Engines that use compressed SMA materials

Abstract

An energy recovery apparatus and method comprising: an engine comprising a plurality of elongated shape memory alloy (SMA) elements or negative thermal expansion (NTE) elements configured as a core and connected to a drive mechanism, an immersion chamber adapted to house the engine and adapted to be sequentially filled with a fluid to expand and contract the SMA or NTE elements through heating and cooling cycles of the SMA or NTE elements, and a compression device configured to apply a compressive mechanical force to at least one of the SMA elements or at least one of the NTE elements, the applied compressive mechanical force further compressing the at least one SMA element or the at least one NTE element during a cooling cycle.

Description

[Technical field]

[0001] This application relates to energy recovery, particularly to engines utilizing shape memory alloy (SMA) or negative thermal expansion (NTE) materials. [Background technology]

[0002] Low-grade heat, generally considered below 100 degrees Celsius, represents a significant waste energy stream in industrial processes, power generation, and transportation applications. The capture and reuse of such waste streams is desirable. One example of a technology that has been proposed for this purpose is the thermoelectric generator (TEG). Unfortunately, TEGs are relatively expensive. Another highly experimental approach that has been proposed to capture such energy is the employment of shape memory alloys.

[0003] Shape memory alloys (SMAs) are alloys that "remember" their initial cold-forged shape, once deformed, and then return to their previous deformed shape when heated. These materials are lightweight, solid substitutes for traditional actuators such as hydraulic, pneumatic, and motor-based systems.

[0004] The three main types of shape memory alloys are copper-zinc-aluminum-nickel, copper-aluminum-nickel, and nickel-titanium (NiTi) alloys, although SMAs can also be made by alloying zinc, copper, gold, and iron, for example. This list is not exhaustive.

[0005] Such material storage has been adopted and proposed since the early 1970s for use in heat recovery processes, particularly by constructing SMA engines to recover energy from heat as motion. Recent publications related to energy recovery devices include commonly assigned US Pat. No. 6,399,313 (WO 2013 / 087490). The energy recovery device comprises an engine core having a plurality of elongated wires arranged in a bundled configuration or tightly wrapped together. It is desirable to convert the contraction of SMA or negative thermal expansion (NTE) wire materials into mechanical power in an efficient manner. SMA materials exhibit complex stress-strain-temperature relationships. In general, the transformation of SMA materials from a "de-twinned" martensite phase to an austenite phase involves a combination of stress and temperature.

[0006] Patent document 2 (GB 2,533,357 Exergyn) deals with the use of an antagonistic arrangement of a core that provides the restoring force to the material in the stretched martensite state and a spring that dampens deflections with smooth operation. Patent document 3 (US 2014 / 007572 GM Global) describes a method to improve the performance of the material at various high environmental temperatures by providing the right amount of restoring force in the martensite state. Patent document 4 (US 5,442,914 Otsuka) discloses a shape memory alloy (SMA) heat engine that includes at least one mount by a conical disk spring attached to a perforated tube. The engine works by applying tension to the SMA heat engine, which does not provide efficient power output, and the tensile stress leads to the failure of the SMA material.

[0007] Fatigue life is a major issue with tension or stress on SMA materials, as they have a tendency to break, as occurs in the prior art mentioned above. In cases where SMA wire is used, the wire breaks. When a load is applied to the wire in the fully martensite (or fully austenite) phase, it will strain according to the Young's modulus. The wire will naturally develop into austenite and twin martensite states even when no external stress is applied. A drawback of unloaded shape memory alloys is the fact that the wire does not undergo a specific bending, but the transition occurs based only on temperature difference. To obtain a useful power output from the wire cycling operation, it must be stressed. The magnitude of the stress depends on the desired deformation. Problems have been found with limited SMA wire elongation associated with some shape memory alloys or NTE materials. In addition, the elongation limitation occurs because a low enough wire temperature is not reached during the cooling / relaxation cycle. This limitation on the amount of wire strain available for recovery during the power stroke means that the power output is limited. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2013 / 087490 [Patent Document 2] British Patent No. 2,533,357 Exergyn [Patent Document 3] U.S. Patent Application Publication No. 2014 / 007572 GM Global [Patent Document 4] U.S. Patent No. 5,442,914 Otsuka Summary of the Invention [Problem to be solved by the invention]

[0009] It is therefore an object to provide an improved system and method for generating increased power output from an SMA or NTE engine core for use in an energy recovery system. [Means for solving the problem]

[0010] According to the present invention, as set out in the appended claims, there is provided an energy recovery device comprising an engine comprising a plurality of shape memory alloy (SMA) elements or negative thermal expansion (NTE) elements configured to define a core and optionally connected to a drive mechanism, an immersion chamber adapted to house the engine and adapted to be sequentially filled with a fluid to expand and contract the SMA elements upon heating and cooling cycles of the SMA elements, and a compression device configured to apply a compressive force to at least one of the SMA elements during the heating and / or cooling cycles.

[0011] The present invention uses a mechanical compression device and method to compress the SMA elements that define the core during use. Engine compression increases material fatigue life and reduces overall core maintenance. This reduces overall life cycle costs and simplifies system design, as access to the SMA components for maintenance purposes is not required. Additionally, the use of a compressed core design allows for the use of lower-cost, lower-grade SMA materials, and allows for increased cycle rates, resulting in reduced SMA material usage.

[0012] Mechanical compression of SMA elements will reduce maintenance costs and enable lower efficiency power generation technologies, opening up the market for many power generation applications.

[0013] In one embodiment, a step of applying controlled compression is provided.

[0014] In another embodiment, there is provided an energy recovery device comprising: an engine comprising a plurality of elongated shape memory alloy (SMA) or negative thermal expansion (NTE) elements fixed at a first end and connected at a second end to a drive mechanism; and an immersion chamber adapted to house the engine and adapted to be sequentially filled with a fluid to expand and contract the SMA elements upon heating and cooling cycles of the SMA elements, wherein a controlled mechanical compression is applied to at least one of the SMA elements during the cooling cycle.

[0015] In one embodiment, the SMA element comprises at least one mounting body with multiple plates, at least two plates made of shape memory alloy assembled one above the other.

[0016] In one embodiment, the plates are assembled one above the other, and each plate is machined with a number of fluid ports that allow the passage of a fluid at a particular temperature through the mount, the fluid is introduced into the mount through the intake port, passes through the mount, and is discharged to the outside through the exhaust port.

[0017] In a preferred embodiment of the invention, the inlet and outlet ports are separate structural units and are formed using the same SMA as that used to fabricate the plates, and further, at least one of the mountings of the multiple SMA plates comprises an SMA core.

[0018] In one embodiment, an additive manufacturing or 3D printing process is used to form the SMA elements or SMA plates.

[0019] For a preferred embodiment of the present invention, the SMA core is disposed inside a housing having a plurality of buckling supports adapted to maintain the integrity of the mounting plate by at least one SMA core during application of a load.

[0020] In one embodiment, the composition of the SMA forming each of the plurality of mounting plates is the same, hi another embodiment of the invention, the composition of the SMA forming at least one plate is different from that of the other plates of the mounting body.

[0021] In another embodiment of the invention, multiple SMA cores are disposed within a housing, with the composition of the SMA forming the plates mounted on one SMA core being different from the composition of the SMA forming the plates mounted on another SMA core.

[0022] The present invention increases the surface area between the SMA material and the fluid, and the fluid only comes into contact with the SMA material as it passes through the SMA plate mount, reducing overall heat loss.

[0023] The inlet and outlet port configurations using SMA materials further reduce heat loss.The mounting configurations described in this invention resist buckling reducing the need for external supports.

[0024] In one embodiment, the compression device comprises an electromechanical actuator.

[0025] In one embodiment, the compression device includes a hydraulic compression module configured to apply pressure to the piston using pressurized hydraulic fluid.

[0026] The housing and buckling supports ensure that the SMA plates are thermally insulated and can withstand applied hydraulic loads while allowing movement of the individual mounts when in compression. The present invention also allows for easy retrofitting of the engine core due to the ease of replacing one SMA mount with another.

[0027] This means that when better SMA compositions become available, it is easy to replace plate mounts formed from older SMA compositions with plate mounts formed from new and improved SMA compositions.

[0028] In one embodiment, an engine core for use in energy recovery is provided, comprising at least one support body made of a plurality of plates, at least two of which are formed from a shape memory alloy and assembled one above the other, and the plurality of shape memory alloy plates have a plurality of fluid ports, e.g., serpentine-shaped ports, adapted to allow fluid to pass through the support body; an intake port adapted to introduce fluid into the support body; and an exhaust port adapted to discharge the fluid introduced from the intake port to the outside, wherein the intake port and the exhaust port are formed from a shape memory alloy.

[0029] In another embodiment, an engine for use in energy recovery is provided, comprising at least one support body made of a plurality of plates, at least two of which are formed of a shape memory alloy and assembled one above the other, the plurality of shape memory alloy plates having at least one fluid port adapted to allow the passage of a fluid through the support body; a compression device configured to apply a compressive mechanical force to at least one of the SMA plates during a heating cycle and / or a cooling cycle; an intake port adapted to introduce fluid into the support body; and an exhaust port adapted to discharge the fluid introduced from the intake port to the outside, wherein the intake port and the exhaust port are formed of a shape memory alloy.

[0030] In one embodiment, the compression device applies a mechanical force to at least one of the SMA plates during a cooling cycle. [Brief description of the drawings]

[0031] The invention will be more clearly understood from the following description of embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which: [Figure 1] 1 illustrates the behavior cycle of an SMA material during heating and cooling cycles. [Figure 2a] FIG. 1 is a perspective view of a preferred embodiment of the present invention. [Figure 2b] 1 illustrates a housing having fluid inlet and outlet ports to house an engine, according to an embodiment of the present invention; [Figure 3a] 1 illustrates a preferred embodiment of the present invention, showing side and top views of multiple SMA materials placed on top of each other; [Figure 3b] 1 illustrates a preferred embodiment of the present invention, showing side and top views of multiple SMA materials placed on top of each other; [Figure 4] FIG. 1 is a front view of a preferred embodiment of the present invention. [Figure 5a] 1 illustrates several phasing configurations with different engine cores used in an energy recovery system. [Figure 5b] 1 illustrates several phasing configurations with different engine cores used in an energy recovery system. [Figure 5c] 1 illustrates several phasing configurations with different engine cores used in an energy recovery system. [Figure 5d] 1 illustrates several phasing configurations with different engine cores used in an energy recovery system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The present invention relates to a heat recovery system, e.g., an engine, that can use either Shape Memory Alloys (SMAs) and other Negative Thermal Expansion Materials (NTEs), both of which are referred to as elastocaloric materials, to generate greater power output from a heated fluid using compression. The present invention provides an engine cycle in which the SMAs are compressed. In the compression mode, fatigue life is increased and is no longer limited. The compressive loads are much higher than the tensile loads, thus resulting in high efficiency.

[0033] A known energy recovery device is described in commonly assigned WO 2013 / 087490, which is hereby incorporated by reference in its entirety.

[0034] In such applications, the contraction of such materials when exposed to a heat source is captured and converted into usable mechanical work. A material useful as a working element in such engines has proven to be nickel-titanium alloy (NiTi). This alloy is a well-known shape memory alloy with numerous applications across a variety of industries. It will be appreciated that in the context of the present invention, suitable SMA or NTE materials may be used. Elongated bodies or wires have been proposed in such engines, however, it has been found that the wires are prone to breakage due to the applied stresses.

[0035] Force is generated through the contraction and expansion of the SMA material during hot and cold cycling within the working core via a piston transmission mechanism. An important aspect of this system is that a reliable assembly can be fabricated to perform high force, low displacement work for a maximum number of work cycles.

[0036] Figure 1 illustrates the SMA material working cycles during heating and cooling cycles. The invention described herein outlines a system and method for increasing the working output of a shape memory alloy during high and low temperature cycling. An important aspect of the invention is the compression of the SMA material during cycling.

[0037] In compression mode, the fatigue life of the SMA material or core is increased and is no longer limited. Compressive loads are much higher than tensile loads, therefore compressing the SMA material results in increased power output and increased efficiency.

[0038] The thermodynamic engine cycle may consist of a classical gas cycle such as the Stirling, Brayton or Ericsson cycle, or any combination of these cycles as illustrated in FIG.

[0039] As shown in Figure 1, a cycle can be configured such that as the SMA material absorbs heat from a high temperature source [Process 1-2], the material attempts to recover from the deformed material state [Martensite-Austenite]. The material then expands and therefore work can be extracted using a hydraulic cylinder or other device.

[0040] Once this process is complete, the heat recovery circuit is used to cool the material temperature until it approaches the cold source temperature [Process 2-3]. At this point, a low compressive load is applied to the material to compress it by increasing the drive temperature. In doing so, the material contracts and rejects heat to the cold source [Process 3-4]. Once complete, the heat recovery circuit is again used to increase the temperature of the material using the heat stored in the heat recovery circuit. At this point, the cycle is complete.

[0041] Compression of the SMA elements or materials during low temperature cycling may be employed using any suitable mechanical or tensioning mechanism, such as a powered module, which may be independently controlled.

[0042] The required strain is achieved by mechanically compressing the SMA element. The power control module for applying compression can be implemented in several ways. Compression of the SMA element can be achieved using a wide range of compression techniques, including electromechanical and hydraulic compression. A suitable electromechanical actuator converts rotary motion from an electric motor into linear motion. Most designs resemble a nut-and-bolt, where a threaded bolt is attached to a motor and can rotate, and a nut is fixed to the component being compressed and can move up and down the shaft of the bolt. In hydraulic compression, pressure is applied to a piston by a pressurized hydraulic fluid. When the pressure is released, the SMA material is allowed to expand.

[0043] FIG. 2a shows a perspective view of a preferred embodiment of the present invention. The disclosed engine comprises at least one mount of multiple plates 101 formed from SMA assembled one above the other. Each of the multiple plates 101 has multiple fluid ports 102 machined therein. The fluid ports 102 are designed to allow the passage of a fluid of a particular temperature through the plate 101 mount. The plate 101 mount is adapted to absorb heat and store energy as the fluid passes through it, and further comprises multiple plate stiffening slots 103. The plate stiffening slots 103 allow for the insertion of sturdy rods to resist buckling under compression. The slots 103 are on the order of a few mm in diameter and run the length of the mount, and the size can be selected based on the desired design.

[0044] FIG. 2b shows an example of a housing in which the plate mount / core is installed. A fluid, e.g. water, at a given temperature is introduced or pumped into the chamber housing the mount / core through one inlet 104 and a fluid outlet 105. The inlet 104 is adapted to introduce the fluid into the mount and outlet 105 is adapted to discharge the fluid introduced through the inlet port to the outside. In a preferred embodiment of the invention, the inlet and outlet ports are independent structural units and are fabricated using the same SMA material as the multi-plate mount to minimize heat loss. Fluid ports 102 machined into each plate significantly increase the surface area between the plate and the fluid and ensure that the fluid is in contact only with the SMA material reducing the overall heat loss. The fluid ports can be configured in any geometric pattern, such as a grid, circular, or polygonal pattern. The SMA plate 101 in the embodiment shown is substantially rectangular in shape. The SMA plates can be considered as the basic building blocks for constructing a certain scale core and engine system. The plate design is correlated with heat transfer optimization and the embodiment shown is merely suggestive. Smaller plates and mounts may be used for scaling down using the same principles. It will be appreciated that the engine operates between high and low stress states. Ideally low stress = low temperature (starting point), high stress = high temperature, with the SMA plates held in compression throughout the cycle. The applied compressive mechanical force further provides additional compression to at least one SMA element during the cooling cycle.

[0045] Figures 3a and 3b illustrate a preferred embodiment of the invention in which the core or SMA material comprises a number of SMA components 101 arranged as a mount of SMA plates 101 to define the engine core. The SMA plates 101 mounted one on top of the other can be compressed during cycling as required. Buckling supports 202 ensure that the SMA plates 101 are thermally insulated and that the whole structure is supported to withstand hydraulic loads.

[0046] The cycle may be single stage or may include multiple stages to increase the temperature range for heat recovery.

[0047] In one embodiment, the cycle may include multiple cores and internal heat recovery between the cores, or heat from a single core may be stored between cycles. This arrangement increases the efficiency of the system.

[0048] The system may include action recovery, where the energy stored in the compressed material is used directly to compress a second SMA component (the engine core), or the energy may be stored and indirectly used to compress additional SMA components at a later stage.

[0049] This stored energy can be stored in the form of pressurized fluid or converted to electricity and stored or used elsewhere in the system.

[0050] Figure 4 shows a front view of another preferred embodiment of the present invention. In the shown view, the mounts of SMA plate 101 forming the SMA core are placed in a housing 201. The housing 201 has a number of buckling supports 202 to maintain the integrity of the SMA core when a load is applied. When a compressive force is applied to the SMA core of the engine, optimizing the location, size and number of the buckling supports is important to estimate the amount of force that can be applied without collapsing the structure, and this ensures optimal extraction of the heat generating properties of the SMA. The housing 201 and the buckling supports 202 ensure that the SMA plate 101 is thermally insulated and that the entire structure is supported to withstand hydraulic loads while allowing movement of the individual mounts under compression.

[0051] It will be appreciated that in the context of the present invention, the engine / core can be assembled in several different configurations as shown in Figure 5. In one embodiment, the composition of at least one plate of the SMA plate mount is different than the other plates of the mount. Different SMA material mixes can be used for different SMA plates within a single mount.

[0052] In another embodiment of the invention, an SMA core with multiple SMA mounts is used, in which each mount consists of plates with different SMA composition, meaning that the plates within the same mount have the same SMA composition.

[0053] In another embodiment of the invention, multiple mounts are used, each mount having multiple SMA plates, each mount having at least one SMA plate with a different alloy composition than the other plates of the same mount.

[0054] Figures 5a to 5d illustrate several staggered configurations of an engine according to another embodiment of the invention. Staggered configurations of SMA plates that can be used to increase Delta-T can be achieved using several approaches. For example, Figure 5a illustrates a mount configuration in which different mixtures of optimized SMA plates can be used in a single mount. For example, plates of Mix 1, Mix 2, Mix 3 are arranged in a single mount. Figure 5b illustrates a multi-mount version of Figure fa. Plate mounts each containing the same SMA mixture interact with other plate mounts containing different SMA mixtures. For example, Mix 1 mount interacts with Mix 2 mount in series in a multi-mount configuration (and so on). Figure 5c is a multi-mount version of Figure 5b. Plate mounts each containing multiple SMA mixtures interact with other plate mounts containing similar or different SMA mixtures in a multi-mount configuration. For example, in a multi-mount arrangement, the stepped arrangements within the mounts may interact in series with stepped arrangements within different or similar mounts. Figure 5d shows a multi-core arrangement, where the cores of plates consisting of multi-mount version 1 or multi-mount version 2 or a combination of both interact together in series to form a stage.

[0055] In this specification, the words "comprise", "comprises", "comprised", "comprising" or any variations thereof, and the words "include", "includes", "included", "including" and any variations thereof, are considered interchangeable in their entirety and are to be accorded the broadest possible interpretation and all opposites thereof.

[0056] The invention is not limited to the embodiments described above, which may vary both in arrangement and detail. [Explanation of symbols]

[0057] 101 SMA Plate 102 Fluid Port 103 Plate Reinforcement Slot 104 Entrance 105 Exit 201 Housing 202 Buckling support

Claims

1. 1. An energy recovery device, comprising: an engine comprising a plurality of shape memory alloy (SMA) or negative thermal expansion (NTE) elements configured to define a core and connected to a drive mechanism; an immersion chamber adapted to house the engine and adapted to be sequentially filled with a fluid to expand and contract the SMA or NTE element with heating and cooling cycles of the SMA or NTE element; a compression device configured to apply a compressive mechanical force to at least one of the SMA elements or at least one of the NTE elements during the heating and / or cooling cycles; An energy recovery device comprising:

2. 2. The energy recovery device of claim 1, wherein the applied compressive mechanical force further compresses the at least one SMA element during the cooling cycle.

3. 3. The energy recovery device according to claim 1 or 2, wherein the SMA element comprises at least one mounting body made of a plurality of plates, at least two plates being made of shape memory alloy and assembled one above the other.

4. 4. The energy recovery device of claim 3, wherein the plurality of shape memory alloy plates comprises a plurality of fluid ports adapted to permit the passage of fluid through the mounting body.

5. The energy recovery system of claim 1 , wherein the compression device comprises an electromechanical actuator.

6. The energy recovery device of claim 1 , wherein the compression device comprises a hydraulic compression module configured to apply pressure to a piston using pressurized hydraulic fluid.

7. 10. The energy harvesting device of claim 1, wherein the SMA elements or plates are formed using an additive manufacturing or 3D printing process.

8. 10. The energy recovery device of claim 1 comprising a plurality of SMA cores disposed within the housing, each core configured to be independently compressed during cycling.

9. 9. An energy recovery device as claimed in claim 8, wherein the composition of the SMA forming the plates mounted on one SMA core is different from the composition of the SMA forming the plates mounted on another SMA core.

10. 1. A method of energy recovery comprising: disposing a plurality of elongated shape memory alloy (SMA) or negative thermal expansion (NTE) elements defining a core and connected at a second end to a drive mechanism; containing the SMA element in a chamber and successively filling it with a fluid such that heating and cooling cycles of the SMA element cause the SMA element or the NTE element to expand and contract; applying mechanical compression to at least one of the SMA element or the NTE element during the cooling and / or heating cycles; The method includes:

11. The method of claim 10, further comprising the step of applying a compressive mechanical force to the at least one SMA element during the cooling cycle.

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