GB2533357A

GB2533357A - Heat transfer in an energy recovery device

Info

Publication number: GB2533357A
Application number: GB1422531.2A
Authority: GB
Inventors: Byrne Ronan
Original assignee: Exergyn Ltd
Current assignee: Exergyn Ltd
Priority date: 2014-12-17
Filing date: 2014-12-17
Publication date: 2016-06-22
Also published as: WO2016097214A1

Abstract

An energy recovery device comprises an engine driven by first and second cores of Shape Memory Alloy (SMA) or Negative Thermal Expansion (NTE) elements A, B. The SMA or NTE cores are housed in respective immersion chambers which are sequentially filled with fluid for heating and/or cooling of the NTE or SMA cores. The first and second cores are in communication with each other via an energy storage element such as a relaxation spring. This prevents overstraining of a core, as a cooling core cannot be forceably returned to its starting position until it is sufficiently relaxed to accept the transformation (e.g. as the phase changes from austenite to martensite).

Description

Heat Transfer in an Energy Recovery Device

Field

s The present application relates to the field of energy recovery and in particular to the use of shape memory alloys (SMA) or Negative Thermal Expansion materials (NTE) for same.

Background

Low grade heat, which is typically considered less than 100 degrees, represents a significant waste energy stream in industrial processes, power generation and transport applications. Recovery and re-use of such waste streams is desirable. An example of a technology which has been proposed for this purpose is a Thermoelectric Generator (TEG). Unfortunately, TEG's are relatively expensive.

IS Another largely experimental approach that has been proposed to recover such energy is the use of Shape Memory Alloys.

A shape-memory alloy (SMA) is an alloy that "remembers" its original, cold-forged shape which once deformed returns to its pre-deformed shape upon heating. This material is a lightweight, solid-state alternative to conventional actuators such as hydraulic, pneumatic, and motor-based systems.

A heat engine concept is under development which utilises Shape Memory Alloy (SMA) or another Negative Thermal Expansion (NTE) material as the working medium. In such an engine, for example as disclosed in PCT Patent Publication number W02013/087490 and assigned to the assignee of the present invention, the forceful contraction of such material on exposure to a heat source is captured and converted to usable mechanical work.

Thus far, a useful material for such a working mass has been found to be Nickel-Titanium alloy (NiTi). This alloy is a well known Shape-Memory Alloy and has numerous uses across different industries.

For example, NiTi wires form the working element of the engine. Force is generated through the contraction and expansion of these elements within the working core, via a piston and crank mechanism.

s The heating and cooling times of reaction for the SMA or NTE elements are not equal. A problem exists where two SMA cores or engines are run in parallel; disparate heating and cooling times results in inefficient operation of the heat engine. This problem can be amplified when more than two cores or engines are run in parallel.

It is therefore an object of the invention to provide a device and method to overcome the above mentioned problem.

Summary

IS According to the invention there is provided, as set out in the appended claims, an energy recovery device comprising: a first NTE or SMA core housed in a first immersion chamber and adapted to be sequentially filled with fluid to allow heating and/or cooling of the first NTE or SMA core; a second NTE or SMA core housed in a second immersion chamber and adapted to be sequentially filled with fluid to allow heating and/or cooling of the second NTE or SMA core; and wherein the first core and second core are in communication with each other via a storage element, said element configured to control the heating and cooling times of each core.

It will be appreciated that by implementing a storage element in the transmission of an antagonistically arranged drive eliminates the issues associated with disparate heating and cooling reaction times.

It will be further appreciated that the storage element configuration of the present invention reduces the possible negative effects of allowing cores to operate in opposing heating-cooling cycles in antagonistic arrangements, whereby the heating and cooling reaction times are not identical.

The present invention can be used to increase the performance of the energy recovery device by improving the performance and fatigue life of the SMA by allowing the cooling elements to return to their martensitic state more naturally as opposed to over-stressing said elements by allowing the heating elements to provide a return force before the cooling elements are ready. The invention effectively provides a mechanical linkage between two or more immersion io chambers.

In one embodiment the storage element comprises a biasing element. In one embodiment the storage element comprises a spring.

In one embodiment the spring is adapted to store the relaxation force from a first heating core required to return a second cooling core back to a desired position.

In one embodiment the storage element can be sized so that an extension of its length equal to the stroke of the SMA wire contraction will result in it storing the relaxation force required to be applied to the cooling wires.

In one embodiment the storage element is configured to store a relaxation force from a heating core, said force is sufficient to return a cooling core back to its starting position, and only supply that force when the cooling core is in a position to receive same.

In another embodiment there is provided an energy storage element for connecting a first NTE or SMA core housed in a first immersion chamber and adapted to be sequentially filled with fluid to allow heating and/or cooling and a second NTE or SMA core housed in a second immersion chamber and adapted to be sequentially filled with fluid to allow heating and/or cooling.

Brief Description of the Drawings

The invention will be more clearly understood from the following description of s an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:-Figure 1 illustrates a prior art energy recovery system using SMA or NTE materials; Figure 2 illustrates a first embodiment of the present invention; and Figure 3 illustrates a number of states showing operation of the embodiment described with respect to Figure 2.

Detailed Description of the Drawings

The invention relates to a heat recovery system is under development which IS can use either Shape Memory Alloys (SMA) or Negative Thermal Expansion materials (NTE) to generate power from low grade heat.

An exemplary known embodiment of an energy recovery device will now be described with reference to Figure 1 which provides energy recovery device employing a SMA engine indicated by reference numeral 1. The SMA engine 1 comprises an SMA actuation core. The SMA actuation core is comprised of SMA material clamped or otherwise secured at a first point which is fixed. At the opposing end, the SMA material is clamped or otherwise secured to a drive mechanism 2. Thus whilst the first point is anchored the second point is free to move albeit pulling the drive mechanism 3. An immersion chamber 4 adapted for housing the SMA engine and is adapted to be sequentially filled with fluid to allow heating and/or cooling of the SMA engine. Accordingly, as heat is applied to the SMA core it is free to contract. Suitably, the SMA core comprises a plurality of parallel wires, ribbons or sheets of SMA material. Typically, a deflection in and around 4% is common for such a core. Accordingly, when a 1 m length of SMA material is employed, one might expect a linear movement of approximately 4cm to be available. It will be appreciated that the force that is provided depends on the mass of wire used. Such an energy recovery device is described in PCT Patent Publication number W02013/087490, assigned to the assignee of the present invention, and is incorporated fully herein by reference.

For such an application, the contraction of such material on exposure to a heat source is captured and converted to usable mechanical work. A useful material for the working element of such an engine has been proven to be Nickel-Titanium alloy (NiTi). The SMA actuation core is comprised of a plurality SMA material clamped or otherwise secured at a first point which is fixed. In this application a core engine is described for use in an energy recovery device comprising a plurality of Shape Memory Alloys (SMA) or Negative Thermal Expansion (NTE) elements fixed at a first end and connected at a second end to a drive mechanism. The holder is a holder configured with a plurality of slots adapted to receive the plurality of Shape Memory Alloys (SMA) or NTE elements, for example Nickel Titanium wires. The SMA wires are substantially elongated and arranged in a parallel orientation to make up a core that is housed in a chamber.

A problem exists where two SMA cores or engines are run in parallel disparate heating and cooling times results in inefficient operation of the overall heat 20 engine. This problem can be amplified when more than two cores or engines are run in parallel.

Figure 2 illustrates a first embodiment of the present invention. A first NTE or SMA core housed in a first immersion chamber and adapted to be sequentially filled with fluid to allow heating and/or cooling of the first NTE or SMA core. A second NTE or SMA core housed in a second immersion chamber and adapted to be sequentially filled with fluid to allow heating and/or cooling of the second NTE or SMA core. The first core and second core are in communication with each other via a storage element, wherein the storage element is configured to control the heating and cooling times of each core.

The use of the storage element, for example a spring, within the antagonistic connection between two cores alleviates the issue of over straining caused by simultaneously alternating between heating and cooling cycles of these cores. The purpose of this storage element, or spring, is to store the relaxation force from a heating core, which is required to return a cooling core back to its starting position, but to only supply that force when the cooling core is willing to accept it.

In operation, as the SMA wire in core A heats, it contracts, pulling on the antagonistic connection to core B. The addition of the relaxation spring will allow for storage of this energy. This means that if core B has not begun to transition from austenite to martensite fast enough, the energy applied by the contracting SMA will be stored in the spring as opposed to straining the cooling wires. This spring can be sized so that an extension of its length equal to the stroke of the SMA wire contraction will result in it storing the relaxation force required to be applied to the cooling wires.

Fig 3 illustrates the invention in operation showing the different states between heating and cooling cycles. Fig 3(a) shows the antagonistic couple in an initial state where core A is fully heated and B is fully cooled.

Fig 3(b) shows a state in which core A has begun its cooling cycle, but its SMA wire has yet to begin its transformation to martensite, while B has begun heating and its SMA wire has begun transforming into austenite, thereby contracting. This contraction applies a force to the relaxation spring, which will absorb the appropriate amount of energy while no strain is applied to the wires contained in core B. Fig 3(c) shows the next stage in the cores operation. Core A has begun to expand as the SMA contained therein has begun its phase change to martensite, and is returned to its original position by the energy stored in the relaxation spring.

It will be appreciated that a relaxation spring is described in the context of the present invention other storage elements other than a spring can be used to provide the necessary energy required.

In the specification the terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms include, includes, included and including" or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.

The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.

Claims

Claims 1. An energy recovery device comprising: a first NTE or SMA core housed in a first immersion chamber and s adapted to be sequentially filled with fluid to allow heating and/or cooling of the first NTE or SMA core; a second NTE or SMA core housed in a second immersion chamber and adapted to be sequentially filled with fluid to allow heating and/or cooling of the second NTE or SMA core; and wherein the first core and second core are in communication with each other via a storage element, said element configured to control the heating and cooling times of each core.
2. The energy recovery device of claim 1 wherein the storage element is comprises a biasing element.
3. The energy recovery device of claim 1 or 2 wherein the storage element comprises a spring.
4. The energy recover device of claim 3 wherein the spring is adapted to store the relaxation force from a first heating core required to return a second cooling core back to a desired position.
5. The energy recovery device of any preceding claim wherein the storage element can be sized so that an extension of its length equal to the stroke of the SMA wire contraction will result in it storing the relaxation force required to be applied to the cooling wires.
6. The energy recover device of any preceding claim wherein the storage element is configured to store a relaxation force from a heating core, said force is sufficient to return a cooling core back to its starting position, and only supply that force when the cooling core is in a position to receive same.
7. An energy storage element for connecting a first NTE or SMA core housed in a first immersion chamber and adapted to be sequentially filled with fluid to allow heating and/or cooling and a second NTE or SMA core housed in a second immersion chamber and adapted to be sequentially filled with fluid to allow heating and/or cooling.