TWO PHASE MICRO-CHANNEL HEAT SINK

CROSS-REFERENCE TO RELATED APPLICATIONS The present application claims priority from co-pending provisional patent application Serial No. 61/004821 , filed November 30, 2007, entitled "Two Phase Cross-Connected Micro-Channel Heat Sink for Thermal Management of High- Heat Flux Commercial and Defense Electronic Devices".

BACKGROUND OF THE INVENTION

Improvements in performance of electronic devices with simultaneous reductions in weight and volume have resulted in ever-increasing waste heat densities from the devices and a search for improvements in the efficiency of heat sink designs. Current and near future high-performance commercial/defense electronic devices require dissipation of heat fluxes on the order of one hundred watts per square centimeter. Because the reliability and life span of electronics are both strongly affected by temperature, increasingly efficient cooling techniques are desired to reduce the maintenance costs and increase the service life of high-power-density and other electronic devices.

Two-phase micro-channel heat sinks might provide a solution for removing waste heat from high-power density devices. Conventional two-phase micro-channel heat sinks utilize micro-size parallel channels as coolant flow passages for the flow of boiling liquid coolant. There are a number of potential merits for such two-phase micro-channel heat sinks. However, significant barriers to the use of such two-phase micro-channel heat sinks remain. In particular, conventional two-phase micro-channel heat sinks have shown appreciable deviation from predicted behavior. For example, conventional two- phase micro-channel heat sinks are subject to temperature and pressure flow instabilities. Such instabilities may cause oscillations in the flow. Severe flow instabilities preclude safe operation and predictable cooling performance of conventional two-phase micro-channel heat sinks.

Accordingly, what is needed is an improved heat sink that may be used in connection with micro-channel heat sinks.

BRIEF SUMMARY OF THE INVENTION A method and system for providing a heat sink are described. The heat

sink includes at least one inlet, at least one outlet, a plurality of flow micro- channels, and at least one cross-connect channel. The plurality of flow micro- channels are defined by a plurality of channels walls, connect the inlet(s) with the outlet(s) and accommodate a flow of coolant between the at least one inlet and the at least one outlet. The at least one cross-connect channel is configured to connect at least a portion of the plurality of flow micro-channels. The cross- connect channel(s) also at least partially equilibrate a pressure field for boiling of the coolant across the portion of the plurality of flow micro-channels.

According to the method and system disclosed herein, the heat sink may provide two-phase cooling without severe flow oscillations. Consequently, improved cooling efficiency may be maintained. For example, include low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, low flow rate requirement, and relatively uniform temperature distribution along the stream- wise direction may be achieved.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 depicts a plan view of an exemplary embodiment of a two-phase micro-channel heat sink. FIG. 2 depicts perspective, side, and plan views of a portion of an exemplary embodiment of a two-phase micro-channel heat sink.

FIG. 3 depicts a plan view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink.

FIG. 4 depicts a plan view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink.

FIG. 5 depicts a plan view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink.

FIG. 6 depicts a plan view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink. FIG. 7 depicts a plan view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink.

FIG. 8 depicts a side view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink.

FIG. 9 depicts perspective and side views of a portion of another

exemplary embodiment of a two-phase micro-channel heat sink.

FIG. 10 depicts a plan view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink having a reservoir.

FIG. 11 depicts a plan view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink having a reservoir.

FIG. 12 depicts plan and end views of a portion of another exemplary embodiment of a two-phase micro-channel heat sink.

FIG. 13 depicts plan and end views of a portion of another exemplary embodiment of a two-phase micro-channel heat sink. FIG. 14 depicts a perspective view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink.

FIG. 15 depicts a view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink.

FIG. 16 depicts a view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink.

FIG. 17 depicts a high-level flow chart of an exemplary embodiment of a method for providing and using a two-phase micro-channel heat sink.

DETAILED DESCRIPTION OF THE INVENTION The method and system relate to heat sinks. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the embodiments and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the method and system are not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features described herein.

The method and system are mainly described in terms of particular systems provided in particular implementations. However, one of ordinary skill in the art will readily recognize that this method and system will operate effectively in other implementations. The method and system will also be described in the context of particular methods having certain steps. However, the method and system operate effectively for other methods having different and/or additional steps not inconsistent with the method and system.

A method and system for providing a heat sink are described. The heat sink includes at least one inlet, at least one outlet, a plurality of flow micro- channels, and at least one cross-connect channel. The plurality of flow micro- channels are defined by a plurality of channels walls, connect the inlet(s) with the outlet(s) and accommodate a flow of coolant between the at least one inlet and the at least one outlet. The at least one cross-connect channel is configured to connect at least a portion of the plurality of flow micro-channels. The cross- connect channel(s) also at least partially equilibrate a pressure field for boiling of the coolant across the portion of the plurality of flow micro-channels. FIG. 1 depicts a plan view of an exemplary embodiment of a two-phase micro-channel heat sink 100. FIG. 2 depicts perspective, side, and plan views of a portion of the exemplary embodiment of a two-phase micro-channel heat sink 100. Note that FIGS. 1-2 are not drawn to scale. Referring to FIGS. 1-2, the heat sink 100 includes flow micro-channels 102, cross-connect channels 104, channel walls 106, inlet 108, and outlet 110. The heat sink 100 may also include a plate

112, depicted in a portion of FIG. 2. For clarity, not all flow micro-channels 102, cross-connect channels 104, and channel walls 108 are labeled. Further, another number of flow micro-channels 102 and/or another number of cross- connect channels 104 may be used. The substrate for the base of the heat sink 100 is generally fabricated from one or more high thermal conductivity solid materials, such as copper or silicon. The flow micro-channels 102, as well as the cross-connect channels, 104 may be formed in the substrate by techniques such as micro-machining. However, the flow micro-channels 102, cross-connect channels 104 and channel walls 106 may be formed in another manner. During operation, the heat sink 100 is attached to a heat-dissipating device (not shown), such as an electronic device. Heat generated by the device(s) may be transferred to the heat sink 100, then to a coolant (not shown) flowing through the heat sink. The coolant flows generally from the inlet 108 to the outlet 110. The flow of coolant through the heat sink 100 dissipates the heat from the heat sink 100 and thus from the device(s) being cooled.

The micro-channel heat sink 100 is a two-phase heat sink. Although termed a two-phase heat sink, the micro-channel heat sink 100 may operate in a single-phase or a two-phase mode. For a relatively high coolant flow rate and/or

a relatively low dissipative heat flux, the coolant passing through the heat sink may maintain its liquid single-phase state throughout the heat sink 100. In such a situation, the micro-channel heat sink 100 operates as a single-phase heat sink. If the coolant flow rate is sufficiently low and/or the heat flux to be dissipated is sufficiently large, the liquid coolant may reach its boiling point while still flowing through the heat sink 100, and flow boiling occurs. This results in the heat sink 100 operating as a two-phase heat sink. During operation in such a two-phase mode, the latent heat exchange associated with transition of the coolant from liquid to vapor may more efficiently remove heat from the two-phase micro- channel heat sink.

In the embodiment shown, the flow micro-channels 102 are a series of parallel, symmetric, rectangular cross-section micro-slots, or depression, formed in a base. The flow micro-channels 102 have a width and are defined by channel walls 106, which also have a width and height. The flow micro-channels 102 may be no larger than in the microscale regime. For example, flow micro-channels may range from ten to one thousand microns in width for certain embodiments. Smaller widths may also be possible. The channel walls 106 may have a thickness in the one hundred micron range, a height in the hundreds of microns range. However, other channel cross-sections, widths, heights, channel directions are possible for the flow micro-channels 102. In some embodiments, the flow micro-channels may not be parallel, linear, symmetric, and/or rectangular. Similarly, in some embodiments, the flow micro-channels may have varying widths. For example, a particular flow micro-channel may have a width that changes along the length of the flow micro-channel. In addition, one flow micro-channel 102 may not have the same width as another flow micro-channel

102. The flow micro-channels 102 may be closed using the cover plate 112. The inlet 108 and outlet 110 correspond to plenums at inlet and outlet ends of the two-phase micro-channel heat sink 100. The inlet 108 and outlet 110 are used to introduce coolant to and discharge coolant from the flow micro-channels 102, respectively. Thus, coolant flows along the flow micro-channels 102 from the inlet 108 to the outlet 110. Stated differently, the flow micro-channels 102 are configured to carry the coolant, which may exist in one or two-phases, between the inlet 108 and outlet 110.

The two-phase micro-channel heat sink 100 also includes cross-connect

channels 104. In the embodiment shown, the cross-connect channels 104 are micro-channels. In such an embodiment, the cross-connect channels 104 may be no larger than in the microscale regime. For example, in some embodiments, the cross-connect channels 104 may have a width in the range of ten to one thousand microns. Smaller widths may also be possible. Although shown as having the same width and being of rectangular cross-section, other channel cross-sections, widths, heights, and channel directions are possible for the cross-connect micro-channels 104. In some embodiments, the cross-connect may not be parallel, linear, symmetric, and/or rectangular. Similarly, some embodiments, the cross-connect channels 104 may have varying widths. For example, a particular cross-connect channel may have a width that changes along the length of the cross-connect channel. In addition, one cross-connect channel 104 may not have the same width as another cross-connect channel 104. The cross-connect channels 104 may be closed using the cover plate 112. The coolant flows generally from the inlet 108 to the outlet 110. In the embodiment shown, the cross-connect channels 104 are substantially perpendicular to the direction of flow. This is in contrast to the flow micro- channels 102. The cross-connect channels 104 thus extend substantially transverse to the flow direction and, in the embodiment shown, to the direction of the flow micro-channels 102. Some cross-connect channels 104, such as the channel 104A, do not extend across the entire width, W1 , of the two-phase micro-channel heat sink 100. Other cross-connect channels 104, such as the channel 104B, do extend across the entire width of the two-phase micro-channel heat sink 100. In some embodiments, all cross-connect channels 104 may extend across the entire width of the two-phase micro-channel heat sink. In other embodiments, none of the cross-connect channels may extend across the width of the two-phase micro-channel heat sink. In the embodiment shown, the cross- connect channels 104 occur at regular intervals. Thus, the cross-connect channels 104 are uniformly spaced along the flow direction. For example, in one embodiment, the cross-connect channels 104 occur at one millimeter intervals.

However, in another embodiment, the cross-connect channels 104 need not be uniformly spaced and/or may occur at intervals having other distances.

The cross-connect channels 104 may be used to at least partially equilibrate a pressure field for boiling of the coolant across the portion of the

plurality of flow micro-channels. The cross-connect channels 104 allow for vapor and/or liquid communication between flow micro-channels 104. When the two- phase micro-channel heat sink 100 operates in a two-phase mode, the pressure of the boiling coolant may equilibrate along the length of each cross-connect channel 104. Stated differently, the pressure may be uniform along each cross- connect channel 104. As a result, the pressure of the coolant flowing through the flow micro-channels 102 is equilibrated across at least a portion of the width, W1 , of the two-phase micro-channel heat sink 100. For a cross-connect channel, such as the channel 104A, the pressure of the boiling coolant is equilibrated across only a part of the width of the two-phase micro-channel heat sink 100.

Thus, a cross-connect channel 104 on the other side of a channel wall 106 may have a different pressure. For example, the cross-connect channel 104A may have one pressure, while the channel (not labeled) on the other side of the channel wall 106A from the cross-connect channel 104A may have a different pressure. For a cross-connect channel 104, such as the channel 104B, the pressure of the boiling coolant may equilibrate across the entire width of the two- phase micro-channel heat sink 100. Consequently, the cross-connect channels 104 correspond to regions of uniform pressure across multiple flow micro- channels 102. As a result, the pressure of coolant traversing the flow micro- channels 102 may vary more uniformly between the inlet 108 and the outlet 110.

Consequently, pressure oscillations may be reduced.

As discussed above, the cross-connect channels 104 may occur at various intervals and are used to equilibrate pressure along their length. The location, length, and other features of the cross-connect channels 104 might vary based upon the implementation. In some embodiments, cross-connect channels

104 may be located at larger intervals as long as the cross-connect channels 104 are sufficiently close that severe pressure oscillations are reduced or eliminated in the operating range of the heat sink 100. In other embodiments, the cross-connect channels 104 may be more closely spaced. However, in such embodiments, it is desirable to locate the cross-connect channels 104 sufficiently far apart that a satisfactory flow of coolant through the flow micro-channels 102 is also maintained.

The two-phase micro-channel heat sink 100 may be used to achieve a variety of benefits. High efficiency cooling may be accomplished because the

latent heat of the liquid-to-vapor phase transition may be used to provide enhanced heat transfer. Furthermore, the combination of the flow micro- channels 102 and cross-connect channels 104 allow for reduced pressure oscillations and stable flow of the boiling liquid coolant. These attributes may enable the two-phase micro-channel heat sink 100 to stably and repeatably dissipate high heat fluxes, particularly from small areas. The two-phase micro- channel heat sink 100 may also have low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, and a smaller flow rate requirement. A more uniform temperature variation in the flow direction and higher convective heat transfer coefficients may also be achieved. Consequently the two-phase micro-channel heat sink 100 may be suitable for thermal management of high-power-density electronic devices including but not limited to devices such as high-performance microprocessors, laser diode arrays, high-power components in radar systems, switching components in power electronics, x-ray monochromator crystals, avionics power modules, and spacecraft power components.

FIG. 3 depicts a plan view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink 100'. For clarity, FIG. 3 is not drawn to scale. The two-phase micro-channel heat sink 100' is analogous to the two- phase micro-channel heat sink 100. Consequently, portions of the two-phase micro-channel heat sink 100' are labeled similarly. The two-phase micro-channel heat sink 100' thus includes flow micro-channels 102', cross-connect channels 104', channel walls 106', inlet 108', and outlet 110' corresponding to flow micro- channels 102, cross-connect channels 104, channel walls 106, inlet 108, and outlet 110, respectively. The flow micro-channels 102', cross-connect channels

104', channel walls 106', inlet 108', and outlet 110' may also have analogous structure and/or size to flow micro-channels 102, cross-connect channels 104, channel walls 106, inlet 108, and outlet 110, respectively. In addition, the two- phase micro-channel heat sink 100' may be made of the same materials, made using the same techniques as, and function in a similar manner to the two-phase micro-channel heat sink 100. For clarity, not all flow micro-channels 102', cross- connect channels 104', and channel walls 108' are labeled. The heat sink 100' may also include a plate (not shown) used to cover the channels 102' and 104'. Further, another number of flow micro-channels 102' and/or another number of

cross-connect channels 104' may be used.

The flow micro-channels 102' are parallel, symmetric, of rectangular cross-section, and defined by channel walls 106', which also have a width and height. However, other channel cross-sections, widths, heights, channel directions are possible for the flow micro-channels 102'. In some embodiments, the flow micro-channels 102' may not be parallel, linear, symmetric, and/or rectangular. Similarly, some embodiments, the flow micro-channels 102' may have varying widths. In addition, one flow micro-channel 102' may not have the same width as another flow micro-channel 152. The two-phase micro-channel heat sink 100' includes cross-connect channels 104' that may equilibrate the pressure of boiling coolant along their length. The cross-connect channels 104' extend across the entire width WV of the two-phase micro-channel heat sink 100' and occur at regular intervals. Fluid communication is thus provided between all of the flow micro-channels 102'. This allows for pressure to equilibrate between the flow micro-channels 102' across the entire width, WV, of the two-phase micro-channel heat sink 100'. The cross-connect channels 104' may thus provide isobars between the inlet 108' and the outlet 110'. In the embodiment shown, the cross-connect channels 104' are micro-channels. In such an embodiment, the cross-connect channels 104' may be no larger than in the microscale regime. The cross-connect channels

104' are also sufficiently close that severe pressure oscillations are reduced or eliminated in the operating range of the heat sink 100'. Because the cross- connect channels 104' extend across the entire width of the two-phase micro- channel heat sink 100', it is expected that their ability to reduce or eliminate severe pressure oscillations is improved. Further, the cross-connect channels

104' are spaced sufficiently far apart that a sufficient flow of coolant through the flow micro-channels 102' is also maintained.

The two-phase micro-channel heat sink 100' may share the benefits of the two-phase micro-channel heat sink 100. For example, high efficiency cooling, reduced pressure oscillations and stable flow of the boiling liquid coolant, as well as stable and repeatable dissipation of high heat fluxes, particularly from small areas. The two-phase micro-channel heat sink 100' may also have low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, and a smaller flow rate

requirement. A more uniform temperature variation in the flow direction and higher convective heat transfer coefficients may also be achieved. Consequently the two-phase micro-channel heat sink 100' may be suitable for thermal management of high-power-density electronic devices. FIG. 4 depicts a plan view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink 150. For clarity, FIG. 4 is not drawn to scale. The two-phase micro-channel heat sink 150 is analogous to the two- phase micro-channel heat sink 100. Consequently, portions of the two-phase micro-channel heat sink 150 are labeled similarly. The two-phase micro-channel heat sink 150 thus includes flow micro-channels 152, cross-connect channels

154, channel walls 156, inlet 158, and outlet 160 corresponding to flow micro- channels 102, cross-connect channels 104, channel walls 106, inlet 108, and outlet 110, respectively. Consequently, the flow micro-channels 152, cross- connect channels 154, channel walls 156, inlet 158, and outlet 160 have analogous functions to flow micro-channels 102, cross-connect channels 104, channel walls 106, inlet 108, and outlet 110, respectively. The flow micro- channels 152, cross-connect channels 154, channel walls 156, inlet 158, and outlet 160 may also have analogous structure and/or size to flow micro-channels 102, cross-connect channels 104, channel walls 106, inlet 108, and outlet 110, respectively. In addition, the two-phase micro-channel heat sink 150 may be made of the same materials, made using the same techniques as, and function in a similar manner to the two-phase micro-channel heat sink 100. For clarity, not all flow micro-channels 152, cross-connect channels 154, and channel walls 158 are labeled. The heat sink 150 may also include a plate (not shown) used to cover the channels 152 and 154. Further, another number of flow micro- channels 152 and/or another number of cross-connect channels 154 may be used.

The flow micro-channels 152 are parallel, symmetric, of rectangular cross- section, and defined by channel walls 156, which also have a width and height. However, other channel cross-sections, widths, heights, channel directions are possible for the flow micro-channels 152. In some embodiments, the flow micro- channels 152 may not be parallel, linear, symmetric, and/or rectangular. Similarly, some embodiments, the flow micro-channels 152 may have varying widths. In addition, one flow micro-channel 152 may not have the same width as

another flow micro-channel 152.

The two-phase micro-channel heat sink 150 includes cross-connect channels 154 that may equilibrate the pressure of boiling coolant along their length. The cross-connect channels 154 extend across the entire width W2 of the two-phase micro-channel heat sink 150. However, in another embodiment, at least some of the cross-connect channels 154 may not extend across the entire width W2 of the two-phase micro-channel heat sink 150. The cross-connect channels 154 provide communication between the flow micro-channels 152, allowing for pressure to equilibrate between flow micro-channels 152 which each cross-connect channel 154 crosses. In the embodiment shown, the cross- connect channels 154 are micro-channels. In such an embodiment, the cross- connect channels 154 may be no larger than in the microscale regime. Further, the cross-connect channels 154 are also shown as having different widths. However, in other embodiments, the cross-connect channels 154 may have the same width. The cross-connect channels 154 are shown as having varying spacing. For example, spacings L1 and L2 are used for some of the cross- connect channels 154. The cross-connect channels 154 are still sufficiently close that severe pressure oscillations are reduced or eliminated in the operating range of the heat sink 150. Further, the cross-connect channels 154 are also spaced sufficiently far apart that a sufficient flow of coolant through the flow micro-channels 152 is also maintained.

The two-phase micro-channel heat sink 150 may share the benefits of the two-phase micro-channel heat sink 100. For example, high efficiency cooling, reduced pressure oscillations and stable flow of the boiling liquid coolant, as well as stable and repeatable dissipation of high heat fluxes, particularly from small areas. The two-phase micro-channel heat sink 150 may also have low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, and a smaller flow rate requirement. A more uniform temperature variation in the flow direction and higher convective heat transfer coefficients may also be achieved. Consequently the two-phase micro-channel heat sink 150 may be suitable for thermal management of high-power-density electronic devices.

FIG. 5 depicts a plan view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink 200. For clarity, FIG. 5 is not drawn to

scale and only a small portion of the two-phase micro-channel heat sink 200 is shown. In addition, for simplicity, the inlet(s) and outlet(s) are not shown. The two-phase micro-channel heat sink 200 is analogous to the two-phase micro- channel heat sink 100. Consequently, portions of the two-phase micro-channel heat sink 200 are labeled similarly. The two-phase micro-channel heat sink 200 thus includes flow micro-channels 202, cross-connect channels 204, and channel walls 206 corresponding to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. Consequently, the flow micro-channels 202, cross-connect channels 204, and channel walls 206 have analogous functions to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. The flow micro-channels 202, cross- connect channels 204, and channel walls 206 may also have analogous structure and/or size to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. In addition, the two-phase micro-channel heat sink 200 may be made of the same materials, made using the same techniques as, and function in a similar manner to the two-phase micro-channel heat sink 100. For clarity, not all flow micro-channels 202, cross-connect channels 204, and channel walls 208 are labeled. The heat sink 200 may also include a plate (not shown) used to cover the channels 202 and 204. Further, another number of flow micro-channels 202 and/or another number of cross- connect channels 204 may be used.

The flow micro-channels 202 have a width and height and are defined by channel walls 206, which also have a width and height. The flow micro-channels 202 may also have a rectangular cross-section. However, other channel cross- sections, widths, heights, channel directions are possible for the flow micro- channels 202. In some embodiments, the flow micro-channels may not be parallel, linear, symmetric, and/or rectangular. Similarly, some embodiments, the flow micro-channels 202 may have varying widths. In addition, one flow micro- channel 202 may not have the same width as another flow micro-channel 202. Further, the flow micro-channels 202 are curved, rather than linear. Thus, as can be seen in FIG. 5, various shapes of the flow micro-channels 202 may be used.

The two-phase micro-channel heat sink 200 includes cross-connect channels 204 that may equilibrate the pressure of boiling coolant along their length and provide communication between flow micro-channels 202. Some of

the cross-connect channels 204, such as the cross-connect channel 204A, do not extend across the entire width of the two-phase micro-channel heat sink 200. However, in another embodiment, all or none of the cross-connect channels 204 may extend across the entire width of the two-phase micro-channel heat sink 200. In the embodiment shown, the cross-connect channels 204 are micro- channels. In such an embodiment, the cross-connect channels 204 may be no larger than in the microscale regime. Further, the cross-connect channels 204 are also shown as having different widths. However, in other embodiments, the cross-connect channels 204 may have the same width. The cross-connect channels 204 are shown as having varying spacing. The cross-connect channels

204 are still sufficiently close and sufficiently long that severe pressure oscillations are reduced or eliminated in the operating range of the heat sink 200. Further, the cross-connect channels 204 are also spaced sufficiently far apart and sufficiently thin that a sufficient flow of coolant through the flow micro- channels 202 is also maintained.

The two-phase micro-channel heat sink 200 may share the benefits of the two-phase micro-channel heat sinks 100 and 150. For example, high efficiency cooling, reduced pressure oscillations, stable flow of the boiling liquid coolant, stable and repeatable dissipation of high heat fluxes, low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, and a smaller flow rate requirement may be achieved. A more uniform temperature variation in the flow direction and higher convective heat transfer coefficients may also be achieved. Consequently the two-phase micro-channel heat sink 200 may be suitable for thermal management of high-power-density electronic devices.

FIG. 6 depicts a plan view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink 250. For clarity, FIG. 6 is not drawn to scale and only a portion of the two-phase micro-channel heat sink 250 is shown. In addition, for simplicity, the inlet(s) and outlet(s) are not shown. The two-phase micro-channel heat sink 250 is analogous to the two-phase micro-channel heat sink 100. Consequently, portions of the two-phase micro-channel heat sink 250 are labeled similarly. The two-phase micro-channel heat sink 250 thus includes flow micro-channels 252, cross-connect channels 254, and channel walls 256 corresponding to flow micro-channels 102, cross-connect channels 104, and

channel walls 106, respectively. Consequently, the flow micro-channels 252, cross-connect channels 254, and channel walls 256 have analogous functions to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. The flow micro-channels 252, cross-connect channels 254, and channel walls 256 may also have analogous structure and/or size to flow micro- channels 102, cross-connect channels 104, and channel walls 106, respectively. In addition, the two-phase micro-channel heat sink 250 may be made of the same materials, made using the same techniques as, and function in a similar manner to the two-phase micro-channel heat sink 100. For clarity, not all flow micro-channels 252, cross-connect channels 254, and channel walls 258 are labeled. The heat sink 250 may also include a plate (not shown) used to cover the channels 252 and 254. Further, another number of flow micro-channels 252 and/or another number of cross-connect channels 254 may be used.

The flow micro-channels 252 have a height, a varying width, and are defined by channel walls 256, which also have a width and height. The flow micro-channels 252 may also have a rectangular cross-section. However, other channel cross-sections, widths, heights, channel directions are possible for the flow micro-channels 252. In the embodiment shown, the flow micro-channels 252 have varying widths, but are otherwise substantially parallel. In some embodiments, the flow micro-channels 252 may not be parallel, linear, symmetric, and/or may have other cross-sections. Thus, as can be seen in FIG. 6, various shapes of the flow micro-channels 252 may be used.

The two-phase micro-channel heat sink 250 includes cross-connect channels 254 that may equilibrate the pressure of boiling coolant along their length. Further the cross-connect channels 254 provide communication between flow micro-channels 252. Some of the cross-connect channels 254, such as the cross-connect channel 254A, do not extend across the entire width of the two- phase micro-channel heat sink 250. However, in another embodiment, all or none of the cross-connect channels 254 may extend across the entire width of the two-phase micro-channel heat sink 250. In the embodiment shown, the cross-connect channels 254 are micro-channels. In such an embodiment, the cross-connect channels 254 may be no larger than in the microscale regime. Further, the cross-connect channels 254 are also shown as substantially the same width. However, in other embodiments, the cross-connect channels 254

may have the different widths. The cross-connect channels 254 are shown as having uniform spacing. In another embodiment, the cross-connect channels 254 may not be uniformly spaced. The cross-connect channels 254 are still sufficiently close and sufficiently long that severe pressure oscillations are reduced or eliminated in the operating range of the heat sink 250. Further, the cross-connect channels 254 are also spaced sufficiently far apart and sufficiently thin that a sufficient flow of coolant through the flow micro-channels 252 is also maintained.

The two-phase micro-channel heat sink 250 may share the benefits of the two-phase micro-channel heat sinks 100, 150, and 200. For example, high efficiency cooling, reduced pressure oscillations, stable flow of the boiling liquid coolant, stable and repeatable dissipation of high heat fluxes, low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, and a smaller flow rate requirement may be achieved. A more uniform temperature variation in the flow direction and higher convective heat transfer coefficients may also be achieved. Consequently the two-phase micro-channel heat sink 250 may be suitable for thermal management of high-power-density electronic devices.

FIG. 7 depicts a plan view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink 300. For clarity, FIG. 7 is not drawn to scale and only a portion of the two-phase micro-channel heat sink 300 is shown. In addition, for simplicity, the inlet(s) and outlet(s) are not shown. The two-phase micro-channel heat sink 300 is analogous to the two-phase micro-channel heat sink 100. Consequently, portions of the two-phase micro-channel heat sink 300 are labeled similarly. The two-phase micro-channel heat sink 300 thus includes flow micro-channels 302, cross-connect channels 304, and channel walls 306 corresponding to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. Consequently, the flow micro-channels 302, cross-connect channels 304, and channel walls 306 have analogous functions to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. The flow micro-channels 302, cross-connect channels 304, and channel walls 306 may also have analogous structure and/or size to flow micro- channels 102, cross-connect channels 104, and channel walls 106, respectively. In addition, the two-phase micro-channel heat sink 300 may be made of the

same materials, made using the same techniques as, and function in a similar manner to the two-phase micro-channel heat sink 100. For clarity, not all flow micro-channels 302, cross-connect channels 304, and channel walls 308 are labeled. The heat sink 300 may also include a plate (not shown) used to cover the channels 302 and 304. Further, another number of flow micro-channels

30and/or another number of cross-connect channels 304 may be used.

The flow micro-channels 302 have a height, a width, and are defined by channel walls 306, which also have a width and height. The flow micro-channels 302 may also have a rectangular cross-section. However, other channel cross- sections, widths, heights, channel directions are possible for the flow micro- channels 302. In the embodiment shown, the flow micro-channels 302 are substantially parallel. In some embodiments, the flow micro-channels 302 may not be parallel, linear, symmetric, and/or may have other cross-sections. Thus, various shapes of the flow micro-channels 302 may be used. The two-phase micro-channel heat sink 300 includes cross-connect channels 304. The cross-connect channels 304 are used provide communication between flow micro-channels 302 and to equilibrate the pressure of boiling coolant along the length of the cross-connect channels 304. Some of the cross- connect channels 304, such as the cross-connect channel 304A, do not extend across the entire width of the two-phase micro-channel heat sink 300. However, in another embodiment, all or none of the cross-connect channels 304 may extend across the entire width of the two-phase micro-channel heat sink 300. In the embodiment shown, the cross-connect channels 304 are micro-channels. In such an embodiment, the cross-connect channels 304 may be no larger than in the microscale regime. Further, the cross-connect channels 304 are also shown as having varying widths. However, in other embodiments, the cross-connect channels 304 may each have a uniform width. The cross-connect channels 304 are shown as having varied spacing. In another embodiment, the cross-connect channels 304 may be uniformly spaced. The cross-connect channels 304 are still sufficiently close and sufficiently long that severe pressure oscillations are reduced or eliminated in the operating range of the heat sink 300. Further, the cross-connect channels 304 are also spaced sufficiently far apart and sufficiently thin that a sufficient flow of coolant through the flow micro-channels 302 is also maintained.

The two-phase micro-channel heat sink 300 may share the benefits of the two-phase micro-channel heat sinks 100, 150, 200, and 250. For example, high efficiency cooling, reduced pressure oscillations, stable flow of the boiling liquid coolant, stable and repeatable dissipation of high heat fluxes, low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, and a smaller flow rate requirement may be achieved. A more uniform temperature variation in the flow direction and higher convective heat transfer coefficients may also be achieved. Consequently the two-phase micro-channel heat sink 300 may be suitable for thermal management of high-power-density electronic devices.

FIG. 8 depicts perspective and side views of a portion of another exemplary embodiment of a two-phase micro-channel heat sink 350. For clarity, FIG. 8 is not drawn to scale and only a portion of the two-phase micro-channel heat sink 350 is shown. In addition, for simplicity, the inlet(s) and outlet(s) are not shown. The two-phase micro-channel heat sink 350 is analogous to the two- phase micro-channel heat sink 100. Consequently, portions of the two-phase micro-channel heat sink 350 are labeled similarly. The two-phase micro-channel heat sink 350 thus includes flow micro-channels 352, cross-connect channels 354, and channel walls 356 corresponding to flow micro-channels 102, cross- connect channels 104, and channel walls 106, respectively. Consequently, the flow micro-channels 352, cross-connect channels 354, and channel walls 356 have analogous functions to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. The flow micro-channels 352, cross- connect channels 354, and channel walls 356 may also have analogous structure and/or size to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. In addition, the two-phase micro-channel heat sink 350 may be made of the same materials, made using the same techniques as, and function in a similar manner to the two-phase micro-channel heat sink 100. For clarity, not all flow micro-channels 352, cross-connect channels 354, and channel walls 358 are labeled. The heat sink 350 may also include a plate 362 used to cover the channels 352 and 364. Further, another number of flow micro-channels 352 and/or another number of cross-connect channels 354 may be used.

The flow micro-channels 352 have a height, a width, and are defined by

channel walls 356, which also have a width and height. The flow micro-channels 352 may also have a rectangular cross-section. However, other channel cross- sections, widths, heights, channel directions are possible for the flow micro- channels 352. In the embodiment shown, the flow micro-channels 352 are substantially parallel and have the same width and height. In some embodiments, the flow micro-channels 352 may not be parallel, linear, symmetric, of similar width and height, and/or may have other cross-sections. Thus, various shapes of the flow micro-channels 352 may be used.

The two-phase micro-channel heat sink 350 includes cross-connect channels 354. The cross-connect channels 354 provide communication between the flow micro-channels 352 and a uniform pressure along the length of each cross-connect channel 354. Some of the cross-connect channels 354, such as the cross-connect channel 354A, do not extend across the entire width of the two-phase micro-channel heat sink 350. However, in another embodiment, all or none of the cross-connect channels 354 may extend across the entire width of the two-phase micro-channel heat sink 350. In the embodiment shown, the cross-connect channels 354 are micro-channels. In such an embodiment, the cross-connect channels 354 may be no larger than in the microscale regime. Further, the cross-connect channels 354 are also shown as having uniform width. However, in other embodiments, the widths of the cross-connect channels

354 may vary. The cross-connect channels 354 are shown as having uniform spacing. In another embodiment, the spacing between the cross-connect channels 354 may vary. The cross-connect channels 354 are still sufficiently close and sufficiently long that severe pressure oscillations are reduced or eliminated in the operating range of the heat sink 350. Further, the cross-connect channels 354 are also spaced sufficiently far apart and sufficiently thin that a sufficient flow of coolant through the flow micro-channels 352 is also maintained. In addition, the depths of the flow micro-channels 352 and the cross- connect channels 354 differ. The flow micro-channels 352 have a depth d1 , while the cross-connect channels 354 have a depth d2 less than d1. In one embodiment, the depth d2 may be not more than one third the depth d1. However, the depth d2 is sufficient to allow communication between flow micro- channels 352 connected via the cross-connect channels 354. The cross-connect channels 354 thus have a depth that is sufficient to allow pressure of boiling

coolant to equilibrate along the length of the cross-connect channel 354. Thus, pressure oscillations may still be reduced. Although shown as having a uniform depth, the cross-connect channels 354 may have varying depths. Further, the flow micro-channels 352 may also have varying depths. The two-phase micro-channel heat sink 350 may share the benefits of the two-phase micro-channel heat sinks 100, 150, 200, 250, and 300. For example, high efficiency cooling, reduced pressure oscillations, stable flow of the boiling liquid coolant, stable and repeatable dissipation of high heat fluxes, low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, and a smaller flow rate requirement may be achieved. A more uniform temperature variation in the flow direction and higher convective heat transfer coefficients may also be achieved. Consequently the two-phase micro-channel heat sink 350 may be suitable for thermal management of high-power-density electronic devices. FIG. 9 depicts perspective and side views of a portion of another exemplary embodiment of a two-phase micro-channel heat sink 400. For clarity, FIG. 9 is not drawn to scale and only a portion of the two-phase micro-channel heat sink 350 is shown. In addition, for simplicity, the inlet(s) and outlet(s) are not shown. The two-phase micro-channel heat sink 400 is analogous to the two- phase micro-channel heat sink 100. Consequently, portions of the two-phase micro-channel heat sink 400 are labeled similarly. The two-phase micro-channel heat sink 400 thus includes flow micro-channels 402, cross-connect channels 404, and channel walls 406 corresponding to flow micro-channels 102, cross- connect channels 104, and channel walls 106, respectively. Consequently, the flow micro-channels 402, cross-connect channels 404, and channel walls 406 have analogous functions to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. The flow micro-channels 402, cross- connect channels 404, and channel walls 406 may also have analogous structure and/or size to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. In addition, the two-phase micro-channel heat sink 400 may be made of the same materials, made using the same techniques as, and function in a similar manner to the two-phase micro-channel heat sink 100. For clarity, not all flow micro-channels 402, cross-connect channels 404, and channel walls 408 are labeled. The heat sink 400 may also

include a plate 412 used to cover the channels 402 and 404. Further, another number of flow micro-channels 402 and/or another number of cross-connect channels 404 may be used.

The flow micro-channels 402 have a height, a width, and are defined by channel walls 406, which also have a width and height. The flow micro-channels

402 may also have a rectangular cross-section. However, other channel cross- sections, widths, heights, channel directions are possible. In the embodiment shown, the flow micro-channels 402 are substantially parallel and have the same width and height. In some embodiments, the flow micro-channels 402 may not be parallel, linear, symmetric, of similar width and height, and/or may have other cross-sections. Thus, various shapes and directions may be used for the flow micro-channels 402. Further, although shown as slots (or depressions), the flow micro-channels 402 might be formed using apertures.

The two-phase micro-channel heat sink 400 includes cross-connect channels 404. The cross-connect channels 404 provide communication between the flow micro-channels 402 and a uniform pressure along the length of each cross-connect channel 404. Some of the cross-connect channels 404 do not extend across the entire width of the two-phase micro-channel heat sink 350. However, in another embodiment, all or none of the cross-connect channels 404 may extend across the entire width of the two-phase micro-channel heat sink

400. In the embodiment shown, the cross-connect channels 404 are micro- channels. In such an embodiment, the cross-connect channels 404 may be no larger than in the microscale regime. The cross-connect channels 404 are also shown as having uniform width. However, in other embodiments, the widths of the cross-connect channels 404 may vary. The cross-connect channels 404 are shown as having uniform spacing. In another embodiment, the spacing between the cross-connect channels 404 may vary. The cross-connect channels 404 are still sufficiently close and sufficiently long that severe pressure oscillations are reduced or eliminated in the operating range of the heat sink 400. Further, the cross-connect channels 404 are also spaced sufficiently far apart and sufficiently thin that a sufficient flow of coolant through the flow micro-channels 402 is also maintained.

In addition, the flow micro-channels 402 and the cross-connect channels 404 differ. In the embodiment shown, the flow micro-channels 402 are formed as

slots, while the cross-connect channels 404 are formed by apertures in the channel walls 406. The size of the apertures for the cross-connect channels is sufficient large to allow communication between flow micro-channels 402 connected via the cross-connect channels 40. The cross-connect channels 404 thus have a depth that is sufficient to allow pressure of boiling coolant to equilibrate along the length of the cross-connect channel 354. Thus, pressure oscillations may still be reduced. Although shown as having a uniform depth, the cross-connect channels 404 may have varying depths. Further, the flow micro- channels 402 may also have varying depths. The two-phase micro-channel heat sink 400 may share the benefits of the two-phase micro-channel heat sinks 100, 150, 200, 250, 300 and 350. For example, high efficiency cooling, reduced pressure oscillations, stable flow of the boiling liquid coolant, stable and repeatable dissipation of high heat fluxes, low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, and a smaller flow rate requirement may be achieved. A more uniform temperature variation in the flow direction and higher convective heat transfer coefficients may also be achieved. Consequently the two-phase micro-channel heat sink 350 may be suitable for thermal management of high-power-density electronic devices. FIG. 10 depicts a plan view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink 450. For clarity, FIG. 10 is not drawn to scale. The two-phase micro-channel heat sink 450 is analogous to the two- phase micro-channel heat sink 100. Consequently, portions of the two-phase micro-channel heat sink 450 are labeled similarly. The two-phase micro-channel heat sink 450 thus includes flow micro-channels 452, cross-connect channels

454, channel walls 456, inlet 458, and outlet 460 corresponding to flow micro- channels 102, cross-connect channels 104, channel walls 106, inlet 108, and outlet 110, respectively. Consequently, the flow micro-channels 452, cross- connect channels 454, channel walls 456, inlet 458, and outlet 460 have analogous functions to flow micro-channels 102, cross-connect channels 104, channel walls 106, inlet 108, and outlet 110, respectively. The flow micro- channels 452, cross-connect channels 454, and channel walls 456 may also have analogous structure and/or size to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. In addition, the two-phase

micro-channel heat sink 450 may be made of the same materials, made using the same techniques as, and function in a similar manner to the two-phase micro-channel heat sink 100. For clarity, not all flow micro-channels 452, cross- connect channels 454, and channel walls 458 are labeled. The heat sink 450 may also include a plate (not shown) used to cover the channels 452 and 454.

Further, another number of flow micro-channels 452 and/or another number of cross-connect channels 454 may be used.

In addition to the flow micro-channels 452, cross-connect channels 454, and channel walls 456, the two-phase micro-channel heat sink 450 includes one or more reservoirs 464. The reservoirs 464 may be formed simply by widening a portion of cross-connect channel(s) 454, or in another manner. The depth of the reservoir(s) 464 may, but need not, be the same as the depth(s) of the flow micro-channels 452 and/or the depth of the cross-connect channels 454. In addition, the reservoirs are sufficiently small that a sufficient flow of coolant through the flow micro-channels 402 is also maintained and that pressure can still be equilibrated along the cross-connect channels 154. Thus, pressure oscillations may still be reduced. The presence of the reservoirs 464, therefore, may not prevent the two-phase micro-channel heat sink 450 from functioning.

The two-phase micro-channel heat sink 450 may share the benefits of the two-phase micro-channel heat sinks 100, 150, 200, 250, 300, 350, and 400. For example, high efficiency cooling, reduced pressure oscillations, stable flow of the boiling liquid coolant, stable and repeatable dissipation of high heat fluxes, low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, and a smaller flow rate requirement may be achieved. A more uniform temperature variation in the flow direction and higher convective heat transfer coefficients may also be achieved. Consequently the two-phase micro-channel heat sink 450 may be suitable for thermal management of high-power-density electronic devices.

FIG. 11 depicts a plan view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink 500. For clarity, FIG. 11 is not drawn to scale. The two-phase micro-channel heat sink 500 is analogous to the two- phase micro-channel heat sink 100. Consequently, portions of the two-phase micro-channel heat sink 500 are labeled similarly. The two-phase micro-channel heat sink 500 thus includes flow micro-channels 502, cross-connect channels

504, channel walls 506, inlet 508, and outlet 510 corresponding to flow micro- channels 102, cross-connect channels 104, channel walls 106, inlet 108, and outlet 110, respectively. Consequently, the flow micro-channels 502, cross- connect channels 504, channel walls 506, inlet 508, and outlet 460 have analogous functions to flow micro-channels 102, cross-connect channels 104, channel walls 106, inlet 108, and outlet 110, respectively. The flow micro- channels 502, cross-connect channels 504, and channel walls 506 may also have analogous structure and/or size to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. In addition, the two-phase micro-channel heat sink 500 may be made of the same materials, made using the same techniques as, and function in a similar manner to the two-phase micro-channel heat sink 100. For clarity, not all flow micro-channels 502, cross- connect channels 504, and channel walls 508 are labeled. The heat sink 500 may also include a plate (not shown) used to cover the channels 502 and 504. Further, another number of flow micro-channels 502 and/or another number of cross-connect channels 504 may be used.

In addition to the flow micro-channels 502, cross-connect channels 504, and channel walls 506, the two-phase micro-channel heat sink 500 includes a moat 514. The moat 514 may be considered analogous to the reservoirs 464 of the heat sink 450. Although shown as surrounding channels 502 and 504, the moat 514 may reside at only a portion of the edges of the two-phase micro- channel heat sink 500. The moat 514 may be formed simply by widening a portion of cross-connect channel(s) 504 and/or flow micro-channel 502, or in another manner. The depth of the moat 514 may, but need not, be the same as the depth(s) of the flow micro-channels 502 and/or the depth of the cross- connect channels 504. In addition, the reservoirs are sufficiently small that a sufficient flow of coolant through the flow micro-channels 502 is also maintained and that pressure can still be equilibrated along the cross-connect channels 154. Thus, pressure oscillations may still be reduced. The presence of the moat 514, therefore, may not prevent the two-phase micro-channel heat sink 500 from functioning.

The two-phase micro-channel heat sink 500 may share the benefits of the two-phase micro-channel heat sinks 100, 150, 200, 250, 300, 350, 400, and 450. For example, high efficiency cooling, reduced pressure oscillations, stable flow of

the boiling liquid coolant, stable and repeatable dissipation of high heat fluxes, low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, and a smaller flow rate requirement may be achieved. A more uniform temperature variation in the flow direction and higher convective heat transfer coefficients may also be achieved. Consequently the two-phase micro-channel heat sink 500 may be suitable for thermal management of high-power-density electronic devices.

FIG. 12 depicts plan and end views of a portion of another exemplary embodiment of a two-phase micro-channel heat sink 550. For clarity, FIG. 12 is not drawn to scale. In addition, for simplicity the two-phase micro-channel heat sink 550 is depicted as including only a few flow micro-channels. However, another number of flow micro-channels may be used. The two-phase micro- channel heat sink 550 is analogous to the two-phase micro-channel heat sink 100. Consequently, portions of the two-phase micro-channel heat sink 550 are labeled similarly. The two-phase micro-channel heat sink 550 thus includes flow micro-channels 552, cross-connect channel 554, channel walls 556, and plate 562 corresponding to flow micro-channels 102, cross-connect channels 104, channel walls 106, and plate 112, respectively. Consequently, the flow micro- channels 552, cross-connect channel 554, channel walls 556, and plate 562 have analogous functions to flow micro-channels 102, cross-connect channels

104, channel walls 106, and plate 112, respectively. The flow micro-channels 552, cross-connect channel 554, and channel walls 556 may also have analogous structure and/or size to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. In addition, the two-phase micro-channel heat sink 550 may be made of the same materials, made using the same techniques as, and function in a similar manner to the two-phase micro-channel heat sink 100. For clarity, not all flow micro-channels 552, cross- connect channels 554, and channel walls 558 are labeled. Further, another number of flow micro-channels 552 and/or another number of cross-connect channels 554 may be used.

In the embodiment shown, the two-phase micro-channel heat sink 550 may include a cross-connect channel 554 that runs the entire length of the heat sink 550 in the flow direction. Although depicted as extending across the entire width of the heat sink 550 (transverse to the flow direction), the cross-connect

channel 554 may extend across only a portion of the width of the heat sink 550. Further, multiple cross-connect channels 554 might be used. In the embodiment shown, the cross-connect channel 554 occupies the space between the channel walls 556 and the plate 562. Thus, the cross-connect channel 554 may be used to provide a more uniform pressure field along the entire two-phase micro- channel heat sink 550.

The two-phase micro-channel heat sink 550 may share the benefits of the two-phase micro-channel heat sinks 100, 150, 200, 250, 300, 350, 400, 450, and 500. For example, high efficiency cooling, reduced pressure oscillations, stable flow of the boiling liquid coolant, stable and repeatable dissipation of high heat fluxes, low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, and a smaller flow rate requirement may be achieved. A more uniform temperature variation in the flow direction and higher convective heat transfer coefficients may also be achieved. Consequently the two-phase micro-channel heat sink 550 may be suitable for thermal management of high-power-density electronic devices. However, it is expected that the performance of the two-phase micro- channel heat sink 550 may be less efficient than the two-phase micro-channel heat sinks 100, 150, 200, 250, 300, 350, 400, 450, and 500 because a single, larger cross-connect channel 554 is used.

FIG. 13 depicts plan and end views of a portion of another exemplary embodiment of a two-phase micro-channel heat sink 550'. For clarity, FIG. 13 is not drawn to scale. In addition, for simplicity the two-phase micro-channel heat sink 550' is depicted as including only a few flow micro-channels. However, another number of flow micro-channels may be used. The two-phase micro- channel heat sink 550' is analogous to the two-phase micro-channel heat sink 550 and thus to the two-phase micro-channel heat sink 100. Consequently, portions of the two-phase micro-channel heat sink 550' are labeled similarly. The two-phase micro-channel heat sink 550' thus includes flow micro-channels 552', cross-connect channel 554', channel walls 556', and plate 562' corresponding to flow micro-channels 102', cross-connect channels 104', channel walls 106', and plate 112', respectively. Consequently, the flow micro-channels 552', cross- connect channel 554', channel walls 556', and plate 562' have analogous functions to flow micro-channels 102, cross-connect channels 104, channel walls

106, and plate 112, respectively. The flow micro-channels 552', cross-connect channel 554', and channel walls 556' may also have analogous structure and/or size to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. In addition, the two-phase micro-channel heat sink 550' may be made of the same materials, made using the same techniques as, and function in a similar manner to the two-phase micro-channel heat sink 100. For clarity, not all flow micro-channels 552', cross-connect channels 554', and channel walls 558' are labeled. Further, another number of flow micro-channels 552' and/or another number of cross-connect channels 554' may be used. In the embodiment shown, the two-phase micro-channel heat sink 550' may include a cross-connect channel 554' that runs the entire length of the heat sink 550' in the flow direction. Alternatively, multiple cross-connect channels 554 might be used. Although functioning in an analogous manner to the cross- connect channel 554, the cross-connect channel 554' may be formed by providing a depression, or slot, in the plate 562'. Thus, the cross-connect channel 554' may be simpler to fabricate.

The two-phase micro-channel heat sink 550' may share the benefits of the two-phase micro-channel heat sinks 100, 150, 200, 250, 300, 350, 400, 450, 500, and 550. For example, high efficiency cooling, reduced pressure oscillations, stable flow of the boiling liquid coolant, stable and repeatable dissipation of high heat fluxes, low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, and a smaller flow rate requirement may be achieved. A more uniform temperature variation in the flow direction and higher convective heat transfer coefficients may also be achieved. Consequently the two-phase micro- channel heat sink 550 may be suitable for thermal management of high-power- density electronic devices. However, it is expected that the performance of the two-phase micro-channel heat sink 550' may be less efficient than the two-phase micro-channel heat sinks 100, 150, 200, 250, 300, 350, 400, 450, and 500 because a single, larger cross-connect channel 554' is used.

FIG. 14 depicts a perspective view of a portion of another exemplary embodiment of a two-phase micro-channel heat sink 600. For clarity, FIG. 14 is not drawn to scale. In addition, for simplicity the two-phase micro-channel heat sink 600 is depicted as including only a few flow micro-channels. However,

another number of flow micro-channels may be used. The two-phase micro- channel heat sink 600 is analogous to the two-phase micro-channel heat sink 100. Consequently, portions of the two-phase micro-channel heat sink 600 are labeled similarly. The two-phase micro-channel heat sink 600 thus includes flow micro-channels 602, cross-connect channels 604, channel walls 606, and plate

602 corresponding to flow micro-channels 102, cross-connect channels 104, channel walls 106, and plate 112, respectively. Consequently, the flow micro- channels 602, cross-connect channels 604, channel walls 606, and plate 602 have analogous functions to flow micro-channels 102, cross-connect channels 104, channel walls 106, and plate 112, respectively. The flow micro-channels

602, cross-connect channel 604, and channel walls 606 may also have analogous structure and/or size to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. In addition, the two-phase micro-channel heat sink 600 may be made of the same materials, made using the same techniques as, and function in a similar manner to the two-phase micro-channel heat sink 100. For clarity, not all flow micro-channels 602, cross- connect channels 604, and channel walls 608 are labeled. Further, another number of flow micro-channels 602 and/or another number of cross-connect channels 604 may be used. In the embodiment shown, the two-phase micro-channel heat sink 600 provides cross-connect channels 604 in the plate 612, rather than in the portion including the flow micro-channels 602. Thus, the cross-connect channels 604 occupy the space between the channel walls 606 and the plate 612. The cross- connect channels 604 provided could be analogous to any of the cross-connect channels 104, 154, 204, 254, 304, 354, 404, 454, and 504. Thus, the cross- connect channel 604 may be used to provide a more uniform pressure field along the entire two-phase micro-channel heat sink 600.

The two-phase micro-channel heat sink 600 may share the benefits of the two-phase micro-channel heat sinks 100, 150, 200, 250, 300, 350, 400, 450, and 500. For example, high efficiency cooling, reduced pressure oscillations, stable flow of the boiling liquid coolant, stable and repeatable dissipation of high heat fluxes, low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, and a smaller flow rate requirement may be achieved. A more uniform temperature

variation in the flow direction and higher convective heat transfer coefficients may also be achieved. Consequently the two-phase micro-channel heat sink 600 may be suitable for thermal management of high-power-density electronic devices. However, it is expected that the performance of the two-phase micro- channel heat sink 600 may be less efficient than the two-phase micro-channel heat sinks 100, 150, 200, 250, 300, 350, 400, 450, and 500 because a reduced communication between flow micro-channels 602 may be provided.

FIG. 15 depicts a portion of another exemplary embodiment of a two- phase micro-channel heat sink 650. For clarity, FIG. 15 is not drawn to scale. In addition, for simplicity the two-phase micro-channel heat sink 650 is depicted as including only a few flow micro-channels/cross-connect channels. However, another number of flow micro-channels/cross-connect channels may be used. The two-phase micro-channel heat sink 650 is analogous to the two-phase micro-channel heat sink 100. Consequently, portions of the two-phase micro- channel heat sink 600 are labeled similarly. The two-phase micro-channel heat sink 650 thus includes flow micro-channels 652, cross-connect channels 654, and channel walls 656 corresponding to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. The view shown could be for a set of flow micro-channels 652 and/or a set of cross-connect channels 654. The flow micro-channels 652, cross-connect channels 654, and channel walls

656 have analogous functions to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. The flow micro-channels 652, cross-connect channels 654, and channel walls 656 may also have analogous structure and/or size to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. In addition, the two-phase micro-channel heat sink 650 may be made of the same materials, made using the same techniques as, and function in a similar manner to the two-phase micro-channel heat sink 100. Further, another number of flow micro-channels 652 and/or another number of cross-connect channels 654 may be used. In the embodiment shown, the two-phase micro-channel heat sink 650 utilizes flow micro-channels 652 and/or cross-connect channels 654 having profiles that are not rectangular. Thus, the channel walls 656 may or may not be vertical. Despite their shape, the flow micro-channels 652 would still carry coolant between the inlet and outlet. Similarly, the cross-connect channels 654

may be used to provide a more uniform pressure field along the entire two-phase micro-channel heat sink 650.

The two-phase micro-channel heat sink 650 may share the benefits of the two-phase micro-channel heat sinks 100, 150, 200, 250, 300, 350, 400, 450, and 500. For example, high efficiency cooling, reduced pressure oscillations, stable flow of the boiling liquid coolant, stable and repeatable dissipation of high heat fluxes, low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, and a smaller flow rate requirement may be achieved. A more uniform temperature variation in the flow direction and higher convective heat transfer coefficients may also be achieved. Consequently the two-phase micro-channel heat sink 650 may be suitable for thermal management of high-power-density electronic devices.

FIG. 16 depicts a portion of another exemplary embodiment of a two- phase micro-channel heat sink 650'. For clarity, FIG. 16 is not drawn to scale. In addition, for simplicity the two-phase micro-channel heat sink 650' is depicted as including only a few flow micro-channels. However, another number of flow micro-channels may be used. The two-phase micro-channel heat sink 650' is analogous to the two-phase micro-channel heat sinks 100 and 650. Consequently, portions of the two-phase micro-channel heat sink 600' are labeled similarly. The two-phase micro-channel heat sink 650' thus includes flow micro-channels 652', cross-connect channels 654', and channel walls 656' corresponding to flow micro-channels 102/652, cross-connect channels 104/654, and channel walls 106/656, respectively. The view shown could be for a set of flow micro-channels 652' and/or a set of cross-connect channels 654'. The flow micro-channels 652', cross-connect channels 654', and channel walls 656' have analogous functions to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. The flow micro-channels 652', cross- connect channels 654', and channel walls 656' may also have analogous structure and/or size to flow micro-channels 102, cross-connect channels 104, and channel walls 106, respectively. In addition, the two-phase micro-channel heat sink 650' may be made of the same materials, made using the same techniques as, and function in a similar manner to the two-phase micro-channel heat sink 100. Further, another number of flow micro-channels 652 and/or

another number of cross-connect channels 654' may be used.

In the embodiment shown, the two-phase micro-channel heat sink 650' utilizes flow micro-channels 652' and/or cross-connect channels 654' having asymmetric profiles that include linear and curved portions. Despite their shape, the flow micro-channels 652' would still carry coolant between the inlet and outlet. Similarly, the cross-connect channels 654' may be used to provide communication between flow micro-channels and, therefore a more uniform pressure field along the entire two-phase micro-channel heat sink 650' in the flow direction. Thus, the specific profile of the cross-connect channels 654' and/or flow micro-channels 652' may not preclude the heat sink 650' from operating as a two-phase, stable heat sink.

The two-phase micro-channel heat sink 650' may share the benefits of the two-phase micro-channel heat sinks 100, 150, 200, 250, 300, 350, 400, 450, 500, and 650. For example, high efficiency cooling, reduced pressure oscillations, stable flow of the boiling liquid coolant, stable and repeatable dissipation of high heat fluxes, low thermal resistance to heat dissipation, large surface-area-to-volume ratio, small heat sink weight and volume, small liquid coolant inventory, and a smaller flow rate requirement may be achieved. A more uniform temperature variation in the flow direction and higher convective heat transfer coefficients may also be achieved. Consequently the two-phase micro- channel heat sink 650' may be suitable for thermal management of high-power- density electronic devices.

FIG. 17 depicts a high-level flow chart of an exemplary embodiment of a method 700 for providing and using a two-phase micro-channel heat sink. For simplicity, steps may be omitted or combined with other steps. The method 700 is described in the context of the heat sink 100. However, one of ordinary skill in the art will recognize that the method 100 may be used in providing another heat sink including but not limited to the heat sinks 150, 200, 250, 300, 350, 400, 450, 500, 550, 550', 600, 650, and 650'. Further, although described in the context of providing a single heat sink or components thereof, multiple heat sinks and/or components may be provided substantially simultaneously.

A plurality of flow micro-channels 102 is provided, via step 702. In one embodiment, step 702 includes micro-machining a high conductivity material. For example, slots may be formed in a substrate block of high conductivity

material. These slots are used as the flow micro-channels 102.

One or more cross-connect channels are provided, via step 704. The cross-connect channels 104 are formed generally transverse to the flow direction. Thus, the cross connect channels 104 may be substantially perpendicular to the flow micro-channels. Step 704 may include micro-machining slots and/or apertures in the substrate block. Alternatively, the plate 112 may be formed to include the cross-connect channel(s) 104 therein.

At least one inlet is provided, via step 706. Step 706 may be performed by fabricating an inlet plenum and coupling the plenum to the substrate block. At least one outlet is provided, via step 708. Step 708 may be performed by fabricating an outlet plenum and coupling the plenum to the substrate block. Any additional fabrication of the two-phase micro-channel heat sink 100 may then be completed. For example, the plate 112 may be affixed to the substrate block. The two-phase micro-channel heat sink may be thermally coupled to the device from which heat is desired to be dissipated, via step 710. In addition, step 710 may include mechanically coupling the heat sink 100 with the heat producing device, such as an electronic device.

Using the method 700, a two-phase micro-channel heat sink, such as the heat sink 150, 200, 250, 300, 350, 400, 450, 500, 550, 550', 600, 650, and/or 650' may be provided and used. Thus, the benefits of the heat sink 150, 200,

250, 300, 350, 400, 450, 500, 550, 550', 600, 650, and/or 650' may be achieved. A method and system for providing a two-phase cross-connected micro- channel heat sink has been disclosed. Although various embodiments have highlighted specific features, one of ordinary skill in the art will recognize that various features might be combined in other embodiments. The method and system have also been described in accordance with the embodiments shown. However, and one of ordinary skill in the art will readily recognize that there could be variations to the embodiments, and any variations would be within the spirit and scope of the present application. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.