, allowing the casing to expand and restore clearance to a default state. The material selection and geometric configuration ensure that these movements remain within 10 safe mechanical limits, preserving casing integrity and alignment.
[0035] In certain embodiments, thermal sensors or insulating layers may be integrated to manage heat distribution and ensure uniform SMA activation. The response time of the SMA-based deformation is calibrated based on the thermal gradient, mass of SMA material, and 15 compressor speed profile.
[0036] Additionally, provisions may be included for selective activation of SMA zones, such that clearance is adjusted asymmetrically or only in regions where temperature thresholds are exceeded. This targeted response enhances efficiency and minimizes unnecessary 20 material strain.
[0037] The invention may work during manufacturing or as a retrofit solution for existing compressors. In the manufacturing process, SMA components are embedded during casting or machining of the casing. For retrofit applications, modular SMA inserts or sleeves may be 25 bonded to the inner casing surface using high-temperature adhesives or mechanical fasteners.
[0038] The system operates entirely passively, without electronic control, sensors, or feedback loops. This results in a simplified design with fewer points of failure, reduced energy 30 consumption, and minimal maintenance requirements.
[0039] The adaptive clearance system is especially beneficial for Variable-load HVAC and refrigeration systems, oil and gas processing plants with fluctuating pressure conditions, manufacturing lines requiring responsive compressor output, Energy-conscious facilities 35 aiming to reduce carbon footprint, amongst other fields.
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[0040] The invention is adaptable to both oil-injected and oil-free screw compressors and scalable for different sizes and capacities. It offers a universal solution for enhancing compressor performance without the complexity or cost of active control systems.
[0041] Fig. 1 illustrates a cross-sectional view of the rotor casing in a screw compressor. It 10 highlights the internal surface of the casing where the rotor operates. Specific regions along the inner circumference of the casing wall, close to the rotor periphery, are designated for embedding Shape Memory Alloy (SMA) elements. These SMA elements are configured to adaptively control radial clearance by responding to thermal changes during compressor operation. 15
[0042] Fig. 2 presents a longitudinal sectional view of the rotor casing. It provides a perspective of the internal axial flow path of the rotor within the casing. The embedding zones for the SMA elements are positioned along the length of the casing walls that maintain direct proximity to the rotor. These SMA elements contract or expand based on temperature 20 fluctuations, thereby optimizing the radial clearance dynamically.
[0043] Fig. 3 shows an isometric view of the screw compressor assembly with the rotor casing fully enclosed. The overall configuration of the compressor housing, along with the rotor containment structure, is depicted to provide a comprehensive view of the compressor layout 25 incorporating the adaptive SMA-based clearance system.
[0044] Fig. 4 illustrates a cross-sectional view of the rotor casing with embedded SMA elements integrated into the inner casing wall. These SMA elements are distributed in defined zones for effective radial clearance control. The figure emphasizes how these embedded 30 elements interact with the rotor interface to regulate the operating gap during varying thermal conditions.
[0045] Fig. 5 illustrates a flowchart representing the adaptive radial clearance control process based on SMA activation. It outlines the functional steps, including temperature sensing (if 35 applicable), SMA thermal response, casing deformation, and clearance modulation. This
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schematic provides an overview of the passive control mechanism governing the SMA system 5 during compressor operation.
[0046] The present invention offers several significant advantages over traditional fixed-clearance compressor systems. By utilizing Shape Memory Alloys (SMAs) embedded within the casing structure, the system passively adjusts radial clearances in real time based on 10 thermal conditions without the need for active sensors, actuators, or control electronics. This not only improves the overall energy efficiency of screw compressors but also extends operational life by minimizing wear and leakage losses across varying load conditions. The simplicity of the passive system architecture ensures ease of integration, minimal maintenance, and a lower total cost of ownership. Additionally, the design's adaptability 15 makes it suitable for both oil-injected and oil-free screw compressors, further broadening its industrial applicability.
[0047] Beyond screw compressors, the core principles of this invention—adaptive clearance control through thermally responsive smart materials—may be extended to other rotating 20 machinery where thermal expansion and clearance are critical, such as gearboxes, turbines, scroll compressors, or even pumps operating under fluctuating thermal and pressure environments. In the future, this technology could be scaled down for micro-compressors in electronics cooling systems or adapted for high-performance aerospace and automotive applications, where dynamic thermal management is crucial. Its passive, sensor-free nature 25 positions the invention as a foundational platform for next-generation, self-regulating mechanical systems with applications in both existing and emerging industrial domains. , Claims:We Claim: 5
1.
A screw compressor comprising a rotor, a rotor casing surrounding the rotor, and a drive mechanism for rotating the rotor
characterized in which
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the rotor casing is embedded with one or more Shape Memory Alloy (SMA) elements configured to dynamically adjust radial clearance between the rotor and the casing in response to temperature variations during compressor operation,
wherein the SMA elements expand or contract based on temperature changes. 15
2.
The screw compressor as claimed in claim 1, wherein the SMA elements are embedded circumferentially around the inner surface of the rotor casing.
3.
The screw compressor as claimed in claim 1, wherein the SMA elements are made 20 from a Copper-Aluminium-Nickel (Cu-Al-Ni) alloy having a transformation temperature within the typical operational temperature range of the compressor.
4.
The screw compressor as claimed in claim 1, wherein the SMA elements revert to a predefined shape when the casing temperature exceeds a threshold. 25
5.
The screw compressor as claimed in claim 1, wherein the radial clearance adjustment is achieved without mechanical actuators, slide valves, magnetic bearings, or variable frequency drives.
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6.
The screw compressor as claimed in claim 1, wherein the SMA elements are configured to deform the rotor casing in response to temperature changes occurring during normal compressor operation, thereby modifying the radial clearance between the rotor and the casing.
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7.
The screw compressor as claimed in claim 1, wherein the SMA elements are integrated 5 into the casing such that their shape transformation causes a displacement of the casing wall toward or away from the rotor axis, resulting in a change in radial clearance.
8.
The screw compressor as claimed in claim 1, wherein the SMA elements are positioned in slots or cavities formed within the casing material and bonded using high-10 temperature-resistant adhesive or mechanical fasteners.