Immersion cooling of electronic systems using vapour chambers and vibratory systems

Abstract

The present invention relates to equipment for cooling an electronic component (21), comprising a thermally conductive substrate (23) seated on the one hand against the surface of said electronic component (21) and on the other hand against a heat transfer element which is connected to a cooling means, characterized in that the heat transfer element is constituted by a vapour chamber (16b) thermally connecting the electronic component (21) to the base of the heat sink and the fins (16a) thereof, which are immersed in a chamber (11) filled with a cooling liquid.

Description

Cooling of immersed electronic systems using vapor chambers and vibration systems Scope of the invention

[0001] The present invention relates to the field of cooling electronic circuits.

[0002] Cooling computer systems is becoming a major challenge for many applications in telecommunications, data management, and cybersecurity. This is because the power density to be dissipated is increasing due to the miniaturization of computer components, particularly CPUs (Central Processing Units) and GPUs (Graphics Processing Units), and the resulting increase in computing power. On the other hand, the acceptable temperature limit for a computer processor chip remains constant, at around 85°C.

[0003] As central processing units gain in frequency and number of cores, their heat production intensifies, requiring more efficient cooling solutions to avoid malfunctions and damage related to overheating.

[0004] In a central processing unit, the heat generated comes from the Joule effect, where the current flowing through the transistors heats the circuit. Without effective dissipation, this heat can lead to slowdowns, failures, or even the destruction of the component. In the era of early processors, such as the 33 MHz 486, heat dissipation was relatively simple because the chips generated little heat. However, with increasing frequencies and the proliferation of cores, processor power consumption skyrocketed, necessitating far more complex and efficient cooling systems.

[0005] Early cooling solutions consisted of simple aluminum heat sinks. Gradually, these devices improved, incorporating materials with higher thermal conductivity, such as copper, and adopting optimized geometries to increase the surface area for heat exchange with the surrounding fluid. The advent of vapor chambers represented a significant advancement in the field of heat transfer for electronic circuits. These flat devices, consisting of a hermetically sealed metal enclosure containing a working fluid, ensure rapid and homogeneous heat distribution across their entire surface through an internal cycle of evaporation and condensation.

[0006] A vapor chamber is designed to capture heat from a localized area, such as directly above an electronic component, and transfer it to larger dissipation areas, such as fins, heat sinks, or other heat exchange surfaces. The two-dimensional nature of heat transfer within the vapor chamber optimizes the use of available surface area and improves overall cooling efficiency, even in a confined space.

[0007] These vapor chambers can be integrated directly into the base of a heat sink, attached to an electronic module, or incorporated into more complex assemblies including fin structures or fluid exchangers. They are compatible with various heat dissipation methods, including natural or forced convection, as well as liquid environments, and can be sized according to specific constraints of size and thermal performance. Alongside vapor chamber heat sinks, another technology has emerged since 2007: standalone liquid cooling (also known as "watercooling"). This technology uses a closed-loop liquid circuit to cool the central processing unit.

[0008] The choice of a vapor chamber and its internal configuration depends primarily on the thermal envelope of the electronic circuit, the spatial distribution of hot zones, and the environmental operating conditions. Effective temperature control improves the stability and performance of electronic components, even under high-power operating conditions.

[0009] In summary, cooling electronic circuits has become a major challenge with the increasing performance of processors. Solutions such as vapor chamber heatsinks and liquid cooling now offer effective ways to keep CPU and GPU temperatures under control, ensuring both performance and component longevity. State of the art

[0010] Patent application EP3422835A1 relates to a cooling system for high-power-density electronic components, particularly in the fields of computing and servers. The invention is based on the use of a dielectric fluid bath, such as an insulating oil, in which the electronic boards carrying the components to be cooled are immersed. The fluid reservoir is designed to maintain a stable temperature, ensuring both heat dissipation and electrical protection of the circuits. The system comprises a tank containing the fluid, means for promoting natural or forced convection of the liquid, and heat exchangers arranged inside the tank. These exchangers transfer the heat accumulated by the fluid to a secondary circuit, for example, water, thus enabling efficient removal of the thermal energy.The device can also be configured to utilize the heat thus recovered, particularly for heating premises or producing hot water.

[0011] According to this solution, heat dissipation relies on the forced circulation of a dielectric fluid in a reservoir, via a pump and heat exchangers. This implies increased mechanical complexity, risks of failure related to moving parts, and the need for regular maintenance.

[0012] US patent 2005 / 0178529 describes a liquid cooling system for electronic components (CPUs, GPUs, etc.). Heat from the component is transferred to a conductive plate and then to a fluid circulating in a closed loop (pump, pipes, heat exchanger). Several variations are proposed: liquid circulation in a channel in direct contact with the component surface, the use of vibrating or oscillating elements to improve heat transfer, and the possible presence of secondary finned heat sinks cooled by air circulation.

[0013] The system is active and relies on forced fluid circulation. This leads to a risk of failure, a need for additional power, and more extensive maintenance. The device requires several components (pump, piping, secondary heat exchanger, fans). Integration is therefore more complex, especially for compact applications. Furthermore, the heat from the component must pass through several stages (plate → fluid → heat exchanger → air or water). Each interface generates heat losses and reduces overall efficiency, and the use of pumps and fans generates noise and increases power consumption, which is a disadvantage in sensitive environments (high-density computing, medical, aerospace).

[0014] US patent 2006 / 060331 proposes a cooling system for electronic components in which the aim is to improve heat exchange by disrupting the thermal boundary layer that forms around surfaces in contact with the cooling fluid.

[0015] Two approaches are described: the use of vibratory means (e.g., piezoelectric actuators) applied to heat sinks, and the injection of air or gas bubbles into the fluid, creating local turbulence around the surfaces to be cooled. This system is also based on active fluid cooling (liquid circulation via a pump), and vibrating or bubbling devices are complementary means of increasing efficiency. Solution provided by the invention

[0016] To overcome these drawbacks, the present invention relates to a method having the following characteristics.

[0017] It relates to a cooling equipment for an electronic component comprising a thermally conductive substrate applied against the surface of said electronic component on the one hand, and a heat transfer element on the other hand connected to a cooling means, characterized in that said heat transfer element consists of a vapor chamber, thermally connecting said electronic component to a heat sink formed by fins immersed in a chamber filled with a coolant.

[0018] Advantageously, said heat sink is equipped with at least one actuator applying a vibratory motion to said fins.

[0019] Preferably, said at least one actuator applies a vibratory motion with a frequency between 20 kHz and 1 MHz.

[0020] According to a particular embodiment, said at least one actuator is of the piezoelectric type.

[0021] Advantageously, said chamber has a bottom equipped with at least one bubbler arranged in the lower part of said chamber, vertically above said fins of said heat sink.

[0022] Preferably, the fins of said heat sink are vertical.

[0023] Advantageously, the bubbler is supplied by a pump controlled for constant or sequential operation.

[0024] In one variant, the equipment further includes a dielectric fluid cooling circuit comprising: a heat exchanger and a circulation pump, ensuring the circulation of a heat transfer fluid in this cooling circuit. Detailed description of a non-limiting example of implementation

[0025] The present invention will be better understood upon reading the following description, concerning a non-limiting example of an embodiment illustrated by the accompanying drawings where:

[0026] This represents a schematic front view of an alternative embodiment

[0027] This represents a schematic top view of a variant embodiment

[0028] This represents a schematic projected view of an alternative implementation

[0029] This presents a 3D cross-section showing: heating element, heat sink and the bubbling system.

[0030] This presents the model of the bubbler (17)

[0031] Ladonne the impact of the injection of air bubbles (12) between the fins (16a) on the evolution of GPU and liquid temperatures.

[0032] Presents the impact of injecting air bubbles (12) between the fins (16a) on the thermal performance of the cooling system, with the convection coefficient (h).

[0033] Principle of the invention: use of a vapor plate / vapor chamber (16b) for heat transfer between the electronic component and fins immersed in a coolant.

[0034] The principle of the invention is based on the heat transfer between the electronic component to be cooled and a chamber containing a coolant by means of a vapor chamber having at one end a conduction surface with the surface of the electrical component and at the other end fins immersed in the coolant contained in the reservoir.

[0035] A vapor chamber, as defined in this patent, is a passive heat transfer device used to transfer heat from a hot source to a cold point. It consists of a sealed, flattened thermosiphon plate operating on the principle of a fluid's phase change, enabling rapid heat transfer with a small temperature difference.

[0036] More specifically, a vapor chamber, as defined in this patent, refers to a passive heat transfer device consisting of a hermetically sealed plate containing a heat transfer fluid. Its operation is based on successive cycles of fluid evaporation near a hot zone and condensation near a cold zone. This mechanism ensures efficient heat transfer between the hot source and the cold zone without the need for active mechanical means such as a pump.

[0037] This vapor chamber allows the heat sink to be relocated to a cooling enclosure. In preferred embodiments of the invention, the cooling system is designed to improve heat exchange by means that disrupt the thermal layer, by vibration of the cooling fins, and / or by the diffusion of bubbles brushing against the cooling fins.

[0038] Detail of the construction of the steam plate / steam chamber (16b)

[0039] The vapor chamber consists of a hermetically sealed metal enclosure, typically made of copper or aluminum, materials with high thermal conductivity. This flat enclosure contains a working fluid chosen according to the application and the target temperature range, such as water, alcohol, ammonia, or certain refrigerants. The interior of the plate is lined with a porous material or a capillary structure, ensuring fluid recirculation by capillary action. When the surface of the vapor chamber in contact with the heat source (for example, an electronic component) transfers its energy to the fluid, the fluid evaporates. The vapor then propagates through the enclosure to the cooler areas of the plate, where it condenses, releasing heat. The condensed liquid is then drawn back to the hot area by capillary action, ensuring a continuous heat transfer cycle.

[0040] The vapor chamber can transfer large amounts of heat with a small temperature difference between its hot and cold zones. Its operation requires no external energy, making it particularly suitable for systems demanding reliability, compactness, and a long service life.

[0041] It allows for very efficient heat dissipation in a confined space, which is particularly advantageous for high power density electronic devices.

[0042] The vapor chamber is associated, on its cold side, with fins or another heat exchange structure in order to increase the contact area with the cooling fluid and improve heat transfer to the environment.

[0043] Secondary principle of the invention according to a first alternative: vibration of the fins immersed in the coolant.

[0044] According to this first alternative, the cooling system includes the use of vapor chambers and piezoelectric actuators to optimize heat dissipation, particularly when immersed.

[0045] According to the general principle of the invention, vapor chambers allow for the efficient distribution and transport of heat through an evaporation-condensation cycle of a working fluid contained within their hermetically sealed enclosure. By positioning the "hot" zone of the vapor plate in contact with the heat source and its "cold" zone at the level of heat exchange surfaces or heat sinks located in a part of the immersion tank more conducive to heat dissipation, the heat is transferred to a zone better suited for removal. The vapor chambers, as designed, possess a very high equivalent conductivity of up to 6000 W / (mK), or 15 to 20 times that of a copper plate.

[0046] The heat sink incorporates vibrating fins. Actuators are designed to vibrate the heat sink fins at ultrasonic frequencies, between 20 kHz and 1 MHz. These vibrations add mechanical motion to the fins, creating agitation at the contact surface with the fluid.

[0047] These vibrations break down the thermal boundary layers that naturally form around the fins, where stagnant fluid prevents optimal heat exchange. By breaking down this layer, the vibrations improve heat transfer between the heat sink fins and the fluid.

[0048] By eliminating this thermal resistance, heat is transferred more efficiently, making the heat dissipation system more efficient without requiring an increase in the dissipation surface area or tank size.

[0049] This system maximizes heat transfer without significantly increasing energy consumption. The piezoelectric actuators consume little energy, and the bubble injection uses negligible energy to generate a significant flow. This dual effect—vibration and turbulence—improves the overall efficiency of the heat dissipation system without overloading the power supply.

[0050] Thanks to this approach, the device promises much more efficient thermal management in immersion, using a remote heat flow and a combination of mechanical movements to accelerate heat dissipation, while minimizing energy consumption and thermal impact on electronic components.

[0051] Secondary principle of the invention according to a second alternative: rising of bubbles between the fins immersed in the coolant.

[0052] An alternative approach is to break the thermal layer by injecting bubbles to increase turbulence. By injecting air in the form of bubbles into the fluid within the cooling chamber, controlled turbulence is generated in the surrounding liquid. The bubbles introduce disordered movements into the fluid, which increases convection and promotes mixing of the fluid heated by the fins with the cooler surrounding fluid.

[0053] This turbulence also helps to break the boundary layers around the fins, complementing the piezoelectric vibrations. Thus, the movement of the bubbles amplifies the heat dissipation effect by creating additional flows with minimal energy consumption.

[0054] Advantageously, these fins are arranged vertically, perpendicular to a base pierced by bubblers that release bubbles which rise to the surface along the surface of the fins. According to this advantageous embodiment, the invention relates to the method of injecting the bubbles, which does not result from vaporization of the liquid phase upon contact with hot spots, but from the injection of air bubbles into the base of the liquid cooling chamber, preferably vertically above cooling fins thermally connected to the electronic circuits, and preferably with a sequential release of bubbles.

[0055] By combining the electronic circuit with a heat sink, with the whole assembly immersed in the dielectric liquid, the effect of the bubbles which break the formation of the thermal boundary layer is significantly improved, thus improving the efficiency of heat exchange with the dielectric fluid.

[0056] To reduce the number of thermal interfaces ensuring heat transfer between the liquid, the cooling fins and the electronic components, and to improve heat exchange, the invention provides for: directly thermally coupling the electronic component with a heat sink having fins arranged in vertical planes, immersing the assembly in a dielectric liquid, injecting bubbles from the lower part towards the heat sink. Description of an example of architecture

[0057] The figure represents a front view of an electronic circuit cooling device according to the invention.

[0058] Lare represents a top view of an electronic circuit cooling device according to the invention.

[0059] The figure represents a projected view of an electronic circuit cooling system according to the invention.

[0060] The electronic circuit (21) to be cooled, for example GPU or CPU, is mounted on a printed circuit board. A thin layer of thermal paste is applied between the vapor plate / vapor chamber (16b) and the electronic circuit, to ensure efficient heat transfer to a more efficient vapor chamber.

[0061] The vapor chamber (16b) is a two-phase heat transfer device, ensuring the transfer of heat from the hot spot to the cold spot constituted by the heat sink (16) having a plurality of fins (16a) arranged in vertical planes, and immersed in a tank (11) filled with dielectric liquid.

[0062] The dielectric liquid, an electrical insulator up to 20 kV, is a thermally conductive fluid that meets the thermal performance and safety criteria governed by certain standards such as those of OCP (Open Compute Project).

[0063] The dielectric fluid (2) is a thermally conductive but electrically non-conductive or essentially dielectric fluid. The immersion fluid must have two very specific physical properties.

[0064] The fluid must be dielectric over the operating voltage range of the components that will be immersed in it; that is, it must be insulating to prevent short circuits.

[0065] The fluid must have suitable thermo-physical properties to be a good heat transfer fluid (high heat capacity, good thermal conductivity, etc.).

[0066] Examples of such fluids include demineralized water, fluorocarbon fluids and mineral or synthetic oils, and more particularly technical fluids of the type EC-110™ from EngineeredFluids or EGEN DCC 100R8™ from Motul, although the invention described is not limited to any particular dielectric fluid.

[0067] As an example, the thermophysical properties of these two liquids are as follows

[0068] [Table 1] Table 1 Properties EC-110EGEN DCC 100R8 Unit (SI) Density at 20 °C 820790 kg / m³ Coefficient of volumetric expansion 0.000670.00075K⁻¹Kinematic viscosity at 40 °C7.258.2 mm² / sThermal conductivity at 40 °C0.13740.140 W / (m·K)Specific heat at 40 °C2 212.12 237 J / (kg·K)Dielectric constant (40 °C)2.102.07–Voltage resistivity (40 °C)>1×10 16 >1×10 12 Ω·m Breakdown voltage (20 °C) >6030kV Flash point 170168°C

[0069] The vapor chamber (16b) has an outer shell formed by a metal plate, made of copper or aluminum. This tube is hermetically sealed to maintain a partial vacuum inside and a porous structure, which allows the working fluid to vaporize at low temperatures. The working fluid, for example water, ethanol, or ammonia, plays a central role in the heat transfer process. The choice of fluid depends on the operating temperature range of the vapor chamber. For temperatures around 85°C, water is often used because it has thermodynamic characteristics well-suited to these conditions.

[0070] A capillary wick made of a porous material lines the inner wall of the vapor chamber (16b). It is, for example, made from sintered metal, metal fibers, or mesh, and its role is to transport the liquid fluid by capillary action from the hot zone, the electronic component (21), to the fins (16a). It is thanks to this wick that the vapor chamber operates passively without a pump as long as the capillary pressure remains greater than the pressure drop of the liquid phase in the porous structure. The heat transferred by the electronic component (21) causes the working fluid to evaporate, thus absorbing thermal energy.

[0071] At the other end of the sealed vapor chamber, at the heat sink (16), the working fluid cools and returns to a liquid state, releasing heat into a heat sink, after passing as vapor through the void delimited by the porous structure (wick). This intermediate section has a zone in which the vapor rises towards the condensation zone and a channel to allow the liquid to return to the hot zone through the wick.

[0072] The vapor chamber operates on the principle of phase change. When heat is applied by the electronic circuit (21) to the hot end, the working fluid vaporizes. The vapor moves to the other end, which has the fins of the heat sink (16), where it releases its heat and condenses. The liquid then returns to the first hot end by capillary action through the wick, and the cycle repeats as long as there is a temperature difference between the two ends and a liquid phase is present (without drying out).

[0073] This structure allows the vapor chamber to transport large amounts of heat quickly and efficiently, with a very low temperature gradient.

[0074] The heat sink (16) has a network of parallel fins (16a) arranged in vertical planes. This fin network (16a) is immersed in a chamber (11) optionally associated with a liquid cooling circuit, for example a dielectric liquid, or a heat exchanger (20), a circulation pump (19), ensuring the circulation of a heat transfer fluid in this cooling circuit.

[0075] The fins are 0.7 mm thick and spaced 2 mm apart with a height of 40 mm.

[0076] The chamber (11) consists of a tank containing a liquid. The liquid contained in the chamber (11) must have suitable thermo-physical properties to be a good heat transfer fluid (high heat capacity, good thermal conductivity, etc.).

[0077] To improve cooling efficiency, air bubbles are injected from two points: at the inlet of the channels formed by the fins (16a) and at mid-height of the fins. The injection nozzles are positioned perpendicular to the base of the heat sink (16), and are horizontal. This disrupts the formation of the thermal boundary layer on the surface of the fins (16a) through turbulence generated near the heat exchange surfaces.

[0078] The needles used for bubble injections have an internal diameter of ~0.84 mm.

[0079] Depending on the nature and especially the viscosity of the coolant, the tank includes a circulation pump injecting the liquid through nozzles arranged on the bottom of the tank 11.

[0080] Bubble injection occurs through a 0.84 mm inlet at a velocity of 1 m / s for 0.5 s every 2 s. The liquid velocity at the domain inlet is 5 cm / s, while air is injected periodically at a velocity of 1 m / s. The temperature of both fluids is 300 K.

[0081] The injection of gas bubbles is carried out by a bubbler (17) powered by an air compressor. The bubbler (17) consists, for example, of porous bars or perforated membranes ensuring the formation of bubbles on the wall of a shear flow.

[0082] To increase the residence time of the bubbles between the fins, a hood (15) is placed on the heat sink (16). This allows the bubbles to pass all the way through the vertical channels formed by the fins.

[0083] The 5W powered air pump generates an airflow that is unevenly distributed between the two bubblers.

[0084] The electronic component to be cooled has a maximum thermal power density of ~80W / cm² or 700W over a surface area of ​​32x26mm². Its temperature remains around 85°C.

[0085] The use of such a cooling system makes it possible to achieve a temperature difference of ~25°C between the liquid and the CPU / GPU electronic component (21) Bubble injection sequencing

[0086] This presents the temporal evolution of the average temperature of the die of a GPU with a surface area of ​​25x25 mm². To achieve the target thermal power density (80W / cm²), its thermal power was set at 500W. Initially, temperatures continue to rise because the liquid cooling loop (18, 19, 20) was not implemented. Then, without injection, a rapid temperature increase of approximately 2°C / min is observed. The temperature difference between the electronic component and the liquid stabilizes at 31°C. Injecting bubbles reduces this value to 25°C. The initially low cooling observed without injection is likely due to the establishment of the thermal boundary layer. Indeed, in the first moments, the hot processor is in direct contact with the cooler liquid, creating a significant heat flow away from the GPU that is not offset by the GPU's heat generation.Conversely, as the fluid heats up and the thermal boundary layer establishes itself, the heat transfer between the processor and the fluid decreases and becomes less than the internal heat generation, and therefore the CPU heats up. To illustrate this, the convective heat transfer coefficient, defined by equation 1, is plotted as a function of time on the graph.

[0087] (1)

[0088] Or , T CPU and T f represent respectively the heat flux density at the surface of the processor, the surface temperature of the processor and the average temperature of the fluid.

[0089] Without injection, the convective heat transfer coefficient curve is characteristic of the establishment of the thermal boundary layer around the processor, reaching a value of 26,000 W / m² / K: a significant value already achieved through the use of the vapor chamber. Furthermore, with bubble injection, significant fluctuations are observed, and more importantly, it is clearly visible that the thermal boundary layer does not have time to establish itself and is constantly destroyed. Consequently, the average convective heat transfer coefficient remains around 30,000 W / m² / K, representing a 15% improvement compared to cooling without injection.

[0090] The sequential injection of bubbles generates turbulence and prevents the formation of the thermal boundary layer around the processor. This significantly improves its cooling.

[0091] Despite the satisfactory nature of these results, they can be improved for the following reasons: Only one bubbler was used at the base of the fins. Distributing the bubble injection to two locations (base and mid-height of the fins) would improve the results. The fin structure could be improved, as it currently presents obstructions within the channels formed by the fins, which "slows down" the injected bubbles. The heat sink used for the tests was not designed for immersion cooling. A fume hood was not used in this case.

[0092] With the aforementioned improvements, a maximum temperature difference of 20°C can be expected between the electronic component and the dielectric liquid, specifically for a 700W GPU generated on a 32x26 mm² surface. Reference symbol list

[0093] 10: Dielectric liquid

[0094] 11: Tank

[0095] 12: Bubbles

[0096] 13: Air pump

[0097] 14: Air hose

[0098] 15: Hood

[0099] 16: Heat sink

[0100] 16a: Heat sink fin

[0101] 16b: Steam chamber

[0102] 17: Bubbler

[0103] 17a: Air chamber of the bubbler

[0104] 17b: Needles

[0105] 18: Liquid pipe

[0106] 19: Liquid pump

[0107] 20: Heat exchanger

[0108] 21: Electronic component (CPU or GPU)

[0109] 22: Thermal Interface Material (TIM)

[0110] 23: Electronic circuit

Claims

Cooling equipment for an electronic component (21) comprising a thermally conductive substrate applied against the surface of said electronic component (21) on the one hand, and a heat transfer element on the other hand connected to a cooling means, characterized in that said heat transfer element consists of a passive heat transfer vapor chamber (16b) used to transport heat from a hot source to a cold point operating on the principle of the changing phase of a fluid, said passive sealed vapor chamber (16b) thermally connecting said electronic component (21) to a heat sink (16) formed by fins (16a) immersed in a chamber (11) filled with a coolant. Cooling equipment according to claim 1 characterized in that said heat sink (16) is provided with at least one actuator applying a vibratory movement to said fins (16a). Cooling equipment according to claim 1 characterized in that said at least one actuator applies a vibratory motion of a frequency between 20 Khz and 1 Mhz. Cooling equipment according to claim 1 characterized in that said at least one actuator is of the piezoelectric type. Cooling equipment according to claim 1 characterized in that said fins (16a) of said heat sink (16) are vertical. Cooling equipment according to claim 1 characterized in that said chamber has a bottom equipped with two bubblers (17) arranged at the base and mid-height of the fins with needles oriented towards the base of the vertically placed heat sink. Electronic component cooling equipment according to the preceding claim characterized in that said bubbler (17) is supplied by a pump controlled for sequential operation. Electronic component cooling equipment according to claim 1 characterized in that it further comprises a dielectric liquid cooling circuit including: a first liquid-liquid exchanger immersed in the chamber (11) and in the dielectric liquid contained in this chamber (11), a heat exchanger (20), a circulation pump (19), ensuring the circulation of a heat transfer fluid in this cooling circuit.

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