Porous foamy copper evaporator with gas-phase flow guide structure

Abstract

The invention provides a porous foamy copper evaporator with a gas-phase flow guide structure, the evaporator comprises a plate-shaped cover plate and a plate-shaped bottom plate, a micro-channel, a flow equalizing groove, a working medium inlet, a working medium outlet and a confluence groove are processed on the bottom plate, and the cover plate comprises the gas-phase flow guide structure; the microchannel is arranged in the middle of the bottom plate; the length direction of the microchannel is parallel to the gas-phase flow guide structure; the gas-phase flow guide structure is arranged in the middle of the cover plate and corresponds to the micro-channel of the bottom plate in position; the flow equalizing groove and the flow converging groove are formed in the two edge portions of the bottom plate in the length direction and communicate with the working medium inlet and the working medium outlet correspondingly. The bottom plate micro-channel, the flow equalizing groove and the cover plate gas-phase flow guide structure are made of foamy copper porous materials. The evaporator is made of a foamy copper porous material, the convection heat exchange area is increased, and phase change heat absorption of a working medium is facilitated; the gas-phase flow channel is formed in the cover plate, the situation that working medium flowing is blocked by bubbles generated by working medium phase change is relieved, the pressure drop is reduced, and the temperature uniformity is improved.

Description

Technical Field

[0001] The invention relates to a heat exchanger technology, in particular to a porous foam copper evaporator with a gas phase flow guiding structure. Background Art

[0002] A heat exchanger is a widely used device that exchanges heat between objects at different temperatures to meet production and living needs. Since Watt invented the first heat exchanger capable of condensing heat in 1774, separating the condensation process from the steam engine, heat exchanger technology has flourished over the past 250 years, with a wide variety of heat exchangers emerging for widespread use in fields such as petroleum, chemical engineering, power generation, and refrigeration. Heat exchangers can be categorized by their intended purpose as heaters, coolers, condensers, and evaporators.

[0003] The concept of microchannel evaporators was first proposed by Tuckerman and Pease in the 1980s. At the time, microchannel evaporators were primarily used to address heat dissipation challenges in the electronics field. In this field, microchannel heat sinks demonstrated excellent heat dissipation capabilities, successfully addressing the heat accumulation issues in electronic systems at the time. Consequently, they attracted the attention of more researchers and were applied to a wider range of heat dissipation fields.

[0004] A microchannel evaporator can be combined with a reservoir, pump, condenser, and regenerator to form a pump-driven two-phase circuit. Its operating principle is as follows: Driven by a pump, the subcooled working fluid first passes through the regenerator, where it undergoes heat exchange with the two-phase working fluid flowing out of the evaporator, heating it to near saturation temperature before flowing into the evaporator. The heat source heats the evaporator, where the working fluid absorbs heat and transforms into a gas-liquid two-phase system. The system then flows to the condenser, where it exchanges heat with the outside world before entering the next operating cycle.

[0005] This invention improves existing microchannel evaporators based on a pump-driven two-phase system. It proposes a novel porous copper foam evaporator with a gas-phase flow-guiding structure. This improves the evaporator's heat transfer capacity, temperature uniformity, and flow velocity uniformity within the evaporator's internal flow channels. It meets the high heat flux density dissipation requirements of power electronics, while also offering a high energy efficiency compared to air cooling, saving significant energy and improving energy efficiency. Summary of the Invention

[0006] The present invention provides a porous copper foam evaporator with a gas phase guide structure, which improves the material and structure of the evaporator, thereby solving the above-mentioned technical problems.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows:

[0008] A porous copper foam evaporator with a gas-phase flow-guiding structure. The base plate 2-1 is machined with a working medium inlet and outlet 3-1, a flow-balancing groove 3-2, microchannels 3-3, small channels 3-4, and a confluence groove. The cover plate 2-2 defines a gas-phase flow-guiding structure 4-1. The microchannels are located in the middle of the base plate 2-1, their lengths parallel to the direction of the gas-phase flow-guiding structure 4-1. The gas-phase flow-guiding structure 4-1 is located in the middle of the cover plate 2-2, corresponding to the positions of the microchannels in the base plate 2-1. The flow-balancing grooves 3-2 are located at both edges of the base plate along its length, connecting to the working medium inlet and outlet 3-1. The working medium inlet and outlet 3-1 is located in the middle of the end face of the base plate 2-1. The base plate microchannels 3-3, flow-balancing grooves 3-2, and the cover plate gas-phase flow-guiding structure 4-1 are made of porous copper foam.

[0009] As an improvement, a rectangular flow balancing groove 3-2 is designed at the inlet of the microchannel and a rectangular confluence groove is set at the outlet.

[0010] One improvement is that the microchannel is set in the middle part of the base plate 2-1, and the overall microchannel of the base plate is obtained by an array of 8 unit structures.

[0011] One improvement is to open 3-4 small rectangular grooves at the bottom of the microchannel, whose size is 18% of the size of the microchannel, to increase the convection heat exchange area.

[0012] As an improvement, a gas phase guide structure 4-1 is opened on the top of the cover plate, and three gas phase guide structures 4-1 correspond to one microchannel structure of the bottom plate 2-1.

[0013] As an improvement, the microchannel and gas phase flow guide structure 4-1 adopts porous foam copper material, and the evaporator pressure drop satisfies the formula:

[0014]

[0015]

[0016] Where: μ f is the Darcy velocity, i.e., the seepage velocity; v is the fluid flow velocity in the evaporator; ∈ is the porosity of the porous copper foam; Δp is the pressure drop before and after the working fluid passes through the porous copper foam evaporator; L is the length of the porous medium along the flow direction; μ is the dynamic viscosity of the working fluid; K is the permeability of the porous copper foam; ρ is the density of the working fluid; C is the inertia coefficient, which characterizes the blockage of the fluid by the complex structure inside the porous medium.

[0017] Preferably, the bottom plate is a microchannel 3-3 structure, and the bottom plate 2-1 has a thickness of 3 mm, a length of 120 mm, and a width of 25 mm.

[0018] Preferably, the number of microchannels 3-3 on the evaporator bottom plate is 8, and the unit structure of a single microchannel 3-3 is 106 mm long, 2 mm wide, and 2 mm high; the microchannel spacing is 0.7 mm.

[0019] Preferably, the cover plate is provided with a gas-phase guide structure 4-1, each microchannel corresponds to three gas-phase guide structures 4-1, a single gas-phase guide structure 4-1 is 108 mm long, 0.35 mm wide and 0.35 mm high; the interval between the gas-phase guide structures 4-1 is 0.24 mm.

[0020] Preferably, R1233zd is used as the working fluid.

[0021] Preferably, the porous copper foam material has a porosity of 80% and a pore density of 500 PPI.

[0022] Preferably, the working fluid enters the evaporator working fluid inlet 3-1 through a pipeline and is evenly distributed to the eight microchannels 3-3 under the action of the flow equalization groove 3-2. The bottom of the microchannel 3-3 is a heat source, and the small grooves 3-4 opened at the bottom increase the heat exchange area and enhance the heat exchange effect; the gas phase floats to the gas phase guide structure 4-1 of the cover plate, which alleviates the blockage of bubbles on the liquid phase working fluid and reduces pressure loss.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1) The present invention uses a porous copper foam material to make the evaporator, which can provide more phase change sites for the working fluid, help the working fluid phase change heat transfer, increase the working fluid contact area, and improve the heat exchange efficiency

[0025] 2) The present invention provides a gas phase guide structure 4-1 on the cover plate, which helps to alleviate the bubbles generated by the phase change of the working fluid from blocking the flow of the liquid phase working fluid, improves the flow rate uniformity, and reduces the pressure drop.

[0026] 3) The present invention opens small grooves 3-4 at the bottom of the evaporator microchannel to effectively increase the heat exchange area. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the pump-driven two-phase circuit structure of the present invention

[0028] Figure 2 This is a schematic diagram of the appearance of the porous copper foam evaporator of the present invention

[0029] Figure 3 This is a schematic diagram of the bottom plate structure of the porous copper foam evaporator of the present invention.

[0030] Figure 4 This is a schematic diagram of the structure of the porous copper foam evaporator cover plate of the present invention

[0031] Figure 5 This is a cross-sectional schematic diagram of the porous copper foam evaporator of the present invention.

[0032] Figure 6 This is a side view of the porous copper foam evaporator of the present invention DETAILED DESCRIPTION

[0033] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0034] In the description of the present invention, terms such as "inside", "outside", "up", "down", "front", "back", "left", and "right" that indicate directions or positional relationships are based on the positions or orientational relationships shown in the accompanying drawings, and do not indicate or imply that the described devices or components must have a specific installation and operating direction, and therefore cannot be understood as limiting the present invention.

[0035] It should be noted that, in the description of the present invention, the terms "disposed" and "installed" should be understood broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to direct connections, indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances. Furthermore, the terms "one" and "two" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly indicate the number of technical features being referred to.

[0036] A mechanical pump drives a two-phase fluid circuit, such as Figure 1 As shown, the pump-driven two-phase circuit includes a mechanical pump 1-1, an evaporator 1-2, a condenser 1-3, a liquid reservoir 1-4, a regenerator 1-5, a sensor 1-6, and an electric ball valve 1-7. During operation, the subcooled working fluid, driven by the mechanical pump 1-1, enters the regenerator 1-5. There, the subcooled working fluid fully exchanges heat with the two-phase hot working fluid that has passed through the evaporator 1-2, reaching the phase transition temperature before entering the evaporator 1-2. The evaporator 1-2 absorbs heat from the heat source and heats up. The working fluid that has reached the phase transition temperature undergoes a phase change, absorbing heat to lower the temperature of the heat source. After exiting the evaporator, the two-phase working fluid flows into the regenerator 1-5, heating the subcooled working fluid that has flowed into the evaporator 1-2. The fluid then enters the condenser 1-3, where it exchanges heat with the outside air, liquefies back into a liquid phase, and enters the next cycle. Reservoirs 1-4 in the system store, supply, and stabilize the working fluid. Evaporators 1-2 are essential components in pump-driven two-phase systems. Currently, evaporators primarily utilize solid metal materials and flat microchannel structures, but their performance, including heat transfer capacity, temperature uniformity, and flow uniformity, needs to be improved.

[0037] As an improvement. Figure 2 、 3As shown in Figures 4 and 5, the evaporator consists of a base plate 2-1 and a cover plate 2-2. The base plate 2-1 includes four core parts: an inlet and outlet 3-1, a flow trough 3-2, a microchannel 3-3, and a small groove 3-4. The cover plate 2-2 is provided with a gas phase guide structure 4-1. The evaporator is made of a porous foam copper matrix 5-1 with an aluminum shell 5-2 attached to the outside. Compared with traditional solid aluminum, copper and other solid material microchannel evaporators, the porous foam copper evaporator has a complex three-dimensional mesh pore structure inside. When the working fluid flows through the foam copper flow channel, the turbulence of the working fluid will increase significantly compared to the traditional solid metal flow channel, which helps to destroy the thermal boundary layer, increase the temperature gradient of the fluid, reduce the thermal resistance of the turbulent boundary layer, and thus improve the heat exchange efficiency, so that its convective heat transfer coefficient reaches 21864W / (m 2 ·K), increased by 30%-50%. The copper foam evaporator features numerous small pores on the flow channel sidewalls, allowing the fluid to fully infiltrate the inner wall under capillary force, improving the evaporator's temperature uniformity. The cold plate temperature difference is less than 2.3°C, a reduction of more than 50%. Furthermore, copper foam has a significantly higher specific surface area than traditional solid metal for the same volume. This helps the evaporator achieve a larger effective heat exchange surface area within a smaller volume, enabling evaporator miniaturization and increasing the integration of pump-driven two-phase systems.

[0038] As an improvement, Figure 5 The present invention adds a gas-phase guide structure 5-3 to the top of the microchannel inside the porous copper foam evaporator, and opens a small groove 5-4 at the bottom. When the working medium changes phase in the traditional linear microchannel, the gas-phase microbubbles may merge during the flow process, which will cause the bubbles to grow rapidly and spread downstream to form a gas plug that blocks the flow channel. This will affect the replenishment of the liquid-phase working medium and cause the flow channel to dry up. In response to this, the present invention adds a gas-phase guide structure 5-3 to the top of the microchannel. When the gas-phase working medium is generated, it will float to the gas-phase guide structure 5-3 and flow separately from the liquid-phase working medium, effectively preventing the flow channel from drying up and the heat transfer capacity from decreasing due to the accumulation of the gas-phase working medium, thereby improving the flow rate uniformity by 40%. At the same time, the small groove 5-4 at the bottom of the microchannel increases the effective heat transfer area in the microchannel and increases the overall heat exchange capacity of the evaporator.

[0039] Preferably, the porous copper foam evaporator adopts a porous copper foam material with a porosity of 500PPI. In addition to the physical parameters of the metal skeleton of the foam material itself, the parameters of its internal structure also have a great influence on its heat transfer characteristics. The pore density refers to the number of holes per inch (PPI) of the foam metal material. Through experiments, the convective heat transfer coefficients corresponding to the copper foam evaporators with different pore densities were compared, and the results showed that the convective heat transfer coefficient of the porous copper foam evaporator was the largest at 500PPI. At this time, the pore density is moderate, neither too low, so that the working fluid can be disturbed by the copper foam skeleton when flowing through the porous copper foam evaporator, thereby enhancing the turbulence of the working fluid flow and enhancing the heat exchange capacity; nor too high, so that the metal skeleton accounts for a large proportion and has a larger effective heat exchange area.

[0040] As a preference, Figure 6 The depth of the equalizing groove 6-1 of the porous copper foam evaporator is 2.5mm. The depth of the groove between the internal inlet and the microchannel of the traditional evaporator is too small to play the role of equalizing flow, often resulting in uneven flow distribution between microchannels, which causes uneven heat exchange temperature distribution in each microchannel and even local high temperature and dryness. The equalizing groove 6-1 of the present invention is 2.5mm lower than the bottom of the microchannel, which will allow the working fluid to enter the equalizing groove 6-1 first and then enter each microchannel at the same time. This will greatly improve the problem of uneven distribution of working fluid between the flow channels of the microchannel, and avoid the problem of uneven heat absorption capacity of each flow channel due to uneven distribution of working fluid, resulting in local heat accumulation and excessive dryness of some flow channels.

[0041] As a preferred choice, R1233zd is selected as the working fluid, which has the advantages of large latent heat of vaporization, suitable phase change temperature, low viscosity, non-flammability, non-toxicity, relatively stable and compatible with other materials. It meets the performance requirements of the pump-driven two-phase system in terms of operating temperature range, stability, temperature uniformity, etc.

[0042] In addition, it should be noted that the entire device can adjust the number and size of each component according to different application scenarios. This specific implementation example and its description purpose cannot be understood as indicating or implying relative importance or implicitly indicating the indicated technical features.

[0043] In summary, the innovations of this product are as follows:

[0044] (1) The innovative use of porous copper foam as the evaporator base material improves the convective heat transfer coefficient of the evaporator and improves the temperature uniformity of the evaporator cold plate. At the same time, its high specific surface area contributes to the miniaturization of the evaporator.

[0045] (2) An innovative gas phase flow guide structure is opened, which allows the liquid phase and gas phase to flow separately, avoiding the accumulation of gas phase working fluid interfering with the flow of liquid phase working fluid, thereby inducing uneven distribution of working fluid between flow channels and leading to local evaporation.

[0046] Although the present invention has been disclosed above with reference to preferred embodiments, the present invention is not limited thereto. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope defined by the claims.

Claims

1. A porous copper foam evaporator with a gas-phase flow-guiding structure. The base plate is machined with microchannels, a working fluid inlet, a working fluid outlet, a flow-equalizing groove, and an outlet confluence groove. The cover plate is provided with a gas-phase flow-guiding structure. The microchannels are arranged in the middle of the base plate, with their length parallel to the direction of the gas-phase flow-guiding structure. The gas-phase flow-guiding structure is arranged in the middle of the cover plate, its position corresponding to the position of the base plate microchannels. The flow-equalizing groove and the confluence groove are arranged at the two edges along the length of the base plate, respectively connected to the working fluid inlet and working fluid outlet. The working fluid inlet and outlet are located in the middle of the base plate end face. The base plate microchannels, flow-equalizing grooves, and the cover plate gas-phase flow-guiding structure are made of porous copper foam.

2. The evaporator according to claim 1, wherein A rectangular flow balancing groove is designed at the inlet of the microchannel, and a rectangular confluence groove is set at the outlet.

3. The evaporator according to claim 1, wherein The number of microchannels on the evaporator bottom plate is 8, and the single microchannel unit structure is 106 mm long, 2 mm wide, and 2 mm high; the microchannel spacing is 0.7 mm.

4. The evaporator according to claim 1, wherein A small rectangular groove is opened at the bottom of the microchannel, and its size is 18% of the microchannel size to increase the convection heat exchange area.

5. The evaporator according to claim 1, wherein The cover plate is provided with gas phase flow channels, and each microchannel corresponds to three gas phase flow channels. A single gas phase flow channel is 108 mm long, 0.35 mm wide, and 0.35 mm high; the gas phase flow channels are spaced 0.24 mm apart.

6. The evaporator according to claim 1, wherein The microchannel and gas phase guide structure adopt porous foam copper material, and the evaporator pressure drop satisfies the formula: Where: μ f is the Darcy velocity, i.e., the seepage velocity; v is the fluid flow velocity in the evaporator; ∈ is the porosity of the porous copper foam; Δp is the pressure drop before and after the working fluid passes through the porous copper foam evaporator; L is the length of the porous medium along the flow direction; μ is the dynamic viscosity of the working fluid; K is the permeability of the porous copper foam; ρ is the density of the working fluid; C is the inertia coefficient, which characterizes the blockage of the fluid by the complex structure inside the porous medium.

7. The evaporator material according to claim 1, wherein: The material porosity is 80% and the pore density is 500PPI.

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