A wavy curve microchannel and precooler

Abstract

The present invention belongs to the field of heat transfer channels for precoolers, and specifically relates to a wavy curved microchannel, wherein the microchannel includes a plurality of variable-amplitude peak-valley structures, and the cross-sectional configuration of the microchannel satisfies the configuration equation in a polar coordinate system. The microchannel provided by the present invention presents a curved channel structure as a whole, which can reduce the thickness of the thermal boundary layer, enhance the flow mixing effect of the wall and mainstream areas, and improve the heat transfer performance compared to conventional straight channels. At the same time, a variable-amplitude peak-valley structure is superimposed on the basis of the overall curved channel configuration. On the one hand, it avoids the problem that conventional curved channels are prone to the problem that the curvature gradually decreases with the flow direction, and on the other hand, it avoids the problem that equal-amplitude peak-valley structures are prone to interference at the axis of the microchannel. Finally, a microchannel configuration with good flow mixing effect and strong heat transfer capacity is obtained.

Description

Technical Field

[0001] The invention belongs to the field of heat transfer channels of precoolers, and in particular relates to a wavy curve microchannel and a precooler. Background Art

[0002] The precooler is the core component of the precooled combined cycle engine, and the need to enhance heat exchange is one of the biggest challenges in the structural design of the precooler. At present, the heat transfer capacity of conventional-scale channels can no longer meet the heat transfer requirements of the heat transfer channels in the precooler. Tuckerman and Pease were the first to use microchannels with water as a coolant to study the heat transfer of electronic circuits, demonstrating that microchannels have extremely high heat transfer capabilities. REL conducted experiments on the heat transfer unit JMHX (SABRE precooler capability test module) composed of microchannels, verifying that the use of microchannels in the structural design of the precooler can greatly improve the surface area to volume ratio and heat transfer capacity, revealing the application prospects of microchannels in the design of small, lightweight and efficient precoolers.

[0003] Traditional microchannel heat exchangers are generally straight channels with a single cross-section, such as rectangular, triangular, circular, or trapezoidal. Although they all have good heat transfer characteristics, they have some shortcomings: for example, the streamlines of the coolant in the channel are almost straight, resulting in uneven fluid mixing, and the thickening of the thermal boundary layer along the flow direction is likely to lead to deterioration of heat transfer. Studies have found that creating grooves in the microchannel, adding fins or ribs, adding porous media, and machining rough surfaces can interrupt and develop the thermal boundary layer, promote the generation of vortices and the mixing of fluids, and thus improve the heat transfer performance of the microchannel.

[0004] In order to further enhance heat transfer in microchannels, scholars have proposed a curved microchannel configuration scheme and found that compared with straight microchannels, curved channels often have larger heat transfer areas and higher heat transfer rates in a compact space. The study believes that the secondary flow caused by centrifugal force in the curved channel strengthens the flow mixing near the wall and in the mainstream area, thereby enhancing the heat transfer capacity. Based on the results of experiments and numerical simulations, Sui et al. explained in detail the reasons why the sinusoidal microchannel has good heat transfer performance. The curvature of the flow channel causes transverse vortices to be generated on the cross section perpendicular to the flow direction. These transverse vortices are called Dean vortices, and their size and number are closely related to the Reynolds number. It is also possible to change and grow into chaotic convection along the flow direction. Later, some scholars further proposed that the larger the amplitude of the sinusoidal curve, the better the heat transfer performance.

[0005] For curved microchannels, the introduction of centrifugal force causes the flow and thermal boundary layer to become thinner, achieving enhanced heat transfer. However, as the channel curvature decreases, the centrifugal force and secondary flow will weaken, resulting in a thicker thermal boundary layer and worsened heat transfer. In practical applications, a decrease in the curvature of curved channels is often inevitable. For example, in the most common spiral curved channel, the channel curvature gradually decreases with the mainstream direction, resulting in a significant weakening of the heat transfer capacity. Therefore, how to make good use of the heat transfer advantages of curved channels over straight channels while avoiding the weakening of secondary flow and thickening of the thermal boundary layer due to changes in curvature has become an important and promising issue in the design of curved microchannel configurations. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a wavy curve microchannel and a precooler which still have good heat transfer capability under the premise that the overall curvature of the curved channel decreases.

[0007] The present invention provides a wavy curve microchannel, wherein the microchannel includes a plurality of variable amplitude peak-valley structures, and the cross-sectional configuration of the microchannel satisfies the configuration equation in a polar coordinate system:

[0008]

[0009] Where R is the polar diameter of the wavy microchannel, and θ is the polar angle;

[0010] a and b are the parameters of the Archimedean spiral, i.e., the smooth curve channel equation without superimposed peak-valley structure, and both a and b are positive;

[0011] n is the number of variable amplitude peak-trough structures;

[0012] A is the maximum amplitude in the n peak-trough structures, and A is not equal to 0;

[0013] θ1 is 1 / 2 of the maximum polar angle.

[0014] Furthermore, the cross section of the microchannel is rectangular.

[0015] Furthermore, the cross section of the microchannel satisfies the channel cross section equation:

[0016]

[0017] Where, L in is the length of the rectangular channel, W in is the width of the rectangular channel, D h It represents the equivalent diameter of the channel, that is, the size of the rectangular channel.

[0018] Furthermore, the microchannel includes five peak-valley structures.

[0019] Furthermore, interfaces are provided at both ends of the microchannel.

[0020] Furthermore, the microchannel is integrally formed by 3D printing.

[0021] The present invention also provides a precooler comprising the above-mentioned wavy curve microchannel.

[0022] The beneficial effect of the present invention is that, based on a compact microchannel precooler, the present invention optimizes the design of a smooth curved microchannel in which the coolant flows, and adds a variable amplitude wavy structure to a rectangular equal-section channel of a certain hydraulic diameter to obtain a variable amplitude peak-trough structural configuration in which the amplitude changes with the polar angle.

[0023] The microchannel provided by the present invention exhibits an overall curved channel structure. Compared to conventional straight channels, it can reduce the thickness of the thermal boundary layer, enhance flow mixing between the wall and the mainstream region, and improve heat transfer performance. Furthermore, a variable-amplitude peak-trough structure is superimposed on the overall curved channel configuration. This avoids the drawback of conventional curved channels, where the curvature gradually decreases with the flow direction, and also avoids the interference problem of a constant-amplitude peak-trough structure at the microchannel axis. The result is a microchannel configuration with excellent flow mixing and strong heat transfer capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Attachment Figure 1 Schematic diagram of a smooth curved microchannel configuration in the prior art;

[0025] Attachment Figure 2 This is a schematic diagram of a wavy curve microchannel configuration according to an embodiment of the present invention;

[0026] Attachment Figure 3 for Figure 2 Schematic diagram of the longitudinal section at point A;

[0027] Attachment Figure 4 This is a schematic diagram of a second configuration of a wavy curve microchannel according to a second embodiment of the present invention;

[0028] Attachment Figure 5 Schematic diagram of three configurations of three wavy curve microchannels according to an embodiment of the present invention;

[0029] Attachment Figure 6 Schematic diagram of four configurations of four wavy curve microchannels according to an embodiment of the present invention;

[0030] Attachment Figure 7 for Figure 2 Schematic diagram of the structure after the interface is installed;

[0031] Attachment Figure 8 Schematic diagram of the change of curvature radius along the flow direction in a smooth curved microchannel;

[0032] Attachment Figure 9 Schematic diagram of the variation of the curvature radius along the flow direction in a wavy curve microchannel with the maximum amplitude in n peak-valley structures in one embodiment;

[0033] Attachment Figure 10 A schematic diagram of the variation of the curvature radius along the flow direction in a wavy microchannel with the maximum amplitude in n peak-trough structures in one embodiment;

[0034] Attachment Figure 11 It is a schematic diagram of the change of the instantaneous local heat transfer coefficient in single-phase flow heat transfer;

[0035] Attachment Figure 12 is the average heat transfer coefficient distribution diagram in the smooth curve microchannel;

[0036] Attachment Figure 13 The average heat transfer coefficient distribution diagram of the wavy curve microchannel with the maximum amplitude (2 mm) in n peak-valley structures in one embodiment;

[0037] Attachment Figure 14 This is a distribution diagram of the average heat transfer coefficient in the wavy curve microchannel with the maximum amplitude (3 mm) in n peak-valley structures in one embodiment.

[0038] In the figure, 1-microchannel; 2-interface. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0040] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0041] In addition, the terms "first," "second," and so on, used in this disclosure are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referenced. Thus, a feature specified as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of this disclosure, "plurality" means at least two, such as two or three, unless otherwise specifically defined.

[0042] In the present invention, unless otherwise specified or limited, the terms "connection" and "fixation" should be understood in a broad sense. For example, "fixation" can mean fixed connection, detachable connection, or integration; it can mean mechanical connection, electrical connection, physical connection, or wireless communication connection; it can mean direct connection or indirect connection through an intermediate medium; it can mean internal communication between two elements or interaction between two elements, unless otherwise specified. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in this field can implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0044] As attached Figure 2-14 As shown, the present invention provides a wavy curve microchannel, wherein the microchannel 1 includes a plurality of variable amplitude peak-valley structures, and the cross-sectional configuration of the microchannel 1 satisfies the configuration equation in the polar coordinate system:

[0045]

[0046] Where R is the polar diameter of the wavy microchannel, and θ is the polar angle;

[0047] a and b are the parameters of the Archimedean spiral, i.e., the smooth curve channel equation without superimposed peak-valley structure, and both a and b are positive;

[0048] n is the number of variable amplitude peak-trough structures, where variable amplitude means that the amplitudes of every two peak-trough structures are inconsistent, and the amplitude of a single peak-trough structure, that is, the maximum distance from the equilibrium position, is related to the channel polar angle and is not a constant value;

[0049] A is the maximum amplitude in the n peak-trough structures, and A is not equal to 0;

[0050] θ1 is 1 / 2 of the maximum polar angle.

[0051] In the formula, Archimedean spirals a, b, the number n of variable amplitude peak-trough structures, and the maximum amplitude A among the n peak-trough structures are setting parameters determined according to actual size requirements, and the polar diameter R, polar angle θ, and 1 / 2 maximum polar angle θ1 are obtained parameters obtained according to the configuration equation and the setting parameters. Therefore, the present invention only needs to input the setting parameters into the configuration equation according to actual size requirements to finally obtain the microchannel configuration.

[0052] refer to Figure 1,When A = 0 mm, it means that the microchannel has no superimposed peak-valley structure and is only a smooth curve channel controlled by the Archimedean spiral equation;

[0053] When A≠0mm, it indicates a curved channel with a peak-valley structure, such as Figure 2 As shown, this is a schematic diagram of one of the wavy curve microchannel structures obtained according to the requirements of the configuration equation.

[0054] Based on a compact microchannel precooler, the present invention optimizes the design of a smooth curved microchannel in which the coolant flows, and adds a variable-amplitude wavy structure to a rectangular equal-section channel with a certain hydraulic diameter, thereby obtaining a variable-amplitude peak-trough structural configuration in which the amplitude changes with the polar angle.

[0055] The microchannel provided by the present invention exhibits an overall curved channel structure. Compared to conventional straight channels, it can reduce the thickness of the thermal boundary layer, enhance flow mixing between the wall and the mainstream region, and improve heat transfer performance. Furthermore, a variable-amplitude peak-trough structure is superimposed on the overall curved channel configuration. This avoids the drawback of conventional curved channels, where the curvature gradually decreases with the flow direction, and also avoids the interference problem of a constant-amplitude peak-trough structure at the microchannel axis. The result is a microchannel 1 configuration with excellent flow mixing and strong heat transfer capability.

[0056] In one embodiment, reference Figure 3 The cross section of the microchannel 1 is rectangular, and the cross section of the microchannel 1 is rectangular, which is convenient for production and processing.

[0057] In one embodiment, reference Figure 3 , when the cross section of microchannel 1 is rectangular, it satisfies the following channel cross section equation:

[0058]

[0059] Where, L in is the length of the rectangular channel, W in is the width of the rectangular channel, D h It represents the equivalent diameter of the channel, that is, the size of the rectangular channel.

[0060] refer to Figure 7 In one embodiment, interfaces 2 are provided at both ends of the microchannel 1 to facilitate the communication between the microchannel 1 and other pipelines of the precooler.

[0061] In one embodiment, the microchannel 1 is formed by 3D printing as an integrated whole, and is preferably made of GH3536 high-temperature alloy, which can meet the design requirements of the precooler microchannel unit in terms of processing technology and heat transfer performance.

[0062] In one embodiment, the microchannel 1 includes five peak-valley structures, see Figure 3-Figure 5 Configuration diagram provided.

[0063] The present invention also provides a precooler, comprising the above-mentioned wavy microchannel

[0064] The present invention also provides a specific embodiment for comparison and testing, which is as follows:

[0065] Figure 1 is the configuration diagram of the smooth curved microchannel under the rectangular cross section. Figure 4-Figure 6 The three wavy curve microchannel configuration diagrams with different size parameters are shown in Table 1. The experimental section configuration parameters corresponding to the above four microchannel configurations are shown in Table 1:

[0066] Table 1 Microchannel configuration parameters

[0067] microchannel Corresponding attached figure a / mm b / mm <![CDATA[W in / mm]]> <![CDATA[L in / mm]]> <![CDATA[D h / mm]]> A / mm <![CDATA[d w / mm]]> n θ / ° Microchannel 1 Figure 1 80 40 0.8 2 1.14 0 0.5 0 106 Microchannel 2 Figure 4 80 40 0.8 2 1.14 2 0.5 5 106 Microchannel 3 Figure 5 80 40 0.8 2 1.14 3 0.5 5 106 Microchannel 4 Figure 6 80 40 0.8 4 1.33 2 0.5 5 106

[0068] Experiments and verifications were conducted on the four microchannel configurations provided in Table 1 above. It was found that the spiral microchannel with a superimposed variable amplitude peak-trough structure has better heat transfer performance than the smooth curved channel, and is a practical design configuration for the precooler heat transfer unit. The results are shown below:

[0069] (1) Changes in the curvature radius along the microchannel configuration

[0070] Figure 8 Schematic diagram of the change of curvature radius along the flow direction in the smooth curved microchannel (microchannel 1). Figure 9 Schematic diagram of the change of curvature radius along the flow direction in the wavy microchannels (microchannel 2 and microchannel 3) with a maximum amplitude of 2 mm in the peak-valley structure. Figure 10 Schematic diagram of the change of the curvature radius along the flow direction in a wavy curve microchannel (microchannel four) with a maximum amplitude of 3 mm in the peak-valley structure.

[0071] according to Figures 8-10 It can be seen that for the smooth curve microchannel (microchannel one), the rate of decrease in the radius of curvature gradually slows down as the arc position moves downstream. Compared with the smooth curve, the wavy curve microchannels (microchannels two, three, and four) with superimposed peak-trough structures keep the radius of curvature at a relatively low level in most areas along the flow, which is significantly smaller than the radius of curvature of the basic smooth curve microchannel configuration. Since the local Dean number increases with decreasing curvature radius, from an overall perspective, the introduction of the peak-trough structure increases the Dean number along the flow, strengthens flow mixing, and significantly enhances the secondary flow of the mainstream in the local and overall channel under the influence of centrifugal force.

[0072] (2) Local heat transfer characteristics

[0073] like Figure 11 Schematic diagram of the change of instantaneous local heat transfer coefficient in single-phase flow heat transfer.

[0074] according to Figure 11 It can be seen that the change in configuration leads to a significant change in the local heat transfer characteristics. In a conventional straight channel (not shown in the figure), the thermal boundary layer becomes thicker as the flow develops downstream, and the convective heat transfer coefficient continues to decrease along the way. However, in a smooth curved channel, the Dean number at the local position continues to increase along the way because the radius of curvature decreases with the increase of the arc position. As a result, the secondary flow induced by the centrifugal force strengthens the disturbance of the mainstream, and the influence of the Dean vortex at the corresponding local position is enhanced, which strengthens the mixing of the near-wall fluid and the mainstream and destroys the thermal boundary layer, so that the local heat transfer coefficient maintains an increasing trend within a larger arc range. However, as the flow further develops downstream of the channel, the thickness of the fully developed thermal boundary layer increases significantly. At the same time, due to the slowing trend of the decreasing radius of curvature of the smooth curved channel, that is, the growth rate of the local Dean number gradually weakens, the disturbance range of the secondary flow on the flow section cannot be further improved, the degree of interference with the thermal boundary layer is reduced, and the local heat transfer coefficient slowly decreases.

[0075] For the wavy curved channel, the introduction of the wavy structure superimposes the curvature of the amplitude structure on the original configuration curvature, significantly reducing the curvature radius at the peak and trough positions and significantly increasing the local Dean number. Under the same operating conditions as the smooth curved channel, its local heat transfer characteristics undergo significant changes. While the wall temperature fluctuates, the local heat transfer coefficient at the peak and trough oscillates. The additional curvature in the trough weakens the curvature of the basic configuration of the smooth curved channel, while the additional curvature at the peak strengthens the curvature of the basic configuration, resulting in a weakening of the secondary flow disturbance at the trough, a reduction in the vortex influence range, and a slight decrease in the local heat transfer coefficient. At the peak, the superposition of the amplitude and basic curvature causes a significant increase in the local Dean number, significantly improving the heat transfer coefficient. At the same time, because the disturbance caused by the amplitude is more influential, the vortex generated by the upstream amplitude on the flow is further transmitted and amplified by the downstream amplitude, thus maintaining the upward trend of the local heat transfer coefficient.

[0076] (3) Average heat transfer characteristics

[0077] Figure 12 is the average heat transfer coefficient distribution diagram in the smooth curve microchannel, Figure 12 The average heat transfer coefficient distribution diagram of the wavy curve microchannel (microchannel 2 and microchannel 3) with a maximum amplitude of 2 mm in the peak-valley structure is shown in FIG. Figure 13 This is the average heat transfer coefficient distribution diagram in the wavy curve microchannel (microchannel four) with a maximum amplitude of 3 mm in the peak-valley structure.

[0078] As shown in the figure, compared with the basic smooth-curve microchannel, the average heat transfer coefficient of the 2mm-amplitude wavy microchannel increased by 1.5%, and the average heat transfer coefficient of the 3mm-amplitude wavy microchannel increased by 3.5% at a similar Reynolds number (Re≈35). When the Reynolds number rises to Re≈101, the corresponding average heat transfer enhancements reach 19% and 23%, respectively. This indicates that the introduction of the wavy structure to change the local curvature radius enhances secondary flow and promotes the average heat transfer capacity of the microchannel. The magnitude of the heat transfer enhancement increases significantly with increasing flow velocity.

[0079] The contents not described in detail in this specification belong to the prior art known to those skilled in the art.

Claims

1. A wavy microchannel, characterized in that: The microchannel (1) includes a plurality of variable amplitude peak-valley structures, and the cross-sectional configuration of the microchannel (1) satisfies the configuration equation in a polar coordinate system: ； Where, is the extreme diameter of the wavy curve microchannel, is the polar angle; 、 is the Archimedean spiral, i.e. the smooth curve channel equation parameter without superimposed peak-valley structure, 、 All are positive values; is the number of variable amplitude peak-trough structures; for The maximum amplitude in the peak-trough structure, Not equal to 0; is 1 / 2 of the maximum polar angle; The microchannel (1) includes five peak-valley structures; Interfaces (2) are provided at both ends of the microchannel (1).

2. The wavy curve microchannel according to claim 1, wherein: The cross section of the microchannel (1) is rectangular.

3. The wavy curve microchannel according to claim 2, wherein: The cross section of the microchannel (1) satisfies the channel cross section equation: ； Where, is the length of the rectangular flow channel, is the width of the rectangular channel, Indicates the equivalent diameter of the channel.

4. The wavy curve microchannel according to any one of claims 1 to 3, characterized in that: The microchannel (1) is formed by 3D printing.

5. A precooler, characterized in that: The invention comprises the wavy curve microchannel as described in any one of claims 1 to 4.

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