Micro-channel heat exchanger

Abstract

The microchannel heat exchanger comprises a heat exchange shell and a plurality of protruding elements, a plurality of parallel fluid channels are formed in the heat exchange shell in a penetrating mode, the fluid channels are linear, and the inner bottom wall of each fluid channel is fixedly provided with the multiple protruding elements at intervals; the multiple protruding elements are arranged in the fluid channels, the multiple protruding elements in every two adjacent fluid channels are symmetrically arranged in a pairwise mode, a circulation gap exists between each protruding element and the two opposite side walls of the corresponding fluid channel, each protruding element is internally provided with an X-shaped crossed split seam, the X-shaped crossed split seams are communicated with the two circulation gaps, and when fluid enters the fluid channels through the fluid inlets, the X-shaped crossed split seams are communicated with the two circulation gaps. Each protruding element can guide fluid to flow in the direction of the fluid outlet through the two circulation gaps and the X-shaped crossed split seams in a split flow mode. The problems that in the prior art, a traditional straight micro-channel heat exchanger is insufficient in cold and hot fluid mixing, poor in heat dissipation capacity, large in wall surface temperature difference and large in local hot spot are solved.

Description

Technical Field

[0001] The invention relates to the technical field of heat exchangers, and in particular to a microchannel heat exchanger. Background Art

[0002] Microchannel Heat Exchangers are highly efficient and compact heat exchange devices with very small flow channel sizes, usually between tens to hundreds of microns. These devices are widely used in many industries due to their high efficiency, compactness and light weight, such as aerospace, automotive, electronic cooling and other applications that require efficient heat management.

[0003] With the influence of high heat flux density brought by the high integration of electronic devices, the traditional air-cooled heat exchange method has great limitations, while the microchannel heat exchanger with high efficiency heat exchange has broad application prospects. The existing microchannel generally adopts a straight channel structure. In the straight channel, due to the thick boundary layer in the flow direction, there are problems such as insufficient mixing of cold and hot fluids, poor heat dissipation capacity, large wall temperature difference, and local hot spots. Therefore, it is very necessary to carry out work on the structural design of microchannels and microchannel preparation methods. At the same time, it is also very necessary to use the enhanced heat transfer mechanism to explore the flow and heat transfer performance of new microchannel heat exchangers. Based on this, a new microchannel structure is designed and its structure is optimized to meet the high heat dissipation requirements under different environments. Summary of the invention

[0004] The purpose of the present invention is to overcome the above technical deficiencies and provide a microchannel heat exchanger to solve the problems of insufficient mixing of cold and hot fluids, poor heat dissipation capacity, large wall temperature difference and local hot spots in traditional straight microchannel heat exchangers in the prior art.

[0005] In order to achieve the above technical objectives, the present invention adopts the following technical solutions: The present invention provides a microchannel heat exchanger, comprising a heat exchange shell and a plurality of protruding elements, wherein the heat exchange shell is provided with a plurality of fluid channels parallel to each other, and the plurality of fluid channels are all in a straight line shape, the inner bottom wall of each of the fluid channels is provided with a plurality of protruding elements at intervals, and the plurality of protruding elements in two adjacent fluid channels are symmetrically arranged in pairs, and there is a flow gap between each of the protruding elements and the opposite side walls of the fluid channel, each of the protruding elements is provided with an X-shaped cross slit, and the X-shaped cross slit is connected with the two flow gaps, and when the fluid enters the fluid channel through the fluid inlet, each of the protruding elements can guide the fluid to flow toward the fluid outlet through the two flow gaps and the X-shaped cross slit.

[0006] In one embodiment, the heat exchange shell includes a base plate and a cover plate, a plurality of mutually parallel grooves are provided in the base plate, and the cover plate is fixedly connected to the base plate to close the plurality of grooves to form a fluid channel.

[0007] In one embodiment, the protruding element is in a teardrop shape as a whole, and includes a round head and a pointed tail, wherein the round head faces the direction of the fluid inlet and the pointed tail faces the direction of the fluid outlet.

[0008] In one embodiment, the thicknesses of the plurality of protruding elements in the fluid channel and along the fluid flow direction are arranged to decrease gradually.

[0009] In one embodiment, the thicknesses of two adjacent protrusion elements in the fluid channel are arranged in a high and low pattern.

[0010] In one embodiment, the thicknesses of the plurality of protruding elements in the fluid channel and along the fluid flow direction are symmetrically arranged to first increase and then decrease.

[0011] In one embodiment, the maximum lateral width of the protruding elements is 1.8 mm, the width of the X-shaped cross slits is 0.2 mm, the minimum width of the flow gap is 0.22 mm, and the distance between adjacent protruding elements is 5.5 mm.

[0012] In one embodiment, the protruding element is in a rhombus shape as a whole, and two opposite vertex angles of the protruding element correspond to the fluid inlet and the fluid outlet respectively.

[0013] In one embodiment, the protruding element is in a triangular shape as a whole, and a vertex angle of the protruding element corresponds to the fluid inlet.

[0014] In one embodiment, the inner and outer surfaces of the heat exchange shell and the surfaces of the plurality of protruding elements are coated with a nanocomposite coating.

[0015] Compared with the prior art, the present invention provides a microchannel heat exchanger, in which a plurality of protrusion elements are fixedly provided at intervals through the inner bottom wall of the fluid channel, and the plurality of protrusion elements in two adjacent fluid channels are symmetrically arranged in pairs, and there is a flow gap between each protrusion element and the opposite side walls of the fluid channel, and an X-shaped cross slit is opened in each protrusion element, and the X-shaped cross slit is connected with the two flow gaps. When the fluid enters the fluid channel through the fluid inlet, each protrusion element can guide the fluid to flow toward the fluid outlet through the two flow gaps and the X-shaped cross slit, which can effectively divert the fluid and generate "vortex phenomenon" and "secondary flow phenomenon", destroying the temperature boundary layer and the fluid boundary layer of the fluid, thereby improving the flow disturbance ability of the fluid and improving the heat dissipation capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is an exploded schematic diagram of a microchannel heat exchanger provided by an embodiment of the present invention; Figure 2 is a structural schematic diagram of a microchannel heat exchanger provided by an embodiment of the present invention; Figure 3 is a schematic diagram of the internal structure of a microchannel heat exchanger provided by an embodiment of the present invention; Figure 4 It is a schematic structural diagram of a bionic water droplet cross-slit type protruding element provided by an embodiment of the present invention; Figure 5 is a schematic structural diagram of a diamond-shaped cross-slit type protruding element provided in an embodiment of the present invention; Figure 6 is a schematic structural diagram of a triangular cross-slit type protruding element provided by an embodiment of the present invention; Figure 7 It is a temperature cloud diagram of a comparative experiment of a bionic water drop cross-slit type, a diamond cross-slit type and a triangle cross-slit type microchannel heat exchanger provided in an embodiment of the present invention; Figure 8 It is a comparative local streamline diagram of the diamond cross-slit type, triangle cross-slit type and bionic water drop cross-slit type microchannel heat exchangers provided in the embodiments of the present invention; Fig. 9 It is a Nusselt number comparison experiment diagram of the bionic water drop cross-slit type, diamond cross-slit type and triangle cross-slit type microchannel heat exchangers provided in the embodiment of the present invention; Fig.10 It is a comparative experimental diagram of comprehensive performance evaluation factors of microchannel heat exchangers with bionic water droplet cross slits, diamond cross slits and triangle cross slits provided in an embodiment of the present invention; Fig.11 The embodiments of the present invention provide a gradient decreasing type, a first increasing and then decreasing type, and a high and low alternating type. A schematic diagram of the structure of the fluid channel; Fig.12 It is a temperature cloud diagram of the control experiment of the gradient decreasing type, the increasing type and then decreasing type, and the high and low alternating type distribution of the bionic water drop cross-slit structure provided by the embodiment of the present invention; Fig.13 It is a comparative local streamline diagram of the bionic water drop cross-slit structure provided by the embodiment of the present invention in the distribution of increasing first and then decreasing, high and low alternating and gradient decreasing types; Fig.14 It is a Nusselt number comparison experiment diagram of the gradient decreasing type, the increasing type then decreasing type and the high and low alternating type distribution of the bionic water drop cross-slit structure provided by the embodiment of the present invention; Fig.15It is a comparative experimental diagram of comprehensive performance evaluation factors of the gradient decreasing type, the increasing first and then decreasing type, and the high and low alternating type distribution of the bionic water droplet cross-slit structure provided by the embodiment of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] In order to solve the technical problems of insufficient mixing of cold and hot fluids, poor heat dissipation capacity, large wall temperature difference and local hot spots in traditional straight microchannel heat exchangers in the prior art, the present invention provides a microchannel heat exchanger that can separate the fluid, cause the fluid to produce "eddy flow phenomenon" and "secondary flow phenomenon", and improve the heat exchange efficiency.

[0019] See also Figure 1-Figure 6 , Figure 1-Figure 6 A microchannel heat exchanger in one embodiment of the present invention comprises a heat exchange shell 1 and a plurality of protruding elements 2, wherein the heat exchange shell 1 is provided with a plurality of fluid channels 10 parallel to each other, and the plurality of fluid channels 10 are all in a straight line shape, the inner bottom wall of each fluid channel 10 is fixedly provided with a plurality of protruding elements 2 at intervals, and the plurality of protruding elements 2 in two adjacent fluid channels 10 are symmetrically arranged in pairs, and there is a flow gap 2a between each protruding element 2 and the opposite side walls of the fluid channel 10, each protruding element 2 is provided with an X-shaped cross slit 2b, and the X-shaped cross slit 2b is connected with the two flow gaps 2a, and when the fluid enters the fluid channel 10 through the fluid inlet, each protruding element 2 can guide the fluid to flow through the two flow gaps 2a and the X-shaped cross slit 2b to flow toward the fluid outlet.

[0020] In this specific embodiment, the heat exchange shell 1 includes a base plate 11 and a cover plate 12. The base plate 11 is provided with a plurality of grooves parallel to each other. The cover plate 12 is fixedly connected to the base plate 11 to close the plurality of grooves to form a fluid channel 10. The heat exchange shell 1 is made of an aluminum alloy plate. Of course, in other embodiments, the heat exchange shell 1 can also be made of a copper plate or a stainless steel plate.

[0021] In one embodiment, the protruding element 2 is in the shape of a water drop as a whole, and the protruding element 2 is a bionic water drop cross-slit structure. The protruding element 2 includes a round head 21 and a pointed tail 22, and the round head 21 faces the direction of the fluid inlet, and the pointed tail 22 faces the direction of the fluid outlet.

[0022] It should be noted that when the fluid (cooling medium) enters the fluid channel through the fluid inlet, the flow gap 2a formed between the protruding element 2 and the opposite side walls of the fluid channel 10, and the X-shaped cross slit 2b can effectively divert the fluid and generate "eddy flow phenomenon" and "secondary flow phenomenon", which greatly improves the turbulence effect and thus improves the heat dissipation efficiency of the heat exchanger.

[0023] Specifically, Figure 4 As shown, the maximum transverse width L1 of the protruding element is 1.8 mm, the width L2 of the X-shaped cross slit is 0.2 mm, the minimum width L3 of the flow gap 2a is 0.22 mm, and the distance L4 between adjacent protruding elements is 5.5 mm.

[0024] On the basis of the above solution, in order to further enhance the flow disturbance effect, specifically, the thickness of the plurality of protruding elements 2 in the fluid channel 10 and along the fluid flow direction is set to decrease. That is, by improving the arrangement of the plurality of protruding elements 2 in the fluid channel 10, the heights of the plurality of protruding elements 2 are set to decrease in sequence from the fluid inlet to the fluid outlet, thereby enhancing the flow disturbance effect of the fluid and further improving the heat dissipation performance.

[0025] In one embodiment, the thicknesses of two adjacent protruding elements 2 in the fluid channel may be arranged in a high and low pattern. In other embodiments, the thicknesses of a plurality of protruding elements 2 in the fluid channel and along the fluid flow direction are arranged symmetrically, first increasing and then decreasing.

[0026] Among them, the thickness of multiple protruding elements 2 is 0.3-0.5mm. In this specific embodiment, the thickness of the first protruding element 2 contacting the fluid inlet of the fluid channel model of gradient decreasing type A is 0.5mm, and then the thickness of the protruding element 2 decreases by 0.02mm until the thickness of the last protruding element 2 at the fluid outlet is 0.3mm; for the fluid channel model of high and low alternating type B, the thickness of the first protruding element 2 relative to the fluid inlet is 0.5mm, and the thickness of the adjacent second protruding element 2 is 0.3mm, and then this form is repeated periodically, and the overall structure presents a high and low alternating arrangement; the thickness of the first protruding element 2 at the fluid inlet of the fluid channel model of increasing first and then decreasing type C is 0.3mm, which increases to 0.5mm with a gradient of 0.04mm, and then gradually decreases to the fluid outlet with a protruding thickness of 0.5mm at the same gradient, and the thickness of the last protruding element 2 is 0.3mm. from Fig.12It can be seen that in each group of microchannel models, the arrangement of increasing first and then decreasing reaches the high temperature zone faster, but its high temperature area is the smallest, while the high temperature area of ​​the gradient decreasing type is the largest. At the same time, it can be found that the high temperature area of ​​the high and low alternating type is not much different from that of the gradient decreasing type. Further, by observing the fluid inlet stage, it can be found that the gradient decreasing type arrangement can enter the higher temperature area faster than the high and low alternating type, indicating that among these different arrangements, the gradient decreasing type arrangement has more violent disturbances and better heat transfer effect.

[0027] The comparative local streamline diagrams of the bionic water drop cross-slit structure provided by the embodiment of the present invention are the first increasing and then decreasing type, the high and low alternating type and the gradient decreasing type. Fig.13 It can be seen that vortices of different sizes are generated inside the fluid channels with different arrangements. The generation of vortices further strengthens the disturbance of the secondary flow and enhances the heat exchange. It is worth noting that in front of the protruding element 2, the gradient decreasing model has symmetrical and larger vortices, while the first increasing and then decreasing and high and low alternating models have larger vortices in front, but the shapes are small and asymmetrical; at the end part of the protruding element 2, the first increasing and then decreasing and gradient decreasing models produce an obvious pair of vortices. The main reason for this is that the fluid in the fluid channel changes with the protruding element 2, and its flow form also produces corresponding regular movements. Among them, the gradient decreasing arrangement plays a good role in guiding the fluid flow, and although the high and low alternating arrangement also causes periodic changes in the flow, it is not conducive to the formation of vortices, and there are more disordered disturbances.

[0028] In another embodiment, if Figure 5 As shown, the protruding element 2 is in a rhombus shape as a whole, and two opposite vertex angles of the protruding element 2 correspond to the fluid inlet and the fluid outlet respectively, that is, the protruding element 2 is a rhombus cross-slit structure.

[0029] In other embodiments, Figure 6 As shown, the protruding element 2 is in a triangular shape as a whole, and a vertex of the protruding element 2 corresponds to the fluid inlet, that is, the protruding element 2 is a triangular cross-slit structure.

[0030] Specifically, see Figure 7As shown, the experimental temperature cloud diagrams of the microchannel heat exchangers of the bionic water droplet cross-slit type, diamond cross-slit type and triangle cross-slit type structures provided by the embodiments of the present invention, the present invention conducts a comparative experiment through the fluid to test the heat exchange performance of the bionic water droplet cross-slit type microchannel heat exchanger, the fluid flows from the fluid inlet to the fluid outlet, and the color of the temperature cloud diagram on the top surface during the process reflects the violent disturbance of the fluid in the microchannel and the uniformity of the temperature distribution, the uniformity of the temperature distribution of the bionic water droplet cross-slit type microchannel heat exchanger is better than that of the other two groups of models, the fluid temperature at the fluid inlet is relatively low as the flow proceeds, the fluid temperature gradually increases, and finally the temperature at the fluid outlet reaches a high temperature and then flows out, it can be seen from the top surface temperature cloud diagram that the temperature change span is not large, the temperature change fluctuation is small, and the uniformity of the fluid flow is good.

[0031] Further, please refer to Figure 8. From the comparative local streamline diagrams of the microchannel heat exchangers of the diamond cross-slit type, triangle cross-slit type and bionic water drop cross-slit type provided in the embodiments of the present invention, it can be seen that the front end of the bionic water drop cross-slit type structure produces a violent collision with the incoming flow direction, and a large vortex is generated in front of the structure. The generation of the vortex causes the fluid boundary layer to be continuously and effectively destroyed, thereby enhancing the heat exchange. Although small vortices of different sizes are generated inside the three X-shaped cross-slits and are beneficial to the enhanced heat exchange of the secondary flow, the tail of the bionic water drop cross-slit type structure has a better curve, and the pointed tail 22 has a protrusion like a small tail. This structure enables the secondary flow to effectively converge into the mainstream and the fluid is not easy to be turbulent, thereby reducing the kinetic energy loss of the fluid.

[0032] Specifically, at the fluid inlet (x=0), the inlet fluid material is liquid water, and the constant temperature of the fluid at the inlet is T in =293K, constant speed is u in =0.4m / s (corresponding to an inlet Reynolds number of 368); at the fluid outlet (x = 60mm), the relative outlet pressure is set to P out =0; the bottom surface is set as a constant heat source with a temperature of T=385K; at the interface where the fluid contacts the solid, the boundary conditions of the solid-liquid interface are applied, while the top surface and the remaining walls of the fluid channel are set as adiabatic conditions, and the symmetry conditions are used on both sides of the boundary. The numerical solution uses a high-precision solver. When the residual error of the solution is reduced to 10 -6 When the value is below , it is considered that the numerical stability has been reached. Finally, the heat exchange efficiency of the heat exchanger is measured by evaluating the Nusselt number and the overall performance index.

[0033] Furthermore, the heat transfer effect of the heat exchanger is further improved by arranging the protruding elements of the cross-slits of the bionic water droplets in a gradient decreasing manner in the microchannel.

[0034] See also Fig.12 The temperature cloud diagram of the control experiments of the bionic water droplet cross-slit structure with gradient decreasing, increasing first and then decreasing, and high and low alternating distribution provided by the embodiment of the present invention shows that by observing the fluid inlet stage, it can be found that the gradient decreasing arrangement can enter the higher temperature area faster than the high and low alternating arrangement. At the same time, the high temperature area of ​​the gradient decreasing arrangement is the largest, indicating that among these different arrangements, the gradient decreasing arrangement has more intense disturbance and better heat transfer effect.

[0035] In addition, since the surface of the microchannel heat exchanger is also prone to dirt accumulation, this not only greatly reduces the efficiency of heat transfer, but also increases the workload and complexity of equipment cleaning and maintenance. Under high-speed flow and high-temperature operating conditions, the wear resistance of the materials used in the heat exchanger becomes extremely critical, and traditional materials are often unable to meet the durability requirements. Therefore, the use of coating technology to treat the surface of the heat exchanger can not only improve its corrosion resistance, but also ensure that it continues to maintain efficient heat transfer performance.

[0036] Furthermore, a high heat transfer nanocomposite coating is applied to the outer surface of the heat exchange shell 1, the inner surface of the fluid channel 10, and the surface of the bionic water droplet cross-slit protrusion element. In this specific embodiment, a coating method for the nanocomposite coating is also included: S1: At room temperature, 5 g of epoxy resin was preheated to 40° C., and then 1 g of nano-silicon dioxide, 0.5 g of carbon nanotubes, 0.5 g of graphene, 10 ml of ethyl acetate and 1 g of curing agent were added, and magnetic stirring was performed for 30 minutes until the mixture was uniformly mixed to obtain a first coating; S2: 2 g of nano-titanium dioxide, 1 g of fluorinated graphene, 10 ml of ethyl acetate, and 1 g of methyltrichlorosilane were mixed and ultrasonically stirred, and then 0.5 g of multi-walled carbon nanotubes and 0.5 g of 1H,1H,2H,2H-perfluorodecyltriethoxysilane were added, and magnetic stirring was performed for 30 minutes until the mixture was uniform, thereby obtaining a second coating; S3: Then, cleaning and pretreatment are performed. The sealed microchannel heat exchanger is placed in an ultrasonic cleaning tank using a neutral cleaning agent, the temperature is controlled at 45°C, and ultrasonic cleaning is performed for 30 minutes. After cleaning, it is rinsed with deionized water to ensure that there is no residual cleaning agent, and then dried naturally and then dried; S4: Spray the first coating and the second coating on the inner and outer walls of the microchannel heat exchanger in sequence. Use an airless spray device to spray the first coating on the inner and outer walls of the microchannel heat exchanger in sequence, and cure each layer in an oven at 70°C for 1 hour after coating. Under a vacuum environment, use a magnetron sputtering device to spray the second coating on the inner and outer walls of the microchannel heat exchanger in sequence, and cure each layer in an oven at 70°C for 30 minutes after sputtering.

[0037] Specifically, the introduction of nano-silicon dioxide and cyclopentane resin improves the anti-corrosion and heat transfer performance of the coating; the addition of fluorinated graphene and nano-titanium dioxide gives the coating excellent hydrophobic self-cleaning performance. The two-layer structure design not only improves the corrosion resistance of the coating, but also takes into account the heat transfer performance and self-cleaning function, adapting to the application requirements in different environments. The microchannel surface is coated by integrating the use of airless spraying and magnetron sputtering processes. This significantly improves the uniformity of the high heat transfer anti-corrosion coating on the inner wall of the new microchannel heat exchanger, effectively avoiding the occurrence of coating accumulation or material shortage, thereby greatly extending the overall service life of the heat exchanger.

[0038] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A microchannel heat exchanger, characterized in that: It comprises a heat exchange shell and a plurality of protruding elements, wherein a plurality of fluid channels parallel to each other are provided through the heat exchange shell, and the plurality of fluid channels are all in a straight line shape, a plurality of protruding elements are fixedly provided at intervals on the inner bottom wall of each fluid channel, and the plurality of protruding elements in two adjacent fluid channels are symmetrically arranged in pairs, a flow gap exists between each protruding element and the opposite side walls of the fluid channel, an X-shaped cross slit is provided in each protruding element, and the X-shaped cross slit is connected with the two flow gaps, and when the fluid enters the fluid channel through the fluid inlet, each protruding element can guide the fluid to flow toward the fluid outlet through the two flow gaps and the X-shaped cross slit.

2. The microchannel heat exchanger according to claim 1, characterized in that: The heat exchange shell comprises a base plate and a cover plate. A plurality of grooves parallel to each other are provided in the base plate. The cover plate is fixedly connected to the base plate to close the plurality of grooves to form a fluid channel.

3. The microchannel heat exchanger according to claim 1, characterized in that: The protruding element is in a teardrop shape as a whole, and comprises a round head and a pointed tail, wherein the round head faces the direction of the fluid inlet, and the pointed tail faces the direction of the fluid outlet.

4. The microchannel heat exchanger according to claim 1, characterized in that: The thicknesses of the plurality of protruding elements in the fluid channel and along the fluid flow direction are arranged to decrease gradually.

5. The microchannel heat exchanger according to claim 1, characterized in that: The thicknesses of two adjacent protruding elements in the fluid channel are arranged in a high and low pattern.

6. The microchannel heat exchanger according to claim 1, characterized in that: The thicknesses of the plurality of protruding elements in the fluid channel and along the fluid flow direction are symmetrically arranged to first increase and then decrease.

7. The microchannel heat exchanger according to claim 3, characterized in that: The maximum lateral width of the protruding element is 1.8 mm, the width of the X-shaped cross slit is 0.2 mm, the minimum width of the flow gap is 0.22 mm, and the distance between adjacent protruding elements is 5.5 mm.

8. The microchannel heat exchanger according to claim 1, characterized in that: The protruding element is in a rhombus shape as a whole, and two opposite vertex angles of the protruding element correspond to the fluid inlet and the fluid outlet respectively.

9. The microchannel heat exchanger according to claim 1, characterized in that: The protruding element is in a triangular shape as a whole, and a vertex of the protruding element corresponds to the fluid inlet.

10. The microchannel heat exchanger according to claim 1, characterized in that: The inner and outer surfaces of the heat exchange shell and the surfaces of the plurality of protruding elements are coated with a nano-composite coating.

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