Protective Element for use in an Energy Recovery Device

Field

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, TEGs are relatively expensive. 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 under development 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 WO2013/087490 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 US2005/150223 (Rey et al) and US2012/017582 (Lewis). In the context of the present application a plurality of elongated NiTi wires form a working core of an engine. Force is generated through the contraction and expansion of the wires within the working core, via a piston and crank mechanism. An important aspect of this system to operate efficiently is the ability to secure the NiTi elements at both ends such that a strong and reliable union is created, enabling high-force, low displacement work to be performed for a maximum number of working cycles. Nickel Titanium alloy is considerably harder and tougher than the steel material that might be used to hold the wires together. A problem is therefore that the NiTi elements wear or otherwise fatigue the steel elements at the points at which they are in contact. In the case of a bundle of wires making up the core, this would be the boundary at which the outermost NiTi wire elements are located. In the case of a "salt shaker" bundle type holder, this would be the steel boundary point of contact for each wire hole.

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

Summary

According to the invention there is provided, as set out in the appended claims, an energy recovery device comprising:

a drive mechanism ;

an engine comprising a plurality of Negative Thermal Expansion (NTE) elements fixed at a first end by a holder element and connected at a second end to a drive mechanism wherein a protective element is positioned adapted to protect the holder element from movement of the NTE elements. In all bundle holder concepts, the cyclic expansion and contraction of the wire elements against a steel / aluminium (or other non-NiTi material) can cause significant wear and tear during the lifetime of the unit, as NiTi or SMA material is significantly harder than the other elements. The solution to this is to ensure that the cycling SMA/ NTE elements are only ever in contact with other NiTi elements.

In one embodiment the second element may be presented as a gasket or seal at the outer perimeter at which the cycling elements come in contact with the bracket.

In one embodiment the protective element comprises a gasket seal. In one embodiment the protective material comprises Negative Thermal

Expansion (NTE) material.

In one embodiment the protective element is substantially O shaped. The invention enables the NiTi wires to be fixed in such a way that the high force developed by their contraction can be safely transmitted such that mechanical work can be produced.

In one embodiment there is provided an engine comprising a plurality of Negative Thermal Expansion (NTE) elements fixed at a first end by a holder element and connected at a second end to a drive mechanism wherein a protective element is positioned and adapted to protect the holder element from movement of the NTE elements. In another embodiment there is provided a protective element positioned and adapted to protect a holder element from movement of SMA or NTE elements in an energy recovery device during use.

Brief Description of the Drawings

The invention will be more clearly understood from the following description of 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 one end of a SMA actuation core comprising a plurality of SMA wires clamped or otherwise secured at a first point;

Figure 3 illustrates an embodiment of the invention wherein the plurality of SMA wires clamped or otherwise secured at a first point; and

Figures 4 and 5 illustrate 3D perspective views of the invention similar to the embodiment shown in Figure 3. Detailed Description of the Drawings

The invention relates to a heat recovery system is under development which 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 an 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 is 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. Higher deflections can also be acheived. 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 WO2013/087490, 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 wires clamped or otherwise secured at a first point which is fixed.

In order to secure the SMA wires in the engine, it is required to develop a system that can anchor each wire at both ends, in such a fashion as will allow it to operate under high load. This system has been designated as the "bundle holder". The bundle holder should overcome two specific problems:

1 ) Transmit the high-force, low displacement load of the SMA wires during operation. This is a single degree of freedom (DOF) system whereby one end of the bundle is secured and remains stationary, whilst the opposing end is free to move in one axis of displacement to enable the movement of a piston or other energy generating device to generate energy.

2) Enable the close-packing of the wires, insofar as possible, to enable maximum heat transfer from the transiting water to the wire and vice versa, as shown in Figure 2.

Figure 2 illustrates a plurality of wires, 1 a, 1 b, 1 c arranged in a bundle configuration and held together by a clamp device 1 0 or other mechanism to hold the wires together.

Such a core is described in UK patent application number 1409679.6, assigned to Exergyn. 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 elements are fixed at one end by means of a holder or clamp to secure the elements together. In one embodiment 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 alloy wires. The SMA wires are substantially elongated and arranged in a parallel orientation to make up a core that is housed in a chamber.

As mentioned above Nickel Titanium alloy is considerably harder and tougher than the steel material that might be used in the bundle holder. A problem is therefore that the NiTi elements or wires wear or otherwise fatigue the steel elements at the points at which they are in contact when the SMA wires contract and expand during use.

The solution to the above problem is to ensure that the thermally cycling SMA material, i.e. the material which stands the most opportunity for causing wear and fatigue, can only be in direct contact with other NiTi or other toughened material, i.e. they should not come directly in contact with the steel.

In order to achieve this, a ring of SMA material or other toughened material, is placed at the boundary of the working SMA wires and the steel bundle holder. In so doing, the steel is protected from the flexing of the active wire elements - which cyclically expand and contract during thermal cycling - and thus is protected from premature wear. The SMA - SMA boundary ensures a strong interface between the active material and the force transmitting bundle holder.

Figure 3 illustrates an embodiment of the invention wherein the plurality of SMA wires 1 a, 1 b, 1 c are clamped or otherwise secured 10 at a first point showing a ring of SMA material or toughened material which acts as a protective element 1 1 . In effect the invention provides a gasket 1 1 or gasket seal 1 1 to interface between the end of the SMA wires 1 a, 1 b, 1 c and the clamp 10 or holder mechanism to prevent wear and tear of the holder mechanism.

Figures 4 and 5 illustrate 3D perspective views of the invention similar to the embodiment shown in Figure 3. It will be appreciated that the protective element 1 1 and holder 10 be the one element and integrally formed in some applications, as illustrated in Figure 5. Figure 5 shows the gasket or seal 1 1 integrally formed with the holder mechanism 10.

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.