Patent Description:
Thermal management is typically required or desired in various electronic devices, powered systems, and other devices or systems where thermal energy (heat) can adversely impact performance of or damage device or system components. For example, batteries often experience heating during use, and thermal management is typically required or desired in order to maintain the batteries within specified temperature ranges. These temperature ranges can be defined to maintain operational efficiency of the batteries, ensure long-term usage of the batteries, or avoid damage to the batteries.

<CIT> discloses a heat switch for transferring heat between a heat source and a heat sink which comprises: an expandable fluid container located in a direct conductive heat transfer relationship with said heat source, said container containing fluid adapted to expand said container when said fluid is heated, heat transfer means associated with said expandable fluid container and in heat transfer contact with said heat source, said heat transfer means being adapted to be forced into contact with said heat sink by said expandable fluid container within a narrow predetermined temperature range whereby to transmit heat from said heat source to said sink, and biased overload means between said heat transfer means and said heat sink whereby to prevent excessive force between said heat transfer means and said heat sink when heat is being conducted there between.

This disclosure is directed to a phase change material (PCM)-based conductive thermal actuator switch.

In a first embodiment, an apparatus comprises: multiple thermal actuator switches configured to control a transfer of thermal energy through the apparatus, the thermal actuator switches arranged in a stacked configuration, each thermal actuator switch comprising: first and second plates; a piston movable between the first and second plates; and a phase change material configured to (i) expand to move a surface of the piston into a first position and (ii) contract to allow the surface of the piston to move into a second position, the surface of the piston thermally contacting the first plate and increasing thermal energy transfer between the first and second plates when in one of the first and second positions, the surface of the piston spaced apart from the first plate and decreasing thermal energy transfer between the first and second plates when in another of the first and second positions; wherein different ones of the thermal actuator switches comprise different phase change materials that expand or contract at different temperatures.

In a second embodiment, a system comprises: at least one heat source; at least one heat sink; and the apparatus of the first embodiment configured to control a transfer of thermal energy between the at least one heat source and the at least one heat sink.

In a third embodiment, a method comprises: receiving thermal energy at multiple thermal actuator switches from at least one heat source, the thermal actuator switches arranged in a stacked configuration; and controlling a transfer of the thermal energy between the at least one heat source and at least one heat sink using the thermal actuator switches; wherein each thermal actuator switch comprises: first and second plates; a piston movable between the first and second plates; and a phase change material configured to (i) expand to move a surface of the piston into a first position and (ii) contract to allow the surface of the piston to move into a second position, the surface of the piston thermally contacting the first plate and increasing thermal energy transfer between the first and second plates when in one of the first and second positions, the surface of the piston spaced apart from the first plate and decreasing thermal energy transfer between the first and second plates when in another of the first and second positions; wherein different ones of the thermal actuator switches comprise different phase change materials that expand or contract at different temperatures.

<FIG>, described below, and the various embodiments used to describe the principles of the present disclosure are by way of illustration only and should not be construed in any way to limit the scope of this disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any type of suitably arranged device or system.

As described above, thermal management is typically required or desired in various electronic devices, powered systems, and other devices or systems where thermal energy (heat) can adversely impact performance of or damage device or system components. For example, batteries often experience heating during use, and thermal management is typically required or desired in order to maintain the batteries within specified temperature ranges. These temperature ranges can be defined to maintain operational efficiency of the batteries, ensure long-term usage of the batteries, or avoid damage to the batteries.

This disclosure provides various thermal actuator switches that can be used for thermal management or other purposes. Each of the thermal actuator switches includes a piston that can be used to form and break a thermal connection or otherwise facilitate and impede thermal energy transfer between at least one heat source (such as a power-dissipating or warmer device) and at least one heat sink (such as a cold plate). At least one phase change material (PCM) in each thermal actuator switch can change phase and expand/contract based on localized heating/cooling in the thermal actuator switch to move the piston within the thermal actuator switch. In some cases, when the phase change material in a thermal actuator switch is heated, the phase change material can expand and move the piston in the thermal actuator switch to form a thermal connection (or improve a thermal connection) between the heat source(s) and the heat sink(s). When the phase change material in the thermal actuator switch is cooled, the phase change material can contract, and a spring-loaded mechanism, a magnet, or other return mechanism can be used to push or pull the piston and break the thermal connection (or lessen the thermal connection) between the heat source(s) and the heat sink(s). Other configurations can have a phase change material that expands when cooled and that contracts when heated, which again can move the piston to form (or improve) and break (or lessen) a thermal connection.

In this way, the phase change material in each thermal actuator switch can be used to provide passive switching of the thermal actuator switch. Also, the actuation of each thermal actuator switch can be used to control the contacting surface area between the piston and another component of the thermal actuator switch, which allows the surface area used for thermal energy transfer to be easily controlled. In some embodiments, the actuation of each thermal actuator switch is linear based on the movement of the piston. Further, through the use of the return mechanism, each thermal actuator switch may be used to repeatedly form and break (or increase and decrease) the thermal connection between the heat source(s) and the heat sink(s).

In addition, multiple thermal actuator switches may be used in any suitable serial and/or parallel arrangement(s) to provide desired thermal energy transfer paths between at least one heat source and at least one heat sink. For example, an array of parallel thermal actuator switches may be positioned across at least one battery or other heat source(s) and used to transfer thermal energy away from the heat source(s). This may be useful, for instance, in reducing or avoiding the creation of a temperature gradient across the surface(s) of the heat source(s). As another example, multiple thermal actuator switches may be stacked in series, where different thermal actuator switches have phase change materials that expand/contract at different temperature thresholds. This may, for example, allow the overall thermal transfer behavior of the thermal actuator switches to be tuned for a particular application. As a particular example, this may allow the stacked thermal actuator switches to form/break (or facilitate/ inhibit) one or more thermal connections between the heat source(s) and the heat sink(s) at different temperatures. As a result, for instance, one of multiple stacked thermal actuator switches may form or improve a thermal connection between the heat source(s) and the heat sink(s) at a lower temperature to enable a first rate of thermal energy transfer. Another of the stacked thermal actuator switches may form or improve the same or another thermal connection between the heat source(s) and the heat sink(s) at a higher temperature to enable a second (larger) rate of thermal energy transfer. Combinations of these approaches may also be used, such as when multiple sets of series-coupled (stacked) thermal actuator switches are arranged in a parallel array.

<FIG> illustrate an example PCM-based conductive thermal actuator switch <NUM> according to this disclosure. In particular, <FIG> and <FIG> illustrate perspective views of the thermal actuator switch <NUM> in different operational configurations, and <FIG> and <FIG> illustrate cross-sectional views of the thermal actuator switch <NUM> in the different operational configurations. Note that certain components of the thermal actuator switch <NUM> in <FIG> and <FIG> are shown in transparent outline form for ease of illustration and explanation.

As shown in <FIG> and <FIG>, the thermal actuator switch <NUM> may include or be associated with a housing, such as one formed using a top plate <NUM> and a bottom plate <NUM>. Each plate <NUM> and <NUM> represents a structure that can be thermally coupled to at least one heat source or at least one heat sink. For example, the top plate <NUM> may be thermally coupled to at least one heat sink, and the bottom plate <NUM> may be thermally coupled to at least one heat source (or vice versa). Each plate <NUM> and <NUM> may be formed using any suitable material(s), such as one or more metals or other material(s) having high thermal conductivity. Each plate <NUM> and <NUM> may also be formed in any suitable manner. In addition, each plate <NUM> and <NUM> may have any suitable size, shape, and dimensions.

In some cases, the plates <NUM> and <NUM> may optionally be separated by a thermally-insulative material <NUM>, which is shown only in <FIG> and <FIG> for ease of illustration. The thermally-insulative material <NUM> can help to reduce or minimize the thermal conductivity between the plates <NUM>-<NUM>, which can help to reduce or minimize thermal energy transfer between the plates <NUM>-<NUM> themselves except when needed or desired. The thermally-insulative material <NUM> may be formed from any suitable material(s), such as a thermally-insulative epoxy or other material(s) used to attach the plates <NUM>-<NUM> or a fiberglass washer or other structure(s) positioned between the plates <NUM>-<NUM>. The thermally-insulative material <NUM> may also be formed in any suitable manner. In addition, the thermally-insulative material <NUM> may have any suitable size, shape, and dimensions.

A piston formed by a piston base <NUM> and a piston plate <NUM> is positioned and movable between the plates <NUM> and <NUM>. For example, the top plate <NUM> may include a recess formed between sidewalls of the plate <NUM>, and at least part of the piston plate <NUM> can be positioned and movable up and down within this recess. Similarly, the bottom plate <NUM> may include a recess formed between sidewalls of the plate <NUM>, and at least part of the piston base <NUM> can be positioned and movable up and down within that recess. The piston formed by the piston base <NUM> and the piston plate <NUM> may be formed using any suitable material(s), such as one or more metals or other material(s) having high thermal conductivity. The piston may also be formed in any suitable manner. In addition, the piston may have any suitable size, shape, and dimensions.

As shown in this example, the piston base <NUM> may take the form of an annular cylinder or other structure having an internal cavity, and a phase change material <NUM> is positioned within the internal cavity of the piston base <NUM>. In this particular example, the phase change material <NUM> is positioned between the piston plate <NUM> and a portion of the bottom plate <NUM> that projects into the piston base <NUM>. The phase change material <NUM> is thereby able to contact a portion of the bottom plate <NUM>, and the bottom plate <NUM> can prevent downward movement of the phase change material <NUM>. The phase change material <NUM> represents at least one material that can expand and contract suitable amounts based on temperature.

The phase change material <NUM> is used in the thermal actuator switch <NUM> to move the piston plate <NUM> between different positions in order to facilitate or inhibit thermal energy transfer between the plates <NUM> and <NUM>. For example, in <FIG> and <FIG>, the phase change material <NUM> is in a contracted state, which in some cases may occur when the phase change material <NUM> is at a lower temperature. In this state, the piston plate <NUM> is spaced apart from the top plate <NUM>, at least along the major upper surface of the piston plate <NUM>. The side surfaces of the piston plate <NUM> may or may not contact the top plate <NUM> here. In this operational configuration, thermal energy transfer between the plates <NUM>-<NUM> can be reduced or minimized. As a result, there may be little thermal energy transfer between the heat source(s) and the heat sink(s) that are thermally coupled to the plates <NUM>-<NUM>. In some embodiments, the piston plate <NUM> may be completely separated from and not contact the plate <NUM> at all in this operational configuration.

In <FIG> and <FIG>, the phase change material <NUM> is in an expanded state, which in some cases may occur when the phase change material <NUM> is at a higher temperature. In this state, the piston plate <NUM> contacts the top plate <NUM>, at least along the upper major surface of the piston plate <NUM>. Again, the side surfaces of the piston plate <NUM> may or may not contact the top plate <NUM> here. In this operational configuration, thermal energy transfer between the plates <NUM>-<NUM> can be increased or maximized because the piston base <NUM> and the piston plate <NUM> contact both plates <NUM>-<NUM> simultaneously, providing a pathway for thermal energy to flow between the plates <NUM>-<NUM> through the highly-conductive piston. As a result, there may be much higher thermal energy transfer between the heat source(s) and the heat sink(s) that are thermally coupled to the plates <NUM>-<NUM>. Note here that the thermally-insulative material <NUM> can help to thermally insulate the plates <NUM>-<NUM> from each other, such as when the thermally-insulative material <NUM> has sufficient thickness to produce a high thermal resistance. This forces thermal energy to travel between the plates <NUM>-<NUM> primarily through the piston, rather than flowing directly between the plates <NUM>-<NUM> themselves, which would inadvertently thermally short circuit (fully or to some degree) the intended function of the actuator.

In this way, the thermal actuator switch <NUM> uses the phase change material <NUM> to passively control heat transfer between the heat source(s) and the heat sink(s) that are thermally coupled to the plates <NUM>-<NUM>. That is, the thermal actuator switch <NUM> can use the volumetric expansion and volumetric contraction properties of the phase change material <NUM> to actuate the piston plate <NUM> between two positions, which causes the surface contact area between the top plate <NUM> and the piston plate <NUM> to increase and decrease based on temperature. In some cases, the movement of the piston plate <NUM> may be performed in a completely passive manner, meaning the piston plate <NUM> is moved due to the expansion and contraction of the phase change material <NUM> based on thermal energy received from the heat source(s) and rejected to the heat sink(s). No additional heaters or coolers may be required here to cause expansion or contraction of the phase change material <NUM> (although that may not be the case in other embodiments).

Moreover, the thermal actuator switch <NUM> here may allow for rigid contact between the heat source(s) and the heat sink(s). In some cases, the thermal actuator switch <NUM> allows for rigid contact in the entire volume between the heat source(s) and the heat sink(s). This is because the plates <NUM>-<NUM> can be securely coupled to one another, which in some cases can provide large stable surfaces along the top of the top plate <NUM> and along the bottom of the bottom plate <NUM> (such as for mechanical couplings). In addition, depending on the design of the thermal actuator switch <NUM>, the thermal actuator switch <NUM> can provide for tunable thermal isolation in the "thru" direction (vertically in <FIG>) and tunable thermal isolation in the "in-plane" direction (horizontally in <FIG>).

Note that the heat source(s) and the heat sink(s) used with the thermal actuator switch <NUM> may represent any suitable source(s) and destination(s) for thermal energy. For example, in a "cold environment" scenario, at least one heater may be used to heat one or more devices. In this scenario, the one or more devices to be heated can represent the heat source, and at least one cold plate can be provided that represents the heat sink. Here, one or more thermal actuator switches <NUM> can be used to remove excess thermal energy from the one or more devices to the cold plate(s), such as when excessive thermal energy is provided to the one or more devices by the heater. In this example, limited heater power may be conserved while increasing or maximizing structural support for the one or more devices (since the thermal actuator switches <NUM> may primarily remain in the opened position shown in <FIG> and <FIG>). The one or more devices here may represent any suitable device(s) to be heated, such as one or more batteries, processors, or other devices used in a cold environment (such as in space applications). In some cases, the one or more thermal actuator switches <NUM> can be opened and closed to help keep the one or more devices between upper and lower target operating temperatures or within a target operating temperature range.

In a "hot environment" scenario, one or more devices may generate heat, and at least one cold plate can be used to receive thermal energy from the one or more devices in order to cool the one or more devices. In this scenario, the one or more devices can represent the heat source, and the at least one cold plate can represent the heat sink. Here, one or more thermal actuator switches <NUM> can be used to facilitate the transfer of thermal energy between the one or more devices and the cold plate(s). In this example, thermal energy dissipation to the heat sink may be maximized, such as when the thermal actuator switches <NUM> primarily remain in the closed position shown in <FIG> and <FIG>. The one or more devices here may represent any suitable device(s) to be cooled, such as one or more batteries, processors, or other devices. Again, in some cases, the one or more thermal actuator switches <NUM> can be opened and closed to maintain the one or more devices between upper and lower target operating temperatures or within a target operating temperature range.

When the phase change material <NUM> contracts here, the piston may need external assistance in order to separate the piston plate <NUM> from the top plate <NUM>. Any suitable return mechanism may be used here to provide the force needed to separate the piston plate <NUM> from the top plate <NUM>. In some embodiments, for example, one or more springs <NUM> can be positioned between the piston plate <NUM> and the top plate <NUM>. The top plate <NUM> in this example includes recesses <NUM>, although recesses may also or alternatively be included in the piston plate <NUM>. As shown in <FIG> and <FIG>, when the phase change material <NUM> is contracted, the springs <NUM> can help to push the piston plate <NUM> away from the top plate <NUM>. As shown in <FIG> and <FIG>, when the phase change material <NUM> expands, the spring force of the springs <NUM> is overcome, which compresses the springs <NUM> and allows the piston plate <NUM> to contact the top plate <NUM>.

Note that the use of one or more springs <NUM> represents one example return mechanism for moving the piston plate <NUM> away from the top plate <NUM>. However, other return mechanisms are also possible. For instance, at least one magnet <NUM> may be positioned in or on the piston plate <NUM>, and the at least one magnet <NUM> may be attracted to one or more magnets <NUM> in or on the bottom plate <NUM> and/or repelled by one or more magnets <NUM> in or on the top plate <NUM>. In these embodiments, any suitable number of magnets may be used in any suitable positions in the piston plate <NUM> and one or more of the plates <NUM>-<NUM>. The use of magnetism may offer some reliability improvements over the use of springs <NUM> (such as potential hysteresis associated with mechanical springs), although the actual reliabilities of springs and magnets can vary depending on the implementation.

One or more instances of the thermal actuator switch <NUM> may find use in a large number of applications. For example, the thermal actuator switches <NUM> may be used in numerous devices where batteries, processors, or other components need to be maintained at specified temperatures or within specified temperature ranges. As particular examples, the thermal actuator switches <NUM> may be used in satellites, unmanned aerial vehicles, and other systems where limiting power consumption may be necessary or desirable and where passive designs can improve long-term reliability. As other particular examples, the thermal actuator switches <NUM> may be used in manufacturing systems or manufacturing messaging systems, such as in additive manufacturing systems. In general, this disclosure is not limited to any particular application of the thermal actuator switch <NUM>, and this disclosure is not limited to any particular types of heat source(s) and heat sink(s) used with the thermal actuator switch <NUM>.

<FIG> and <FIG> illustrate another example PCM-based conductive thermal actuator switch <NUM> according to this disclosure. The thermal actuator switch <NUM> has many of the same design characteristics (and the same advantages, benefits, and applications) as the thermal actuator switch <NUM> described above. For brevity, only some of these design characteristics are described below, but the various design characteristics, advantages, benefits, and applications of the thermal actuator switch <NUM> described above are equally applicable to the thermal actuator switch <NUM>.

As shown in <FIG> and <FIG>, the thermal actuator switch <NUM> includes a top plate <NUM> and a bottom plate <NUM>, which may be optionally separated by a thermally-insulative material <NUM>. A piston formed by a piston base <NUM> and a piston plate <NUM> is positioned and movable between the plates <NUM> and <NUM>. For example, the top plate <NUM> may include a recess formed between sidewalls of the plate <NUM>, and at least part of the piston base <NUM> can be positioned and movable up and down within this recess. Similarly, the bottom plate <NUM> may include a recess formed between sidewalls of the plate <NUM>, and at least part of the piston plate <NUM> can be positioned and movable up and down within that recess. In some cases, the piston base <NUM> may take the form of an annular cylinder or other structure having an internal cavity. In this example, the top plate <NUM> itself defines an internal cavity within which a phase change material <NUM> is positioned, and the internal cavity of the top plate <NUM> may or may not reside within an internal cavity of the top plate <NUM> (depending on the design of the piston). In this particular example, the phase change material <NUM> is positioned between the piston base <NUM> and a portion of the top plate <NUM>. The phase change material <NUM> is thereby able to contact a portion of the top plate <NUM>, and the top plate <NUM> can prevent upward movement of the phase change material <NUM>. The phase change material <NUM> represents at least one material that can expand and contract suitable amounts based on temperature.

In this example, the piston can be used to selective form (or improve) and break (or lessen) a thermal connection between the plates <NUM> and <NUM>. More specifically, when the phase change material <NUM> is in an expanded state as shown in <FIG>, the piston plate <NUM> is pushed away from one or more flanges or other projections <NUM> of the bottom plate <NUM>, helping to reduce or lessen the thermal connection. When the phase change material <NUM> is in a contracted state as shown in <FIG>, the piston plate <NUM> is pushed into the one or more flanges or other projections <NUM> of the bottom plate <NUM>, helping to form or improve the thermal connection. Note, however, that the positions of the piston plate <NUM> and the flange(s) or other projection(s) <NUM> of the bottom plate <NUM> could be reversed, such as when the piston plate <NUM> is positioned over the flange(s) or other projection(s) <NUM> of the bottom plate <NUM>. In that case, expansion of the phase change material <NUM> can form/improve the thermal connection by pushing the piston plate <NUM> into the flange(s) or other projection(s) <NUM>, and contraction of the phase change material <NUM> can break/lessen the thermal connection by allowing the piston plate <NUM> to move away from the flange(s) or other projection(s) <NUM>.

One or more springs <NUM> can be used as a return mechanism to provide a force needed to push the piston plate <NUM> into the flanges or other projections <NUM> of the bottom plate <NUM> (in the configuration shown here) or to push the piston plate <NUM> away from the flanges or other projections <NUM> of the bottom plate <NUM> (in the alternate configuration where the piston plate <NUM> is above the flanges or other projections <NUM>). Note, however, that other return mechanism may be used in the thermal actuator switch <NUM>, such as at least some of the magnets <NUM>-<NUM> described above. While not shown here, a recess may be formed in the bottom plate <NUM> for each spring <NUM> in a similar manner as the recesses <NUM> described above.

One or more thermal straps <NUM> may optionally be positioned within the phase change material <NUM> and possibly extend from the top plate <NUM> to the piston base <NUM>. The thermal strap(s) <NUM> may be used to help heat the phase change material <NUM> more rapidly in response to an elevated temperature or cool the phase change material <NUM> more rapidly in response to a lowered temperature, which can help the phase change material <NUM> to change phase more rapidly. While the thermal strap(s) <NUM> may permit a small amount of thermal energy transfer between the top plate <NUM> and the piston base <NUM>, there may be little thermal energy transfer between the plates <NUM> and <NUM> while the piston plate <NUM> is spaced apart from the flanges or projections <NUM>. Each thermal strap <NUM> may be formed from any suitable material(s), such as one or more metals, a pyrolytic graphite sheet, or other material(s) having high thermal conductivity. Each thermal strap <NUM> may also be formed in any suitable manner and have any suitable size, shape, and dimensions. In addition, any suitable number of thermal straps <NUM>, including a single strap, may be used here.

<FIG> and <FIG> illustrate yet another example PCM-based conductive thermal actuator switch <NUM> according to this disclosure. The thermal actuator switch <NUM> has many of the same design characteristics (and the same advantages, benefits, and applications) as the thermal actuator switches <NUM> and <NUM> described above. For brevity, only some of these design characteristics are described below, but the various design characteristics, advantages, benefits, and applications of the thermal actuator switches <NUM> and <NUM> described above are equally applicable to the thermal actuator switch <NUM>.

One or more projections <NUM> of the top plate <NUM> can extend into the internal cavity in which the phase change material <NUM> is positioned. Also or alternatively, one or more projections <NUM> of the piston base <NUM> can extend into the internal cavity in which the phase change material <NUM> is positioned. In some cases, both projections <NUM> and projections <NUM> can be used and can be interleaved or otherwise used in different lateral locations. Either or both projections <NUM> and <NUM> can be used to provide a larger surface area through which thermal energy can flow into and out of the phase change material <NUM>, top plate <NUM>, or piston base <NUM>. As a result, either or both projections <NUM> and <NUM> may be used to help heat the phase change material <NUM> more rapidly in response to an elevated temperature or cool the phase change material <NUM> more rapidly in response to a lowered temperature, which can help the phase change material <NUM> to change phase more rapidly. Each projection <NUM> and <NUM> may be formed in any suitable manner and have any suitable size, shape, and dimensions. Also, any suitable number of projections <NUM> (including no projections) and/or any suitable number of projections <NUM> (including no projections) may be used here.

Various types of phase change materials <NUM>, <NUM>, <NUM> may be used in the thermal actuator switches <NUM>, <NUM>, <NUM> depending on the implementation. Examples of phase change materials that may be used include water, paraffin wax, salt hydrate, solder, or indium alloy. In some embodiments, the phase change material is selected so that the phase change material contracts at lower temperatures and expands at higher temperatures. Various forms of paraffin wax, salt hydrate, solder, and indium alloy are examples of phase change materials that behave in this manner. In other embodiments, the phase change material is selected so that the phase change material expands at lower temperatures and contracts at higher temperatures. Water is an example of a phase change material that behaves in this manner. Thus, the selection of the phase change material to be used can depend (at least in part) on (i) whether a thermal connection between top and bottom plates is formed or improved in response to expansion or contraction of the phase change material and (ii) whether the thermal connection between the top and bottom plates is broken or lessened in response to expansion or contraction of the phase change material.

Although <FIG> illustrate examples of PCM-based conductive thermal actuator switches <NUM>, <NUM>, <NUM>, various changes may be made to <FIG>. For example, the sizes, shapes, and dimensions of each thermal actuator switch <NUM>, <NUM>, <NUM> and its components may vary as needed or desired. For instance, each piston's shape or aspect ratio may be optimized to achieve a desired balance between travel and force. In some cases, the piston plate <NUM>, <NUM>, <NUM> may be kept as thin as possible to insulate the sides of the piston plate <NUM>, <NUM>, <NUM> from contacting the housing (primarily the top or bottom plate) of the thermal actuator switch <NUM>, <NUM>, <NUM>. Also, a low thermal conductivity material may be positioned on or along the interface between the piston plate <NUM>, <NUM>, <NUM> and the top or bottom plate in order to increase thermal resistance and reduce friction at those locations. Further, various additional features may be used with the thermal actuator switches <NUM>, <NUM>, <NUM>. As a particular example, one or more thermal interface materials may be used at the contact interfaces between the piston plate <NUM>, <NUM>, <NUM> and the top and bottom plates <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> to limit thermal resistance. As another particular example, one or more thermal interface materials may be used at the contact interfaces between the thermal actuator switch <NUM>, <NUM>, <NUM> and the heat source(s)/heat sink(s) to limit thermal resistance. As yet another particular example, thermal insulation may be used to help ensure that thermal energy transfer occurs substantially through the piston of the thermal actuator switch <NUM>, <NUM>, <NUM>. In addition, multiple phase change materials <NUM>, <NUM>, <NUM> may be used in the thermal actuator switch <NUM>, <NUM>, <NUM>, such as when the housing of the thermal actuator switch <NUM>, <NUM>, <NUM> can handle appropriate stresses near the transition temperatures of the phase change materials <NUM>, <NUM>, <NUM>.

It should be noted that while "top" and "bottom" are used to describe the plates <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> of the thermal actuator switches <NUM>, <NUM>, <NUM>, this does not impart any structural or usage limitations on the thermal actuator switches <NUM>, <NUM>, <NUM>. The terms "top" and "bottom" are used merely as a matter of convenience to refer to the positions of the plates as specifically shown in the figures. Each of the thermal actuator switches <NUM>, <NUM>, <NUM> can be implemented or used in an inverted manner, in a sideways orientation, or in any other suitable orientation or configuration as needed or desired.

It should also be noted that any combination of features shown in <FIG> could be used in a single thermal actuator switch, whether or not that specific combination of features is shown in the figures or described above. Thus, for instance, the thermal actuator switch <NUM> could include a plate <NUM> or <NUM> with one or more flanges or other projections <NUM> or <NUM>. Also, the thermal actuator switches <NUM> and <NUM> may include thermal straps <NUM>, or the thermal actuator switches <NUM> and <NUM> may include one or both of projections <NUM> and projections <NUM>. In addition, each thermal actuator switch could include any suitable number of each component shown in the figure(s).

<FIG> illustrates a first example stacked arrangement <NUM> of PCM-based conductive thermal actuator switches according to this disclosure. As shown in <FIG>, the stacked arrangement <NUM> includes multiple thermal actuator switches <NUM>-<NUM> that are thermally (and possibly mechanically) coupled in series. Each thermal actuator switch <NUM>-<NUM> may represent a separate instance of the thermal actuator switch <NUM>, <NUM>, or <NUM> described above, although each thermal actuator switch <NUM>-<NUM> may have any other suitable design in which a piston moves based on expansion/contraction of a phase change material.

In some embodiments, the thermal actuator switches <NUM>-<NUM> include different phase change materials <NUM>, <NUM>, <NUM>. For instance, the thermal actuator switch <NUM> may have one or more phase change materials <NUM>, <NUM>, <NUM> with a lower transition temperature, and the thermal actuator switch <NUM> may have one or more phase change materials <NUM>, <NUM>, <NUM> with a higher transition temperature (or vice versa). In some cases, the lower transition temperature may be about <NUM>° C or within a range including <NUM>° C, and the higher transition temperature may be about <NUM>° C or within a range including <NUM>° C. This stacked arrangement <NUM> therefore allows one of the thermal actuator switches <NUM>-<NUM> to close (such as by expanding or contracting its phase change material <NUM>, <NUM>, <NUM>) at lower temperatures and both of the thermal actuator switches <NUM>-<NUM> to close at higher temperatures. As a result, this helps to provide tunable thermal isolation in the "thru" direction.

As with the thermal actuator switch <NUM>, <NUM>, or <NUM> described above, the stacked arrangement <NUM> allows for passive control of thermal energy transfer between at least one heat source <NUM> and at least one heat sink <NUM>. The at least one heat source <NUM> represents any suitable source of thermal energy, and the at least one heat sink <NUM> represents any suitable destination for the thermal energy. Note that the at least one heat source <NUM> may optionally include or be associated with one or more heaters <NUM>, such as in a cold environment where the heater(s) <NUM> may be needed to heat one or more devices.

<FIG> illustrates a second example stacked arrangement <NUM> of PCM-based conductive thermal actuator switches according to this disclosure. The stacked arrangement <NUM> here is similar to the stacked arrangement <NUM>. As shown in <FIG>, the stacked arrangement <NUM> includes multiple thermal actuator switches <NUM>-<NUM> that are thermally coupled in series. Each thermal actuator switch <NUM>-<NUM> may represent a separate instance of the thermal actuator switch <NUM>, <NUM>, or <NUM> described above, although each thermal actuator switch <NUM>-<NUM> may have any other suitable design in which a piston moves based on expansion/contraction of a phase change material.

In this configuration, the stacked arrangement <NUM> is not physically positioned between at least one heat source <NUM> and at least one heat sink <NUM>. Instead, the stacked arrangement <NUM> is positioned elsewhere, and thermal conductors <NUM> and <NUM> are used to thermally couple the thermal actuator switches <NUM> and <NUM> to the heat source(s) <NUM> and heat sink(s) <NUM>. Each thermal conductor <NUM> and <NUM> represents any suitable structure configured to transfer thermal energy to or from a thermal actuator switch. Effectively, the thermal conductors <NUM> and <NUM> here function as heat straps to provide thermal energy to and from the stacked arrangement <NUM>. Each thermal conductor <NUM> and <NUM> may be formed using any suitable material(s), such as one or more metals, a pyrolytic graphite sheet, or other material(s) having high thermal conductivity. Each thermal conductor <NUM> and <NUM> may also be formed in any suitable manner. In addition, each thermal conductor <NUM> and <NUM> may have any suitable size, shape, and dimensions.

A thermally-insulative material <NUM> may optionally be positioned between the thermal conductors <NUM> and <NUM> or portions of the thermal conductors <NUM> and <NUM>. The thermally-insulative material <NUM> can help to reduce thermal conduction between the thermal conductors <NUM> and <NUM> in order to inhibit thermal energy transfer directly between the thermal conductors <NUM> and <NUM>. The thermally-insulative material <NUM> may be formed from any suitable material(s), such as a thermally-insulative epoxy or other material(s) used to hold the thermal conductors <NUM> and <NUM> or a fiberglass sheet or other structure(s) positioned between the thermal conductors <NUM> and <NUM>. The thermally-insulative material <NUM> may also be formed in any suitable manner. In addition, the thermally-insulative material <NUM> may have any suitable size, shape, and dimensions. Note that if the thermal conductors <NUM> and <NUM> extend beyond the thermally-insulative material <NUM> (as is shown in the embodiment of <FIG>), the thermal conductors <NUM> and <NUM> may be reinforced if needed or desired. For instance, at least the portions of the thermal conductors <NUM> and <NUM> extending beyond the thermally-insulative material <NUM> may be formed using pyrolytic graphite sheets or other material(s) and reinforced using Kapton or other reinforcement material(s).

In some embodiments, each of the stacked arrangements <NUM>, <NUM> of PCM-based conductive thermal actuator switches may be implemented as follows. The thermal actuator switch that is activated (closed) to enable thermal energy transport through the switch at a higher temperature can be placed closer to a heat sink. The thermal actuator switch that is activated (closed) to enable thermal energy transport through the switch at a lower temperature can be placed closer to a heat source. This may be done to help prevent the thermal actuator switch with the higher activation temperature from "clamping" to a hot environmental temperature at some point that is beyond the control of the overall system (since there may be no active cooling in the loop). Instead, the thermal actuator switch with the higher activation temperature can be clamped to a colder temperature, which can be controlled (such as via a heater). In some cases, the way that the two stacked switches close and open can be opposite of one another, such as when one switch has a phase change material that expands at higher temperatures and the other switch has a phase change material that contracts at higher temperatures. In particular embodiments, water can be used in one of the stacked switches since it tends to behave in the opposite manner than many other phase change materials. Note, however, that the configurations of the switches can be adjusted as needed or desired so that the desired activations of the switches are achieved.

Although <FIG> and <FIG> illustrate examples of stacked arrangements <NUM>, <NUM> of PCM-based conductive thermal actuator switches, various changes may be made to <FIG> and <FIG>. For example, a stacked arrangement of PCM-based conductive thermal actuator switches may be used in any suitable manner. Also, a stacked arrangement of PCM-based conductive thermal actuator switches may include more than two thermal actuator switches, and the thermal actuator switches may or may not include more than two phase change materials that expand/contract at different temperatures.

<FIG> illustrates an example array <NUM> of PCM-based conductive thermal actuator switches according to this disclosure. As shown in <FIG>, the array <NUM> includes array elements, where each array element includes a thermal actuator switch <NUM>. As can be seen here, the thermal actuator switches <NUM> are arranged in parallel, meaning the thermal actuator switches <NUM> can each independently be used to transfer thermal energy between at least one heat source and at least one heat sink. Each thermal actuator switch <NUM> may represent a separate instance of the thermal actuator switch <NUM>, <NUM>, or <NUM> described above, although each thermal actuator switch <NUM> may have any other suitable design in which a piston moves based on expansion/contraction of a phase change material. In some embodiments, each array element in the array <NUM> shown in <FIG> may include a stacked arrangement of multiple thermal actuator switches <NUM>, such as the arrangement shown in <FIG>.

The use of a parallel arrangement of thermal actuator switches <NUM> can help to control the temperature of one or more devices and to control a temperature gradient across the one or more devices. For example, the one or more devices can be maintained within a desired temperature range and can maintain a desired temperature gradient (or have a temperature gradient within a desired temperature gradient range) across one or more surfaces of the device(s). In this example, the thermal actuator switches <NUM> are generally arranged in rows, and the rows are staggered relative to one another (meaning each thermal actuator switch <NUM> is not aligned with thermal actuator switches <NUM> in the adjacent rows). This type of arrangement may be useful in helping to reduce or minimize lateral heat transfer between the thermal actuator switches <NUM>. However, aligned thermal actuator switches <NUM> may also be used.

Note that the sizes of the thermal actuator switches <NUM> shown here can vary, as can the spacings between the thermal actuator switches <NUM> in each row and the spacings between the thermal actuator switches <NUM> in different rows. In some cases, the spaces between the thermal actuator switches <NUM> can be at least partially filled, such as by one or more thermally-insulative materials that help to limit thermal conduction substantially to the locations where the thermal actuator switches <NUM> are positioned.

Although <FIG> illustrates one example of an array <NUM> of PCM-based conductive thermal actuator switches, various changes may be made to <FIG>. For example, a parallel arrangement of PCM-based conductive thermal actuator switches may be used in any suitable manner. Also, an array <NUM> of PCM-based conductive thermal actuator switches may include any suitable number of thermal actuator switches <NUM> in any suitable layout.

The following describes example embodiments of this disclosure that implement or relate to PCM-based conductive thermal actuator switches. However, other embodiments may be used in accordance with the teachings of this disclosure.

In a first embodiment, an apparatus includes multiple thermal actuator switches configured to control a transfer of thermal energy through the apparatus, where the thermal actuator switches are arranged in a stacked configuration. Each thermal actuator switch includes first and second plates and a piston movable between the first and second plates. Each thermal actuator switch also includes a phase change material configured to (i) expand to move a surface of the piston into a first position and (ii) contract to allow the surface of the piston to move into a second position. The surface of the piston thermally contacts the first plate and increases thermal energy transfer between the first and second plates when in one of the first and second positions. The surface of the piston is spaced apart from the first plate and decreases thermal energy transfer between the first and second plates when in another of the first and second positions. Different ones of the thermal actuator switches include different phase change materials that expand or contract at different temperatures.

In a second embodiment, a system includes at least one heat source and at least one heat sink. The system also includes multiple thermal actuator switches configured to control a transfer of thermal energy between the at least one heat source and the at least one heat sink, where the thermal actuator switches are arranged in a stacked configuration. Each thermal actuator switch includes first and second plates and a piston movable between the first and second plates. Each thermal actuator switch also includes a phase change material configured to (i) expand to move a surface of the piston into a first position and (ii) contract to allow the surface of the piston to move into a second position. The surface of the piston thermally contacts the first plate and increases thermal energy transfer between the first and second plates when in one of the first and second positions. The surface of the piston is spaced apart from the first plate and decreases thermal energy transfer between the first and second plates when in another of the first and second positions. Different ones of the thermal actuator switches include different phase change materials that expand or contract at different temperatures.

In a third embodiment, a method includes receiving thermal energy at multiple thermal actuator switches from at least one heat source, where the thermal actuator switches are arranged in a stacked configuration. The method also includes controlling a transfer of the thermal energy between the at least one heat source and at least one heat sink using the thermal actuator switches. Each thermal actuator switch includes first and second plates and a piston movable between the first and second plates. Each thermal actuator switch also includes a phase change material configured to (i) expand to move a surface of the piston into a first position and (ii) contract to allow the surface of the piston to move into a second position. The surface of the piston thermally contacts the first plate and increases thermal energy transfer between the first and second plates when in one of the first and second positions. The surface of the piston is spaced apart from the first plate and decreases thermal energy transfer between the first and second plates when in another of the first and second positions. Different ones of the thermal actuator switches include different phase change materials that expand or contract at different temperatures.

Any single one or any suitable combination of the following features may be used with the first, second, or third embodiment. Each thermal actuator switch may include a return configured to move the piston when the phase change material contracts. The return of each thermal actuator switch may include one or more springs or magnets. The thermal actuator switches may include first and second thermal actuator switches, the first and second thermal actuator switches may respectively include first and second phase change materials, and the first phase change material may expand or contract at a different temperature than the second phase change material. An array may include multiple array elements, and each array element may include two or more of the thermal actuator switches in the stacked configuration. Multiple heat straps may transport thermal energy to and from the thermal actuator switches.

It may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The phrase "associated with," as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like.

Claim 1:
An apparatus comprising:
multiple thermal actuator switches (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) configured to control a transfer of thermal energy through the apparatus, the thermal actuator switches arranged in a stacked configuration, each thermal actuator switch comprising:
first and second plates (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>. <NUM>);
a piston (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) movable between the first and second plates; and
a phase change material (<NUM>, <NUM>, <NUM>) configured to (i) expand to move a surface of the piston into a first position and (ii) contract to allow the surface of the piston to move into a second position, the surface of the piston thermally contacting the first plate and increasing thermal energy transfer between the first and second plates when in one of the first and second positions, the surface of the piston spaced apart from the first plate and decreasing thermal energy transfer between the first and second plates when in another of the first and second positions;
wherein different ones of the thermal actuator switches comprise different phase change materials that expand or contract at different temperatures.