Parallel multi-branch flow distribution method based on two-phase cooling technology

Abstract

The invention discloses a parallel multi-branch flow distribution method based on a two-phase flow cooling technology. The parallel multi-branch flow distribution method is a design method for achieving accurate flow distribution based on structural design instead of depending on accessories such as a flow adjusting unit, a monitoring unit and a resistance adjusting unit. The method mainly comprises the following three steps: design and verification of parallel branch cold plate runner structure parameters, simulation design of a flow distribution structure and design of a liquid collection cavity structure. Accurate distribution of two-phase flow can be achieved without depending on accessories such as an electromagnetic valve and a constant flow valve, high-integration-level design of equipment is facilitated, high stability of flowing boiling heat exchange can be achieved, the number of connectors in a two-phase cooling system can be fully reduced, and then the leakage risk of cooling working media such as Freon is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of two-phase cooling, and in particular relates to a parallel multi-branch flow distribution method based on the two-phase cooling technology. Background Art

[0002] High power and high integration are important development trends of active phased array radar (AESA) and micro-mechanical system technology (MEMS). Among them, the third-generation semiconductor materials represented by GaN and the three-dimensional integrated micro-system technology represented by SIP and SOC are the key technologies to achieve the above two. The high heat flux density chip cooling problem caused by this has become one of the main bottlenecks restricting the improvement of the combat capability of weapons and equipment. The traditional single-phase liquid cooling method can no longer meet the heat dissipation needs of electronic equipment. Among them, the research on the pump-driven two-phase liquid cooling system of a single loop is relatively mature, while the pump-driven two-phase liquid cooling system with multiple parallel branches has different flow resistances in each branch due to the different heat consumption of each branch. It is very easy to cause flow instability and cause overheating and damage to the equipment.

[0003] The Chinese patent application number is 202110938474.0, which discloses a pump-driven two-phase liquid cooling system and flow control method for achieving stable flow distribution. The pump-driven two-phase liquid cooling system in the patent includes multiple parallel liquid cooling units, and the parallel two-phase liquid cooling units include several parallel liquid cooling branches, each of which is connected in series with a solenoid valve, a constant flow valve and a regenerator. The invention achieves uniform distribution of flow in each cooling branch by separately setting a solenoid valve, a constant flow valve and a regenerator in each cooling branch, avoiding dry burning, and adjusting the pump operation state and the on-off of the cooling branch according to the operation state of the cooling branch.

[0004] This technical invention achieves uniform flow distribution by setting solenoid valves, constant flow valves and regenerators in each cooling branch. The problem is that the presence of solenoid valves, constant flow valves and regenerators in each cooling branch will cause each branch to occupy a large equipment volume. This solution cannot be used on platforms such as missile-borne and satellite-borne platforms with strict space size restrictions and many cooling branches. The solenoid valves and constant flow valves on each cooling branch need to be controlled by a controller, so the system requires more complex control logic, and the presence of solenoid valves, constant flow valves and other devices in each branch increases the failure rate of the equipment and the risk of system leakage.

[0005] The Chinese patent with application number 202010919278.4 discloses a device and method for stabilizing multiple parallel branches of a two-phase cooling system. The device includes a control unit, a monitoring unit, a flow regulating unit, and a cold plate with a heat load for each branch, and a pipeline: the control unit performs negative feedback regulation according to the temperature on the branch, and the temperature signal is converted into an electrical signal, which serves as a driving control signal for the flow regulating unit to adjust; the monitoring unit collects the flow and temperature signals on the branch where it is located, and feeds them back to the control unit; the flow regulating unit adjusts the two-phase cooling medium flow of the branch where it is located according to the driving control signal; the cold plate is provided with a two-phase cooling flow channel; the pipeline connects the flow regulating unit, the monitoring unit, and the cold plate with a heat load of each branch to form a parallel two-phase working medium passage. The present invention can solve the uneven flow distribution and flow instability caused by the unbalanced heat load of multiple parallel branches of the two-phase cooling system through functions such as inlet throttling and flow regulation, and ensure that each branch is not burned due to excessive temperature.

[0006] This technical invention includes multiple parallel branches, each branch includes a flow regulating unit, a monitoring unit, a resistance regulating unit and a cold plate with a heat load, so it has the same problem as the above invention, and the system is complex in actual use. Summary of the invention

[0007] The present invention proposes a multi-branch flow distribution method based on two-phase flow cooling technology, aiming to solve the problem of multi-branch flow distribution of two-phase cooling medium under the condition of limited space size.

[0008] The technical solution to realize the present invention is: a parallel multi-branch flow distribution method based on two-phase cooling technology, which is suitable for realizing parallel multi-branch flow distribution of two-phase cooling medium inside a confined space, and the steps are as follows:

[0009] Step 1, designing a flow distribution device;

[0010] Step 2, design and verify the internal flow channel structure parameters of the parallel branch cold plate 2;

[0011] Step 3, perform flow distribution structure simulation design;

[0012] Step 4, designing the liquid collecting cavity structure;

[0013] Step 5: Distribute traffic.

[0014] Compared with the prior art, the present invention has the following significant advantages:

[0015] (1) It is easy to realize the flow distribution of multiple parallel branches in a confined space, occupies a small space, has a compact structure, and can fully realize the high integration and lightweight design of the two-phase cooling system.

[0016] (2) According to the heat dissipation requirements of different branches, uneven flow distribution can be achieved, which can ensure that the flow boiling heat transfer has good stability.

[0017] (3) Multiple parallel branches do not require accessories such as solenoid valves and constant flow valves, which fully reduces the number of interfaces in the pipeline and greatly reduces the occurrence rate of system failures and the risk of refrigerant leakage in the pipeline. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the internal flow channel structure parameters of the cold plate with rectangular flow channels described in the present invention.

[0019] Figure 2 It is a schematic diagram of the overall assembly structure of the parallel branch flow distribution device based on the two-phase cooling technology described in the present invention.

[0020] Figure 3 It is a schematic diagram of the parallel multi-branch flow distribution framework structure based on the two-phase cooling technology described in the present invention.

[0021] Figure 4 It is a schematic diagram of the reverse side open cover structure of the parallel branch flow distribution frame based on the two-phase cooling technology described in the present invention.

[0022] Figure 5 It is a front structural schematic diagram of the parallel branch flow distribution framework based on the two-phase cooling technology described in the present invention.

[0023] Figure 6 It is a structural schematic diagram of the parallel branch cold plate described in the present invention.

[0024] Figure 7 It is a schematic diagram of the open cover structure of the parallel branch cold plate described in the present invention.

[0025] In the figure, 1, flow distribution frame; 2, parallel branch cold plate; 11, flow distribution body; 12, flow distribution cover; 110, liquid supply port; 111, liquid outlet; 112, liquid distribution cavity; 113, liquid collection cavity; 114, parallel branch liquid supply through hole; 115, parallel branch liquid outlet through hole; 116, sealing joint installation hole; 117, parallel branch cold plate installation positioning hole; 118, cold plate fastening threaded hole; 119, cavity support column; 21 parallel branch cold plate body; 22, parallel branch cold plate cover; 23, parallel branch cold plate inlet; 24, parallel branch cold plate outlet; 25, parallel branch cold plate flow channel; 26, heat source; 27, sealing joint; 28, parallel branch cold plate installation positioning pin. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] 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 components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0028] In addition, in the present invention, the descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0029] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation" and the like should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; "connection" can be a mechanical connection or an electrical connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] 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 the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0031] The following will further introduce the specific implementation method, as well as the technical difficulties and inventive points of this invention in combination with this design example.

[0032] The present invention provides a parallel multi-branch flow distribution method based on two-phase cooling technology, which is suitable for realizing parallel multi-branch flow distribution of two-phase cooling medium inside a confined space, and includes the following main steps:

[0033] Step 1: Design a flow distribution device.

[0034] Combination Figure 2 to Figure 7The flow distribution device includes a flow distribution frame 1, a parallel branch cold plate 2 and a plurality of sealing joints 27, wherein the flow distribution frame 1 is formed by welding a flow distribution body 11 and a flow distribution cover plate 12 through stir friction welding or other methods, and a liquid separation cavity 112 and a liquid collection cavity 113 are formed inside the flow distribution frame 1 after welding, and a liquid supply port 110, a liquid outlet port 111, a parallel branch liquid supply through hole 114, a parallel branch liquid outlet through hole 115, a sealing joint mounting hole 116, a parallel branch cold plate mounting positioning hole 117, a cold plate fastening threaded hole 118, and a cavity support column 119 are processed on the flow distribution body 11, wherein the liquid supply port 110 is interconnected with the liquid separation cavity 112, the liquid outlet port 111 is interconnected with the liquid collection cavity 113, and the liquid separation cavity 112 and the liquid collection cavity 113 are connected to the parallel branch cold plate 2 through a circular through hole. The flow distribution frame 1 and the parallel branch cold plate 2 are sealed and connected via a sealing joint 27 with a through hole inside, and are finally fastened and assembled by fastening screws.

[0035] The parallel branch cold plate 2 is formed by welding the parallel branch cold plate body 21 and the parallel branch cold plate body 22 by stir friction welding or other methods. The parallel branch cold plate inlet 23, the parallel branch cold plate outlet 24 and the parallel branch cold plate flow channel 25 are formed on the parallel branch cold plate body 21 by mechanical processing. After the parallel branch cold plate 2 is processed, the heat source 26, the sealing joint 27 and the parallel branch cold plate installation positioning pin 28 are assembled.

[0036] The cooling medium (such as Freon) first enters the liquid separation chamber 112 from the liquid supply port 110, flows through the liquid separation chamber 112, and then enters the parallel branch cold plate 2 through the sealing joint 27 with a through hole. After boiling heat exchange occurs in the parallel branch cold plate 2, the cooling medium in a gas-liquid two-phase state enters the liquid collecting chamber 113 again through the sealing joint 27 with a through hole, and finally flows out of the liquid outlet 111 after mixing in the liquid collecting chamber 113. At this point, the cooling medium such as Freon completes the flow distribution and heat exchange work.

[0037] Step 2, design and verify the internal flow channel structural parameters of the parallel branch cold plate 2. The flow channel structural parameters of the parallel branch cold plate are designed using the average temperature difference method. When the system is in a stable working state, the phase change temperature point is constant, so it is assumed that the gas phase and liquid phase physical parameters of the cooling medium are constant. There are two types of phase change heat transfer in the phase change process, one is nucleate boiling dominated by bubble generation and separation, and the other is convective boiling heat transfer dominated by annular flow, so the total two-phase heat transfer coefficient is the superposition of the two boiling processes, and the pressure drop of the parallel branch cold plate is mainly composed of acceleration pressure drop and friction pressure drop. The total heat transfer coefficient and total pressure drop are theoretically calculated according to Issam Mudawar's empirical formula. Under the design dryness and the determined cold plate structure size restrictions, the optimal rectangular flow channel structural parameters are determined by the above empirical formula. When the heat load on the parallel branch cold plate 2 is different, the design of the flow channel structural parameters should ensure that the total pressure drop of different parallel branch cold plates is equal. Finally, the parallel branch cold plates under different working conditions and lengths are verified and tested to see if they have equal pressure drops. If there is a large difference in the pressure drops of different parallel branch cold plates, the internal flow channel structure parameters can be appropriately adjusted to ensure that the pressure drops of different parallel branch cold plates are as equal as possible. This is a key step in determining whether the flow distribution design is successful. The definition of the cold plate flow channel structure parameters is shown in Figure 1 .

[0038] The design of the flow channel inside the cold plate includes the calculation of two control parameters: heat transfer coefficient and pressure drop. The present invention adopts the average temperature difference method to carry out the structural design of the cold plate flow channel. In order to simplify the calculation, it is necessary to make the following assumptions about the flow process of the cooling medium in the two-phase cold plate:

[0039] Assumption 1: Flow is in a fully developed state;

[0040] Assumption 2: The fluid is considered to be a continuous medium;

[0041] Assumption 3: Neglect viscous dissipation.

[0042] The heat transfer process of the two-phase cold plate mainly occurs inside the flow channel. The inner wall of the flow channel and the surface of the fins are the areas of heat exchange. Its working process can be considered as a steady-state heat transfer process. The heat transfer process consists of the following three links:

[0043] a. Heat transfer from the heat generating components inside the chip to the outer surface of the cold plate, i.e. heat conduction;

[0044] b. Heat transfer from the outer surface of the cold plate to the inner surface of the cold plate and the surface of the fins, that is, heat conduction;

[0045] c. Heat transfer from the inner surface of the cold plate to the heat exchange medium, including convection heat transfer and phase change heat transfer.

[0046] When the average temperature difference method is used to design the cold plate flow channel, since the phase change temperature of the cooling medium at different positions inside the cold plate is close to constant, the physical parameters of its gas phase and liquid phase can be considered to be constant. According to the number of chips on a single cold plate and the heat consumption, the total heat exchange is:

[0047] Q 总 =nQ1

[0048] Among them, Q 总 is the total heat transfer of a single phase change cold plate, n is the number of heat source chips on the cold plate, and Q1 is the heat consumption of a single heat source chip.

[0049] The dryness at the outlet of the primary cold plate is x, and the mass flow rate m of the required cooling medium can be obtained by calculation. 总 :

[0050]

[0051] Among them, h fg It is the latent heat of vaporization of the cooling medium.

[0052] For a cold plate with rectangular flow channels, the heat sink analysis method is used to Figure 1 The flow channel unit cell shown in the figure is analyzed, and the wall temperature T w and phase transition temperature T sat Has the following relationship:

[0053]

[0054] Where: q is the average heat flux density of the cold plate heating surface, q H is the average heat flux density of the effective heating surface of the cold plate, W ch is the width of the channel, H ch is the height of the channel, λ is the thermal conductivity of the cold plate, W s is the thickness of the rectangular fin, h tp is the total two-phase heat transfer coefficient, T sat is the liquid saturation temperature of the selected cooling medium, and η and m are intermediate variables.

[0055] Therefore, the average temperature difference Δt m for:

[0056] Δt m =T w -T sat

[0057] By looking up the heat exchanger design manual, the heat transfer coefficient k0 is initially selected and the heat transfer area A is calculated. o .

[0058]

[0059] Based on the heat transfer area, the number of flow channel cells required inside the cold plate can be estimated. Once the size and number of flow channel cells are determined, the mass flow rate G of the cooling medium inside the cold plate can be calculated.

[0060]

[0061] Among them, m 总 Represents the mass flow rate of the cooling medium, A 流通截面 Represents the area of ​​the flow cross section.

[0062] Flow velocity u at the minimum cross section:

[0063]

[0064] Among them, ρ f is the density of the liquid coolant.

[0065] Actual heat exchange area A 总 for:

[0066] A 总 =A 流道底面 +A 流道侧面

[0067] Among them, A 流道底面 is the area of ​​the bottom surface of the flow channel, A 流道侧面 is the area of ​​the side of the flow channel.

[0068] For the calculation of heat transfer coefficient during phase change, the temperature of the fluid changes little during phase change, so the thermal properties of the gas phase and liquid phase are constant. h The relevant calculations are performed as characteristic lengths, and finally the Reynolds number, boiling number, and Weber number are calculated.

[0069] In the phase change process, there are two types of phase change heat transfer, one is nucleate boiling dominated by bubble generation and separation, and the other is convective boiling heat transfer dominated by annular flow. Therefore, the total phase change heat transfer coefficient is the superposition of the two boiling processes. The calculation process of the convective heat transfer coefficient is as follows:

[0070] Liquid phase Reynolds number Re f Defined as:

[0071]

[0072] Where: x is the dryness of the cooling medium, μ f is the dynamic viscosity of the cooling fluid liquid phase.

[0073] The boiling number Bo is defined as:

[0074]

[0075] Where: q H is the average heat flux density of the effective heating surface of the cold plate, h fg is the latent heat of vaporization.

[0076] Comparative pressure P R is defined as:

[0077]

[0078] Where: P is the internal pressure of the cold plate, P crit is the critical pressure of the cooling medium.

[0079] Liquid Weber number We fo is defined as:

[0080]

[0081] Where: σ is the surface tension coefficient of the cooling medium.

[0082] Lockhart-Martinelli parameter X tt Defined as:

[0083]

[0084] Where: μ is the dynamic viscosity of the cooling medium, ρ is the density of the cooling medium, subscript g represents the gas phase, and subscript f represents the liquid phase.

[0085] Nucleate boiling heat transfer coefficient h nb Defined as:

[0086]

[0087] Convective boiling heat transfer coefficient h cb Defined as:

[0088]

[0089] Where: P H is the perimeter length of the microchannel section that is heated, P F is the perimeter length of the microchannel section, Bo is the boiling number, Re is the Reynolds number, Pr is the Prandtl number, λ f is the thermal conductivity of the cooling medium liquid phase, We fo is the Weber number of the liquid phase, P is the internal pressure of the cold plate, P crit is the critical pressure of the cooling medium, P R is the relative pressure, ρ is the density of the cooling medium, D h is the hydraulic diameter, x is the dryness of the cooling medium, X tt is the Lockhart-Martinelli number, the subscript g indicates the gas phase, and the subscript f indicates the liquid phase.

[0090] Overall boiling heat transfer coefficient h tp Defined as:

[0091]

[0092] Among them, h nb is the nucleate boiling heat transfer coefficient, h cb is the convective boiling heat transfer coefficient.

[0093] The cooling medium transfers heat through the two-phase cold plate wall. The entire heat exchange process can be considered a steady-state heat transfer process. According to the calculation formula of the heat transfer process, the total heat transfer coefficient k based on the cold plate surface is:

[0094]

[0095] Among them, δ is the wall thickness of the two-phase cold plate, and λ is the thermal conductivity of the cold plate.

[0096] Verify the heat transfer coefficient:

[0097]

[0098] The pressure loss of a two-phase cold plate generally includes three parts: gravity pressure drop, acceleration pressure drop, and friction resistance pressure drop. Since the gravity pressure drop in this cold plate is small and can be ignored, only the acceleration pressure drop and friction resistance pressure drop are considered here.

[0099] Δp tp =Δp tp,A +Δp tp,F

[0100] Among them, Δp tp is the total pressure drop of the two-phase cold plate, Δp tp,A is the accelerating pressure drop, Δp tp,F is the friction resistance pressure drop.

[0101] Accelerating pressure drop gradient Defined as:

[0102]

[0103] Among them, ν g is the gas specific volume of the cooling medium, ν f is the liquid specific volume of the cooling medium, and x is the dryness of the cooling medium.

[0104] The void fraction α is defined as:

[0105]

[0106] Friction resistance pressure drop gradient Defined as:

[0107]

[0108] Among them, C is the pressure drop factor and X1 is the intermediate variable.

[0109] X1 is defined as:

[0110]

[0111] f g represents the friction factor in the gas phase, f f Represents the friction factor in the gas phase.

[0112] Friction factor f m The calculation formula is:

[0113]

[0114]

[0115] Here, the friction factor f m , in gas phase m = g, in liquid phase m = f; in gas phase Liquid phase μ f is the dynamic viscosity of the cooling medium liquid phase, μ g is the dynamic viscosity of the cooling medium in gas phase.

[0116] The definition of the pressure drop factor C is:

[0117]

[0118] Non-boiling pressure drop factor C non-boiling is defined as:

[0119]

[0120] Where: subscript f o Represents only liquid phase, subscript g o Represents gas phase only.

[0121] Suratman number of the gas phase go is defined as:

[0122]

[0123] Among them, μ g is the gas phase dynamic viscosity coefficient of the cooling medium, ρ g is the gas phase density of the cooling medium.

[0124] According to the above calculation method, the flow channel structure parameters of the cold plate with different heat loads and different size constraints can be calculated, and the flow channel structure parameters of the cold plate can be fine-tuned to make different parallel branch cold plates have the same pressure drop.

[0125] The lengths of the plurality of parallel branch cold plates are the same, but the heat loads are different;

[0126] The lengths of the above-mentioned multiple parallel branch cold plates are different, and the heat loads are also different;

[0127] The above-mentioned multiple parallel branch cold plates are arranged asymmetrically in structure, and the liquid distribution cavity structure and the liquid collection cavity structure are in an asymmetrical state;

[0128] The sealing joint between the flow distribution frame and the parallel branch cold plate is replaced with other joints that can ensure gas-liquid two-phase sealing;

[0129] The flow distribution frame in the above-mentioned flow distribution device is two separate structural parts, rather than an integrated structure.

[0130] Step 3: Conduct flow distribution structure simulation design.

[0131] Under the conditions of certain heat load and design dryness of each parallel branch, the flow rate of each parallel branch can be determined, from which the total flow rate of the system that needs to dissipate heat can be known. Since cooling media such as Freon are in a supercooled liquid state before entering the parallel branch, the structure design of the liquid distribution cavity is carried out according to the method of multi-parallel branch flow distribution of single-phase liquid cooling, and the flow rate is controlled by adjusting the diameter of the through hole between the liquid distribution cavity and the parallel branch cold plate. In order to ensure that the flow distribution frame and the flow distribution cover are easy to weld and form, a cylinder can be appropriately added inside the liquid distribution cavity as a supporting structure, which can not only play a role in flow regulation, but also can fully improve the structural strength.

[0132] Step 4: Design the liquid collecting chamber structure.

[0133] The liquid collecting chamber is located at the outlet of the parallel branch cold plate. The parallel branch cold plate and the liquid collecting chamber are connected through a through hole. After the cooling medium such as Freon enters the parallel branch cold plate, its dryness increases continuously along the flow direction. Since the liquid-gas density ratio of cooling medium such as Freon is relatively large, the diameter of the through hole at the outlet of the parallel branch cold plate should be increased as much as possible. The gas-liquid two-phase state of the working medium flowing out of different parallel branch cold plates enters the liquid collecting chamber and is fully mixed to form an isopressure chamber. Therefore, the size of the liquid collecting chamber should be increased as much as possible while ensuring the strength of the flow distribution frame structure. Usually, a cylindrical support structure is added inside the liquid collecting chamber to reduce the difficulty of welding and increase the structural strength. Finally, the gas-liquid two-phase state of the working medium in the liquid collecting chamber flows out through the liquid outlet.

[0134] Step 5: Distribute traffic.

[0135] According to the selected dryness value and the total heat consumption of the system, a cooling medium such as Freon with a set mass flow rate enters the liquid separation chamber 112 through the liquid supply port 110 of the flow distribution device. Since the cooling medium such as Freon is in a supercooled liquid state at this time, the liquid separation chamber 112 has an isobaric chamber function. Then, the cooling medium such as Freon enters each parallel branch cold plate 2 through the parallel branch liquid supply through hole 114 with different apertures under the action of the system pressure. The mass flow rate entering the parallel branch cold plate 2 is achieved by controlling the aperture of the parallel branch liquid supply through hole 114. In step 2, the two-phase cold plates with different heat loads and different size constraints are controlled by controlling the flow channel section parameters of the parallel branch cold plate 2 to achieve the same pressure drop. Therefore, the cooling medium in the two-phase state has the same pressure when entering the liquid collection chamber 113 at this time. After entering the liquid collecting chamber 113 through different parallel branch cold plates 2, the two-phase cooling medium is fully mixed in the liquid collecting chamber 113 and then flows out of the flow distribution device through the liquid outlet 110. At this time, the flow distribution and boiling heat exchange of the two-phase cooling medium are completed.

[0136] Embodiment 1:

[0137] like Figure 2 As shown, a certain type of phased array platform structure has 16 cold plates in total, and the length and heat load of the 8 long cold plates in the middle are both twice that of the short cold plates on both sides. Therefore, this embodiment needs to realize the flow distribution of 16 parallel branch cold plates.

[0138] Design and verification of cold plate flow channel structural parameters. Figure 7 As shown, the flow channel form of this embodiment is selected as a rectangular flow channel. Relying on the Issam Mudawar empirical formula, it is calculated that the flow channel width of the 8 long cold plates in the middle is 13.7mm and the depth is 5mm. Rectangular fins with a thickness of 0.75mm are arranged in the middle of the flow channel. The spacing between the fins is 1.25mm. There are 10 rows of rectangular fins arranged along the width direction of the flow channel. The flow channel width of the 8 short cold plates on both sides is 11.2mm and the depth is 3mm. Rectangular fins with a thickness of 0.75mm are arranged in the middle of the flow channel. The spacing between the rectangular fins is 1.25mm. There are 8 rows of rectangular fins arranged along the width direction of the flow channel. After actual testing, the flow rate of the long cold plate and the short cold plate matches the heat load under the condition that the heat load and volume flow rate are both 2 times the relationship, and the pressure drop of the two cold plates is nearly equal.

[0139] Simulation design of flow distribution structure. The design of flow distribution structure includes the design of liquid distribution cavity and the determination of through-hole size. First, according to the heat load and design dryness, the total flow of cooling medium such as Freon required by the flow distribution device and the flow required by each parallel branch cold plate can be calculated, and then the simulation calculation of flow distribution can be carried out. Cooling medium such as Freon is in a single-phase liquid state before entering the parallel branch cold plate, and because the cold plate flow channel designed in the first step has the same total pressure drop, the Fluent software is used here to simulate and calculate according to the flow distribution method of single-phase liquid cooling. The flow distribution between different parallel branch cold plates is achieved by changing the diameter of the through-hole from the liquid distribution cavity to the parallel branch cold plate. The through-hole diameter of the middle 8 long cold plates is 5mm, and the through-hole diameter of the 8 short cold plates on both sides is 3.5mm. After determining the diameter of the through-hole connected to different cold plates, according to the simulation flow field diagram, a cylindrical cavity support column is added at the position where the flow velocity inside the liquid distribution cavity is close to zero, so as to increase the structural strength after welding.

[0140] Design of the liquid collecting cavity structure. Since this embodiment is a miniaturized platform, the sub-liquid cavity and the liquid collecting cavity are designed as an integrated layout. The dryness of cooling media such as Freon continues to increase after flowing through the parallel branch cold plate, and the liquid-to-gas density ratio of cooling media such as Freon is relatively large. In order to ensure that the cooling media in the gas-liquid two-phase state are smoothly discharged from the parallel branch, the diameter of the through hole here is designed to be 6mm. Similarly, in this embodiment, a cylindrical cavity support column is appropriately added to the liquid collecting cavity to increase the structural strength after welding. All the gas-liquid two-phase cooling media converge in the liquid collecting cavity and are fully mixed before flowing out of the flow distribution device through the liquid outlet.

[0141] Finally, after experimental verification, it was found that the design of this embodiment can accurately realize the flow distribution of multiple parallel branches based on the two-phase cooling technology, and can ensure the flow stability of the two-phase cooling system under the designed working conditions.

Claims

1. A parallel multi-branch flow distribution method based on two-phase cooling technology, characterized in that: It is suitable for realizing parallel multi-branch flow distribution of two-phase cooling medium inside a confined space. The steps are as follows: Step 1, designing a flow distribution device; Step 2, designing and verifying the internal flow channel structure parameters of the parallel branch cold plate (2); Step 3: Conduct flow distribution structure simulation design; Step 4, designing the liquid collecting cavity structure; Step 5: Distribute traffic.

2. The parallel multi-branch flow distribution method based on two-phase cooling technology according to claim 1 is characterized in that: In step 1, the flow distribution device is designed as follows: The flow distribution device comprises a flow distribution frame (1), a parallel branch cold plate (2) and a plurality of sealing joints (27), wherein the flow distribution frame (1) is formed by welding two parts, namely a flow distribution body (11) and a flow distribution cover plate (12), and after welding, a liquid distribution cavity (112) and a liquid collection cavity (113) are formed inside the flow distribution frame (1), and the flow distribution body (11) is processed with a liquid supply port (110), a liquid outlet port (111), a parallel branch liquid supply through hole (114), a parallel branch liquid outlet through hole (115), and a sealing joint installation hole (116). 6) parallel branch cold plate installation positioning holes (117), cold plate fastening threaded holes (118), and cavity support columns (119), wherein the liquid supply port (110) is interconnected with the liquid separation chamber (112), the liquid outlet (111) is interconnected with the liquid collection chamber (113), and the liquid separation chamber (112) and the liquid collection chamber (113) are connected to the parallel branch cold plate (2) through circular through holes; the flow distribution frame (1) and the parallel branch cold plate (2) are sealed and connected through a sealing joint (27) with a through hole inside, and finally fastened and assembled by fastening screws; The parallel branch cold plate (2) is formed by welding a parallel branch cold plate body (21) and a parallel branch cold plate body (22); a parallel branch cold plate inlet (23), a parallel branch cold plate outlet (24) and a parallel branch cold plate flow channel (25) are formed on the parallel branch cold plate body (21) by mechanical processing; after the parallel branch cold plate (2) is processed, a heat source (26), a sealing joint (27) and a parallel branch cold plate installation positioning pin (28) are assembled; The cooling medium first enters the liquid separation chamber (112) from the liquid supply port (110), flows through the liquid separation chamber (112), and then enters the parallel branch cold plate (2) through the sealing joint (27) with a through hole. After boiling heat exchange occurs in the parallel branch cold plate (2), the cooling medium in a gas-liquid two-phase state enters the liquid collection chamber (113) through the sealing joint (27) with a through hole again, and finally flows out of the liquid outlet (111) after mixing in the liquid collection chamber (113). At this point, the cooling medium such as Freon completes flow distribution and heat exchange.

3. The parallel multi-branch flow distribution method based on two-phase cooling technology according to claim 2 is characterized in that: In step 2, the internal flow channel structure parameters of the parallel branch cold plate (2) are designed and verified, as follows: The parallel branch cold plate flow channel structural parameters are designed using the average temperature difference method. When the system is in a stable working state, the phase change temperature point is constant, so it is assumed that the gas phase and liquid phase physical parameters of the cooling medium are constant values. There are two types of phase change heat transfer in the phase change process, one is nucleate boiling dominated by bubble generation and separation, and the other is convective boiling heat transfer dominated by annular flow. Therefore, the total two-phase heat transfer coefficient is the superposition of the two boiling processes, and the pressure drop of the parallel branch cold plate is mainly composed of acceleration pressure drop and friction pressure drop. The total heat transfer coefficient and total pressure drop are theoretically calculated according to Issam Mudawar's empirical formula; Under the constraints of designed dryness and determined cold plate structure size, the optimal structural parameters of the rectangular flow channel are determined by the above empirical formula; When the heat loads on the parallel branch cold plates (2) are different, the design of the flow channel structural parameters should ensure that the total pressure drops of the different parallel branch cold plates are equal; Finally, the parallel branch cold plates under different working conditions and lengths are verified and tested to check whether they have equal pressure drops; if there is a large difference in the pressure drops of different parallel branch cold plates, the internal flow channel structure parameters are adjusted to ensure that the pressure drops of different parallel branch cold plates are as equal as possible.

4. The parallel multi-branch flow distribution method based on two-phase cooling technology according to claim 3 is characterized in that: The average temperature difference method is used to carry out the structural design of the cold plate flow channel, and the following assumptions are made for the flow process of the cooling medium in the two-phase cold plate: Assumption 1: Flow is in a fully developed state; Assumption 2: The fluid is considered to be a continuous medium; Assumption 3: Ignore viscous dissipation; The heat transfer process of the two-phase cold plate mainly occurs inside the flow channel. The inner wall of the flow channel and the surface of the fins are the areas of heat exchange. Its working process can be considered as a steady-state heat transfer process. The heat transfer process consists of the following three links: a. Heat transfer from the heat generating components inside the chip to the outer surface of the cold plate, i.e. heat conduction; b. Heat transfer from the outer surface of the cold plate to the inner surface of the cold plate and the surface of the fins, that is, heat conduction; c. Heat transfer from the inner surface of the cold plate to the heat exchange medium, including convection heat transfer and phase change heat transfer; In the design using the average temperature difference method, since the phase change temperature of the cooling medium at different positions inside the cold plate is close to constant, the physical parameters of its gas phase and liquid phase can be considered as constant values; According to the number of chips on a single cold plate and the heat consumption, the total heat exchange is: Q 总 =nQ1 Among them, Q 总 is the total heat transfer capacity of a single phase change cold plate, n is the number of heat source chips on the cold plate, and Q1 is the heat consumption of a single heat source chip; The dryness at the outlet of the cold plate is initially selected as x, and the mass flow rate m of the required cooling medium is calculated. 总 : Among them, h fg The latent heat of vaporization of the cooling medium; For a cold plate with a rectangular flow channel, the flow channel unit cell is analyzed using the heat sink analysis method. The wall temperature T w and phase transition temperature T sat Has the following relationship: Where: q is the average heat flux density of the cold plate heating surface, q H is the average heat flux density of the effective heating surface of the cold plate, W ch is the width of the channel, H ch is the height of the channel, λ is the thermal conductivity of the cold plate, W s is the thickness of the rectangular fin, h tp is the total two-phase heat transfer coefficient, T sat is the liquid saturation temperature of the selected cooling medium, η and m are both intermediate variables; Therefore, the average temperature difference Δt m for: Δt m =T w -T sat By looking up the heat exchanger design manual, the heat transfer coefficient k0 is initially selected and the heat transfer area A is calculated. o ; According to the heat transfer area, estimate the number of flow channel cells required inside the cold plate; According to the size and number of flow channel cells, calculate the mass flow rate G of the cooling medium inside the cold plate; Among them, m 总 Represents the mass flow rate of the cooling medium, A 流通截面 Represents the area of ​​the flow cross section; Flow velocity u at the minimum cross section: Among them, ρ f is the density of the liquid coolant; Actual heat exchange area A 总 for: A 总 =A 流道底面 +A 流道侧面 Among them, A 流道底面 is the area of ​​the bottom surface of the flow channel, A 流道侧面 is the area of ​​the side of the flow channel; For the calculation of heat transfer coefficient during phase change, the temperature of the fluid changes little during phase change, so the thermal properties of the gas phase and the liquid phase are constant. h As the characteristic length, relevant calculations are performed, and finally the Reynolds number, boiling number, and Weber number are calculated; In the phase change process, there are two types of phase change heat transfer, one is nucleate boiling dominated by bubble generation and separation, and the other is convective boiling heat transfer dominated by annular flow. Therefore, the total phase change heat transfer coefficient is the superposition of the two boiling processes. The calculation process of the convective heat transfer coefficient is as follows: Liquid phase Reynolds number Re f Defined as: Where: x is the dryness of the cooling medium, μ f is the dynamic viscosity of the cooling medium liquid phase; The boiling number Bo is defined as: Where: q H is the average heat flux density of the effective heating surface of the cold plate, h fg is the latent heat of vaporization; Comparative pressure P R is defined as: Where: P is the internal pressure of the cold plate, P crit is the critical pressure of the cooling medium; Liquid Weber number We fo is defined as: Where: σ is the surface tension coefficient of the cooling medium; Lockhart-Martinelli parameter X tt Defined as: Where: μ is the dynamic viscosity of the cooling medium, ρ is the density of the cooling medium, subscript g represents the gas phase, and subscript f represents the liquid phase; Nucleate boiling heat transfer coefficient h nb Defined as: Convective boiling heat transfer coefficient h cb Defined as: Where: P H is the perimeter length of the microchannel section that is heated, P F is the perimeter length of the microchannel section, Bo is the boiling number, Re is the Reynolds number, Pr is the Prandtl number, λ f is the thermal conductivity of the cooling medium liquid phase, We fo is the Weber number of the liquid phase, P is the internal pressure of the cold plate, P crit is the critical pressure of the cooling medium, P R is the relative pressure, ρ is the density of the cooling medium, D h is the hydraulic diameter, x is the dryness of the cooling medium, X tt is the Lockhart-Martinelli number, subscript g indicates the gas phase, and subscript f indicates the liquid phase; Overall boiling heat transfer coefficient h tp Defined as: Among them, h nb is the nucleate boiling heat transfer coefficient, h cb is the convective boiling heat transfer coefficient; The cooling medium transfers heat through the two-phase cold plate wall. The entire heat exchange process is considered to be a steady-state heat transfer process. According to the calculation formula of the heat transfer process, the total heat transfer coefficient k based on the cold plate surface is obtained as follows: Among them, δ is the wall thickness of the two-phase cold plate, and λ is the thermal conductivity of the cold plate; Verify the heat transfer coefficient:

5. The parallel multi-branch flow distribution method based on two-phase cooling technology according to claim 4 is characterized in that: The pressure loss of the two-phase cold plate includes three parts: gravity pressure drop, acceleration pressure drop, and friction resistance pressure drop. Since the gravity pressure drop in this cold plate is small and negligible, only the acceleration pressure drop and friction resistance pressure drop are considered here. Δp tp =Δp tp,A +Δp tp,F Among them, Δp tp is the total pressure drop of the two-phase cold plate, Δp tp,A is the accelerating pressure drop, Δp tp,F is the friction resistance pressure drop; Accelerating pressure drop gradient Defined as: Among them, ν g is the gas specific volume of the cooling medium, ν f is the liquid specific volume of the cooling medium, and x is the dryness of the cooling medium; The void fraction α is defined as: Friction resistance pressure drop gradient Defined as: Among them, C is the pressure drop factor, and X1 is the intermediate variable; X1 is defined as: f g represents the friction factor in the gas phase, f f Represents the friction factor in the gas phase; Friction factor f m The calculation formula is: Here, the friction factor f m , in gas phase m = g, in liquid phase m = f; in gas phase Liquid phase μ f is the dynamic viscosity of the cooling medium liquid phase, μ g is the dynamic viscosity of the cooling medium gas phase; The definition of the pressure drop factor C is: Non-boiling pressure drop factor C non-boiling is defined as: Where: subscript f o Represents only liquid phase, subscript g o It represents only the gas phase; Suratman number of the gas phase go is defined as: Among them, μ g is the gas phase dynamic viscosity coefficient of the cooling medium, ρ g is the gas phase density of the cooling medium; According to the above calculation method, the flow channel structure parameters of the cold plate with different heat loads and different size constraints are calculated, and the flow channel structure parameters of the cold plate are fine-tuned to make different parallel branch cold plates have the same pressure drop.

6. The parallel multi-branch flow distribution method based on two-phase cooling technology according to claim 5 is characterized in that: In step 3, the flow distribution structure simulation design is performed as follows: Under the condition that the heat load and design dryness of each parallel branch are certain, the flow rate of each parallel branch is determined, from which the total flow rate of the system required for heat dissipation can be known; since the cooling medium is in a supercooled liquid state before entering the parallel branch, the structure design of the liquid distribution cavity is carried out according to the method of flow distribution of multiple parallel branches of single-phase liquid cooling, and the flow rate is controlled by adjusting the diameter of the through hole between the liquid distribution cavity and the parallel branch cold plate; In order to ensure that the flow distribution frame and the flow distribution cover are easy to weld and form, a cylinder can be appropriately added inside the liquid separation cavity as a supporting structure, which can not only play a role in flow regulation, but also can fully improve the structural strength.

7. The parallel multi-branch flow distribution method based on two-phase cooling technology according to claim 6 is characterized in that: In step 4, the liquid collecting chamber structure is designed as follows: The liquid collecting chamber is located at the outlet of the parallel branch cold plate. The parallel branch cold plate and the liquid collecting chamber are connected through a through hole. After the cooling medium enters the parallel branch cold plate, its dryness increases continuously along the flow direction. Since the liquid-gas density ratio of the cooling medium is relatively large, the diameter of the through hole at the outlet of the parallel branch cold plate should be increased as much as possible; the gas-liquid two-phase state of the working medium flowing out of different parallel branch cold plates enters the liquid collecting chamber and is fully mixed to form an isopressure chamber here. Therefore, the size of the liquid collecting chamber should be increased as much as possible while ensuring the strength of the flow distribution frame structure. Usually, a cylindrical support structure is added inside the liquid collecting chamber to reduce the difficulty of welding and increase the structural strength; finally, the gas-liquid two-phase state of the working medium in the liquid collecting chamber flows out through the liquid outlet.

8. The parallel multi-branch flow distribution method based on two-phase cooling technology according to claim 7 is characterized in that: In step 5, traffic distribution is performed as follows: According to the selected dryness value and the total heat consumption of the system, a cooling medium with a set mass flow rate enters a liquid separation chamber (112) through a liquid supply port (110) of a flow distribution device. Since the cooling medium is in a supercooled liquid state at this time, the liquid separation chamber (112) has an isobaric chamber function. Then, under the action of the system pressure, the cooling medium enters each parallel branch cold plate (2) through parallel branch liquid supply through holes (114) with different apertures. The mass flow rate entering the parallel branch cold plate (2) is controlled by controlling the parallel branch liquid supply through holes (114). 4); by controlling the flow channel cross-sectional parameters of the parallel branch cold plate (2), the two-phase cold plates with different heat loads and different size constraints have the same pressure drop; therefore, at this time, the two-phase cooling medium has the same pressure when entering the liquid collecting chamber (113); the two-phase cooling medium entering the liquid collecting chamber (113) through different parallel branch cold plates (2) is fully mixed in the liquid collecting chamber (113) and then flows out of the flow distribution device through the liquid outlet (110), and at this time, the flow distribution and boiling heat exchange of the two-phase cooling medium are completed.

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