Patent Publication Number: US-2023156959-A1

Title: Liquid-In-Liquid Cooling System for Electronic Components

Description:
BACKGROUND 
     Electronics in cloud data center, blockchain, artificial intelligence, edge, and other computing applications are continually becoming more widespread. End-users of these electronics seek high density computing and reliable operation to enable innovation in machine learning, financial services, life sciences, bitcoin mining, oil and gas prospecting, scientific computing, and other applications. 
     Heat is frequently generated during operation of electronic components. Typically, systems comprising electronic components need to be configured to transfer heat away from these components. For instance, a computer processor may contain a large number of transistors that convert electrical energy into thermal energy during operation, thereby increasing the temperature of the processor. If there is no suitably efficient path for that heat to be transferred away from the processor during operation, the processor may exceed the temperature at which it can be safely operated over the desired operational lifetime. 
     There are a variety of different categories of cooling systems available for cooling electronic components. One category is air cooling in which fans direct air so that it flows over the components. Heat is transferred from the electronic components to the air and carried away in the air flow. Another category is liquid cooling, in which a liquid acts as a heat exchanger to carry heat away from a component. Liquid cooling has major advantages over air cooling in that its fluid properties allow for more efficient transfer of heat. In some cases, liquid cooling may involve a conductive block (e.g., metal block) through which a liquid is passed. In this case, heat may be transferred to the liquid through the conductive block. In other cases, a liquid may be brought into direct contact with a surface of the component, whether by submerging the component in the liquid, or by directing jets of liquid onto the component. 
     Some cooling systems for electronic components supply a liquid directly to the electronic component. One example of this type of approach, often referred to as immersion cooling, involves submerging the electronic components in a liquid that is thermally conductive, but has a sufficiently low electrical conductivity so as not to interfere with electrical operation of the components. Heat generated by the components may be transferred to the liquid in which they are immersed, and this heat can be removed from the system by circulating the liquid through a heat exchanger. Suitable liquids used for immersion cooling may include dielectric liquids, such as oils. 
     While immersion cooling may be effective for some applications, suitable coolant liquids for this approach generally have a lower thermal conductivity than liquids used for other liquid cooling solutions. As a result, immersion cooling tends to be less effective for high power electronic components that generate a lot of heat because the liquid may be unable to transfer a sufficient amount of heat from the high power components to the liquids to effectively cool the components. The dielectric coolants still have improved fluid properties over those of air, however, allowing for improved cooling of lower powered or low power density components compared to other liquid cooling systems (e.g., cold plate solutions as described below). Liquids used as the coolant in immersion cooling also tend to be more expensive than other liquid cooling solutions (e.g., contrast the cost of mineral oil to that of water). 
     Another type of liquid cooling is cold plate liquid cooling, which involves passing a liquid through a cooling block mounted to an electronic component in a surrounding air environment. In this case, heat may be transferred from the electronic component into the liquid coolant via the mounted cooling block. Because cold plate liquid cooling systems are nominally sealed from the surrounding electronics, thermally conductive coolants can be used to remove heat, which results in improved heat transfer capability. However, lower powered or low power density auxiliary electronic components near the cold plate liquid cooling block may also require cooling, which is most easily implemented via fans circulating the ambient air. Fans are typically of low cooling efficacy and can be energy inefficient or infrastructure intensive. With cold plate liquid cooling, there is a risk that condensation may form on the exterior of the system, or a leak forming. Both of these situations may cause a significant amount of damage to the electronic components in the system. 
     Another type of liquid cooling system utilizes a cooling module that is enclosed over a component. These systems, sometimes referred to as direct-to-chip cooling systems, typically utilize a conductive coolant such as water, and are highly effective at cooling. Direct-to-chip cooling systems are arranged so that coolant liquid only contacts non-conductive parts of the component (e.g., the die on the back of a processor), which requires the coolant liquid to be carefully arranged within a closed system that interfaces with the component. As with cold plate liquid cooling, direct-to-chip cooling systems engender a higher risk of condensation forming on the exterior of the system, or springing a leak, which may lead to a significant amount of damage to the components in the electronic system. 
     SUMMARY 
     Embodiments of the present invention provide a cooling system and method of cooling electronic components that mitigate the above-described risks and challenges associated with other liquid cooling systems. In particular, the systems and methods described herein provide a tank (or other vessel) in which a dielectric liquid cools low power electronic components within the tank, while a conductive liquid cools high power electronic components in the tank. The conductive liquid is supplied via a plurality of cooling modules, each arranged on or in proximity to a high power component. 
     According to some embodiments, a cooling module arranged within a tank may enclose an electronic component (e.g., using a fluid-tight seal). Such a cooling module may include one or more fluid inlets and one or more fluid outlets to pass a conductive liquid directly onto the surface of the electronic component and then away from the component and out of the cooling module. It may be noted that such a cooling module differs from prior cooling solutions that use a cold plate that contacts a component via a thermal interface material that is generated by the component such as a thermal paste. In cold plates, only the heat successfully conducted from the electronic component to the cold plate via the thermal interface material is removed by the liquid. In contrast, the cooling module described above directs the liquid directly onto the component itself, and as a result, may cool the component much more efficiently. Alternatively, the cooling module may be configured as a closed cold plate module, in which fluid passes through a closed structure instead of the device surface directly, and which contacts the electronic component via a thermal interface material such as a thermal paste. 
     According to some embodiments, a cooling module arranged within a tank may be arranged in proximity to, but separated from, an electronic component and may comprise one or more nozzles for jetting a conductive cooling liquid onto the electronic component. Suitable structures, such as walls or other barriers, may be formed within the tank (e.g., attached to a PCB or otherwise) to direct conductive liquid droplets to a desired part of the tank for removal. 
     According to some embodiments, one or more electronic components in the tank may be treated to adjust the wettability of their surface(s). For instance, the surfaces of one or more electronic components may be treated to make the surfaces more hydrophobic or hydrophilic (more water repelling or more water attracting, respectively), and/or one or more electronic components may be treated to make the surfaces more oleophobic or oleophilic (more oil repelling or more oil attracting, respectively). Whereas the surface of one or more low power electronic components may be treated to be more hydrophobic and/or oleophilic. Such a configuration may increase the extent to which a dielectric liquid coolant (which may be, or may comprise, an oil) is attracted to the surface of the low power electronic components and decrease the extent to which the dielectric liquid coolant is attracted to the surface of the high power electronic components. Similarly, such a configuration may increase the extent to which a conductive liquid coolant (which may be, or may comprise, water) is attracted to the surface of the high power electronic components and decrease the extent to which the conductive liquid coolant is attracted to the surface of the low power electronic components. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Various aspects and embodiments will be described with reference to the following figures. It should be appreciated that the figures are not necessarily drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. 
         FIG.  1    is a high-level schematic diagram of a liquid-in-liquid cooling system, according to some embodiments; 
         FIG.  2 A  depicts an illustrative implementation of a liquid-in-liquid cooling system in which a cooling module is enclosed around an electronic component, according to some embodiments; 
         FIG.  2 B  is a cross-sectional view of an illustrative cold plate cooling module, implementing jet cooling and forming a fluid tight seal, according to some embodiments; 
         FIG.  2 C  depicts an alternative implementation of the system of  FIG.  2 A  in which the dielectric liquid is circulated within the vessel via a pump, according to some embodiments; 
         FIG.  3 A  depicts a surface-fluid interaction exhibiting high wettability, according to some embodiments; 
         FIG.  3 B  depicts a surface-fluid interaction exhibiting low wettability, according to some embodiments; 
         FIG.  3 C  depicts a high wettability surface-fluid interaction forming a protective fluid barrier against a surface-fluid interaction of a lower wettability, according to some embodiments; 
         FIG.  4    depicts an alternative implementation of the system of  FIG.  2 C  in which the dielectric liquid is circulated within the vessel via a pump and a heat exchanger, according to some embodiments; 
         FIG.  5 A  is a schematic of a system suitable for circulating a dielectric liquid and a conductive liquid through a vessel, according to some embodiments; 
         FIG.  5 B  is a schematic of a system suitable for circulating a dielectric liquid and a conductive liquid through a vessel, and that includes separate pumps for each liquid and a shared heat exchanger, according to some embodiments; 
         FIG.  5 C  is a schematic of a system suitable for circulating a dielectric liquid and a conductive liquid through a vessel, and that includes separate pumps and heat exchangers for each liquid, according to some embodiments; and 
         FIG.  5 D  is a schematic of a system suitable for circulating a dielectric liquid and a conductive liquid through a vessel, and that utilizes an external coolant as the conductive liquid and to cool the dielectric liquid, according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Following below are more detailed descriptions of various concepts related to, and embodiments of, techniques for liquid-in-liquid cooling of electronic components. It should be appreciated that various aspects described herein may be implemented in any of numerous ways. Examples of specific implementations are provided herein for illustrative purposes only. In addition, the various aspects described in the embodiments below may be used alone or in any combination, and are not limited to the combinations explicitly described herein. 
     As an overview of the techniques outlined above,  FIG.  1    depicts a high-level schematic diagram of a liquid-in-liquid cooling system according to some embodiments. In the example of  FIG.  1   , electronic components  102  and  104  are mounted onto a board  101  (e.g., a motherboard, a system hoard, main circuit board, main board, etc.). For purposes of description, components  102  and  104  are referred to herein as “low power” and “high power” components, respectively, although these terms should not be viewed as limiting, as discussed further below. 
     In the example of  FIG.  1   , the board  101  and components  102  and  104  are arranged within a vessel  110  (a portion of which is shown in the drawing), which may be any suitable vessel for holding a liquid. A first liquid  112  is held in the vessel  110 , and is circulated into and out of the vessel as illustrated by the arrows  116  in  FIG.  1   . In addition, as shown by arrows  118  in  FIG.  1   , a second liquid  114  is delivered to the high power component  104  via a cooling module  120  that encloses the high power component  104 . The second liquid  114  is removed from the cooling module  120  after heat from the component  104  is transferred to the second liquid  114 . Various techniques for implementing the delivery of the second liquid  114  may be used, and examples are described below. 
     According to some embodiments, the first liquid  112  may be a dielectric liquid. In some implementations, the first liquid may be, or may comprise, a synthetic oil (e.g. PAO [polyalphaolefin]), a mineral oil (e.g. paraffin oil), a silicone oil, a fluorinated fluid (e.g., FluorInert™ from 3M), or combinations thereof. 
     According to some embodiments, the first liquid  112  may have an electrical conductivity of greater than or equal to 1×10 −12  S/m, 5×10 −12  S/m, 1×10 −11  S/m, 5×10 −11  S/m, or 1×10 −10  S/m. According to some embodiments, the first liquid may have an electrical conductivity of less than or equal to 1×10 −−9  S/m, 1×10 −10  S/m, 5×10 −11  S/m, 1×10 −11  S/m, 5×10 −12  S/m, or 1×10 −12  S/m. Any suitable combinations of the above-referenced ranges are also possible (e.g., the electrical conductivity of the first liquid is greater or equal to 1×10 −12  S/m and less than or equal to 1×10 −10  S/m, etc.). 
     According to some embodiments, the first liquid 112 may have a thermal conductivity of greater than or equal to 0.05 W/m·K, 0.10 W/m·K, 0.15 W/m·K, or 0.20 W/m·K. According to some embodiments, the first liquid may have a thermal conductivity of less than or equal to 0.25 W/m·K, 0.20 W/m·K, 0.15 W/m·K, or 0.10 W/m·K. Any suitable combinations of the above-referenced ranges are also possible (e.g., a thermal conductivity of the first liquid is greater or equal to 0.10 W/m·K and less than or equal to 0.20 W/m·K, etc. 
     According to some embodiments, the first liquid  112  may have a density of greater than or equal to 600 kg/m 3 , 700 kg/m 3 , 800 kg/m 3 , or 900 kg/m 3 . According to some embodiments, the first liquid may have a density of less than or equal to 1000 kg/m 3 , 900 kg/m 3 , 800 kg/m 3 , or 700 kg/m 3 . Any suitable combinations of the above-referenced ranges are also possible (e.g., a density of the first liquid is greater or equal to 700 kg/m 3  and less than or equal to 900 kg/m 3 , etc.). 
     According to some embodiments, the first liquid  112  may have a specific heat of greater than or equal to 1500 J/kg·K, 2000 J/kg·K, 2250 J/kg·K, 2500 J/kg·K, or 2750 J/kg·K. According to some embodiments, the first liquid may have a specific heat of less than or equal to 3000 J/kg·K, 2750 J/kg·K, 2500 J/kg·K, 2250 J/kg·K, or 2000 J/kg·K. Any suitable combinations of the above-referenced ranges are also possible (e.g., a specific heat of the first liquid is greater or equal to 2000 J/kg·K and less than or equal to 2500 J/kg·K, etc.). 
     According to some embodiments, the first liquid  112  may have a dielectric strength of greater than or equal to 1×10 6  V/m, 5×10 6  V/m, 10×10 6  V/m, 15×10 6  V/m or 20×10 6  V/m. According to some embodiments, the first liquid may have a dielectric strength of less than or equal to 35×10 6  V/m, 30×10 6 V/m, 25×10 6  V/m, 20×10 6  V/m or 15×10 6  V/m. Any suitable combinations of the above-referenced ranges are also possible (e.g., a dielectric strength of the first liquid is greater or equal to 10×10 6  V/m and less than or equal to 30×10 6  V/m, etc.). 
     According to some embodiments, the second liquid  114  may be a conductive liquid. In some implementations, the second liquid may be, or may comprise, water, a water-glycol mix (e.g., ethylene glycol, propylene glycol), a liquid metal (e.g., mercury), ammonia, or combinations thereof. 
     According to some embodiments, the second liquid  114  may have an electrical conductivity of greater than or equal to 1×10 −6  S/m, 1×10 −5  S/m, 1×10 −4  S/m, 5×10 −4  S/m, 1×10 −3  S/m, 5×10 −3  S/m, or 1×10 −2  S/m. According to some embodiments, the second liquid may have an electrical conductivity of less than or equal to 1×10 −1  S/m, 1×10 −2  S/m, 5×10 −3  S/m, 1×10 −3  S/m, 5×10 −4  S/m, or 1×10 −4  S/m,. Any suitable combinations of the above-referenced ranges are also possible (e.g., the electrical conductivity of the second liquid is greater or equal to 1×10 −4  S/m and less than or equal to 1×10 −2  S/m, etc.). 
     According to some embodiments, the second liquid  114  may have a thermal conductivity of greater than or equal to 0.30 W/m·K, 0.40 W/m·K, 0.50 W/m·K, 0.60 W/m·K, or 0.70 W/m·K. According to some embodiments, the second liquid may have a thermal conductivity of less than or equal to 0.80 W/m·K, 0.70 W/m·K, 0.60 W/m·K, 0.50 W/m·K, or 0.40 W/m·K. Any suitable combinations of the above-referenced ranges are also possible (e.g., a thermal conductivity of the second liquid is greater or equal to 0.30 W/m·K and less than or equal to 0.70 W/m·K, etc.). 
     According to some embodiments, the second liquid  114  may have a density of greater than or equal to 800 kg/m 3 , 900 kg/m 3 , 1000 kg/m 3 , or 1100 kg/m 3 . According to some embodiments, the second liquid may have a density of less than or equal to 1200 kg/m 3 , 1100 kg/m 3 , 1000 kg/m 3 , or 900 kg/m 3 . Any suitable combinations of the above-referenced ranges are also possible (e.g., a density of the second liquid is greater or equal to 900 kg/m 3  and less than or equal to 1100 kg/m 3 , etc.). 
     According to some embodiments, the second liquid  114  may have a specific heat of greater than or equal to 2500 J/kg·K, 3000 J/kg·K, 3500 J/kg·K, 4000 J/kg·K, or 4500 J/kg·K. According to some embodiments, the second liquid may have a specific heat of less than or equal to 5000 J/kg·K, 4500 J/kg·K, 4000 J/kg·K, 3500 J/kg·K, or 3000 J/kg·K. Any suitable combinations of the above-referenced ranges are also possible (e.g., a specific heat of the second liquid is greater or equal to 3000 J/kg·K and less than or equal to 4500 J/kg·K, etc.). 
     According to some embodiments, the first liquid  112  and/or the second liquid  114  may comprise one or more additives. Suitable additives may include one or more biocides, corrosion inhibitors, surfactants, or combinations thereof. 
     Biocides may include additives to inhibit growth or proliferation of unwanted organisms within a coolant. Some biocides for cooling systems may target limiting growth of algae, which can occur in, for example, water-based coolants when subject to ultraviolet light sources. Suitable examples of biocides that the first liquid and/or second liquid may include, but are not limited to, alcohols, aldehydes, chlorines, chlorine releasing agents (e.g. sodium hypochlorite, peroxygen compounds, etc.), or combinations thereof. 
     Corrosion inhibitors may include additives to prevent or minimize the deterioration of materials, especially that of galvanic corrosion in electrical circuits and fluid systems that have dissimilar metals of varying electrochemical potentials. Suitable examples of corrosion inhibitors that the first liquid and/or second liquid may comprise include, but are not limited to, azole compounds, triazole compounds, sodium nitrite, sodium molybdate, or combinations thereof. 
     Surfactants may comprise, or may be composed of, molecules that have a hydrophilic and a hydrophobic part, resulting in a tendency to accumulate at and maintain interfaces between coolants of different hydrophilicity and between coolants and surfaces. That is, when added to liquids, surfactants may enhance the immiscibility of two fluids, or may alter the wettability of certain fluids to certain surfaces. There are surfactants that, based on their molecular structure, are better suited for forming water droplets in oil, such as mono-valent soaps. Others, such as bi- or tri-valent soaps, are better suited for forming oil droplets in water. Suitable examples of surfactants that the first liquid and/or second liquid may comprise include, but are not limited to, mono-valent soaps, bi-valent soaps, tri-valent soaps, alkyl sulfates, quarternary ammonium salts, ethoxylated alphatic alcohol, amophoacetates, or combinations thereof. 
     According to some embodiments, the low power electronic components  102  may be treated with a surface coating to increase their wettability with respect to the first liquid and/or may be treated with a surface coating to decrease their wettability with respect to the second liquid. A surface coating may, for instance, be a conformal coat and may include coatings such as, but not limited to, fluorinated compounds, chlorinated compounds, silicones, polysiloxanes, urethanes, polyurethanes, acrylics, epoxies, or combinations thereof. 
     According to some embodiments, the high power electronic components  104  may be treated with a surface coating and/or nanofabricated structures to increase their wettability with respect to the second liquid and/or may be treated with a surface coating to decrease their wettability with respect to the first liquid. Examples of suitable coatings may include silicon dioxides, zinc oxides, or combinations thereof. 
     As noted above, while electronic components  102  and  104  are referred to herein as “low power” and “high power” components, these labels are intended to distinguish between different types of electronic components that may be more or less suitable for the two types of liquid cooling embodied by the techniques described herein. As discussed above, since immersion cooling is generally more suitable for comparatively lower power electronic components, such components may be more suited to be cooled by the first liquid in the example of  FIG.  1   . Similarly, since direct-to-chip cooling may be more suitable for comparatively higher power electronic components, such components may be more suited to be cooled by the second liquid in the example of  FIG.  1   . It will be appreciated that either type of cooling may be used to cool an electronic component irrespective of its power consumption, however. As such, whenever “low power” or “high power” are used to refer to an electronic component herein, it will be understood that these terms are not limiting with respect to the electronic component, but are merely used for illustrative and descriptive purposes. 
     As used herein, an “electronic component” may refer to any suitable processor or collection of processors. Such processors may be implemented as integrated circuits, or as one or more processors in an integrated circuit component, including commercially available integrated circuit components known in the art by names such as CPU chips, GPU chips, microprocessor, microcontroller, or co-processor. Alternatively, a processor may be implemented in custom circuitry, such as an AMC, FPGA or semi-custom circuitry resulting from configuring a programmable logic device. As yet a further alternative, a processor may be a portion of a larger circuit or semiconductor device, whether commercially available, semi-custom or custom. The electronic components also need not be limited to processors or computing electronics, as alternative devices such as transformers, power conversion electronics, radio frequency amplifiers or electronics, or other such heat generating electronic components may also be cooled via the techniques described herein. 
     To further illustrate the implementation of the schematic view shown in  FIG.  1   , a more detailed illustration of a liquid-in-liquid cooling system is depicted in  FIG.  2 A . As shown in the example of  FIG.  2 A , system  200  comprises electronic components  202  and  204  mounted onto a board  201  within a vessel  210  that holds a dielectric liquid  212 . A cooling module  206  is mounted over the high power electronic component  204  and includes fluid channels  207   a  and  207   b  through which a conductive liquid  214  flows. Cooling is delivered to high power electronic component  204  via cooling module  206 . The cooling module  206  is configured to surround and enclose the high power electronic component  204 . The conductive liquid  214  may contact the surface of the electronic component  204  and carry heat away from the component. A fluid inlet  208   a  and fluid outlet  208   b  convey the dielectric fluid into and out of the vessel  210 , respectively. Various techniques for implementing the delivery of the first liquid  212  and second liquid  214  may be applied, with examples described below 
     One illustrative example of a cooling module suitable for use as cooling module  206  in  FIG.  2 A  is shown in  FIG.  2 B . As shown in  FIG.  2 B , a cooling module  206  is deployed onto the face of an electronic component  204  (e.g., a lidded surface or a non-electrically conductive silicon die face of a processor). The cooling module includes narrow channels  223  that turns the conductive liquid  214  into jets as it flows into the module through at least one inlet conduit, port, or fitting  221 . The jets  225  impinge directly onto the electronic component  204 . In this embodiment, the conductive liquid  214  is shown both with lighter shading and darker shading in  FIG.  2 B  to visually distinguish the incoming conductive liquid from the conductive liquid within the module after it is jetted. 
     After jetting, the conductive liquid exits the module through at least one outlet conduit, port, or fitting  222 . A fluid tight seal  227  may be disposed between the device surface  204  and the cooling module  206 , so as to nominally contain the conductive liquid coolant within the cooling module  206  and passageways  207   a  and  207   b.  The fluid tight seal  227  may take on any variety of forms, including o-rings, gaskets, adhesives, solders, and/or any suitable sealing technique. Surrounding the cooling module is the dielectric fluid,  212 . 
     Such a configuration shown in  FIG.  2 B  may be considered microjet cooling, which generates high heat transfer coefficient convective flow incident on high power and high power density device surfaces. Other types of cooling modules  206  may also be utilized in the system of  FIG.  2 A , including but not limited to microchannels, mini-channels, pin fins, skived fins, or other cold plate or direct-to-chip cooling technologies. 
     In some embodiments, the cooling module  206  may be attached to the board  201  via one or more suitable fasteners such as clamps, screws, and/or other structures that may be operated to engage and disengage mechanical attachment of the module with the board. 
     In some embodiments, any one or more of fluid inlets  207   a  and  208   a  and fluid outlets  208   a  and  208   b  may comprise one or more filters (not shown in the figures) to remove matter that may, if circulating in the vessel  210 , damage or foul small features in the cooling module  206  and/or on the board  201 . In some cases, the filter(s) may separate out matter than could damage a pump coupled to one or more of the fluid inlets or outlets. 
     In some embodiments, vessel  210  may comprise, or may be coupled to, one or more monitoring systems configured to monitor an amount of one or more additives in the dielectric liquid  212  and/or conductive liquid  214  (e.g., an amount of a surfactant, a biocide, etc.), monitor a resistivity of the dielectric liquid  212  and/or conductive liquid  214 , control for a level of contamination in the dielectric liquid  212  and/or conductive liquid  214 , or combinations thereof. In some embodiments, the system  200  may comprise common fluid manifolds configured to deliver the conductive liquid  214  to a plurality of cooling modules  206 , whether on the same board  201  and/or on a plurality of different boards. 
     An alternative implementation of  FIG.  2 A  is shown in  FIG.  2 C , according to some embodiments. System  250  shown in  FIG.  2 C  is the same as system  200  shown in  FIG.  2 A , except instead of the dielectric liquid  212  being delivered into the vessel  210  via an inlet and removed from the vessel via an outlet, the dielectric liquid is circulated within the vessel using a pump  224 , which has its own fluid inlet and fluid outlet  209   a  and  209   b,  respectively. In the example of  FIG.  2 C , the dielectric liquid  212  may not be circulated into and out of the vessel, but may instead be circulated only within the vessel. In some embodiments, system  250  may comprise a heat exchanger (not shown in  FIGS.  2 A- 2 C ) arranged adjacent to the vessel  210  and configured to transfer away heat from the dielectric liquid  212 . A heat exchanger may additionally or alternatively be arranged to transfer away heat from the conductive liquid  214  in this manner. 
     As discussed above, one advantage of the techniques described herein may be to mitigate problems caused by leaks of conductive liquid, which can occur with a conventional cooling module arranged on an electronic component. To illustrate this effect further,  FIGS.  3 A- 3 C  demonstrate the utility of a dielectric liquid  312  in mitigating the leak risk which traditionally hampers cold plate liquid cooling techniques utilizing conductive coolants. In the field of surface physics, the attraction of a given coolant to a surface is often times characterized by a “contact angle”. A smaller contact angle with the surface (measured through the fluid) signifies a great level of attraction between the liquid and the surface. A larger contact angle signifies a lower level of attraction between the liquid and the surface. 
       FIG.  3 A  provides an example of a high fluid-surface wettability interaction via a comparatively small contact angle. First liquid  312  on surface  302  exhibits an acute contact angle  303 , demonstrating a high affinity (or high wettability) between the liquid  312  and the surface  302 .  FIG.  3 B , on the other hand, shows a second liquid  314  on surface  302  exhibiting an obtuse contact angle  313 , demonstrating a comparatively low affinity (or comparatively low wettability) between the liquid and the surface. Note that the contact angles need not be acute or obtuse to establish relative wettability, but in general smaller contact angles imply greater surface affinity. When liquids  312  and  314  are combined, the high wettability liquid  312  has a greater surface attraction to surface  302  than the low wettability liquid  314 , and therefore the high wettability liquid  312  tends to form a blanket in between the surface  302  and the low wettability liquid  314 . 
     In some embodiments, the dielectric liquid  212  may be chosen to have a comparatively higher surface affinity with respect to low power electronic components  302  and board  301 . The conductive liquid  314  may be chosen to have a comparatively lower surface affinity to low power electronic components  302  and board  301  than that of the dielectric liquid  212 . 
     Therefore, in the event of a leak of the conductive liquid  214  from the cooling module  206 , the conductive liquid can remain in a separate phase as a droplet within the surrounding dielectric liquid  312 , and can remain repelled from the surface of electronic components  302  and board  301 . These effects may restrict interaction between the conductive coolant and the active electrical circuitry, avoiding the potential for damage that may occur in systems with conductive coolants and circuit boards and electronic components in air environments. Said another way, the risk of the conductive liquid doing harm may decrease substantially as the electrical component is encapsulated in a protective layer of dielectric liquid. 
     Another implementation of the schematic view shown in  FIG.  1    is depicted in  FIG.  4 A , according to some embodiments. In the example of  FIG.  4 A , cooling is delivered to a high power electronic component via a plurality of nozzles in a cooling module that is proximate to, but not in contact with, the electronic component. System  400  shown in  FIG.  4 A  comprises electronic components  402  and  404  mounted onto a board  401  within a vessel  410  that holds a dielectric liquid  412 . A fluid inlet  408   a  and fluid outlet  408   b  convey the dielectric fluid into and out of the vessel  410 , respectively. 
     In the example of  FIG.  4 A , a cooling module  409  is mounted onto the high power electronic component  404  and includes a fluid inlet  407   a  and fluid outlet  407   b  through which a conductive liquid  414  flows. The cooling module  409  comprises one or more nozzles that form jets of the conductive liquid when the conductive liquid passes through the module. As shown in  FIG.  4 A , the conductive liquid may be incident on the surface of the electronic component  404  and carry heat away from the component while the conductive liquid is otherwise surrounded by the dielectric liquid  412 . Note that the surface of component  404  is typically an inactive surface of the circuit, such as a lid or non-active die surface Since the two liquids are immiscible, however, the conductive liquid does not generally mix with the dielectric liquid and remains as a separate liquid phase. Furthermore, with the dielectric liquid  412  demonstrating higher surface affinity to board  401  and low power components  402 , the conductive liquid  414  remains repelled by the dielectric liquid  412  and does not cause damage or short circuits. 
     In the example of  FIG.  4 A , the conductive liquid  414  is more dense than the dielectric liquid  412 . As a result, the conductive liquid will eventually sink to the bottom of the vessel  410  to produce a stratified layer of the conductive liquid  415  at the bottom of the vessel. The fluid outlet  407   b  is arranged at, or close to, the bottom of the vessel in this example to remove the conductive liquid that has settled at the bottom of the vessel. 
     In other cases, the conductive liquid  414  may be less dense than the dielectric liquid  412 . In such a case, the conductive liquid will eventually rise to the top of the vessel  410  to produce a layer of the conductive liquid  415  at the top of the vessel. In this case, the fluid outlet  407   b  may instead be arranged close to the top of the vessel. In some embodiments, separating and recovering the conductive liquid  414  may be performed via one or more devices that do not rely on relative density of the two liquids, however. 
     In some embodiments, the cooling module  409  may share a similar structure to the cooling module  206  shown in  FIG.  2 B . An illustrative example of cooling module  409  is shown in  FIG.  4 B . As shown in  FIG.  4 B , a cooling module  409  is deployed in proximity to the face of an electronic component  404  (e.g., a lidded surface or a non-conductive silicon die face of a processor). The cooling module  409  includes narrow channels or nozzles  423  that turns the conductive liquid to jets as it flows into the module through at least one inlet conduit, port, or fitting  421 . The jets  425  of the conductive liquid  414 , impinge directly onto the electronic component  404 . In this embodiment, unlike that of  FIG.  2 B , the surrounding liquid  412  is not the same as that which forms the jets  425 , as the surrounding liquid  412  is the dielectric liquid immersing the electronics. The conductive liquid then undergoes droplet coalescence, due to its immiscibility, to form droplets  438 , which is then disposed of elsewhere in the system as described above. 
     Note that in this configuration, the conductive fluid jets  425  may make direct contact with the heated surface  404  by displacing the dielectric fluid away from the surface  404  due to their elevated momentum by passing through the narrow channels  423 . However, there may be scenarios where a layer, even if microscopic, of dielectric liquid remains between the device surface  404  and cooling jets  425 . This may introduce a minor resistance for heat flow from the heated surface  404  into the conductive coolant, but no substantial change in operation may be expected as a result. 
     In some embodiments, the high power electronic component  404  may be treated with a surface coating and/or nanofabricated structures to increase its wettability with respect to the conductive liquid  414  and/or may be treated with a surface coating to decrease their wettability with respect to the dielectric liquid. For instance, the component  404  may comprise one or more surface coatings that enhance wettability with water-based liquids such as, but not limited to, silicon dioxides, zinc oxides, or combinations thereof. 
     Returning to  FIG.  4 A , in some embodiments, system  400  may include an optional sensor  420  that is configured to monitor a fluid level of the conductive liquid  415  at the bottom of the vessel  410  (e.g., a height of the top of the conductive liquid  415  above the bottom of the vessel). In some implementations, the sensor  420  may include a capacitive sensor. In some implementations, the vessel may comprise a float that floats at the liquid interface (e.g., is less dense than the conductive liquid and more dense than the dielectric liquid) and whose vertical position may be detected by the sensor  420 . In some implementations, the sensor may comprise an optical view port and/or optical sensor to measure index of refraction. In some embodiments, sensor  420  may be coupled to a suitable controller configured to operate a pump coupled to fluid outlet  407   b  based on sensor data produced by the sensor. For example, the controller may turn the pump on when the sensor data indicates the fluid level is above a first threshold and may turn the pump off when the sensor data indicates the fluid level is below a second threshold. In this manner, the fluid level of the conductive liquid at the bottom of the tank may be maintained between two desired thresholds. 
     In some embodiments, any one or more of fluid inlets  407   a  and  408   a  and fluid outlets  408   a  and  408   b  may comprise one or more filters to remove matter that may, if circulating in the vessel  410 , damage and/or foul small features in the cooling module  409  or on the board  401 . In some cases, the filter(s) may separate out matter than could damage a pump coupled to one or more of the fluid inlets or outlets. 
     An alternative implementation of  FIG.  4 A  is shown in  FIG.  4 C , according to some embodiments. System  450  shown in  FIG.  4 C  is the same as system  400  shown in  FIG.  4 A , except instead of the dielectric liquid  412  being delivered into the vessel  410  via an inlet and removed from the vessel via an outlet, the dielectric liquid is circulated within the vessel using a pump  424 , which has its own fluid inlet and fluid outlet  409   a  and  409   b,  respectively. In the example of  FIG.  4 C , the dielectric liquid  412  may not be circulated into and out of the vessel, but may instead be circulated only within the vessel. In some embodiments, system  450  may comprise a heat exchanger arranged adjacent to the vessel  410  and configured to transfer away heat from the dielectric liquid  412 . A heat exchanger may be located within or adjacent to the vessel  410 , and/or a heat exchanger may be located in a separate location (e.g., on the roof or outside of a facility) to transfer heat away from the dielectric liquid  412 . Examples of the latter approach are discussed below. A heat exchanger may additionally or alternatively be arranged to transfer away heat from the conductive liquid  214  in this manner. 
     In any of the embodiments discussed above, an electrically non-conductive conformal coat material may also be applied to one or more boards and/or one or more electronic components to enhance and/or provide a non-electrically conductive layer or dielectric layer between the board and/or components and a conductive liquid. Suitable examples of electrically non-conductive conformal coat materials may include, but are not limited to, polysiloxanes, acrylics, urethanes, polyurethanes, silicones, epoxies, or combinations thereof. A conformal coating may be applied in addition to, or alternatively to, any surface coating(s) discussed above. One reason such a conformal coating may be advantageous is to meet lifetime goals for the system. While, in some cases, the system may function without such a coating, the application of the coating may desirably further extend the operational lifetime of the system. 
     The dielectric liquid and conductive liquid may be supplied to the illustrative systems shown in  FIGS.  2 A and  2 C  in any suitable way, including through the use of one or more pumps to circulate one or both liquids through the vessel and/or cooling module as appropriate. Suitable pumps may include positive displacement pumps (e.g., rotary pumps, reciprocating pumps, etc.), impulse pumps, piston pumps, valveless pumps, or combinations thereof. In some cases, one or more heat exchangers  401  may be arranged adjacent to the vessel (as shown in  FIG.  4   ) to remove heat from the dielectric liquid and/or conductive liquid within the vessel. The systems described below in relation to  FIGS.  5 A- 5 D  may each, in some embodiments, be combined with a vessel in which the electronics components are arranged (e.g., vessel  210  shown in  FIG.  2 A  and  FIG.  2 C ). As such, a single system may comprise the vessel and other elements shown and discussed above in either of  FIGS.  2 A or  2 C  in addition to the elements from any one of  FIGS.  5 A- 5 D  discussed below. In some implementations, this system may be arranged within a single housing. 
       FIGS.  5 A- 5 D  are schematics of various illustrative pumping and heat removal systems that may be coupled to a vessel, including but not limited to those examples shown in  FIGS.  2 A and  2 B . These illustrative systems differ in the manner in which pumping and heat removal is performed, but are not intended to be limiting as other possible systems may also be envisioned. In each of the illustrative systems of  FIGS.  5 A- 5 D , dielectric liquid and conductive liquid are shown entering and exiting the system on the left side of the page. Each of these systems could, for instance, be coupled to the fluid inlets  207   a  and  208   a,  and fluid outlets  207   b  and  208   b,  shown in either of  FIGS.  2 A and  2 B . Moreover, in  FIGS.  5 A- 5 D , heat exchangers are shown with a dashed line to represent an interaction; it will be appreciated that these figures are schematic drawings and in reality heat exchangers typically operate by flowing coolant through the heat exchanger volume facilitating intimate fluid contact for high effectiveness heat transfer between fluids. Any of the heat exchangers described herein may operate by transferring heat from a liquid to another liquid, and/or may operate by transferring heat from a liquid to a gas (e.g., air). 
       FIG.  5 A  is a first illustrative schematic of a system suitable for circulating a dielectric liquid and a conductive liquid through a vessel, according to some embodiments. In the example of  FIG.  5 A , the dielectric liquid  511  and conductive liquid  512  are directed into a common channel, and heat is removed from both liquids in this channel via heat exchanger  518 . The liquids at this stage may be mixed into an emulsion if there is sufficient agitation of the liquids in the channels, or may otherwise retain separate liquid phases. Subsequently, pump  514  provides an impulse for the liquids to be directed back to the vessel after passing through separator  516  which separates out the two types of liquid so that the dielectric liquid and conductive liquid each returns to their respective inlets of the vessel to be recirculated. 
     Fluid separator  516  may be configured to take advantage of differing fluid properties or molecular structures of the two liquids. Examples may include, but are not limited to, centrifuges for liquids of different densities, filtration for fluids of different molecule sizes (e.g., using one or more membranes), electric field separation via differences in polarity or electrical conductivity, or other such techniques. In some embodiments, a separator may or may not be needed for a given system depending on the level of immiscibility of the two fluids. 
       FIG.  5 B  is a schematic of a system suitable for circulating a dielectric liquid and a conductive liquid through a vessel, and that includes separate pumps for each liquid and a shared heat exchanger, according to some embodiments. In the example of  FIG.  5 B , the dielectric liquid  521  and conductive liquid  522  are directed to pumps  524  and  525 , respectively, which each provide impulse for the respective liquid to be directed back into the vessel. A heat exchanger  528  is arranged to remove heat from both liquids as they are circulated. In some embodiments, the heat exchanger  528  may include multiple separated chambers to separately remove heat from both liquids. While the heat exchanger  528  is shown in  FIG.  5 B  as removing heat from the liquids after they pass through the respective pumps, the heat exchanger may instead be arranged to remove heat from the liquids before they pass through the respective pump. 
       FIG.  5 C  is a schematic of a system suitable for circulating a dielectric liquid and a conductive liquid through a vessel, and that includes separate pumps and heat exchangers for each liquid, according to some embodiments. In the example of  FIG.  5 C , the dielectric liquid  531  and conductive liquid  532  are directed to pumps  534  and  535 , respectively, which each provide impulse for the respective liquid to be directed back into the vessel. Heat exchangers  538  and  539  are arranged to remove heat from the dielectric liquid  531  and conductive liquid  532 , respectively, as each liquid is circulated. While the heat exchangers  538  and  539  are shown in  FIG.  5 C  as removing heat from the liquids after they pass through the respective pumps, either or both heat exchangers may instead be arranged to remove heat from one of the liquids before it passes through its respective pump. 
       FIG.  5 D  is a schematic of a system suitable for circulating a dielectric liquid and a conductive liquid through a vessel, and that utilizes an external coolant as the conductive liquid and to cool the dielectric liquid, according to some embodiments. In the example of  FIG.  5 D , the dielectric liquid  541  is directed to pump  544  which provides impulse for the dielectric liquid to be directed back into the vessel. A heat exchanger  548  is arranged to remove heat from the dielectric liquid  541 . While the heat exchanger  548  is shown in  FIG.  5 D  as removing heat from the dielectric liquid after it passes through the pump  544 , the heat exchanger may instead be arranged to remove heat from the dielectric liquid before it passes through the pump. 
     In the example of  FIG.  5 D , the conductive liquid  542  is the same liquid uses as a coolant by the heat exchanger  548 . This may, for instance, be an external source of water (e.g., external to the vessel and system shown in  FIG.  5 D ) that is pumped into the system. This external coolant liquid  549  may be directed into the heat exchanger  548  in addition to being supplied to the fluid inlet  207   a  of the vessel, and may be conveyed out through the fluid outlet  207   b  and combined with the external coolant liquid being conveyed out of the heat exchanger  548  as shown in  FIG.  5 D . 
     The configuration of  FIG.  5 D  may not include a coolant distribution unit (CDU), not shown, which accepts fluid from a facility water loop. The configuration of  FIG.  5 D  may comprise a centralized (in-row) CDU supplying multiple vessels instead of a CDU for each vessel. Such a configuration (or similar) could be possible with the dielectric liquid, too. 
     Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. 
     Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Further, though advantages of the present invention are indicated, it should be appreciated that not every embodiment of the technology described herein will include every described advantage. Some embodiments may not implement any features described as advantageous herein and in some instances one or more of the described features may be implemented to achieve further embodiments. Accordingly, the foregoing description and drawings are by way of example only. 
     The above-described embodiments of the technology described herein can be implemented in any of numerous ways. Various aspects of the present invention may be used alone, in combination, or in a variety of arrangements not specifically discussed in the embodiments described in the foregoing and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments. 
     Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements. 
     The terms “approximately” and “about” may be used to mean within ±20% of a target value in some embodiments, within ±10% of a target value in some embodiments, within ±5% of a target value in some embodiments, and yet within ±2% of a target value in some embodiments. The terms “approximately” and “about” may include the target value. The term “substantially equal” may be used to refer to values that are within ±20% of one another in some embodiments, within ±10% of one another in some embodiments, within ±5% of one another in some embodiments, and yet within ±2% of one another in some embodiments. 
     The term “substantially” may be used to refer to values that are within ±20% of a comparative measure in some embodiments, within ±10% in some embodiments, within ±5% in some embodiments, and yet within ±2% in some embodiments. For example, a first direction that is “substantially” perpendicular to a second direction may refer to a first direction that is within ±20% of making a 90° angle with the second direction in some embodiments, within ±10% of making a 90° angle with the second direction in some embodiments, within ±5% of making a 90° angle with the second direction in some embodiments, and yet within ±2% of making a 90° angle with the second direction in some embodiments. 
     Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.