Cooling of immersion electronic systems using heat pipes and vibration systems

Abstract

The present invention relates to a cooling device for an electronic component (1) comprising a thermally conductive substrate (3) applied to the surface of said electronic component (1) on the one hand, and to a heat transfer element on the other hand connected to a cooling means, characterized in that said heat transfer element consists of a heat pipe (5) thermally connecting said electronic component (1) to a heat sink (10) formed by fins (11) immersed in a chamber (12) filled with a coolant. Abstract figure: Figure 1

Description

Title of the invention: Cooling of immersion electronic systems using heat pipes and vibration systems. Field of the invention

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

[0002] Cooling computer systems is becoming a major issue for many applications in telecommunications, data management, and computer security. This is because the power densities to be dissipated are increasing due to the miniaturization of computer components, particularly central processing units (CPUs) and graphics processing units (GPUs), and the 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, as the chips generated little heat. However, with the increase in frequencies and the multiplication of cores, the power consumption of processors has skyrocketed, requiring much more complex and efficient cooling systems.

[0005] Early cooling solutions consisted of simple aluminum heat sinks. Gradually, these devices became more complex, incorporating copper to improve thermal conductivity, and increasingly larger, with bigger fans to ensure efficient heat dissipation. The development of heat pipes from 2003 onward marked a major advance in central processing unit cooling. These sealed tubes, filled with a liquid, allow the heat generated by the processor to be rapidly transferred to the heat sink fins, where it is dispersed by a fan.

[0006] The "tower" format, based on heat pipes, has become the standard for central processing unit cooling. It combines one or more copper heat pipes. These designs dissipate heat from the processor to a set of metal fins, cooled by large fans. These solutions are particularly popular among overclocking enthusiasts, who seek to increase the performance of their CPUs while maintaining a stable and low operating temperature.

[0007] Alongside heat pipe coolers, another technology has emerged since 2007: liquid cooling (also known as standalone water cooling). This technology uses a closed liquid circuit to cool the central processing unit.

[0008] The choice of a cooling system depends primarily on the thermal envelope of the electronic circuit, that is, the amount of heat it dissipates. Efficient cooling is essential to allow central processing units to reach their maximum performance, particularly through dynamic frequency management mechanisms, such as "Turbo" frequencies, which increase when the processor temperature is kept low.

[0009] In summary, cooling electronic circuits has become a major challenge with the increase in processor performance. Solutions such as heat pipe coolers 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] US patent 20130291368A1 relates to a method and apparatus for bringing the thermal connectors of expansion printed circuit boards into contact, characterized in that they comprise a thermal connector. The apparatus is configured to be brought into contact via the thermal connector of an expansion printed circuit board when the expansion printed circuit board is installed and cooled by a combination of cooling and heat transfer means including heat pipes, fans, and heat sinks.

[0011] US patent 9852963B2 describes a cooling solution for a central processing unit by a fluid. The microprocessor is mounted on a substrate with two surfaces: one surface where the microprocessor is mounted and a second surface opposite the first. An integrated heat sink is placed on the conductive die to distribute the heat it generates. A layer of thermal interface material located between the top surface of the microprocessor and the inner surface of the heat sink conducts heat to the sink. A second layer of thermal interface material is placed on the outer surface of the heat sink, increasing the efficiency of heat transfer. A thermally conductive base element has one face that is directly cooled and a second face in contact with the second layer of material. Thermal interface on the heat diffuser. A heat sink module is sealed against the first face of the thermally conductive element and serves to direct the cooling fluid. The cooling fluid (such as water or a dielectric liquid) is injected under pressure into the inlet chamber via the inlet port. This fluid is then directed to the outlet chamber through a series of orifices. These orifices create jets of liquid that directly strike the surface of the thermally conductive element to be cooled. Heat is then extracted from the surface of the thermally conductive element, and the heated fluid is discharged through the outlet port.

[0012] The disadvantage of this solution is that cooling relies on a complex liquid cooling circuit, which requires pumps, tubing, and more frequent maintenance to prevent failures or leaks. Such a direct liquid cooling system is more vulnerable to pump failures, which can lead to rapid overheating of the processor. A liquid-only cooling system requires an electric pump to circulate the fluid.

[0013] US patent 8705236B2 describes a looped heat pipe for cooling electronic components such as CPUs, ensuring circulation of the working fluid with an auxiliary loop to guarantee rapid start-up and prevent common problems related to fluid drying in the evaporator. A primary loop manages the main heat flow from the component to be cooled. A secondary loop, closer to the condenser, ensures proper system operation even when the device is in a position where the evaporator is located above the condenser ("top heat" mode). This allows the system to operate reliably even under adverse gravitational conditions. Solution provided by the invention

[0014] In order to remedy these drawbacks, the present invention relates to a method having the following characteristics.

[0015] 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 to a heat transfer element on the other hand connected to a cooling means, characterized in that said heat transfer element consists of a heat pipe thermally connecting said electronic component to a heat sink formed by fins immersed in a chamber filled with a coolant.

[0016] Advantageously, said heat sink is provided with at least one actuator applying a vibratory movement to said fins.

[0017] Preferably, said at least one actuator applies a vibratory motion of a frequency between 20 Khz and 1 Mhz.

[0018] According to a particular embodiment, said at least one actuator is of the piezoelectric type.

[0019] Advantageously, said chamber has a bottom equipped with at least one bubbler disposed in the lower part of said chamber, vertically above said fins of said heat sink.

[0020] Preferably, said fins of said heat sink are vertical.

[0021] Advantageously, said bubbler is supplied by a pump controlled for constant or sequential operation.

[0022] According to one variant, the equipment further comprises a dielectric liquid cooling circuit including: - a heat exchanger, - a circulation pump, ensuring the circulation of a heat transfer fluid in this cooling circuit. Detailed description of a non-limiting example of implementation

[0023] 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:

[0024] [Fig-1] [Fig.1] represents a schematic front view of a variant of realization

[0025] [Fig.2] [Fig.2] represents a schematic top view of a variant of realization

[0026] [Fig.3] [Fig.3] represents a schematic projected view of a variant of realization

[0027] [Fig.4] [Fig.4] represents the time evolution curve of bubble injection air for 30 seconds

[0028] [Fig. 5] [Fig. 5] represents the time evolution curve of the temperature of the processor with and without air bubble injection

[0029] [Fig.6] [Fig.6] represents the time evolution curve of the coefficient convective exchange between the processor and the fluid

[0030] Principle of the invention: use of a heat pipe for heat transfer between the electronic component and fins immersed in a coolant.

[0031] 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 heat pipe 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 cooling chamber.

[0032] A heat pipe within the meaning of this patent is a passive heat transfer device used to transport heat from a hot source to a cold point. It operates based on the principle of the changing phase of a fluid, allowing rapid heat transfer with a small temperature difference.

[0033] This heat pipe 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.

[0034] Detail of heat pipe fabrication

[0035] The heat pipe consists of a hermetically sealed metal tube, generally made of copper or aluminum, materials with high thermal conductivity. This tube contains a liquid, the contents of which can vary depending on the application and temperatures, such as water, alcohol, ammonia, or even gases. A porous material or capillary structure lines the inner walls of the tube to allow fluid recirculation. The fluid inside the heat pipe evaporates at the hot end (near the electronic component, for example), absorbing heat. The vapor then moves to the cold end of the heat pipe (such as the heat sink), where it condenses, releasing heat. The condensed liquid then returns to the hot zone due to the capillary forces of the porous material or to gravity, thus enabling a continuous cycle.

[0036] The heat pipe can transport large quantities of heat with a small temperature difference. It requires no external energy to operate, making it ideal for systems requiring reliability and a long service life.

[0037] It allows efficient heat dissipation in a confined space, which is particularly useful in electronic devices.

[0038] The heat pipe is provided at its cold end with cooling fins increasing the thermal interaction surface with the coolant.

[0039] Secondary principle of the invention according to a first alternative: vibration of the fins immersed in the coolant.

[0040] According to this first alternative, the cooling system includes the use of heat pipes and piezoelectric actuators to optimize heat dissipation, particularly when immersed.

[0041] According to the general principle of the invention, heat pipes allow heat to be efficiently transported from one point to another by means of an evaporation-condensation cycle of a working fluid contained within them. By placing the "hot" end of the heat pipes near the heat source and the "cold" end at heat sinks located lower in the immersion tank, the heat is transferred to an area better suited for dissipation.

[0042] The heat sink comprises 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.

[0043] 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.

[0044] 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 the size of the tank.

[0045] This system maximizes heat transfer without significantly increasing energy consumption. The piezoelectric actuators consume little energy, and bubble injection uses negligible energy to generate significant flow. This dual effect—vibrations and turbulence—improves the overall efficiency of the heat dissipation system without overloading the energy supply.

[0046] 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 the thermal impact on electronic components.

[0047] Secondary principle of the invention according to a second alternative: rising of bubbles between the fins immersed in the coolant.

[0048] An alternative is to break the thermal layer by injecting bubbles to increase turbulence. By injecting air in the form of bubbles into the fluid of the cooling chamber, controlled turbulence is generated in the surrounding liquid. The bubbles introduce disordered movements in the fluid, which increases convection and promotes the mixing of the fluid heated in contact with the fins with the cooler surrounding fluid.

[0049] This turbulence also helps to break the boundary layers around the fins, in addition to the piezoelectric vibrations. Thus, the movement of the bubbles amplifies the heat dissipation effect by creating additional flows with minimal energy consumption.

[0050] 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 the cooling fins. thermally associated with electronic circuits, and preferably with sequential bubble release.

[0051] By associating the electronic circuit with a heat sink, the whole being 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.

[0052] 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: a. To directly thermally couple the electronic component with a heat sink having fins arranged in vertical planes, b. Immerse the assembly in a dielectric liquid, c. inject bubbles from the lower part towards the heat sink. Description of an example of architecture

[0053] Figure 1 shows a front view of circuit cooling equipment electronics according to the invention.

[0054] Figure 2 shows a top view of circuit cooling equipment electronics according to the invention.

[0055] Figure 3 represents a projected view of a cooling system electronic circuits according to the invention.

[0056] The electronic circuit (21) to be cooled, for example GPU or CPU, is mounted on a printed circuit board (23). A thin layer of thermal paste (22) is applied between the heat pipe and the electronic circuit to ensure efficient heat transfer to a high-performance heat pipe (15).

[0057] The heat pipe (15) 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 folded tank (11) of liquid.

[0058] The heat pipe (15) has an outer casing formed by a metallic tube, made of copper or aluminum. This tube is hermetically sealed to maintain a partial vacuum inside, 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 heat pipe. For temperatures around 85°C, water is often used because it has thermodynamic characteristics suitable for these conditions.

[0059] A capillary wick made of a porous material lines the inner wall of the heat pipe (15). 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 finned heat sink (16b) to the electronic circuit (21). It is thanks to this wick that the heat pipe operates passively without a pump. The heat transmitted by the electronic component (21) causes the working fluid to evaporate, thus absorbing thermal energy.

[0060] At the other end of the heat pipe, at the heat sink (16), the working fluid cools and returns to a liquid state, thus releasing heat into a heat sink, after passing as vapor through the intermediate section forming a vapor-liquid conduit. This intermediate section has a conduit through which the vapor rises to the condensation zone and a channel to allow the liquid to return to the hot zone through the wick.

[0061] The heat pipe 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 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.

[0062] This structure allows the heat pipe to transport large quantities of heat quickly and efficiently, with a very low temperature gradient.

[0063] 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.

[0064] 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...).

[0065] To improve the efficiency of cooling by the formation of bubbles injected from the bottom (24) to circulate vertically on the surface of the heat sink (16) in order to disrupt the formation of the thermal boundary layer on the surface of the fins (16a) by turbulence produced near the heat exchange surfaces.

[0066] 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 (24), preferably below the bubble injection points. For example, the liquid is injected through the bottom (24) having one or more inlets with a diameter of about 4 mm, with a speed of about 5 cm / s.

[0067] Bubble injection is performed through a 2 mm inlet at a velocity of Im / s for 0.5 s every 2 s, according to a sequence illustrated in [Fig. 4]. The liquid velocity at the domain inlet is 5 cm / s, while air is injected periodically at a velocity of Im / s. The temperature of both fluids is 300 K.

[0068] 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 at the wall of a shear flow. Sequencing of the bubble injection

[0069] Figure 5 shows the time evolution of the average processor temperature. Without air bubble injection (curve 5), a slight cooling is initially observed, followed by a temperature rise to approximately 54°C, while the presence of air (curve 6) allows for rapid cooling of 10°C in 15 seconds, then slower cooling, reaching 13°C after 30 seconds. The initial low cooling observed without injection is probably 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 leaving the CPU that is not compensated by the CPU's heat generation. However, as the fluid heats up and the thermal boundary layer is established, the heat transfer between the processor and the fluid decreases and becomes lower than the internal heat generation, and therefore the CPU heats up.To verify this, the convective heat transfer coefficient, defined by equation 1, is represented as a function of time in [Fig.6].

[0070] (1) VcptrTf)

[0071] where TCpu and Tfre 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.

[0072] 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 approximately 30 W / m²K after 30 seconds. In contrast, 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 stable at around 400 W / m²K, representing a gain of a factor of 13 compared to cooling without injection.

[0073] The sequential injection of bubbles makes it possible to generate turbulence and prevent the formation of the thermal boundary layer around the processor. Thus, the cooling of the latter is much better. List of reference signs

[0074] 10: Liquid dielectric

[0075] ll:Tank

[0076] 12: Bubble

[0077] 13: Air pump

[0078] 14: Air hose

[0079] 15a,15b,15c,15d: Heat pipe

[0080] 16: Heat sink a: Heat sink fin b: Heat sink base thermal

[0081] 17: Bubbler

[0082] 18: Liquid pipe

[0083] 19: Liquid pump

[0084] 20: Heat exchanger

[0085] 21: Electronic component (CPU or GPU)

[0086] 22: Thermal Interface Material (TIM)

[0087] 23: Electronic circuit

Claims

Demands

1. Cooling equipment for an electronic component (1) comprising a thermally conductive substrate (3) applied against the surface of said electronic component (1) on the one hand, and to a heat transfer element on the other hand connected to a cooling means, characterized in that said heat transfer element consists of a heat pipe (5) thermally connecting said electronic component (1) to a heat sink (10) formed by fins (11) immersed in a chamber (12) filled with a coolant.

2. Cooling equipment according to claim 1 characterized in that said heat sink (10) is provided with at least one actuator applying a vibratory movement to said fins (11).

3. 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.

4. Cooling equipment according to claim 1 characterized in that said at least one actuator is of the piezoelectric type.

5. Cooling equipment according to claim 1 characterized in that said fins (11) of said heat sink (10) are vertical.

6. Cooling equipment according to claim 1 characterized in that said chamber has a bottom provided with at least one bubbler (18) disposed in the lower part of said chamber, vertically above said fins of said heat sink (10).

7. Electronic component cooling equipment according to the preceding claim characterized in that said bubbler (18) is supplied by a pump controlled for sequential operation.

8. Electronic component cooling equipment according to claim 1 characterized in that it further comprises a dielectric liquid cooling circuit comprising: - a first liquid-liquid exchanger (15) immersed in the chamber (12) and in the dielectric liquid contained in this chamber (12) - a heat exchanger (20), - a circulation pump (25), ensuring the circulation of a heat transfer fluid in this cooling circuit.

Images