Heat-activated pump with integrated evaporator for electronic chip heat removal

Abstract

A heat-activated pump removes waste heat from an electronic chip. An evaporator integrated into the chip packaging receives heat from the chip, converting a working fluid into vapor. Piping from the evaporator to a heat exchanger and back form a fluid circulation system. A pressure-control valve set for a specified electronic operating temperature allows vaporized working fluid to vent into a liquid-piston chamber, where it expands adiabatically, displacing pumped liquid in a pumping stage and expelling it from the chamber through a unidirectional valve to the shared heat exchanger(s). The heat exchanger(s) has a heatsink transferring heat away to a flow of cooler fluid. The pumped liquid returns in a suction cycle to the chamber through another unidirectional valve. An injector valve returns jets of condensed working fluid to the evaporator in successive brief spurts responsive to periodic pressure pulses in the chamber.

Claims

1. A heat-activated pump for removal of waste heat from an electronic chip, comprising: the electronic chip generating the waste heat; an evaporator containing a working fluid, the evaporator built into and integrated with a packaging of the electronic chip to receive the waste heat from the electronic chip to convert a liquid phase of the working fluid into a vapor of the working fluid; a pressure-control safety valve coupled to an exit port of the evaporator and maintaining the working fluid in the evaporator at a set target pressure and allowing the vaporized working fluid to escape through the exit port whenever the set target pressure is exceeded; a liquid-piston chamber coupled to the pressure-control valve to receive the vaporized working fluid from the evaporator at the set target pressure, the vaporized working fluid expanding adiabatically and displacing a liquid within the liquid-piston chamber, the liquid comprising the liquid phase of the working fluid, expelling the liquid from the liquid-piston chamber in a pumping stage of a thermodynamic cycle; a unidirectional pump-exit check valve coupled to a first exit port of the liquid-piston chamber to allow the working fluid and/or the displaced liquid to exit the liquid-piston chamber; a unidirectional liquid suction-entry check valve coupled to a return port of the liquid-piston chamber to allow the displaced liquid to enter the liquid-piston chamber; a heat exchanger with a heatsink, the heat exchanger coupled to the unidirectional pump-exit check valve to receive the displaced liquid into the heat exchanger, and the unidirectional liquid suction-entry check valve to allow the displaced liquid to return to the liquid-piston chamber in a suction stage of the thermodynamic cycle, the heatsink radiating the waste heat away to a flow of cooler fluid; and a unidirectional injector return check valve coupled to both a second exit port of the liquid-piston chamber and an input port of the evaporator, wherein periodic pressure pulses of the liquid phase of the working fluid from the liquid-piston chamber that temporarily exceed the set target pressure in the evaporator facilitate jets of the liquid phase of the working fluid to replenish the evaporator in successive brief spurts.

2. The heat-activated pump as in claim 1, wherein the evaporator is in the form of microchannels built into the packaging of the electronic chip.

3. The heat-activated pump as in claim 1, wherein the evaporator is a thermally insulative plate with edges bonded to a face of the electronic chip and with a hole for vapor egress and another hole for liquid ingress.

4. The heat-activated pump as in claim 3, wherein the pressure-control safety valve is in the form of a load disc applying deadweight upon the hole for the vapor egress to permit the vapor egress only when the specified target pressure that corresponds to the deadweight is reached.

5. The heat-activated pump as in claim 3, wherein the pressure-control safety valve is in the form of a flexible diaphragm covering the hole for the vapor egress and with a specified thickness and stiffness that flexes open to permit the vapor egress only when the specified target pressure is reached.

6. The heat-activated pump as in claim 1, wherein the liquid-piston chamber and the heat exchanger are in a form of at least one fluid channel accommodated in a single plate housing.

7. The heat-activated pump as in claim 6, wherein the unidirectional pump-exit check valve, the unidirectional liquid suction-entry check valve, and the unidirectional injector return check valve are in a form of balls confined within the at least one fluid channel, the at least one fluid channel having narrow backstops to limit a positional range of the balls.

8. The heat-activated pump as in claim 7, wherein the narrow backstops include O-ring gaskets to seal the at least one fluid channel whenever engaged by a respective one of the balls against a corresponding one of the O-ring gaskets.

9. The heat-activated pump as in claim 6, wherein the at least one fluid channel defining the liquid-piston chamber has a length that accommodates a specified volume of the vaporized working fluid and the displaced liquid.

10. The heat-activated pump as in claim 9, wherein at least one fluid channel defining the liquid-piston chamber has a serpentine arrangement within the single plate housing.

11. The heat-activated pump as in claim 6, wherein the single plate housing with the at least one fluid channel therein has a heat spreader cover in thermal transfer relation to an ambient environment having the flow of the cooler fluid.

12. The heat-activated pump as in claim 11, wherein the heat spreader cover further includes the heatsink attached thereto.

13. The heat-activated pump as in claim 1, further comprising a permanent magnetic material within the displaced liquid in the liquid-piston chamber, and an induction electrical generator surrounding the liquid-piston chamber for generating electrical current.

14. The heat-activated pump as in claim 13, wherein the permanent magnetic material is confined between backstops embedded in a groove defining the liquid-piston chamber, and the induction electrical generator comprises copper windings adjacent to the groove.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic plan view of a heat-driven fluid-operated pump in accord with the present invention for providing a heat activated pump for electronics cooling.

(2) FIG. 2 is a schematic view of a datacenter cooling arrangement using fluid-operated heat activated pumps in accord with the present invention.

(3) FIG. 3 is a perspective view of a heat activated pump as in FIG. 1 for cooling of individual electronic chip components.

(4) FIG. 4 is a close-up of the evaporator portion of the heat activated pump of FIG. 3.

(5) FIGS. 5 and 6 are respective exploded and assembled side sectional views of the heat activated pump body and pressure control valve assembly of the heat activated pump of FIG. 3.

(6) FIGS. 7A-7C are respective perspective, top exterior, and side sectional views of the heat activated pump body of the heat activated pump of FIG. 3 with special focus upon the various pump valves of the piston-suction chamber.

(7) FIGS. 8 and 9 are perspective views of two embodiments of heat activated pump cooling constructions for use with multi-chip circuit boards.

(8) FIG. 10 is an exploded perspective view of a heat activated pump as in FIG. 1 for cooling of space-constrained electronics (as in a smartphone or wearable) FIG. 11 is a top view of the pressure control valve, piston chamber, and heat exchanger portion of the heat activated pump of FIG. 10.

(9) FIG. 12 is a close-up view of piston chamber valves of FIG. 11.

DETAILED DESCRIPTION

(10) Nomenclature

(11) Working Fluid: The fluid whose change in phase is utilized to performing the pumping operation. The working fluid could be selected from a variety of fluid options: water, as well as commonly used or new refrigerants (e.g., R-130, R-245fa, R-407c, R-410a, R-454b, R-1234yf, etc.). In addition to performance and desired temperature range, safety (flammability and exposure limits) will be factors in the choice of working fluid.

(12) Pumped Fluid: The fluid which needs to be pumped from one location to another. This could be the same as the working fluid or it could be a different fluid material altogether. If the pumped fluid is different, it would need to be immiscible with the working fluid. In that case, a separator 113 may be provided (as seen in FIG. 1) at the return port 110 of the liquid-piston chamber 104 to direct only the working fluid material, and not the pumped fluid material, back to the evaporator(s) 101.

(13) Ambient Temperature: The temperature in the general environment around the region or device in focus.

(14) The Heat-Activated Multiphase Fluid-Operated Pump

(15) The HAMFOP pump utilizes heat to pump a fluid. The heat is used to convert a working fluid from liquid to vapor. The vapor is then used to displace the fluid that needs to be pumped.

(16) The principle of operation is as follows, as referenced by the numbered elements in FIG. 1, assuming that both the working fluid and the pumped fluid are the same: 1. Heat is applied to the hot chamber or evaporator 101, which contains a small quantity of the working fluid in liquid form. As it is heated, the working fluid is transformed into vapor 102 at a high pressure based on the amount of heat applied and temperature and sizing of the hot chamber 101. 2. The pressurized vapor pushes against the base of the pressure control valve 103, which is counteracted by a deadweight or equivalent load applied on top of it. Once the pressure of the vapor 102 exceeds the deadweight load, the valve 103 opens and the vapor 102 enters a piston/suction chamber 104, which has a larger area. The larger area ensures that the force applied by the vapor 102 remains high enough to keep the valve 103 open until a desired amount of the vapor 102 exits the hot chamber 101. This operation is similar to the principle of operation of a typical safety valve. 3. When the vapor 102 enters the piston/suction chamber 104, which already contains the fluid 114 that needs to be pumped, the high-pressure vapor 102 rapidly expands and displaces the pump fluid 114 from the entry side of the piston chamber 104 towards an exit side (on the right in FIG. 1). 4. The rapid adiabatic expansion of the vapor 102 induces a periodic pressure pulse that flows through the pumped fluid 114 in the piston chamber 104. Since the pumped fluid 114 is incompressible, this temporarily raises the pressure in the piston chamber 104, while the pressure in the hot chamber 101 temporarily decreases due to the loss of the vapor 102. This creates a positive pressure differential between the piston chamber 104 and the hot chamber 101, which results in the opening of a return valve 111. Due to the pressure pulse generated by the rapid entry of the vapor 102 and the incompressibility of the pumped fluid 114, the pressure in the piston chamber 104 transiently rises to a value above the vapor entry pressure. The increased pressure in the piston chamber 104 causes the return valve 111 to open (acting like an injector). Some of the pumped working fluid 110 flows through the return valve 111 and enters via a replenishment passageway 112 back into the hot chamber 101 for re-heating. Once enough working fluid 110 has flowed into the hot chamber 101 to equilibrate the pressure, the return valve 111 closes. This operation is similar to the function that an injector performs in steam engines: high-pressure vapor is used to push a fluid into a high pressure and high temperature evaporator. In the optional case where the pumped fluid 114 displaced by the working fluid (originally vapor 102, but now again in liquid form after the adiabatic expansion) are different materials that are immiscible, a separator 113 will be provided at the return port 110 of the piston chamber 104 to separate the working fluid from the pump fluid (now both liquids). The construction of separators of immiscible liquids is known. The key is to only allow the working fluid material to return to the hot chamber or evaporator 101, keeping out the different pumped fluid material. If the working and pumped fluids are identical materials, then the separator 113 is not needed. 5. Since the piston chamber 104 now has slightly less fluid, the working vapor 102 continues to expand adiabatically and push against the pumped fluid 114. As the pressure in the piston chamber 104 continues to remain high, the pump exit valve 109 opens and lets out the fluid 114 via a passageway 108 into the heat exchanger 107. This continues until the fluid 114 has been evacuated from the piston chamber 104 and the pressure in the piston chamber 104 reduces to a pressure close to that in the heat exchanger 107. 6. Upon displacing the pumped fluid 114, the vapor 102 remaining in the piston chamber 104 expands into a larger volume, so it condenses, resulting in a reduction in pressure in the piston chamber 104, to a value below the pressure in the heat exchanger 107. As a result, the pump valve 109 closes, completing the pump portion of the cycle and beginning a suction phase. The suction valve 105 now opens due to the negative differential pressure between the heat exchanger 107 and the piston chamber 104, letting fresh working fluid 106 in. Due to the negative differential pressure, fluid 106 is drawn into the piston chamber 104 from the heat exchanger 107. 7. While the pressure in the piston chamber 104 is below that of the heat exchanger 107, the pressure control valve 103 remains closed to ensure no new vapor 102 enters the piston chamber 104 until the piston chamber pressure returns to above the heat exchanger pressure, concluding the suction phase of the cycle. 8. Once the fluid in the piston chamber 104 has been replenished and the pressure is raised to the pressure of the heat exchanger 107, the pressure control valve 103 re-opens, letting in vapor 102 to repeat the cycle. 9. In some embodiments, an electricity generator module may generate an electrical current induced in winding coils around the piston chamber during the continuous cyclic operation of the pump.

(17) In the case where the pumped fluid 114 (and 106) is composed of a different material from the working fluid 102 (and 110), and not merely a different liquid-vapor phase of the same material, a difference in density between the working and pumped fluids can be leveraged to separate them. The elements of such an embodiment are largely identical to structure and operation to those in FIG. 1, except for the addition of a separator, in which the pumped fluid and the working fluid are separated. The pumped fluid 114 and 106 being of lower density would float to the top while the working fluid 102 and 110 would sink to the bottom. Accurate tuning (balancing the precise quantity of working and pumped fluid) would need to be performed to ensure that the separator chamber never ends up without any working fluid at all. If that were to happen, then some of the pumped fluid could enter the hot chamber 101, thus interrupting the cycle.

(18) Heat Activated Pump for Cooling of Large Systems such as racks of PCBAs, Datacenters and other such large electronic systems A heat activated pump system can be used to move fluid around a datacenter as illustrated in FIG. 2, in which multiple heat activated pump units are interconnected together.

(19) Heat activated pumps on devices attached to PCBAs in a rack pump the cooling fluid around in piping running throughout the data center. The datacenter-level heat activated pump system uses this hot pumped fluid from each individual heat activated pump to pump the fluid to the heat exchanger and return the fluid back to the PCBA level devices at a cool temperature to close the circuit as shown in FIG. 2. Individual heat activated pumps 152 are mounted on circuit boards 151 positioned in racks 150. Details of the individual heat activated pumps 152 are as referenced in FIG. 3. Evaporator lines 154 from groups of chips, boards, and racks connect through one or more pressure control valves 155 to one or more associated piston-suction chambers 156. Groupings may encompass an entire datacenter or various subsets of a data center, each grouping having a heat exchanger 159. The piston-suction chamber(s) 156 have a corresponding working fluid return valve 157 coupled to working fluid return lines 153 leading back to the grouping of chips, boards, and racks. Each piston-suction chamber 156 also has a pump valve 161 coupled to a heat exchanger 159, with a suction return line 160 back to the chamber 156 via a suction valve 158. Each grouping operates as described above with reference to FIG. 1.

(20) Heat Activated Pump for Cooling of Electronic Devices Mounted on PCBAs

(21) As seen especially in FIG. 3, key heat activated pump elements for device cooling on PCBAs are:

(22) TABLE-US-00001 Material Element Options Description Printed Circuit Standard The board on which Board 200 Industry different electrical Materials devices are mounted Chip 201 Standard Generic designator for the Industry device that needs to be Materials cooled. It could be a logic chip, memory, optical device etc. It could be a single monolith or a heterogeneous multichip device. Thermal Standard A thin material used to Interface Industry contact two heat Material Materials transferring surfaces. The (TIM) 202 fluid-operated heat activated pump could be bonded directly to the chip or contacted via the TIM material Evaporator High Thermal The outer body of the Enclosure 203 Conductivity: evaporator. This could be Copper, standalone if a metal foam Aluminum, is inserted into the High Temp enclosure. It could be Ceramic etc. integrated with the core Evaporator High Thermal The core is where the Core 204 Conductivity: working vapor is created. Copper, It is designed to have the Aluminum, highest surface area High Temp possible for max heat Ceramic, transfer. Core examples: Metal Foam metal foam, serpentine etc. grooved trenches, or bonded fins Evaporator Top High Thermal Plate to allow vapor to Cover 205 Conductivity: exit the evaporator and Copper, return to it. Comprised Aluminum, of holes strategically High Temp located to allow vapor Ceramic etc. exit and liquid return Could be bolted, soldered, or welded to evaporator and pump Pump 206 Insulating Vapor from evaporator material: enters the pump, flows PTFE, Nylon, through the channel Plastic, or displacing existing fluid. other Vapor condenses in the material channel while displacing coated with the fluid and evacuating insulation the channel, thus creating a low-pressure cavity for fresh fluid to be sucked in. Contains three valves integrated into it: pump fluid out, return some fluid back to evaporator and suck fresh fluid in Valve Balls 207 Plastic, Balls (could also be thin Metal (Steel, discs) designed to allow Tungsten only unidirectional flow etc.), as desired. O-rings Rubber, could also be used with Ceramic the balls to ensure tight seals Pressure Valve High Temp, Thin, flexible gasket Gasket 208 Fluid Vapor designed to seal the Resistant vapor entry into pump (e.g., Silicone) Pressure Valve Copper, Shaft designed to apply Seat 209 Aluminum, solid pressure on valve High Temp gasket, so the vapor does Ceramic, or not enter the pump high temp chamber until the plastic etc. pressure exceeds target load value. Diaphragm 210 Silicone, Diaphragm designed to Rubber, or flex to allow vapor to other escape into second chamber flexible when pressure exceeds material that target load. Diaphragm can can withstand be replaced with O-rings working vapor or metal bellows in other pressure, embodiments as needed chemical and temperature conditions Heat High Thermal Pumped hot liquid flows exchanger 211 Conductivity: from the pump to the heat Copper, exchanger. Heat exchanger Aluminum, has serpentine channels to High Temp move fluid and exchange Ceramic etc. heat with heatsink Could be attached on top of it. bolted, Condensed fluid then soldered, or returns to the pump welded to chamber through the pump suction valve. Heat exchanger could also send fluid to another secondary heat exchanger for more cooling Heatsink 211 High Thermal Heat from the heat (combined with Conductivity: exchanger is transferred heat exchanger) Copper, to the heatsink by Aluminum, conduction. Fins on the High Temp heatsink accelerate heat Ceramic etc. transfer to flowing air. In another embodiment, the heatsink could be more tightly integrated into the heat exchanger like a conventional radiator. Different heatsink fins could be used: wavy, elliptical, slotted etc. The heatsink can be mechanically clamped/bolted down to the PCB to ensure it remains firmly in place over the chip. A backing plate underneath the PCB ensures the board remains supported and the chip is not excessively loaded in-situ or during assembly. Whenever needed, the entire assembly can simply be removed and replaced Load Seat 212 Metal or The seat applies a plastic- mechanical advantage by high rigidity balancing the force of the load on top of it with the vapor counter-pressure from the valve seat. Grooves on the top surface keep the load centered on the load seat. Load 213 High density The target weight that the material: vapor needs to overcome Tungsten, to open the valve. The load Liquid could be a dead weight or Gallium etc. a compression spring that could be deflected to impart the same target load resistance. Load Rigid sheet Designed to hold the load Cover 214 metal or in place and prevent it plastic, from falling off. Also preferably designed to provide a heat back-stop to ensure that insulating. the load does not displace Could be excessively due to vapor bolted, pressure in case the welded, or diaphragm fails. soldered on to the heatsink body

(23) This specific embodiment is for a chip and board horizontally oriented with the heat activated pump mounted on top of the chip. This design can easily be modified to operate with a chip and board vertically oriented as well. In situations where multiple chips are mounted close together (as in chiplets on a single substrate) and some of the chips have lower operating temperature requirements as compared to others (as in memories and logic devices); then their heat paths can be completely separated into two distinct pumps operating independently. The vapor pressure of each pump can be tuned to match the target operating temperature of each chip to be cooled. This way, cross heating is mitigated, and each chip operates close to its own target temperature.

(24) Evaporator

(25) The details of the evaporator are outlined in FIG. 4. It is comprised of three key elements: 1. An enclosure 203 that holds the evaporator core 204 and facilitates the transfer of heat from an external heat source to the evaporator core 204. The region of the enclosure 203 exposed to the heat source needs to be designed to be very high thermal conductivity and low thermal resistance. The rest of the evaporator enclosure 204 is insulated to prevent heat loss. 2. An evaporator core 204, in which the working fluid is converted from liquid to vapor or maintained in vapor form. The key design features of the core 204 are very high surface area to enable effective heat transfer to the liquid. Some embodiments of the core include but are not limited to: a. Metal Foam: porous metallic structures designed to have very high surface area and high heat transfer. b. Metal Mesh/Wool/Screen: high thermal conductivity metal mesh can be used as an effective core. Copper, Aluminum, or other metal mesh structures can be brazed or soldered to the evaporator enclosure to achieve the desired high heat transfer area. c. Serpentine Trench: a metal trench can be machined or stamped into the enclosure to allow the working fluid to move from entry to exit. Using a single directional serpentine trench requires less of the fluid and ensures that most of the heat is used for phase change rather than simply heating the liquid. The trenches can be filled with metal mesh/wool to further enhance heat transfer. d. Cold plates: microchannel or tubular cold plates can be used. 3. Top cover plate 205: this is designed to keep the enclosure 204 sealed and allow exit of the vapor and entry of the liquid. The plate 205 could be welded, bolted, brazed, soldered etc. to the evaporator or be an integrated part of the evaporator body itself.
Pressure Control Valve

(26) The details of the pressure control valve are outlined in FIGS. 5 and 6. It is comprised of these key elements: 1. A gasket 208 that seals the vapor in the evaporator 203, 204 and 205. In very precisely machined structures, the gasket 208 can be dispensed with, and pure solid-solid pressure could be relied upon. 2. A valve shaft 216 that transmits the load from the counterweight 213 to the gasket 208 to keep the pressure below a set value as determined by the weight of the counterweight load 213. 3. A larger second cavity in which the valve shaft 216 sits, which ensures that a force applied by the vapor is still high enough to keep the seal open as the vapor exits the evaporator into the piston. 4. A diaphragm 210 that deflects when the vapor pressure exceeds the counterweight load 213. The diaphragm 210 also prevents the vapor from leaking out of the valve. 5. A load seat 209 that applies a mechanical advantage: one end has a small area and the other has a much larger area to accommodate the larger load 213. The seat 209 also has a cavity in it to hold the load 213 in place. 6. A load 213 that could be a dead-weight or a liquid that keep the valve closed at a set pressure. The load 213 could also be a spring-loaded structure to achieve the same end objective: an applied force. 7. A load cover 214 that encases the dead weight load 213 and holds it all in place. A small hole can be made in the cover to ensure that the air around the dead-weight load 213 always remains constant (atmospheric).
Piston Chamber

(27) The details of the piston are outlined in FIGS. 7A-7C. It is comprised of these key elements: 1. The encasing body 206 (seen in FIG. 3) that holds the chamber in place and houses the different valves 207a-207c. The body 206 needs to be insulated to prevent losses and pre-heat the incoming fluid to improve pumping output. 2. A piston chamber 207d in which the vapor expands and pushes out the pumped fluid. A key benefit of a liquid piston is that infinite potential shapes can be used to make the design compact, space efficient and versatile. 3. The chamber walls of the piston-suction chamber 207d need to be smooth and can be coated with fluid repelling coating to reduce friction losses. The curves in the structure need to be smooth to prevent localized sudden area increases which may cause the vapor to condense prematurely.
Valves

(28) The details of the valves 207a-207c are outlined in FIG. 7C. For compactness, the valves are embedded in the body 206 of the piston pump chamber. This is just one example of the implementation of the valves, they could be implemented in infinite possible geometries and commercially available check valves could also be used. While the image shows the valves only actuated with balls 207e, the balls could be augmented with O-rings, discs, or gaskets depending on the quality of the metrological finish. The valves are actuated by the differential pressure across them.

(29) Heat Exchanger

(30) The details of the heat exchanger and heatsink 211 are outlined in FIG. 3. In this embodiment, the heat exchanger and heatsink 211 are shown as bonded to each other horizontally. Alternatively, the heat exchanger and heatsink could also be in the form of a radiator/heat exchanger, placed remotely from the pump depending on the space available and the access to cooling air. The fluid channels in the heat exchanger could also be structured in infinite possible geometries similar to the piston-suction chamber 207d in FIGS. 7A-7C.

(31) Multiple Chips on PCBA Implementation

(32) The aforementioned implementations are for cooling only one individual electronics device on a PCBA 200. When multiple devices 217 are mounted on a PCBA 200, an example arrangement is shown in FIG. 8.

(33) The fluid-operated heat activated pumps 218 of multiple devices can be joined together to a common heat exchanger 219, as seen in FIG. 9. This ensures that if any one device is running hotter than the others, the cooler device's thermal budget can be consumed by the device requiring more cooling. Thus, the overall thermal performance of the PCBA is optimized. If all the devices are running hotter than target, the heat activated pumps on all the devices will run faster (higher flowrate) while maintaining the devices at their target operating temperature.

(34) The heat exchanger 219 can also be placed in front of the target device so the heat exchanger receives the coolest incoming air and the hot air it releases downstream can be directed at the device to ensure it runs hot.

(35) The heat activated pumps on each device interconnected, convert part of the collective heat dissipated by the devices into useful work to pump the cooling fluid around the devices, to maintain them at a constant target temperature.

(36) Heat Activated Pump for Cooling of Low Wattage Electronics (Smartphones, Wearables, Flat Panels, Etc.)

(37) A fluid-operated heat activated pump for space-constrained devices (smartphones, wearables, etc.) is shown in FIGS. 10-12. Details of each constituent are:

(38) TABLE-US-00002 Material Element Options Description Chip 201 Standard Generic designator for the Industry device that needs to be Materials cooled. It could be a logic chip, memory, optical device etc. It could be a single monolith or a heterogeneous device complex. The silicon chip could have microchannels fabricated on the back side, using a standard Deep Reactive Ion Etching (DRIE) process, typically 50 microns deep. The purpose of the microchannels is to increase the surface area, to enhance boiling. Conventional silicon microchannels have the challenge of restricting the flow of fluid (due to their small dimensions and thus increased resistance to fluid flow). However, this application of silicon microchannels is different because fluid is not pushed through them. Instead, they serve as fins to enable faster heat transfer for boiling. Evaporator Thermal The side facing the chip has Plate 220 insulator 2 holes: one for vapor egress (combined material: 233f and another for liquid with the chip) plastic, ingress 233e. The edges of the polymer, evaporator plate 220 are ceramic etc. bonded to the chip using any industry standard technique: solder, brazing, non-outgassing adhesive, welding etc. Pressure Thermal The load disc 223 transfers Control insulator pressure from the deadweight Valve-Load material: to the evaporator hole to Disc 223 plastic, prevent vapor from exiting polymer, before the deadweight pressure ceramic etc. is reached. The disc could be used standalone or with a gasket/O-ring to achieve leak free contact. The disc could also be a sphere. Pressure Silicone, Diaphragm 224 is designed to Control Rubber, or flex to allow vapor to escape Valve- other flexible into second chamber when Diaphragm 224 material that pressure exceeds target load. can withstand If there is no space for a working vapor deadweight, the diaphragm pressure, itself can be stiffened to act chemical and as the deadweight by tuning temperature its thickness. The diaphragm conditions. It can be replaced with O-rings could also be or metal bellows in other fabricated embodiments as needed. The from silicon diaphragm material is extended or silicon to cover above the piston area carbide using as well, where it serves as a standard wafer thermal insulator preventing lithography heat from leaving the piston techniques 234 through the top high thermal conductivity metal heat spreader. Pressure Metal or The seat 226 applies a Control plastic-high mechanical advantage by Valve-Load rigidity. balancing the force of the Seat 226 load 223 on top of it with the vapor counter-pressure from the valve seat. Grooves on the top surface keep the load 223 centered on the load seat 226. Pressure High Temp, Thin, flexible gasket 227 is Control Fluid Vapor designed to seal a liquid load Valve- Resistant on top of the load seat 226. Gasket 227 (e.g., Silicone) Single Plate Any insulating This accommodates the piston Housing 232 and rigid chamber 221, heat exchanger material 230 with channels 231, and the valves 233a, c and d, 235 in a single plate with small form factor. Piston NA This is a cavity with input Chamber 221 port 215 and built into the evaporator plate 220, towards the heat spreader side. The groove can be a single channel, or it can be a serpentine channel depending on how much volume needs to be displaced. Backstops 234a-b are embedded in the piston groove 234 (in current generating applications only) to ensure that magnetic material suspended in the liquid does not leave the piston-chamber. Heat NA This is a cavity 230 built Exchanger into the evaporator plate 220. 230 It could be a single channel, or a series of channels 231 connected together in parallel. The heat exchanger could also be completely off- the-chip depending on the amount of heat loss required. Inductive Copper This interacts with magnetic electrical winding and material between the backstops generator 236 ferro-magnetic 234a-b to induce a current in material the windings 236. Valves 233a, c NA These are cavities with and d, 235 specific obstructions built into the chambers to allow fluid to flow uni-directionally. 233a is the injector return check valve with small hole 233f returning; 233c is the pump-exit check valve with a groove 233b forming a first exit port of the liquid-piston chamber; 233d is the suction-entry check valve coupled to a groove 233e forming the return port of the liquid-piston chamber. Piston Cover High Thermal This plate closes the pump and Heat Conductivity and isolates it to protect it. It Spreader 225 Material: also transfers heat from the Copper, heat exchanger 230 to the Aluminum etc. ambient environment. It could be attached with thermal adhesive to the chassis of a smartphone, watch etc. A finned heatsink could also be attached to the top if there is convective air cooling available. Valve Balls Plastic, Metal Balls 222 (could also be thin 222 (Steel, discs) designed to allow only Tungsten etc.), unidirectional flow as Rubber, desired. O-rings could also be Ceramic used with the balls to ensure tight seals Pressure Valve High Temp, Thin, flexible gasket 227 Gasket 227 Fluid Vapor designed to seal the vapor Resistant entry into the pump (e.g., Silicone) Load Rigid sheet Designed to hold the load 223 Cover 228 metal or plastic, (solid or liquid) in place and preferably prevent it from falling off. heat insulating. Also designed to provide a If liquid is back-stop to ensure that the used, could be load does not displace made of rubber excessively due to vapor or other flexible pressure in case the material. Could diaphragm fails. be bolted, welded, or soldered on to the heatsink body Load Cover Metal or This is needed when a liquid Top 229 Plastic, Rigid load is used. The liquid load is poured into the load cover to the desired height and then the top is used to seal the cover to prevent spillage.

(39) In vertical space constrained applications, a deadweight load cannot be used, especially if the operating temperature is high. In such situations, the diaphragm itself could be stiffened to act as the load by selecting the appropriate thickness, material, and diameter. In situations where a diaphragm cannot be used, a spring or a liquid dead weight (like Gallium) can be used. The operating principle is Pascal's law: the pressure in a fluid is always the same and the pressure is a function of the height of the fluid.

(40) Taller columns produce higher counterweight. In some situations, the counterweight load may need to be dynamically changed (increased or decreased) while the unit is operating. For instance: the ambient temperature temporarily increases beyond nominal values. A higher ambient temperature means a higher flowrate is required through the heat exchanger to transfer the same amount of heat. If the duty load on the chip is low, the temperature of the chip can be raised slightly, so the pump does more work and increases the flowrate through the heat exchanger. This increase in chip temperature can be accomplished by raising the deadweight value: by increasing the height of the liquid column. This can be achieved by using a bimetallic strip which contracts in diameter, thus raising the height of the liquid column.

(41) In applications where the ambient temperature is too high (e.g., a smartphone left on a car dashboard or an electronic device in a higher than specified ambient environment), the pump will act as a thermal switch where heat from outside the device will not be conducted back into the device. It accomplishes this because the pump is designed to transfer heat from the evaporator to the heat exchanger. If the heat exchanger temperature exceeds the evaporator temperature, the pump will cease to function until the heat exchanger temperature drops below the evaporator temperature.