Multi-branch series-parallel skin runner and design method thereof

Abstract

The invention relates to a multi-branch series-parallel skin runner and a design method thereof, belongs to the technical field of electronic heat dissipation of aircrafts, and solves the problems of large occupied space and large flow resistance of cold source equipment in an existing aircraft heat dissipation system. A multi-branch series-parallel skin flow channel is arranged in skin and comprises a flow channel inlet, a flow channel outlet, a first flow channel unit, a second flow channel unit and a first collecting flow channel. The first flow channel unit comprises a first medium flow channel, a second medium flow channel, a third medium flow channel and a second collecting flow channel; the second flow channel unit comprises a fourth medium flow channel, a fifth medium flow channel, a sixth medium flow channel and a third collecting flow channel; the first flow channel unit and the second flow channel unit are connected in series through the first collecting flow channel and are in mirror symmetry; the first medium flow channel, the second medium flow channel and the third medium flow channel are connected in parallel; and the third medium flow channel, the fourth medium flow channel and the fifth medium flow channel are connected in parallel. The multi-branch series-parallel skin runner is applied to cold source equipment, and is small in space and low in flow resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic heat dissipation of aircraft, and particularly to a multi-branch series-parallel skin flow channel and a design method thereof. Background Art

[0002] With the continuous improvement of the working efficiency of modern aircraft, the electronic devices inside the aircraft, such as navigation systems and control systems, are facing more severe working conditions. First, the continuous improvement of working performance (such as detection range, resolution, etc.) has led to a continuous increase in the power consumption of the devices; second, the design of the aircraft platform tends to be lightweight and miniaturized, resulting in a higher degree of device integration and a further increase in the heat flux density; third, with the increase in the flight time of the aircraft, the electronic devices face a longer working time. In summary, the aircraft platform is facing severe challenges of high power consumption, long working hours, and high heat flux density.

[0003] The existing thermal control measures for aircraft platforms generally use two types of technologies. One is the passive cooling measure based on phase change materials, and its disadvantage is that this passive consumable cold source can only support the device to work for a limited time; the other is the use of compression refrigeration method, and its disadvantage is that it consumes a huge amount of electric energy and has a large volume and mass itself.

[0004] Therefore, it is of great significance to design a cold source device that can be applied to the heat dissipation system of the aircraft platform, which can simultaneously meet the requirements of small space occupation of the aircraft platform by the heat dissipation system, long continuous working time, small flow resistance under high heat flux density, and large heat dissipation area under the conditions of high heat transfer and low flow resistance. Summary of the Invention

[0005] In view of the above analysis, the embodiments of the present invention aim to provide a multi-branch series-parallel skin flow channel and a design method thereof, so as to solve the problems that the cold source device of the heat dissipation system occupies a large space of the aircraft platform and has a large flow resistance when the existing aircraft platform works under high power, long working hours, and high heat flux density.

[0006] The purpose of the present invention is mainly achieved through the following technical solutions:

[0007] On the one hand, the present invention provides a multi-branch series-parallel skin flow channel, which is arranged in the skin and includes a flow channel inlet, a flow channel outlet, a first flow channel unit, a second flow channel unit, and a first collecting flow channel;

[0008] The first flow channel unit includes a first medium flow channel, a second medium flow channel, a third medium flow channel, and a second collecting flow channel;

[0009] The second flow channel unit includes a fourth medium flow channel, a fifth medium flow channel, a sixth medium flow channel, and a third collecting flow channel;

[0010] The first flow channel unit and the second flow channel unit are connected in series through the first collecting flow channel;

[0011] The first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel are all rounded straight-line flow channels;

[0012] The first medium flow channel and the sixth medium flow channel are symmetrically distributed in mirror image, the second medium flow channel and the fifth medium flow channel are symmetrically distributed in mirror image, and the third medium flow channel and the fourth medium flow channel are symmetrically distributed in mirror image;

[0013] The first medium flow channel, the second medium flow channel, and the third medium flow channel are in parallel and converge at the flow channel inlet to form a second converging flow channel;

[0014] The third medium flow channel, the fourth medium flow channel, and the fifth medium flow channel are in parallel and converge at the flow channel inlet and outlet to form a third converging flow channel.

[0015] Further, the flow channel inlet and the flow channel outlet are respectively arranged at both ends of the short side on the right side of the skin.

[0016] Further, the first converging flow channel is a converging flow channel that runs through the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel.

[0017] Further, the second converging flow channel and the third converging flow channel are independent flow channels that are not connected at the flow channel inlet and the flow channel outlet ends.

[0018] Further, the cross-section of the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel perpendicular to the flow direction of the medium in the flow channel is a rectangle, and the sides of the rectangle are transitioned by rounded corners.

[0019] Further, the diameters of the flow channel inlet and the flow channel outlet are equal.

[0020] Further, the radius of the rounded corner of the rectangle satisfies:

[0021] R’ = 1 / 2 * min(W, H);

[0022] Wherein, R’ is the radius of the rounded corner of the rectangle, in mm;

[0023] W is the width of the rectangle, in mm;

[0024] H is the height of the rectangle, in mm.

[0025] Further, the distances between the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel are equal and satisfy:

[0026] 1 / 2 * W ≤ K ≤ 3 / 4 * W;

[0027] where K is the runner spacing, in mm;

[0028] W is the width of the rectangle, in mm.

[0029] The present invention also provides a design method for a multi-branch series-parallel skin runner, which is used to design the above multi-branch series-parallel skin runner, and includes the following steps:

[0030] S1: Obtain the actually available rectangular skin;

[0031] S2: Design the preliminary shape and size of the multi-branch series-parallel skin runner to obtain the size and shape of the target runner;

[0032] S3: According to the size and shape of the target runner, use the sketch tool of the modeling software to draw the basic shape and size of the runner on the plane;

[0033] S4: Use the feature tool of the modeling software to convert the sketch into a three-dimensional solid to obtain the first multi-branch series-parallel skin runner model;

[0034] S5: Use the modeling software to extract the inner cavity model of the first multi-branch series-parallel skin runner model, import it into the simulation software for mesh generation, boundary condition setting, working fluid property parameter and solution parameter setting, and perform solution to obtain the flow resistance, flow rate and average temperature of the runner;

[0035] S6: Analyze the flow resistance, flow rate and average temperature of the six medium runners obtained in step S5. According to the analysis results, optimize the structure of the first multi-branch series-parallel skin runner model to obtain the second multi-branch series-parallel skin runner model, and perform simulation analysis on the flow resistance, flow rate and average temperature of the second multi-branch series-parallel skin runner model;

[0036] According to the simulation analysis results of the second multi-branch series-parallel skin runner model and the first multi-branch series-parallel skin runner model, judge whether the simulation analysis structure meets the stop iteration condition. If it meets, determine the second multi-branch series-parallel skin runner model as the final skin runner model. If it does not meet, optimize the structure of the second multi-branch series-parallel skin runner model, repeat the simulation analysis until the Nth multi-branch series-parallel skin runner model obtained after N iterations meets the stop iteration condition, then it is the final multi-branch series-parallel skin runner model.

[0037] Further, in step S6, the condition for stopping iteration is: the flow resistance of the (N - 1)th multi-branch series-parallel skin runner model is P N-1 , the flow resistance of the Nth multi-branch series-parallel skin runner model is P N , when abs(P N - PN-1 ) / P N-1 When it is ≤ 0.01, stop the iteration to obtain the final multi-branch series-parallel skin flow channel model.

[0038] Compared with the prior art, the present invention can at least achieve one of the following beneficial effects:

[0039] 1. The multi-branch series-parallel skin flow channel of the present invention is arranged inside the skin, and includes a flow channel inlet, a flow channel outlet, a first flow channel unit, a second flow channel unit and a first converging flow channel; the first flow channel unit and the second flow channel unit are connected in series through the first converging flow channel, and three medium flow channels in the first flow channel unit are connected in parallel, and three medium flow channels in the second flow channel unit are connected in parallel; the finally formed multi-branch series-parallel skin flow channel is distributed all over the skin. When the multi-branch series-parallel skin flow channel is applied to the skin heat exchanger of an aircraft, it can maintain the continuous operation of the electronic equipment for more than 2 hours while occupying a relatively small space inside the aircraft platform cabin.

[0040] 2. When the multi-branch series-parallel skin flow channel of the present invention is applied to a heating device with a heat flux density of 50 W / cm 2 in the aircraft platform, it has a relatively small flow resistance and a relatively large heat exchange area.

[0041] 3. When the multi-branch series-parallel skin flow channel of the present invention is applied to the skin heat exchanger of an aircraft, only the skin is appropriately thickened at the flow channel position, without occupying additional space inside the cabin.

[0042] 4. When the multi-branch series-parallel skin flow channel of the present invention is applied to the skin heat exchanger of an aircraft, the heat generated by the electronic equipment is transported to the skin through a circulation pipeline, and then the temperature is reduced through the heat exchange between the skin and the outside air, realizing the application requirements of the cold source equipment in the aircraft heat dissipation system with a small occupied space of the aircraft platform, a long continuous working time, a small flow resistance under a high heat flux density, and a large heat dissipation area; when the multi-branch series-parallel skin flow channel of the present invention is applied to the cold source equipment of an aircraft, the flow resistance of the flow channel ≤ 1700 Pa, and the heat exchange area ≥ 24000 mm 2 .

[0043] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination schemes. Other features and advantages of the present invention will be described in the subsequent specification, and some advantages can be obvious from the specification, or can be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained from the content specifically pointed out in the specification and the drawings. Description of the Drawings

[0044] The drawings are only for the purpose of showing specific embodiments, and are not considered as a limitation to the present invention. Throughout the drawings, the same reference signs represent the same components.

[0045] Figure 1 Schematic diagram of the multi-branch series-parallel skin flow channel of the present invention;

[0046] Figure 2 Combined pressure nephogram of the multi-branch series-parallel skin flow channel of the present invention;

[0047] Figure 3 Structural diagram of the ground verification system in Embodiment 2 of the present invention.

[0048] Reference numerals: 1 - First medium flow channel; 2 - Second medium flow channel; 3 - Third medium flow channel; 4 - Fourth medium flow channel; 5 - Fifth medium flow channel; 6 - Sixth medium flow channel; 7 - First collection flow channel; 8 - Second collection flow channel; 9 - Third collection flow channel; 10 - Flow channel inlet; 11 - Flow channel outlet; 12 - First partition; 13 - Second partition; 14 - Third partition; 15 - Fourth partition; 16 - Fifth partition; D - Diameter of the flow channel inlet; R - Fillet radius of the flow channel corner at the connection of the first medium flow channel and the first collection flow channel; W1 - Distance between the second collection flow channel and the fillet wall surface on the right side of the first partition; W2 - Distance between the second collection flow channel and the fillet wall surface on the right side of the second partition; W3 - Distance between the wall surface of the first collection flow channel and the fillet wall surface on the left side of the second partition; W4 - Distance between the wall surface of the first collection flow channel and the U-shaped bottom wall surface of the third partition; A - A - Cross-section direction; W - Rectangular width of the flow channel cross-section in the A - A direction; H - Rectangular height of the flow channel cross-section in the A - A direction; R' - Fillet radius of the rectangular cross-section of the flow channel in the A - A direction; K - Flow channel spacing. Detailed implementation manners

[0049] The preferred embodiments of the present invention will be specifically described below in conjunction with the accompanying drawings. The accompanying drawings form a part of this application and are used together with the embodiments of the present invention to explain the principles of the present invention, rather than to limit the scope of the present invention.

[0050] A multi-branch series-parallel skin flow channel is arranged inside the skin and includes a flow channel inlet, a flow channel outlet, a first flow channel unit, a second flow channel unit, and a first collection flow channel;

[0051] The first flow channel unit includes a first medium flow channel, a second medium flow channel, a third medium flow channel, and a second collection flow channel;

[0052] The second flow channel unit includes a fourth medium flow channel, a fifth medium flow channel, a sixth medium flow channel, and a third collection flow channel;

[0053] The first flow channel unit and the second flow channel unit are connected in series through the first collection flow channel;

[0054] The first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel are all filleted straight-line flow channels;

[0055] Along the width direction of the skin, the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel are arranged in parallel in turn from the upper long side to the lower long side of the skin; among them, the first medium flow channel and the sixth medium flow channel are mirror-symmetrically distributed, the second medium flow channel and the fifth medium flow channel are mirror-symmetrically distributed, and the third medium flow channel and the fourth medium flow channel are mirror-symmetrically distributed;

[0056] The first medium flow channel, the second medium flow channel, and the third medium flow channel are connected in parallel and converge at the flow channel inlet to form a second converging flow channel;

[0057] The third medium flow channel, the fourth medium flow channel, and the fifth medium flow channel are connected in parallel and converge at the flow channel outlet to form a third converging flow channel;

[0058] One ends of the first medium flow channel, the second medium flow channel, and the third medium flow channel converge and communicate with each other through the second converging flow channel; the other ends of the first medium flow channel, the second medium flow channel, and the third medium flow channel converge and communicate with each other through the first converging flow channel; one ends of the third medium flow channel, the fourth medium flow channel, and the fifth medium flow channel converge and communicate with each other through the third converging flow channel; the other ends of the third medium flow channel, the fourth medium flow channel, and the fifth medium flow channel converge and communicate with each other through the first converging flow channel;

[0059] It can be understood that the first converging flow channel is a converging flow channel that runs through the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel. The second converging flow channel and the third converging flow channel are independent flow channels with non-connected inlet and outlet ends. The medium entering through the flow channel inlet is dispersed through the second converging flow channel and then enters the first medium flow channel, the second medium flow channel, and the third medium flow channel, and then converges to a partial area of the first converging flow channel; after passing through the central area of the first converging flow channel, it is dispersed into the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel, and is connected to the flow channel outlet through the third converging flow channel.

[0060] The first converging flow channel is a trapezoid-like flow channel. The overall shape of this trapezoid-like flow channel is trapezoidal. Specifically, as Figure 1 shown, the lengths of the second medium flow channel and the fifth medium flow channel are equal, the lengths of the third medium flow channel and the fourth medium flow channel are equal, the lengths of the first medium flow channel and the sixth medium flow channel are equal, and the lengths of the second medium flow channel and the fifth medium flow channel are less than the lengths of the third medium flow channel and the fourth medium flow channel, and the lengths of the third medium flow channel and the fourth medium flow channel are less than the lengths of the first medium flow channel and the sixth medium flow channel; and they are centered along the length direction. Therefore, the width of the first converging flow channel at the non-inlet / outlet end of the flow channel shows a stepped change in the middle area, and the width of the edge area is less than the width of the middle area, presenting a trapezoidal shape.

[0061] Among them, the corners where the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel converge to the first converging flow channel are all rounded corners with a radius of R.

[0062] Similarly, the second converging flow channel and the third converging flow channel at one end of the inlet and outlet of the flow channel are also in the shape of a quasi-right-angled trapezoid. The width of the second converging flow channel presents a right-angled trapezoid shape where the width in the edge region is smaller than the width near the width center region, which can ensure uniform flow distribution of the first medium flow channel, the second medium flow channel, and the third medium flow channel. Similarly, the width of the third converging flow channel presents a right-angled trapezoid shape where the width in the edge region is smaller than the width near the width center region, which can ensure uniform flow distribution of the third medium flow channel, the fourth medium flow channel, and the fifth medium flow channel.

[0063] Among them, the corners where the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel converge to the second converging flow channel and the third converging flow channel are all rounded corners with a radius of R.

[0064] It should be noted that there is a first partition board in the shape of "rounded corner straight line" between the first medium flow channel and the second medium flow channel, a second partition board in the shape of "rounded corner straight line" between the second medium flow channel and the third medium flow channel, and a third partition board in the shape of "U" between the third medium flow channel and the fourth medium flow channel. The U opening of the "U"-shaped third partition board faces the short side on the right side of the skin; there is a fourth partition board in the shape of "rounded corner straight line" between the fourth medium flow channel and the fifth medium flow channel, and a fifth partition board in the shape of "rounded corner straight line" between the fifth medium flow channel and the sixth medium flow channel; the lengths of the first partition board, the second partition board, and the third partition board decrease in sequence, the fourth partition board and the second partition board are mirror-symmetrically distributed, and the fifth partition board and the first partition board are mirror-symmetrically distributed; it can be understood that the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel are all cavities opened in the skin, and the skin matrix between the cavities forms a partition structure between the flow channels.

[0065] The cross-section of the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel perpendicular to the direction of the medium flow in the flow channel is a rectangle. The sides of the rectangle are transitioned through rounded corners. The width of the rectangle is W, the height is H, and the radius of the rounded corner is R'. The radius of the rounded corner R' satisfies:

[0066] R' = 1 / 2 * min(W, H);

[0067] The radius of the rounded corner R' satisfying this condition can play a self-supporting role and no additional support is required during the subsequent additive manufacturing process. The unit is all mm.

[0068] The distances between the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel and the sixth medium flow channel are equal, with a spacing of K, in mm, satisfying:

[0069] 1 / 2*W ≤ K ≤ 3 / 4*W;

[0070] When the channel spacing satisfies this condition, the heat dissipation effect of the skin can be improved, and the convective heat transfer amount and heat conduction amount of the skin can be balanced.

[0071] The channel inlets and outlets are cylindrical and are respectively connected to the second collecting channel and the third collecting channel, with a diameter of D for both, satisfying:

[0072] D = 6*W*H / (W + H), in mm;

[0073] When the diameters of the channel inlets and outlets satisfy this condition, it can ensure sufficient flow supply of the medium at the channel inlets and outlets;

[0074] The channel inlets and outlets are respectively arranged at both ends of the short side on the right side of the skin. The distances from the channel inlets to the short side on the right side of the skin and the long side on the upper side of the skin are 3D, and the distances from the channel outlets to the short side on the right side of the skin and the long side on the lower side of the skin are 3D. When the positions of the channel inlets and outlets satisfy this condition, it can ensure that the medium traverses the entire skin channel.

[0075] The fillet radii of the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel and the sixth medium flow channel are all R, satisfying:

[0076] 1 / 2*W ≤ R ≤ 2 / 3*W, in mm;

[0077] When the fillet radius R at the corner of the medium flow channel satisfies this condition, it can ensure the guiding effect of the channel.

[0078] The distance between the wall surface of the first collecting channel and the left fillet wall surface (non-inlet / outlet end wall surface) of the second partition is W3, and the distance between the wall surface of the first collecting channel and the bottom wall surface of the third partition is W4;

[0079] The long sides of the second collecting channel and the third collecting channel are flush (inlet / outlet ends). The distances between the second collecting channel and the right fillet wall surface (inlet / outlet end wall surface) of the first partition and between the third collecting channel and the right fillet wall surface of the fifth partition are equal, being W1; the distances between the second collecting channel and the right fillet wall surface (inlet / outlet end wall surface) of the second partition and between the third collecting channel and the right fillet wall surface of the fourth partition are equal, being W2; satisfying:

[0080] W1 = W3 = 3 / 2*W, W2 = W4 = 3 / 2*W1;

[0081] W1, W2, W3, and W4 satisfy the above conditions, which can evenly distribute the flow rates in the six medium flow channels, making the flow rate ratio in the six medium flow channels close to 1:1:1.

[0082] The present invention also provides a design method for a multi-branch series-parallel skin flow channel for manufacturing the above multi-branch series-parallel skin flow channel, including the following steps:

[0083] S1: Obtain an actually available rectangular skin;

[0084] S2: Design the preliminary shape and dimensions of the multi-branch series-parallel skin flow channel to obtain the dimensions and shape of the target flow channel;

[0085] S3: According to the dimensions and shape of the target flow channel, use the sketch tool of the modeling software to draw the basic shape and dimensions of the flow channel on a plane;

[0086] S4: Use the feature tool of the modeling software to convert the sketch into a three-dimensional solid to obtain the first multi-branch series-parallel skin flow channel model;

[0087] S5: Use the modeling software to extract the inner cavity model of the first multi-branch series-parallel skin flow channel model, import it into the simulation software for mesh generation, boundary condition setting, working fluid property parameter and solution parameter setting, and perform a solution to obtain the flow channel flow resistance, flow channel flow rate, and average temperature;

[0088] S6: Analyze the flow channel flow resistance, flow channel flow rate, and average temperature of the six medium flow channels obtained in step S5. According to the analysis results, optimize the structure of the first multi-branch series-parallel skin flow channel model to obtain the second multi-branch series-parallel skin flow channel model, and perform a simulation analysis on the flow channel flow resistance, flow channel flow rate, and average temperature of the second multi-branch series-parallel skin flow channel model;

[0089] According to the simulation analysis results of the second multi-branch series-parallel skin flow channel model and the first multi-branch series-parallel skin flow channel model, determine whether the simulation analysis structure meets the stop iteration condition. If it meets, determine the second multi-branch series-parallel skin flow channel model as the final skin flow channel model. If it does not meet, optimize the structure of the second multi-branch series-parallel skin flow channel model, repeat the simulation analysis until the Nth multi-branch series-parallel skin flow channel model obtained after N iterations meets the stop iteration condition, which is the final multi-branch series-parallel skin flow channel model.

[0090] Specifically, in step S2, when designing the preliminary shape and dimensions of the multi-branch series-parallel skin flow channel to obtain the dimensions and shape of the target flow channel, it includes the following steps:

[0091] S21: Set the flow channel inlet and flow channel outlet on the skin, and determine the positions and dimensions of the flow channel inlet and flow channel outlet;

[0092] Specifically, the position of the runner inlet is 3D away from the right short side and the upper long side of the skin, and the position of the runner outlet is 3D away from the right short side and the lower side of the skin, where D is the diameter of the runner inlet and the runner outlet.

[0093] S22: Set a first collecting runner on the skin, and the distance between the first collecting runner and the left short side (non-inlet and outlet end wall surface) of the skin > 2 mm;

[0094] S23: Set a first medium runner on the skin. The first medium runner is a rounded straight runner. One end far from the runner inlet is connected to the first collecting runner, the distance from the upper long side of the skin > 2 mm, and the distance from the right short side of the skin > 2 mm;

[0095] Among them, the cross-section (inlet and outlet end wall surface) of the first medium runner perpendicular to the flow direction of the medium in the runner is a rectangle. The sides of the rectangle are transitioned by rounded corners. The width of the rectangle is W, the height is H, and the rounded corner radius is R'. The rounded corner radius R' satisfies: R' = 1 / 2 * min(W, H)

[0096] S24: Set a second medium runner on the skin. The shape and size of the second medium runner are the same as those of the first medium runner. One end far from the runner inlet is connected to the first collecting runner. The distance between the second medium runner and the first medium runner is K, and 1 / 2 * W ≤ K ≤ 3 / 4 * W;

[0097] S25: Set a third medium runner on the skin. The shape and size of the third medium runner are the same as those of the second medium runner. One end far from the runner inlet is connected to the first collecting runner. The distance between the third medium runner and the second medium runner is K, and 1 / 2 * W ≤ K ≤ 3 / 4 * W;

[0098] S26: The first medium runner, the second medium runner, and the third medium runner are in parallel and converge at the runner inlet to form a second collecting runner. The first medium runner, the second medium runner, the third medium runner, and the second collecting runner together form the first runner unit;

[0099] S27: Mirror-symmetrically copy the first runner unit to obtain a second runner unit. The second runner unit and the first runner unit are connected in series through the first collecting runner to obtain the size and shape of the target runner.

[0100] Specifically, in step S5, use modeling software to extract the inner cavity model of the first multi-branch series-parallel skin runner model, import it into simulation software for mesh generation, and perform mesh independence analysis. The mesh scale is D / 100, which can balance simulation efficiency and accuracy;

[0101] Then set the boundary conditions, which are: set the velocity and temperature boundary conditions at the inlet position of the flow channel, with the velocity value being 3.5 - 4 L / min and the temperature value being 50 - 60 °C; set the pressure boundary condition at the outlet position of the flow channel, with the pressure value being 0 - 0.1 MPa; set the thermal boundary condition on the outer surface of the skin, with the convective heat transfer coefficient being 300 - 400 W / (m 2 -K), and the ambient air temperature value being 10 - 20 °C.

[0102] Set the physical property parameters of the working fluid, including the density, specific heat capacity, and viscosity of the working fluid;

[0103] The solution parameters are the number of calculation steps and the convergence residual. The number of calculation steps ≥ 500, and the convergence residual ≤ 1E-6; then perform the simulation operation and solution to obtain the flow resistance of the flow channel and the flow rates of the three medium flow channels.

[0104] Specifically, in step S6, the structural optimization includes adjusting the diameters of the inlet and outlet of the flow channel, widening the distances between the wall surface of the first collecting flow channel and the left rounded corner wall surface of the second partition, the distance between the wall surface of the first collecting flow channel and the U-shaped bottom wall surface of the third partition, the distance between the second collecting flow channel and the right rounded corner wall surface of the first partition, the distance between the third collecting flow channel and the right rounded corner wall surface of the fifth partition, the distance between the second collecting flow channel and the right rounded corner wall surface of the second partition, and the distance between the third collecting flow channel and the right rounded corner wall surface of the fourth partition.

[0105] In step S6, the condition for stopping iteration is: the flow resistance of the (N - 1) multi-branch series-parallel skin flow channel model is P N-1 , and the flow resistance of the N multi-branch series-parallel skin flow channel model is P N , when abs(P N -P N-1 ) / P N-1 ≤ 0.01, stop the iteration to obtain the final multi-branch series-parallel skin flow channel model.

[0106] Specifically, for the final multi-branch series-parallel skin flow channel model obtained in step S6, the distance between the wall surface of the first collecting flow channel and the left rounded corner wall surface of the second partition is W3, and the distance between the wall surface of the first collecting flow channel and the U-shaped bottom wall surface of the third partition is W4; the long sides of the second collecting flow channel and the third collecting flow channel are flush, and the distances between the second collecting flow channel and the right rounded corner wall surface of the first partition and between the third collecting flow channel and the right rounded corner wall surface of the fifth partition are equal, being W1; the distances between the second collecting flow channel and the right rounded corner wall surface of the second partition and between the third collecting flow channel and the right rounded corner wall surface of the fourth partition are equal, being W2; satisfying W1 = W3 = 3 / 2 * W, W2 = W4 = 3 / 2 * W1, mm; the diameters D of the inlet and outlet of the flow channel satisfy D = 6 * W * H / (W + H).

[0107] The multi-branch series-parallel skin flow channel of the present invention can be applied to the cold source equipment in the liquid cooling system of an aircraft. Using a part of the aircraft skin, the flow channel flows through the skin through the inlets and outlets on the inner side of the cabin, and exchanges heat with the outside through the skin, so as to achieve the refrigeration effect.

[0108] Embodiment 1

[0109] The multi-branch series-parallel skin flow channel of this embodiment is as Figure 1 shown. It is arranged in a rectangular skin and includes a flow channel inlet, a flow channel outlet, a first flow channel unit, a second flow channel unit, and a first collecting flow channel;

[0110] The first flow channel unit includes a first medium flow channel, a second medium flow channel, a third medium flow channel, and a second collecting flow channel;

[0111] The second flow channel unit includes a fourth medium flow channel, a fifth medium flow channel, a sixth medium flow channel, and a third collecting flow channel;

[0112] The first flow channel unit and the second flow channel unit are connected in series through the first collecting flow channel;

[0113] The first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel are all rounded straight-line flow channels;

[0114] Along the width direction of the skin, the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel are arranged in parallel in sequence from the upper long side to the lower long side of the skin; among them, the first medium flow channel and the sixth medium flow channel are mirror-symmetrically distributed, the second medium flow channel and the fifth medium flow channel are mirror-symmetrically distributed, and the third medium flow channel and the fourth medium flow channel are mirror-symmetrically distributed;

[0115] The first medium flow channel, the second medium flow channel, and the third medium flow channel are connected in parallel and converge at the flow channel inlet to form a second collecting flow channel;

[0116] The third medium flow channel, the fourth medium flow channel, and the fifth medium flow channel are connected in parallel and converge at the flow channel outlet to form a third collecting flow channel;

[0117] One ends of the first medium flow channel, the second medium flow channel, and the third medium flow channel are converged and interconnected through the second collecting flow channel; the other ends of the first medium flow channel, the second medium flow channel, and the third medium flow channel are converged and interconnected through the first collecting flow channel; one ends of the third medium flow channel, the fourth medium flow channel, and the fifth medium flow channel are converged and interconnected through the third collecting flow channel; the other ends of the third medium flow channel, the fourth medium flow channel, and the fifth medium flow channel are converged and interconnected through the first collecting flow channel;

[0118] The first converging channel is a converging channel that runs through the first medium channel, the second medium channel, the third medium channel, the fourth medium channel, the fifth medium channel, and the sixth medium channel. The second converging channel and the third converging channel are independent channels with non-connected inlet and outlet ends. The medium entering through the channel inlet is dispersed through the second converging channel and then enters the first medium channel, the second medium channel, and the third medium channel, and then converges to a partial area of the first converging channel. After passing through the central area of the first converging channel, it is dispersed into the fourth medium channel, the fifth medium channel, and the sixth medium channel, and is connected to the channel outlet through the third converging channel.

[0119] The first converging channel is a trapezoid-like channel. The overall shape of this trapezoid-like channel is trapezoidal. Specifically, as Figure 1 shown, the lengths of the second medium channel and the fifth medium channel are equal, the lengths of the third medium channel and the fourth medium channel are equal, the lengths of the first medium channel and the sixth medium channel are equal, and the lengths of the second medium channel and the fifth medium channel are less than the lengths of the third medium channel and the fourth medium channel. The lengths of the third medium channel and the fourth medium channel are less than the lengths of the first medium channel and the sixth medium channel. And they are centered along the length direction. Therefore, the width of the first converging channel at the non-inlet / outlet end of the channel shows a stepped change in the width of the middle area, and the width of the edge area is less than the width of the middle area, presenting a trapezoidal shape.

[0120] Among them, the corners where the first medium channel, the second medium channel, the third medium channel, the fourth medium channel, the fifth medium channel, and the sixth medium channel converge to the first converging channel are all rounded corners R.

[0121] Similarly, the second converging channel and the third converging channel at the inlet and outlet ends of the channel are also trapezoid-like right-angled shapes. The width of the second converging channel shows a right-angled trapezoidal shape where the width of the edge area is less than the width of the area near the width center. Similarly, the width of the third converging channel shows a right-angled trapezoidal shape where the width of the edge area is less than the width of the area near the width center.

[0122] Among them, the corners where the first medium channel, the second medium channel, the third medium channel, the fourth medium channel, the fifth medium channel, and the sixth medium channel converge to the second converging channel and the third converging channel are all rounded corners R.

[0123] The cross-sections of the first medium channel, the second medium channel, the third medium channel, the fourth medium channel, the fifth medium channel, and the sixth medium channel in the direction perpendicular to the flow direction of the medium in the channel are rectangles. The sides of the rectangle are transitioned through rounded corners. The width of this rectangle is W = 9 mm, the height is H = 3 mm, and the radius of the rounded corner is R' = 1.5 mm, satisfying R' = 1 / 2 * min(W, H);

[0124] The distances between the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel and the sixth medium flow channel are equal, and the spacing is K = 6 mm, with the unit of mm, satisfying: 1 / 2*W ≤ K ≤ 3 / 4*W;

[0125] The flow channel inlet and the flow channel outlet are cylindrical and are respectively connected to the second converging flow channel and the third converging flow channel, and their diameters are both D = 13.5 mm, satisfying: D = 6*W*H / (W + H);

[0126] The flow channel inlet and the flow channel outlet are respectively arranged at both ends of the short side on the right side of the skin. The distance from the flow channel inlet to the short side on the right side of the skin and the long side on the upper side of the skin is 40.5 mm, and the distance from the flow channel outlet to the short side on the right side of the skin and the long side on the lower side of the skin is 40.5 mm.

[0127] The fillet radii of the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel and the sixth medium flow channel are all R = 5 mm, satisfying: 1 / 2*W ≤ R ≤ 2 / 3*W;

[0128] The distance between the wall surface of the first converging flow channel and the left fillet wall surface (non-inlet section wall surface) of the second partition is W3, and the distance between the wall surface of the first converging flow channel and the bottom wall surface of the third partition is W4; The long sides of the second converging flow channel and the third converging flow channel are flush (at the inlet and outlet ends). The distances between the second converging flow channel and the right fillet wall surface (inlet and outlet end wall surfaces) of the first partition and between the third converging flow channel and the right fillet wall surface (inlet and outlet end wall surfaces) of the fifth partition are equal, which is W1; The distances between the second converging flow channel and the right fillet wall surface (inlet and outlet end wall surfaces) of the second partition and between the third converging flow channel and the right fillet wall surface (inlet and outlet end wall surfaces) of the fourth partition are equal, which is W2; W1 = W3 = 13.5 mm, W2 = W4 = 20.25 mm, satisfying: W1 = W3 = 3 / 2*W, W2 = W4 = 3 / 2*W1.

[0129] The combined pressure contour map of the multi-branch series-parallel skin flow channel in this embodiment is as Figure 2 shown. It can be seen from the figure that the flow resistance obtained from the simulation calculation of the multi-branch series-parallel skin flow channel in this embodiment is 1688.36 Pa.

[0130] Embodiment 2

[0131] The multi-branch series-parallel skin flow channel of Embodiment 1 is actually verified by a ground verification system.

[0132] The structure of the ground verification system is as Figure 3 shown. The verification system consists of a liquid storage tank, a flow meter, a gear pump, a simulated thermal load, a heat dissipation skin and sensors. The sensors are arranged at the flow channel inlet and the flow channel outlet positions of the S-shaped single-series skin flow channel;

[0133] The verification condition is: a heat load of 50 W / cm 2 heat flux;

[0134] Verified by the ground verification system, the flow resistance of the multi-branch series-parallel skin flow channel is 1688.36 Pa, and the heat transfer area is 24415 mm 2 , with good cooling and heat transfer effects.

[0135] Example 3

[0136] This example is a design method for the multi-branch series-parallel skin flow channel of Example 1, including the following steps:

[0137] S1: Obtain the actually available rectangular skin;

[0138] S2: Design the preliminary shape and size of the multi-branch series-parallel skin flow channel to obtain the size and shape of the target flow channel;

[0139] S21: Set the flow channel inlet and the flow channel outlet on the skin, and determine the positions and sizes of the flow channel inlet and the flow channel outlet;

[0140] Specifically, the position of the flow channel inlet is 39 mm from the right short side and the upper long side of the skin, i.e., 3D; the position of the flow channel outlet is 39 mm from the right short side and the lower side of the skin, i.e., 3D, where D = 13 mm, which is the diameter of the flow channel inlet and the flow channel outlet.

[0141] S22: Set the first collecting flow channel on the skin, and the distance from the left short side (non-inlet and outlet end wall surface) of the skin is 4 mm;

[0142] S23: Set the first medium flow channel on the skin. This medium flow channel is a rounded straight-line flow channel. One end far from the flow channel inlet is connected to the first collecting flow channel, and the distance from the upper long side of the skin is 4 mm, and the distance from the right short side of the skin is 4 mm;

[0143] Among them, the cross-section (inlet and outlet end wall surface) of this medium flow channel perpendicular to the flow direction of the medium in the flow channel is rectangular, and the sides of the rectangle are transitioned by rounded corners. The width of the rectangle is W = 9 mm, the height is H = 3 mm, and the rounded corner radius is R' = 1.5 mm. Its rounded corner radius R' satisfies: R' = 1 / 2 * min(W, H)

[0144] S24: Set the second medium flow channel on the skin. The shape and size of the second medium flow channel are the same as those of the first medium flow channel. One end far from the flow channel inlet is connected to the first collecting flow channel. The distance between the second medium flow channel and the first medium flow channel is K = 6 mm, satisfying 1 / 2 * W ≤ K ≤ 3 / 4 * W;

[0145] S25: Set a third medium flow channel on the skin. The shape and size of the third medium flow channel are the same as those of the second medium flow channel. One end far from the flow channel inlet is connected to the first converging flow channel. The distance between the third medium flow channel and the second medium flow channel is K = 6 mm, satisfying 1 / 2*W ≤ K ≤ 3 / 4*W;

[0146] S26: The first medium flow channel, the second medium flow channel, and the third medium flow channel are in parallel and converge at the flow channel inlet to form a second converging flow channel. The first medium flow channel, the second medium flow channel, the third medium flow channel, and the second converging flow channel together form the first flow channel unit;

[0147] S27: Mirror-symmetrically copy the first flow channel unit to obtain a second flow channel unit. The second flow channel unit and the first flow channel unit are connected in series through the first converging flow channel to obtain the size and shape of the target flow channel.

[0148] S3: According to the size and shape of the target flow channel, use the sketch tool of the modeling software to draw the basic shape and size of the flow channel on a plane;

[0149] S4: Use the feature tool of the modeling software to convert the sketch into a three-dimensional solid to obtain the first multi-branch series-parallel skin flow channel model;

[0150] S5: Use the modeling software to extract the inner cavity model of the first multi-branch series-parallel skin flow channel model, import it into the simulation software for mesh generation, boundary condition setting, and solution parameter setting, and then solve it to obtain the flow resistance of the flow channel, the flow rate of the flow channel, and the average temperature;

[0151] Among them, the mesh scale is D / 100, which can balance the simulation efficiency and accuracy;

[0152] The boundary conditions are as follows: Set the velocity and temperature boundary conditions at the flow channel inlet. The velocity value is 3.5 L / min, and the temperature value is 50 °C; Set the pressure boundary condition at the flow channel outlet, and the pressure value is 0.1 MPa; Set the thermal boundary condition on the outer surface of the skin, and the convective heat transfer coefficient is 300 W / (m 2 -K), and the ambient air temperature value is 10 °C;

[0153] Set the working medium physical property parameters: The medium is 65% ethylene glycol solution, with a density of 1069.145 kg / m 3 , a specific heat capacity of 3.165 kJ / kg*K, and a viscosity of 1.91 mPa*s.

[0154] The solution parameters are the number of calculation steps and the convergence residual. The number of calculation steps is 500 steps, and the convergence residual is 1E-6.

[0155] S6: Analyze the flow resistance, flow rate, and average temperature of the six medium flow channels obtained in step S5. According to the analysis results, optimize the structure of the first multi-branch series-parallel skin flow channel model;

[0156] The structure optimization includes: increasing the diameters of the flow channel outlet and inlet to 13.5 mm;

[0157] Widen the distance W3 between the first collecting flow channel wall and the left rounded corner wall of the second partition (non-inlet / outlet end wall) to 13.5 mm, and the distance W4 between the first collecting flow channel wall and the bottom wall of the third partition to 20.25 mm;

[0158] Widen the distance W1 between the second collecting flow channel and the right rounded corner wall of the first partition (inlet / outlet end wall) and the distance between the third collecting flow channel and the right rounded corner wall of the fifth partition (inlet / outlet end wall) to 13.5 mm;

[0159] Widen the distance W2 between the second collecting flow channel and the right rounded corner wall of the second partition (inlet / outlet end wall) and the distance between the third collecting flow channel and the right rounded corner wall of the fourth partition (inlet / outlet end wall) to 20.25 mm; obtain the second multi-branch series-parallel skin flow channel model, and perform simulation analysis on the flow resistance and flow rate of the second multi-branch series-parallel skin flow channel model;

[0160] Among them, the flow resistance of the second multi-branch series-parallel skin flow channel model is P 2 = 1688.36 Pa, and the flow resistance of the first multi-branch series-parallel skin flow channel model is P 1 = 1688.352 Pa, satisfying abs(P N - P N-1 ) / P N-1 ≤ 0.01, stop iteration, and the second multi-branch series-parallel skin flow channel model is the final multi-branch series-parallel skin flow channel model.

[0161] Comparative Example 1

[0162] The multi-branch series-parallel skin flow channel of this comparative example has the same shape as that of Example 1, except that:

[0163] The distances between the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel are equal, and the spacing is K = 4 mm, in mm, not satisfying: 1 / 2 * W ≤ K ≤ 3 / 4 * W;

[0164] The distance between the wall surface of the first converging flow channel and the left rounded corner wall surface (non-inlet / outlet end wall surface) of the second partition is W3, and the distance between the wall surface of the first converging flow channel and the bottom wall surface of the third partition is W4; the long sides of the second converging flow channel and the third converging flow channel are flush. The distances between the second converging flow channel and the right rounded corner wall surface (inlet / outlet end wall surface) of the first partition, and between the third converging flow channel and the right rounded corner wall surface (inlet / outlet end wall surface) of the fifth partition are equal, being W1; the distances between the second converging flow channel and the right rounded corner wall surface (inlet / outlet end wall surface) of the second partition, and between the third converging flow channel and the right rounded corner wall surface (inlet / outlet end wall surface) of the fourth partition are equal, being W2; W1 = W3 = 13.5 mm, W2 = W4 = 13.5 mm, satisfying: W1 = W3 = 3 / 2 * W, and not satisfying W2 = W4 = 3 / 2 * W1.

[0165] Apply the multi-branch series-parallel skin flow channels of Example 1 and Comparative Example 1 to the cold source equipment in the aircraft liquid cooling system, using a part of the aircraft skin. After actual verification by the ground verification system, the flow resistance of the multi-branch series-parallel skin flow channel of Example 1 is 1688.36 Pa, and the heat transfer area is 24415 mm 2 , the flow resistance of the multi-branch series-parallel skin flow channel of Comparative Example 1 is 1836.07 Pa, and the heat transfer area is 25352 mm 2 , and the application of the multi-branch series-parallel skin flow channel of Example 1 to the cold source equipment in the aircraft liquid cooling system is superior to that of Comparative Example 1.

[0166] As described above, only the preferred specific embodiments of the present invention are provided, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A multi-branch series-parallel skin flow channel is arranged inside the skin. Characterized in that, It includes a flow channel inlet, a flow channel outlet, a first flow channel unit, a second flow channel unit, and a first converging flow channel; The first flow channel unit includes a first medium flow channel, a second medium flow channel, a third medium flow channel, and a second converging flow channel; The second flow channel unit includes a fourth medium flow channel, a fifth medium flow channel, a sixth medium flow channel, and a third converging flow channel; The first flow channel unit and the second flow channel unit are connected in series through the first converging flow channel; The first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel are all rounded straight-line flow channels; The first medium flow channel and the sixth medium flow channel are mirror-symmetrically distributed, the second medium flow channel and the fifth medium flow channel are mirror-symmetrically distributed, and the third medium flow channel and the fourth medium flow channel are mirror-symmetrically distributed; The first medium flow channel, the second medium flow channel, and the third medium flow channel are connected in parallel and converge at the flow channel inlet to form a second converging flow channel; The third medium flow channel, the fourth medium flow channel, and the fifth medium flow channel are connected in parallel and converge at the flow channel inlet and outlet to form a third converging flow channel.

2. The multi-branch series-parallel skin flow channel according to claim 1, Characterized in that, The flow channel inlet and the flow channel outlet are respectively arranged at both ends of the short side on the right side of the skin.

3. The multi-branch series-parallel skin flow channel according to claim 1, Characterized in that, The first converging flow channel is a converging flow channel that penetrates along the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel.

4. The multi-branch series-parallel skin flow channel according to claim 1, Characterized in that, The second converging flow channel and the third converging flow channel are independent flow channels that are not connected at the flow channel inlet and outlet ends.

5. The multi-branch series-parallel skin flow channel according to claim 1, Characterized in that, The cross-section of the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel perpendicular to the flow direction of the medium in the flow channel is a rectangle, and the sides of the rectangle are transitioned through rounded corners.

6. The multi-branch series-parallel skin flow channel according to claim 1, Characterized in that, The diameters of the flow channel inlet and the flow channel outlet are equal.

7. The multi-branch series-parallel skin flow channel according to claim 5, Characterized in that, The rounded corner radius of the rectangle satisfies: R’ = 1 / 2 * min(W, H); Wherein, R’ is the rounded corner radius of the rectangle, mm; W is the width of the rectangle, mm; H is the height of the rectangle, mm.

8. The multi-branch series-parallel skin flow channel according to claim 7, Characterized in that, The distances between the first medium flow channel, the second medium flow channel, the third medium flow channel, the fourth medium flow channel, the fifth medium flow channel, and the sixth medium flow channel are equal, satisfying: 1 / 2 * W ≤ K ≤ 3 / 4 * W; Wherein, K is the flow channel spacing, mm; W is the width of the rectangle, mm.

9. A design method for a multi-branch series-parallel skin flow channel, used to design the multi-branch series-parallel skin flow channel according to any one of claims 1-8, Comprising the following steps: S1: Obtain the actually available rectangular skin; S2: Design the initial shape and dimensions of the multi-branch series-parallel skin flow channel to obtain the dimensions and shape of the target flow channel; S3: According to the dimensions and shape of the target flow channel, use the sketch tool of the modeling software to draw the basic shape and dimensions of the flow channel on a plane; S4: Use the feature tool of the modeling software to convert the sketch into a three-dimensional solid to obtain the first multi-branch series-parallel skin flow channel model; S5: Use the modeling software to extract the inner cavity model of the first multi-branch series-parallel skin flow channel model, import it into the simulation software for mesh generation, boundary condition setting, working fluid physical property parameter and solution parameter setting, and perform the solution to obtain the flow resistance of the flow channel, the flow rate of the flow channel and the average temperature; S6: Analyze the flow resistance of the flow channel, the flow rate of the flow channel and the average temperature of the six medium flow channels obtained in step S5. According to the analysis results, optimize the structure of the first multi-branch series-parallel skin flow channel model to obtain the second multi-branch series-parallel skin flow channel model, and perform simulation analysis on the flow resistance of the flow channel, the flow rate of the flow channel and the average temperature of the second multi-branch series-parallel skin flow channel model; According to the results of the simulation analysis of the second multi-branch series-parallel skin flow channel model and the first multi-branch series-parallel skin flow channel model, judge whether the simulation analysis structure meets the stop iteration condition. If it meets, determine the second multi-branch series-parallel skin flow channel model as the final skin flow channel model. If it does not meet, optimize the structure of the second multi-branch series-parallel skin flow channel model, repeat the simulation analysis until the Nth multi-branch series-parallel skin flow channel model obtained after N iterations meets the stop iteration condition, and it is the final multi-branch series-parallel skin flow channel model.

10. According to the design method described in claim 9, characterized in that In step S6, the condition for stopping iteration is that the flow resistance of the (N - 1)-th multi-branch series-parallel skin flow channel model is P N-1 , and the flow resistance of the N-th multi-branch series-parallel skin flow channel model is P N . When abs(P N - P N-1 ) / P N-1 ≤ 0.01, stop iteration to obtain the final multi-branch series-parallel skin flow channel model.

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