Microchannel evaporative cooler and method of microchannel evaporative cooling enhancement

Abstract

The application provides a micro-channel evaporative cooler, and relates to the fields of heat exchange equipment and heat transfer enhancement technology.The fluid reaches the uniform micro-channel and is heated to generate gas-liquid phase change through the fluid inlet, and large bubbles are divided into small bubbles through a bubble dividing mixer at the outlet of the uniform micro-channel, so that the two-phase convection effect is enhanced;the two-phase mixture generated by the bubble dividing mixer is screened at the entrance of the non-uniform micro-channel due to the interface effect of the non-uniform micro-channel, so that a flow structure in which small bubbles and liquid phases are mainly in narrow channels and large bubbles and gas phases flow mainly in wide channels is formed, and the growth of small bubbles and the nucleation of new bubbles occur in the narrow channels, and the large bubbles in the wide channels quickly pass through the plug flow to the annular flow through the coalescence, so that the gas-liquid separation flow is realized in the two-phase flow and the wide and narrow channels, and the critical heat flow and flow stability of the evaporative cooler are improved.

Description

Technical Field

[0001] This invention relates to the field of heat exchange equipment and enhanced heat transfer technology, and in particular to a microchannel evaporative cooler and a method for enhancing microchannel evaporative cooling. Background Technology

[0002] With the continuous advancement and development of science and technology, electronic components are trending towards integration, miniaturization, and compactness. However, microelectronic devices generate more heat, leading to equipment malfunctions, making heat dissipation a current research hotspot. Therefore, microchannel heat exchange technology is increasingly being applied in fields such as aerospace, electronic information technology, air conditioning, and microelectromechanical systems (MEMS).

[0003] Flow boiling refers to the phenomenon of a liquid boiling due to heating during flow. It typically occurs in steam generators, evaporative coolers, and chemical reactors. Flow boiling is accompanied by a series of complex flow pattern changes, from a single-phase flow where the fluid has not yet begun to boil to a foamy flow where heating begins. As the heating intensity increases, the bubbles merge into larger gas plugs. The alternating flow of these gas plugs in the liquid is called slug flow. Then, the flow pattern gradually changes to slug flow, annular flow, and mist flow. Among these, slug flow is unstable, with significant pressure and temperature fluctuations. In industrial applications, shortening the formation and existence time of slug flow is key to improving the heat transfer capacity of evaporative coolers.

[0004] Therefore, how to shorten the formation and existence time of slug flow in order to improve the heat exchange capacity of evaporative coolers has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, one of the objectives of the present invention is to provide a microchannel evaporative cooler to solve the technical problem in the prior art that the heat exchange capacity of the evaporative cooler is poor due to the formation or prolonged existence of slug flow.

[0006] The second objective of this invention is to provide a method for enhancing microchannel evaporative cooling.

[0007] To achieve one of the above objectives, the present invention provides a microchannel evaporative cooler, comprising an evaporative cooler body, the evaporative cooler body having a hollow inner cavity, the evaporative cooler body also having a fluid inlet and a fluid outlet, the fluid inlet and the fluid outlet communicating with the hollow inner cavity, the hollow inner cavity having a uniform microchannel, a bubble splitter mixer and a non-uniform microchannel, the bubble splitter mixer and the non-uniform microchannel being arranged at intervals in the fluid flow direction.

[0008] Optionally, the bubble splitter mixer includes a first bubble splitter mixer and a second bubble splitter mixer, the non-uniform microchannel includes a first non-uniform microchannel and a second non-uniform microchannel, the first bubble splitter mixer is located between the uniform microchannel and the first non-uniform microchannel, and the second bubble splitter mixer is located between the first non-uniform microchannel and the second non-uniform microchannel.

[0009] Optionally, the hollow inner cavity is further provided with an inlet liquid collection chamber, which is connected to the fluid inlet and the uniform microchannel; The hollow inner cavity is also provided with an outlet liquid collection chamber, which is connected to the fluid outlet and the second non-uniform microchannel.

[0010] Optionally, the equivalent diameter of each microchannel in the fluid flow direction is equal.

[0011] Optionally, the non-uniform microchannels are arranged with narrow channels and wide channels alternately in the vertical flow direction, and the equivalent diameter of the wide channels is more than three times that of the equivalent diameter of the narrow channels.

[0012] Optionally, the bubble splitter mixer consists of at least two rows of staggered wedge-shaped splitting columns.

[0013] Optionally, the fluid forms bubbles of varying sizes at the outlet of the uniform microchannel. The bubbles enter the bubble splitter mixer with the fluid. Large bubbles are split into smaller bubbles at the sharp leading edge of the wedge-shaped splitting column. The bubble splitting increases the gas-liquid contact area while keeping the gas phase volume constant. The staggered arrangement of the wedge-shaped splitting columns enhances the two-phase flow effect.

[0014] Optionally, the two-phase mixture flowing out of the bubble splitter flows into the non-uniform microchannel. At the inlet of the non-uniform microchannel, due to the different capillary pressure differences at the gas-liquid interface at the inlet of the wide channel and the narrow channel, the capillary pressure difference that vapor needs to overcome to enter the wide channel is smaller, and the gas-liquid interface tends to enter the wide channel. The capillary pressure difference at the gas-liquid interface can be expressed as:

[0015] p v p is the gas phase pressure. l Let σ be the liquid phase pressure, σ be the interfacial tension, and r be the channel radius. The larger r is, the smaller the capillary pressure difference and the smaller the resistance to the movement of the gas-liquid interface.

[0016] Optionally, the narrow channel of the non-uniform microchannel has a filtering effect on large bubbles, and most of the large bubbles enter the wide channel, forming a flow structure in which the wide channel is dominated by large bubbles and gas phase flow, and the narrow channel is dominated by small bubbles and liquid phase flow.

[0017] To achieve the second objective mentioned above, this invention provides a microchannel evaporative cooling enhancement method. Within a microchannel evaporative cooler, an inlet collection chamber, a uniform microchannel, a bubble-splitting mixer, a non-uniform microchannel, and an outlet collection chamber are sequentially arranged. The cooling medium enters the uniform microchannel from the inlet collection chamber, undergoing a gas-liquid phase change. In the bubble-splitting mixer, large bubbles are split into smaller bubbles at the sharp leading edges of wedge-shaped dividing columns. This bubble splitting increases the gas-liquid contact area while maintaining a constant gas volume. The staggered arrangement of the wedge-shaped dividing columns enhances the two-way convection effect. Due to the wide and narrow channels... The capillary pressure difference at the gas-liquid interface at the inlet of the channel is different. The capillary pressure difference that steam needs to overcome to enter the wide channel is small, and the gas-liquid interface tends to enter the wide channel. Its cross-sectional gas content is higher, which makes it easier to form a thin liquid film convection evaporation heat transfer mode dominated by annular flow in the wide channel. In the narrow channel, the growth of small bubbles and the nucleation process of new bubbles mainly by nucleation boiling occur. This efficient heat transfer mode of thin liquid film convection evaporation and nucleation boiling that coexist in the wide and narrow channels perpendicular to the flow direction significantly improves the heat transfer performance and reduces the flow and heat transfer instability caused by slug flow in traditional microchannels.

[0018] The microchannel evaporative cooler provided by this invention has the following technical effects: This microchannel evaporative cooler mainly consists of an evaporative cooler body containing a hollow inner cavity. The evaporative cooler body also has a fluid inlet and a fluid outlet, which communicate with the hollow inner cavity. The hollow inner cavity contains uniform microchannels, a bubble splitter / mixer, and non-uniform microchannels. The bubble splitter / mixer and the non-uniform microchannels are arranged at intervals in the fluid flow direction. In this invention, the fluid reaches the uniform microchannel through the fluid inlet and undergoes a gas-liquid phase change upon heating. At the outlet of the uniform microchannel, the bubble splitter / mixer breaks large bubbles into smaller ones. Bubbles enhance the two-phase flow effect. The two-phase mixture generated by the bubble separator is filtered at the inlet of the non-uniform microchannel due to the interface effect of the non-uniform microchannel. This results in a flow structure where small bubbles and liquid phase dominate in the narrow channel, while large bubbles and gas phase flow dominate in the wide channel. Small bubbles grow and new bubbles nucleate in the narrow channel, while large bubbles merge and rapidly pass through the slug flow to the annular flow in the wide channel. By enhancing the two-phase flow through gas-liquid separation and achieving gas-liquid separation flow in both the wide and narrow channels, the critical heat flux and flow stability of the evaporative cooler are improved. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a three-dimensional structural schematic diagram of a preferred embodiment of the microchannel evaporative cooler of the present invention; Figure 2 yes Figure 1 A cross-sectional view of a microchannel evaporative cooler; Figure 3 yes Figure 1 Schematic diagram of bubble breakup and gas-liquid separation principle in a microchannel evaporative cooler.

[0021] in, Figures 1-3 : 1. Evaporative cooler body; 11. Top plate; 111. Fluid inlet; 112. Fluid outlet; 12. Floor; 13. Side plate; 14. Hollow inner cavity; 141. Inlet collection chamber; 142. Uniform microchannel; 143. First bubble splitter mixer; 144. First non-uniform microchannel; 1441. Wide channel; 1442. Narrow channel; 145. Second bubble splitter mixer; 146. Second non-uniform microchannel; 147. Outlet collection chamber; 2. Large bubbles; 3. Small bubbles; 4. Circular flow. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0023] As described in the background section, slug flow in the prior art is unstable, with significant pressure and temperature fluctuations. In industrial applications, shortening the formation and existence time of slug flow is the key to improving the heat exchange capacity of evaporative coolers.

[0024] Based on this, the present invention provides a microchannel evaporative cooler. In this invention, the fluid enters a uniform microchannel through the fluid inlet and undergoes a gas-liquid phase change upon heating. At the outlet of the uniform microchannel, a bubble splitter mixes large bubbles into smaller bubbles, enhancing the two-phase flow effect. Due to the interface effect of the non-uniform microchannel, the two-phase mixture generated by the bubble splitter mixes bubbles at the inlet of the non-uniform microchannel, forming a flow structure in the narrow channel dominated by small bubbles and liquid phase, and in the wide channel dominated by large bubbles and gas phase flow. Small bubbles grow and new bubbles nucleate in the narrow channel, while large bubbles merge and rapidly pass through a slug flow to an annular flow in the wide channel. By enhancing the two-phase flow through gas-liquid splitting and achieving gas-liquid separation flow in both the wide and narrow channels, the critical heat flux and flow stability of the evaporative cooler are improved.

[0025] The following is a specific example. Figure 1-3 The technical solution of a preferred embodiment of the microchannel evaporative cooler of the present invention is described in detail.

[0026] The microchannel evaporative cooler in this embodiment is preferably a microchannel evaporative cooler that combines periodic gas-liquid separation mixing with separate flow heat exchange, such as... Figure 1 and Figure 2 As shown, this type of microchannel evaporative cooler includes an evaporative cooler body 1. The evaporative cooler body 1 is preferably a cubic structure, but it is not limited to a cubic structure. It can also be other structures, such as a columnar structure. As long as it has a hollow inner cavity 14 inside, a fluid inlet 111 and a fluid outlet 112 on the surface, and the fluid inlet 111 and the fluid outlet 112 are simultaneously connected to the hollow inner cavity 14, it is within the protection scope of this invention.

[0027] In detail, the evaporative cooler body 1 of this embodiment is specifically composed of a bottom plate 12, a side plate 13 and a top plate 11. The bottom plate 12 and the top plate 11 are arranged opposite to each other, and the side plate 13 is located between the top plate 11 and the bottom plate 12, so that a hollow inner cavity 14 can be formed. The fluid inlet 111 and the fluid outlet 112 are placed on the top plate 11. The fluid inlet 111 is close to one end of the top plate 11, while the fluid outlet 112 is close to the other end of the top plate 11.

[0028] In this embodiment, the hollow inner cavity 14 has an inlet liquid collection cavity 141, a uniform microchannel 142, a bubble splitter mixer, a non-uniform microchannel 142 and an outlet liquid collection cavity 147 in sequence from one side to the opposite side, wherein the bubble splitter mixer and the non-uniform microchannel 142 are arranged at intervals in the fluid flow direction.

[0029] Specifically, the bubble splitter mixer of this embodiment preferably includes a first bubble splitter mixer 143 and a second bubble splitter mixer 145. The non-uniform microchannel 142 of this embodiment preferably includes a first non-uniform microchannel 144 and a second non-uniform microchannel 146. The first bubble splitter mixer 143 is located between the uniform microchannel 142 and the first non-uniform microchannel 144, and the second bubble splitter mixer 145 is located between the first non-uniform microchannel 144 and the second non-uniform microchannel 146.

[0030] like Figure 2 As shown, the hollow cavity is arranged from one side to the other with an inlet collection chamber 141, a uniform microchannel 142, a first bubble splitter mixer 143, a first non-uniform microchannel 144, a second bubble splitter mixer 145, a second non-uniform microchannel 146, and an outlet collection chamber 147. The inlet collection chamber 141 is connected to the fluid inlet 111 and the uniform microchannel 142, and the outlet collection chamber 147 is connected to the fluid outlet 112 and the second non-uniform microchannel 146.

[0031] Continue as Figure 2 As shown, in this embodiment, each row of uniform microchannels 142, the first non-uniform microchannel 144, and the second non-uniform microchannel 146 contains multiple parallel microchannels with smooth sidewall surfaces. The microchannels have rounded corners on both sides along the width direction. The difference is that the equivalent diameters of the microchannels constituting the uniform microchannel 142 are all equal. The microchannels constituting the first non-uniform microchannel 144 and the second non-uniform microchannel 146 are arranged alternately in the fluid flow direction by narrow channels 1442 and wide channels 1441. The equivalent diameter of the wide channel 1441 is more than three times that of the narrow channel 1442.

[0032] Continue as Figure 2 As shown, the first bubble splitter mixer 143 or the second bubble splitter mixer 145 consists of at least two rows of staggered wedge-shaped splitting columns arranged in an alternating periodic array between the two rows of microchannels. This enhances the bubble breaking effect and allows large bubbles 2 to be split into small bubbles 3 at the sharp leading edge of the wedge-shaped splitting columns, thereby strengthening the two-phase convection effect and forming a two-phase mixture.

[0033] The specific process is as follows: Fluid forms bubbles of varying sizes at the outlet of the uniform microchannel 142. These bubbles enter the first bubble splitter mixer 143 or the second bubble splitter mixer 145 with the fluid. Large bubbles 2 are split into smaller bubbles 3 at the sharp leading edge of the wedge-shaped splitting columns. The staggered arrangement of the wedge-shaped splitting columns enhances the two-phase flow effect. The two-phase mixture flowing out from the first bubble splitter mixer 143 or the second bubble splitter mixer 145 flows into the first non-uniform microchannel 144 or the second non-uniform microchannel 146. At the inlet of the first non-uniform microchannel 144 or the second non-uniform microchannel 146, the... Due to the interfacial effect of the microchannel, the interfacial tension of the wide channel 1441 is smaller than that of the narrow channel 1442. Bubbles are screened at the inlet of the first non-uniform microchannel 144 or the second non-uniform microchannel 146, which better achieves gas-liquid separation flow. Since the narrow channel 1442 of the first non-uniform microchannel 144 or the second non-uniform microchannel 146 has a filtering effect on the large bubbles 2, most of the large bubbles 2 tend to enter the wide channel 1441, forming a flow structure in which the wide channel 1441 is dominated by large bubbles 2 and gas phase flow, and the narrow channel 1442 is dominated by small bubbles 3 and liquid phase flow.

[0034] Interfacial tension is a physical quantity that measures the magnitude of the interfacial force between two different substances. Here, it refers to the interfacial tension between a liquid and air. The formula for interfacial tension is:

[0035] pv is the gas phase pressure, pl is the liquid phase pressure, σ is the interfacial tension, and r is the channel radius.

[0036] Because the narrow channel 1442 in the first non-uniform microchannel 144 or the second non-uniform microchannel 146 of this embodiment has a filtering effect on the large bubbles 2, most of the large bubbles 2 tend to enter the wide channel 1441, forming a flow structure in which the wide channel 1441 is dominated by large bubbles 2 and gas phase flow, and the narrow channel 1442 is dominated by small bubbles 3 and liquid phase flow; due to the interface effect at the inlet of the first non-uniform microchannel 144 or the second non-uniform microchannel 146, most of the gas phase enters the wide channel 1441, which has a higher gas content in its cross section, making it easier to flow in the wide channel 1441. Within channel 1441, a heat transfer mode dominated by annular flow 4, known as "thin liquid film convection evaporation," is formed. In narrow channel 1442, the growth of small bubbles 3 and the nucleation process of new bubbles, dominated by "nucleation boiling," occur. This simultaneous existence of two highly efficient heat transfer modes—thin liquid film convection evaporation and nucleation boiling—in both wide channel 1441 and narrow channel 1442 perpendicular to the flow direction significantly improves heat transfer performance, reduces flow and heat transfer instabilities caused by slug flow in traditional microchannels, and features a simple structure, low cost, broad applicability, and wide application prospects.

[0037] In the description of this invention, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," "tail," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0039] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A microchannel evaporative cooler, comprising an evaporative cooler body, the evaporative cooler body having a hollow inner cavity, the evaporative cooler body further having a fluid inlet and a fluid outlet, the fluid inlet and the fluid outlet communicating with the hollow inner cavity, characterized in that, The hollow inner cavity is provided with uniform microchannels, bubble dividers and mixers and non-uniform microchannels, and the bubble dividers and mixers and the non-uniform microchannels are arranged at intervals in the fluid flow direction. The non-uniform microchannels are arranged with narrow channels and wide channels alternately in the vertical flow direction, and the equivalent diameter of the wide channel is more than 3 times the equivalent diameter of the narrow channel. The bubble splitter mixer consists of at least two rows of staggered wedge-shaped splitting columns; The fluid forms bubbles of varying sizes at the outlet of the uniform microchannel. The bubbles enter the bubble splitter mixer with the fluid. Large bubbles are split into smaller bubbles at the sharp leading edge of the wedge-shaped splitting column. Bubble splitting increases the gas-liquid contact area while keeping the gas phase volume constant. The staggered arrangement of the wedge-shaped splitting columns enhances the two-phase revelocity effect. The two-phase mixture flowing out of the bubble splitter flows into the non-uniform microchannel. At the inlet of the non-uniform microchannel, due to the different capillary pressure differences at the gas-liquid interface at the inlet of the wide channel and the narrow channel, the capillary pressure difference that vapor needs to overcome to enter the wide channel is smaller, and the gas-liquid interface is more inclined to enter the wide channel. The capillary pressure difference at the gas-liquid interface can be expressed as: p v p is the gas phase pressure. l Let σ be the liquid phase pressure, σ be the interfacial tension, and r be the channel radius. The larger r is, the smaller the capillary pressure difference and the smaller the resistance to the movement of the gas-liquid interface. The narrow channel of the non-uniform microchannel has a filtering effect on large bubbles, and most of the large bubbles enter the wide channel, forming a flow structure in which the wide channel is dominated by large bubbles and gas phase flow, and the narrow channel is dominated by small bubbles and liquid phase flow.

2. The microchannel evaporative cooler according to claim 1, characterized in that, The bubble splitter mixer includes a first bubble splitter mixer and a second bubble splitter mixer. The non-uniform microchannel includes a first non-uniform microchannel and a second non-uniform microchannel. The first bubble splitter mixer is located between the uniform microchannel and the first non-uniform microchannel, and the second bubble splitter mixer is located between the first non-uniform microchannel and the second non-uniform microchannel.

3. The microchannel evaporative cooler according to claim 2, characterized in that, The hollow inner cavity is also provided with an inlet liquid collection chamber, which is connected to the fluid inlet and the uniform microchannel; The hollow inner cavity is also provided with an outlet liquid collection chamber, which is connected to the fluid outlet and the second non-uniform microchannel.

4. The microchannel evaporative cooler according to claim 1, characterized in that, The equivalent diameter of each microchannel in the fluid flow direction is equal.

5. A method for enhancing microchannel evaporative cooling, characterized in that, Based on the microchannel evaporative cooler according to any one of claims 1-4, the method comprises: The microchannel evaporative cooler is configured with an inlet collection chamber, a uniform microchannel, a bubble-splitting mixer, a non-uniform microchannel, and an outlet collection chamber in sequence. The cooling medium enters the uniform microchannel from the collection chamber at the inlet of the microchannel, where a gas-liquid phase change occurs. In the bubble-splitting mixer, large bubbles are split into smaller bubbles at the sharp leading edges of the wedge-shaped dividing columns. Bubble splitting increases the gas-liquid contact area while maintaining the same gas volume. The staggered arrangement of the wedge-shaped dividing columns enhances the two-way convective effect. Due to the different capillary pressure differences at the gas-liquid interface at the inlets of the wide and narrow channels... The capillary pressure difference that steam needs to overcome to enter the wide channel is small, and the gas-liquid interface tends to enter the wide channel. Its cross-sectional gas content is higher, which makes it easier to form a thin liquid film convection evaporation heat transfer mode dominated by annular flow in the wide channel. In the narrow channel, the growth of small bubbles and the nucleation process of new bubbles mainly occur. This efficient heat transfer mode of thin liquid film convection evaporation and nucleation boiling that coexist in the wide and narrow channels perpendicular to the flow direction significantly improves the heat transfer performance and reduces the flow and heat transfer instability caused by slug flow in traditional microchannels.

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