Active two-phase mist stream cooling system

Abstract

To provide an active two-phase mist stream cooling system.SOLUTION: A cooling system 10 includes: a channel 115 surrounding a heat source; a coolant droplet introducer 112 for vaporizing a coolant droplet as a coolant gas in a channel by heat generated by the heat source in order to introduce the coolant droplet into the channel; a compressor 102 for pumping air containing the coolant gas from a channel subspace to a condenser subspace; and a condenser 107 for condensing the coolant gas into coolant droplets or a coolant liquid. The coolant liquid is introduced into a coolant droplet introducer or being introduced therefor.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] This application relates to cooling systems, and more particularly, to active 2-phase mist-stream cooling systems. [Background technology]

[0002] Conventional cooling systems can be classified by contrasting passive and active, one-phase and two-phase. Within one-phase cooling, systems can be classified by air cooling and liquid cooling. Typical examples of cooling systems for electronic devices range from one-phase cooling systems, such as passive and / or active air cooling, active water cooling, to two-phase cooling systems, such as vapor-chamber heat-spreaders and two-phase liquid immersion cooling. By utilizing the latent heat absorption / release during the gas-liquid phase change, two-phase liquid immersion cooling can achieve extremely high heat dissipation rates.

[0003] However, downsides of two-phase immersion cooling systems include difficulties in installation, vapor containment issues during operation, cumbersome maintenance, and potential interactions between the cooling fluid and electronic components, including cables.

[0004] Therefore, there is a need to improve upon the prior art. Summary of the Invention

[0005] Therefore, the main objective of this application is to provide an active two-phase mist-stream cooling system to remedy the shortcomings of the prior art.

[0006] One embodiment of this application discloses a cooling system including a channel encompassing a heat source, a coolant-droplets introducer configured to introduce coolant droplets into the channel, the coolant droplets being evaporated as a coolant gas in the channel by heat generated by the heat source, a compressor configured to pump an air from a channel subspace to a condenser subspace, the air including the coolant gas, and a condenser configured to condense the coolant gas into coolant droplets or a coolant liquid. The coolant liquid is introduced into or for the coolant-droplets introducer.

[0007] These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. [Brief description of the drawings]

[0008] [Figure 1] 1 illustrates the relationship between vapor pressure versus temperature for various coolants. [Diagram 2] FIG. 1 is a schematic diagram of a cooling system according to an embodiment of the present application. [Diagram 3] FIG. 1 is a schematic diagram of a cooling system according to an embodiment of the present application. [Figure 4]1 illustrates a schematic diagram of a condenser according to an embodiment of the present application. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] All the disadvantages of two-phase immersion cooling systems would disappear if the structure of "immersion in a body of coolant liquid" is modified to "immersion in a moving stream of coolant mist". "Coolant mist" refers to a collection of airborne coolant droplets, i.e. tiny drops of coolant, suspended in a gaseous transport medium, which flows at an appropriate high velocity to form a moving stream of coolant mist.

[0010] In this invention, an active 2-phase mist-stream cooling system is introduced in which a stream or mist-stream (e.g., shown below at 114) containing a gas transport medium into which a mist of suspended coolant droplets is injected is forced (e.g., by active pushing or sucking) into heat generating regions (e.g., shown below at 115) where heat is absorbed as latent vaporization heat when the coolant droplets are infused within the mist-stream vaporize. The resulting coolant vapor, carried by the same gas transport medium, is then forced (e.g., by active pushing or sucking) into a condenser (e.g., shown below at 107) where the coolant vapor condenses back to liquid phase and releases heat (as latent heat of condensation) during the condensation process.

[0011] In this application, unless otherwise specified, the term "air" may be used interchangeably with the term "gaseous transport medium", and both terms may refer to, but are not limited to, atmospheric air or any other suitable gaseous medium in which microscopic coolant droplets may be suspended in an airborne manner to form a mist stream.

[0012] Unless otherwise specified, the term "coolant" in this invention generally refers to a material selected to have a vapor pressure A at boiling point (mk) °C, i.e., k °C below an upper bound m °C of device operating temperature range. For example, in one embodiment for smartphone processor cooling, the upper limit of the processor operating temperature range is typically 85 °C, i.e., m ≈ 85. Assuming a target k of 30 °C, a pressure of 0.7 [ATM] (532 [mmHg]) when using methanol as the coolant will have a boiling point of about 55 °C according to FIG. 1.

[0013] The coolant in the cooling system of the present invention may be selected according to the chemical or physical properties of the coolant as well as practical requirements. Coolant gas or coolant vapor refers to a coolant that is vaporized in the gaseous / vapor phase.

[0014] 2 is a schematic diagram of a cooling system 10 according to an embodiment of this application. The cooling system 10 includes a coolant (selected according to specific requirements), a channel 115 surrounding a heat source 140, a coolant-droplets introducer 112, a compressor 102, a condenser 107, a pressure regulating valve 109, and a heat remover 105. The coolant-droplets introducer 112 may be similar to a mistifier or humidifier, and may include a MEMS fabricated air pumping device, where MEMS is a Micro-Electro-Mechanical System. The coolant droplet introducer 112 is configured to introduce coolant droplets into the channel 115. By absorbing heat generated by / from the heat source 120, the coolant droplets will vaporize as coolant gas (coolant in a gaseous state / phase) in the channel 115. It should be noted that coolant droplets refer to the coolant being in a liquid state / phase, whereas coolant gas refers to the coolant being in a gaseous state / phase.

[0015] The compressor 102 (which may include a MEMS fabricated air pumping device) is configured to pump / suck air from a channel subspace (also denoted 115) to a condenser subspace (also denoted 107). The air pumped / sucked into the condenser subspace 107 consists / contains coolant gas. The compressor 102 is also configured to maintain an air pressure difference between the channel subspace 115 and the condenser subspace 107, such that the air pressure in the channel subspace 115 is lower than the air pressure in the condenser subspace 107. That is, the maintained air pressure difference may be thought of as a lower pressure in the channel 115 and a higher pressure in the condenser 107. In one embodiment, the air pressure in the condenser subspace 107 may be maintained at 1.05 [ATM] and the air pressure in the channel subspace 115 may be maintained at 0.8 [ATM], but is not limited thereto.

[0016] The condenser 107 is configured to condense the coolant gas back into coolant droplets or coolant liquid, i.e., to condense the coolant in gas phase into coolant liquid in liquid phase. The coolant droplets or liquid from the condenser 107 are directed and / or introduced to the coolant-droplets introducer 112.

[0017] It is assumed that the compressor 102 is capable of generating a pressure difference of 0.25 ATM from the inlet to the outlet of the compressor, i.e., the compressor 102 is capable of lowering the pressure in the channel 115 to 0.8 ATM, while raising the pressure in the condenser 107 to 1.05 ATM. Due to such a pressure difference, the coolant evaporates in the channel 115 at a lower boiling power and condenses in the condenser 107 at a higher dew point. In this case, a system of asymmetrical liquid-gas phase transition points (or asymmetrical pairs of boiling point and dew point) is thus generated.

[0018] It should be noted that in cooling systems 10 with asymmetrical liquid-gas phase transition points, even if the temperatures in the channels 115 and the condenser 107 are the same, evaporation (in the channel subspaces 115) and condensation (in the condenser subspaces 107) occur due to pressure differences, absorbing / releasing latent heat while maintaining an approximately constant temperature.

[0019] A pressure regulating valve 109 (which may include a MEMS fabricated venting device) is configured to regulate the pressure difference between the pressure corresponding to the channel sub-space 115 (after the pressure regulating valve 109) and the pressure corresponding to the condenser sub-space 107 (before the pressure regulating valve 109), such that the pressure after the pressure regulating valve 109 (corresponding to the channel sub-space 115) should be lower than the pressure before the pressure regulating valve 109 (corresponding to the condenser sub-space 107). In one embodiment, the pressure regulating valve 109 may be located much closer to the inlet of the channel 115 than the condenser 107 to prevent undesired evaporation of the coolant liquid.

[0020] Condensation of a gas to a liquid is a heat releasing process, so heat remover 105 is configured to remove heat released by condenser 107. In one embodiment, heat remover 105 may be or include, but is not limited to, an air movement device such as a fan or blower (which may also be MEMS fabricated). In other embodiments, heat remover 105 may be or include, but is not limited to, a chilling device or chiller.

[0021] Besides, a conduit 108 is configured to connect the mixture of air and condensed coolant liquid between the condenser 107 and the pressure regulator 109. The mixture of air and coolant vapor injected into the condenser 107 by the compressor 102 will be separated into air and coolant liquid by a condensation process inside the condenser 107. After passing through the pressure regulator 109, the pressure will drop to the level of the channel subspace 115. The air will pass through the air conduit 120, while the coolant liquid will pass through another coolant conduit 110. Optionally, an insulation sleeve 111 may be used to prevent the coolant from evaporating.

[0022] In one embodiment, the coolant-droplets introducer 112 may include a reservoir part and a mister part. The reservoir part is used to store the coolant liquid from the other coolant conduits 110. The mister part may be functionally and structurally the same as or similar to the print head of an inject printer. The mister part may inject microscopic coolant droplets into the airflow carried by conduit 120, toward channel 115. These airborne coolant droplets and the airflow are infused together to form a mist-stream 114, which is formed and injected into a channel 115 from a coolant droplet introducer 112.

[0023] It should be noted that in the operation of the system 10 described above, as long as the coolant droplets in the mist stream do not completely evaporate within the channel subspace 115, the temperature within the channel subspace 115 may remain below or near the boiling point due to potential heat of vaporization absorption.

[0024] In other words, when coolant droplet introducer 112 provides sufficient coolant droplets, the temperature of channel 115 may be maintained not higher than a certain level (corresponding to the boiling point of the coolant at low air pressure) or may be maintained within a certain range (e.g., within 5° C.). Heat generated by the heat source may be absorbed as potential heat of evaporation in channel 115 and released as potential heat of condensation in condenser 107.

[0025] It should be noted that the effect of "the temperature remains below or near the boiling point in the subspace 115" is achieved by the potential heat of vaporization absorption, which means that there is a very uniform temperature throughout the subspace 115.

[0026] In comparison with two-phase immersion cooling systems, the coolant droplets forming such a mist stream are liquid, so the main feature of two-phase immersion cooling, which utilizes the potential heat absorption during the phase change between liquid and gas to achieve a high heat exchange rate, is retained or inherited.

[0027] In contrast, by replacing the "body of liquid" with a "stream of mist", the effective viscosity of the coolant is also significantly reduced compared to two-phase submersion cooling systems. This appreciably lower viscosity creates a new advantage over the original liquid form, namely the tendency of the moving mist to penetrate tiny cracks and crevices and penetrate any small spaces, as long as the droplets are much smaller than the dimensions of those small spaces.

[0028] Additionally, by replacing the "body of liquid" with a "stream of mist", there is no longer a "tank of liquid" that tends to spill and / or leak all over the place, and any issues with a two-phase immersion cooling system, such as installation, operation, or maintenance, become much more "manageable" and "solvable".

[0029] Combining these factors, this "flowing mist stream" of low viscosity coolant opens new possibilities that can be used for one of the most challenging cooling needs in 3D packaged ICs: cooling between multiple silicon layers inside one IC. This means that not only are the compute units such as CPU / GPU / NPU / TPU (Central / Graphics / Neural network / Tensor Processing Unit) the heat source, but the TSVs (through silicon vias) can be part of the heat source as well.

[0030] 3 is a schematic diagram of a cooling system 20 according to an embodiment of the present invention. The cooling system 20 is similar to the cooling system 10. Unlike the cooling system 10, the cooling system 20 employs multiple coolant droplet introducers 112 to distribute the cooling resource (i.e., the coolant droplets) more uniformly than the cooling system 10, thereby preventing the droplets from completely evaporating and the temperature from rising far beyond the boiling point in some regions of the channel 115.

[0031] It should be noted that the condenser 107 shown in Figures 2 and 3 looks like a radiator, but is not limited thereto. The structure, shape, and type of the condenser 107 are not limited. For example, the condenser 107 shown in Figure 4 may include tubes with a repeating pattern of S-shaped curves. Furthermore, the diameter of the tubes in the condenser 107 may gradually narrow from the inlet to the outlet.

[0032] Below, we will describe some of the main differences between the present invention and conventional (active) cooling systems. First, the present invention utilizes the potential heat of phase change between liquid and gas phases to achieve a high heat dissipation rate. Second, the present invention establishes an asymmetric pair of boiling points in the channel 115 and dew points in the condenser 107 by generating different pressures inside the subspaces 115 and 107. The reason for establishing an asymmetric pair is that the pressure in the channel 115 decreases, causing the boiling point to decrease in the channel 115, resulting in the coolant droplets evaporating in the channel 115. Meanwhile, the pressure in the condenser 107 increases, causing the dew point in the condenser 107 to increase, causing the coolant gas to condense into coolant droplets or coolant liquid in the condenser 107. In other words, due to the pressure difference created by the compressor 102, the boiling point (which is a temperature corresponding to the boiling point) of the refrigerant in the channel 115 is lower than the dew point temperature (which is a temperature corresponding to the dew point) of the refrigerant in the condenser.

[0033] In addition, the present invention utilizes a gas transport medium to move the coolant droplets (in liquid phase) in the channels of the cooling system, thus allowing the coolant droplets (in liquid phase) to penetrate through and / or into any small openings / gaps. Furthermore, instead of relying solely on the coolant (liquid) as in two-phase immersion cooling systems, the present invention uses mistification of the coolant droplet introducer 112 to generate a mist stream 114 or a mixture of air and liquid, whereby the coolant infused mist-stream has a viscosity close to (as low as) the gaseous transport medium and a heat dissipation rate close to (as high as) the immersion liquid cooling.

[0034] In summary, this application proposes an active 2-phase mist cooling system that utilizes a coolant droplet injector to form a mist stream and injects it towards a channel surrounding a heat source, and utilizes a compressor to establish a pressure difference between the channel and a condenser. Asymmetric boiling and dew points (at the same temperature) are established. The heat of the heat source is absorbed as potential heat of vaporization and released as potential heat of condensation, while it is possible to maintain the temperature in the channel surrounding the heat source within a certain (narrow) range.

[0035] Those skilled in the art will readily appreciate that numerous modifications and variations of the devices and methods may be made while retaining the teachings of the present invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

Claims

1. 1. A cooling system, comprising: a channel surrounding the heat source; a coolant droplet introducer configured to introduce coolant droplets into the channel, the coolant droplets being vaporized as a coolant gas within the channel by heat generated by the heat source; a compressor configured to pump air from a channel subspace to a condenser subspace, the air including the coolant gas; a condenser configured to condense the coolant gas into coolant droplets or a coolant liquid; The coolant liquid is introduced to the coolant droplet injector or for the coolant droplet injector. Cooling system.

2. The cooling system of claim 1 , comprising a pressure regulating valve configured to regulate a pressure difference between a pressure corresponding to the channel subspace and a pressure corresponding to the condenser subspace.

3. The cooling system of claim 1 , comprising a heat rejector configured to reject heat emitted by the condenser.

4. The cooling system of claim 3 , wherein the heat rejector comprises an air moving device.

5. The cooling system of claim 3 , wherein the heat rejector comprises a cooling device.

6. An air pipeline; a coolant conduit; 10. The cooling system of claim 1.

7. The coolant droplet injector comprises: The device includes a reservoir portion and a mist generating portion, the reservoir portion is configured to store the coolant liquid; The cooling system of claim 1 , wherein the misting portion is configured to inject the coolant droplets into the channel.

8. The cooling system of claim 1 , further comprising: forming a mist stream and injecting the mist stream from the coolant droplet injector into the channel.

9. The cooling system of claim 8 , wherein the mist stream comprises a gas transport medium in which the coolant droplets are injected in suspension.

10. The cooling system of claim 1 , wherein the compressor maintains a pressure differential between the channel subspace and the condenser subspace.

11. The cooling system of claim 10 , wherein the compressor maintains the pressure differential such that a boiling point of the refrigerant in the channels is lower than a dew point temperature of the refrigerant in the condenser.

12. The cooling system of claim 1 , wherein the heat source comprises a through silicon via (TSV) in an integrated circuit (IC) package.

13. the temperature of the channel is maintained not above a particular level or within a particular range; The cooling system of claim 1 , wherein the particular level corresponds to a boiling point of a coolant at a pressure in the channel.

14. The cooling system of claim 1 , wherein the condenser comprises tubes having a repeating pattern of S-shaped curves.

15. 15. The cooling system of claim 14, wherein the diameter of the tubes in the condenser narrows gradually from the inlet to the outlet.

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