WO2018229231A1

WO2018229231A1 - Energy device core for use in an energy recovery device

Info

Publication number: WO2018229231A1
Application number: PCT/EP2018/065895
Authority: WO
Inventors: Kevin O'TOOLE; Georgiana TIRCA
Original assignee: Exergyn Limited
Priority date: 2017-06-16
Filing date: 2018-06-14
Publication date: 2018-12-20
Also published as: GB201709605D0

Abstract

The invention provides energy recovery system comprising a first Shape-Memory Alloy (SMA) or Negative Thermal Expansion (NTE) core and adapted to convert movement of the core into energy in response to a temperature change; a second Shape-Memory Alloy (SMA) or Negative Thermal Expansion (NTE) core in fluid communication with the first core and adapted to convert movement of the second core into energy; a third unbalanced Shape-Memory Alloy (SMA) or Negative Thermal Expansion (NTE) core or Negative Thermal Expansion (NTE) core in fluid communication with the first and second cores and adapted to convert movement of the third core into energy, wherein a fluid provides the temperature change to activate either the first, second or third cores such that the cycle time for activating at least one core is reduced.

Description

Title

Energy Device Core 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 (SMAs) or Negative Thermal Expansion (NTE) materials.

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 employs 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.

The three main types of Shape-Memory Alloys are the copper-zinc-aluminium- nickel, copper-aluminium-nickel, and nickel-titanium (NiTi) alloys but SMAs can also be created, for example, by alloying zinc, copper, gold and iron. The list is non-exhaustive.

The memory of such materials has been employed or proposed since the early 1970s for use in heat recovery processes and in particular by constructing SMA engines which recover energy from heat as motion. Recent publications relating to energy recovery devices include PCT Patent Publication number WO2013/087490, assigned to the assignee of the present invention. It is desirable to translate the contraction of the SMA or NTE material into a mechanical force in an efficient manner. Typically in SMA engines, which is made of a number of elongated SMA wires positioned in a bundle arrangement to define a core, there is a discrepancy between the heating time and cooling time due to a multitude of thermodynamic and material specific factors. Achieving a balance is a difficult problem to solve, and therefore one cycle component will always be faster than the other.

In a balanced configuration, where a number of engine cores are present the quantity of heating cores and cooling cores is equal at any point in time, the system must be run based on the slowest cycle component. This ensures that the wires reaches its designed temperature/strain targets during both heating and cooling. If this is not done, the cycle will be incomplete and system power will be reduced. Within a core configuration where the quantity of cores heating and cooling are equal, the total cycle time (heating and cooling) will be twice that of the slowest time - i.e. twice the cooling time in the example of the low temperature hysteresis. It is not a trivial task and generally is complicated and involves significant energy losses.

It is therefore an object to provide an improved system and method in an energy recovery device with reduced heating/cooling cycle times.

Summary

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

a first Shape-Memory Alloy (SMA) or Negative Thermal Expansion (NTE) core and adapted to convert movement of the core into energy in response to a temperature change;

a second Shape-Memory Alloy (SMA) or Negative Thermal Expansion (NTE) core in fluid communication with the first core and adapted to convert movement of the second core into energy;

a third unbalanced Shape-Memory Alloy (SMA) or Negative Thermal Expansion (NTE) core or Negative Thermal Expansion (NTE) core in fluid communication with the first and second cores and adapted to convert movement of the third core into energy,

wherein a fluid provides the temperature change to activate either the first, second or third cores such that the cycle time for activating at least one core is reduced.

The invention solves the problem of having to cycle the system based on the slowest part of the cycle. Typically the cooling stroke due to the design of the temperature hysteresis band closer to the cold fluid input temperature than the hot fluid input temperature. By releasing this constraint, the system can be cycled faster, meaning that the work of the SMA can be done faster, increasing the output power of the system for no change in stress, strain or temperature input. In other words the invention enables the cycling of the cores according to the fastest cycle time, i.e. hot cycle and overcoming the delay in response that is inherent in the material on the cold side.

In one embodiment the number of cores in the system comprises an unbalanced core ratio. In one embodiment the unbalanced core ratio enables at least one core can be activated based on a fastest cycle period of the first, second or third cores..

In one embodiment the at least one core comprises three temperature stages to activate using a hot phase, an intermediate cooling phase and a cold phase.

In one embodiment the system comprises an uneven number of cores.

In one embodiment the SMA material comprises a Nickel-Titanium alloy (NiTi). According to another embodiment of the invention there is provided a method to recover energy from a hot fluid comprising the steps of:

providing a first Shape-Memory Alloy (SMA) or Negative Thermal Expansion (NTE) core and converting movement of the core into energy in response to a temperature change; providing a second Shape-Memory Alloy (SMA) or Negative Thermal Expansion (NTE) core in fluid communication with the first core and converting movement of the second core into energy;

providing a third unbalanced Shape-Memory Alloy (SMA) or Negative Thermal Expansion (NTE) core or Negative Thermal Expansion (NTE) core in fluid communication with the first and second cores and converting movement of the third core into energy,

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 known energy recovery system;

Figure 2 illustrates a prior art arrangement with an equal heating and cooling arrangement of cores;

Figure 3 illustrates an unequal temperature gradient on heating and cooling due to low temperature hysteresis band; and

Figure 4 illustrates a Heating-Cooling Ratio Core Configuration according to one embodiment of the invention.

Detailed Description of the Drawings

The invention relates to a heat recovery system under development which can use either Shape-Memory Alloys (SMAs) 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 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. It will be appreciated that in the context of the present invention the term 'wire' is used and should be given a broad interpretation to mean any suitable length of SMA or NTE material that can act as a core.

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 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). This alloy is a well-known Shape-Memory Alloy and has numerous uses across different industries. It will be appreciated that any suitable SMA or NTE material can be used in the context of the present invention.

Force is generated through the contraction and expansion of the alloy, presented as a plurality of wires (or bundle), within the working core, via a piston and transmission mechanism. Accordingly, depending on the requirements of a particular configuration and the mass of SMA material needed a plurality of SMA wires may be employed together, spaced substanitally parralell to each other, to form a single core. In one embodiment the core reacts when exposed to the hot and cold streams of fluid. The time of reaction is of most importance when trying to improve the efficiency of power production. The invention described herein provides a system and method to cycle the system on the basis of the fastest cycle component (heating or cooling) where three or more SMA engines are present.

Typically in SMA engines, there is a discrepancy between the heating time and cooling time due to a multitude of thermodynamic and material specific factors. Achieving a balance is difficult, and therefore one cycle component will always be faster than the other.

Figure 2 illustrates a balanced configuration, where the quantity of heating cores and cooling cores is equal at any point in time. The system must be run based on the slowest cycle component. This ensures that the wire reaches its designed temperature/strain targets during both heating and cooling. If this is not done, the cycle will be incomplete and system power will be reduced. Within a core configuration where the quantity of cores heating and cooling are equal, the total cycle time (heating and cooling) will be twice that of the slowest time - i.e. twice the cooling time in the example of the low temperature hysteresis. Figure 2 shows four cores C1 , C2, C3 and C4 arranged in cascade and parallel at times t=1 and t=2 showing the different heating and cooling cycles of four cores. For example, if the heating cycle time is 4 seconds, and the cooling is 5 seconds, the total cycle time will be 2 x 5 = 10 seconds

Figure 3 shows the unequal temperature gradient on heating and cooling due to low hot temperature hysteresis band. Typically in an energy recovery system using a number of cores it is desirable to maintain a relatively narrow and low hot temperature hysteresis curve to allow the material to fully transform into austenite during heating. Due to this low hysteresis band, the cold cycle time will be larger than the hot cycle time (i.e. the difference in between the hot fluid temperature - Af > cold fluid temperature - Mf).

There is another factor coming from an inherent property of the alloy material making up the wire that is preventing the material to change phase while exposed to cold fluid as fast as when it is exposed to hot fluid. The shape memory alloys are slower to react when needed to change phase from austenite to martensite under stress. The de-twinned martensitic state is a stress induced phase in which the internal structure of the alloy changes. In the austenitic state it is the alloy's parent state resulting from the manufacturing process, so that the material has an affinity to transform to it if the temperature condition is met.

To overcome this problem, additional cores can be added to the system to allow a longer 'soak' time for the slower cycle component, in this case the cold cycle of the engine such that an uneven amount of cores are present in the system.

The addition of extra cores means that while the soak/immersive time is increased for the cold cycle, there is also a core available for activation (firing) subsequent to the faster cycle component (i.e. the hot cycle) at any point in time. This effectively allows the system to be cycled on the basis of the fastest cycle component (usually the heating cycle component) - which increases the power output.

The system does not change from the normal two hot two cold cores configuration because the additional cores are only meant to prepare the two cold firing cores needed in the power producing system. Their purpose is solely to decrease the cold heat transfer time so that the power output is calculated based on the heating time, which is much faster. Essentially the cores comprises three temperature stages to activate using a hot phase, an intermediate cooling phase and a cold phase, shown as t=1 ; t=2 and t=3 in Figure 4 illustrating a six core configuration. In this case, when an additional cycle state is added to the total cycle, the cycle will now have one heating cycle period, and two cooling cycle periods. This configuration can work for 1 :2 heating to cooling ratio, or for 1 :n heating to cooling ratios where n is a larger number than 1 .

In this 1 :2 ratio, the additional cores means that the amount of energy released during a cycle is increased by 1 .5 times, while the total cycle time is also increased by 1 .5 times. Similar to the example above, if the heating time period is 4 seconds, and the cooling time period is 5 seconds, the system provides a total of 8 seconds for cooling to complete (of which only 5 seconds is required), whilst being able to fire hot cores every 4 seconds. The total cycle time in this six core configuration is therefore 12 seconds to release 1 .5 times the energy of the four core configuration. This is equivalent of using an 8 second total cycle time in a four core configuration, meaning an increase in power output by 20%. The net effect of using an unbalanced core ratio such as this is that the system can be cycled based on the fastest cycle period (either hot or cold), unlike the balanced/equal core configuration where the system must be cycled based on the slowest cycle period. 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

1 . An energy recovery system comprising:

characterised in that:

2. The energy recovery system as claimed in claim 1 wherein the number of cores in the system comprises an unbalanced core ratio.

3. The energy recovery system as claimed in claim 2 wherein the unbalanced core ratio comprises at least one core can be activated based on a fastest cycle period of the first, second or third cores.

4. The energy recovery system as claimed in any preceding claim wherein the at least one core comprises three temperature stages and configured to activate using a hot phase, an intermediate cooling phase and a cold phase.

5. The energy recovery system as claimed in any preceding claim wherein the system comprises an uneven number of cores.

6. The energy recovery system as claimed in any preceding claim wherein the SMA material comprises a Nickel-Titanium alloy (NiTi).

7. A method to recover energy from a fluid comprising the steps of:

providing a first Shape-Memory Alloy (SMA) or Negative Thermal Expansion (NTE) core and converting movement of the core into energy in response to a temperature change;

providing a second Shape-Memory Alloy (SMA) or Negative Thermal Expansion (NTE) core in fluid communication with the first core and converting movement of the second core into energy;

providing a third unbalanced Shape-Memory Alloy (SMA) or Negative Thermal Expansion (NTE) core or Negative Thermal Expansion (NTE) core in fluid communication with the first and second cores and converting movement of the third core into energy; and

immersing the cores in a fluid to provide a temperature change to activate either the first, second or third cores such that a cycle time for activating at least one core is reduced.