A phase change direct cooling system

Abstract

The application discloses a phase change direct cooling system and belongs to the technical field of battery cooling, comprising a refrigerant pipeline, the refrigerant pipeline comprising a liquid pipeline, a gas-liquid two-phase pipeline and a gas pipeline; the final pipe diameter of the refrigerant pipeline is obtained in the following manner: a, the gas-liquid two-phase pipeline selects a standard model pipe with the minimum absolute difference value according to the calculated theoretical two-phase pipeline pipe diameter, then the minimum standard mass flow rate and the standard saturation temperature drop are obtained and scoring judgment is performed until the final pipe diameter meeting the requirements is obtained; b, the liquid pipeline selects the pipe diameter of the standard model pipe with the minimum absolute difference value as the final pipe diameter according to the calculated theoretical liquid pipeline pipe diameter; c, the gas pipeline selects the pipe diameter of the standard model pipe with the minimum absolute difference value as the final pipe diameter according to the calculated theoretical gas pipeline pipe diameter. The application realizes uniform distribution of refrigerant and improves the overall temperature uniformity of the battery under the premise of ensuring the reliability of oil return by reasonably determining the pipeline structure and the pipe diameter.

Description

Technical Field

[0001] This invention belongs to the field of battery cooling technology, specifically relating to a phase change direct cooling system. Background Technology

[0002] Energy storage technology is a crucial means of meeting the large-scale integration of renewable energy and an important component of distributed energy systems and the electric vehicle industry. Due to their high efficiency, good dynamic characteristics, long lifespan, and near-independence from terrain, energy storage batteries are widely used in energy storage power stations, battery swapping stations, and other similar scenarios. As energy storage systems develop towards larger capacity and higher energy density, battery thermal management issues are becoming increasingly prominent. Excessive battery temperature or uneven temperature distribution directly affects the battery's charge and discharge efficiency, capacity decay rate, and lifespan, and in severe cases, may even lead to thermal runaway and other safety accidents.

[0003] In the field of battery thermal management, cooling technology has evolved from air cooling to liquid cooling, and then to phase change direct cooling. Liquid cooling generally refers to single-phase liquid cooling, where the cooling medium exists in a single liquid state, currently mainly using ethylene glycol aqueous solution as the cooling medium. Phase change direct cooling, on the other hand, uses refrigerant direct cooling, with special chemical refrigerants such as R134a and R410A as the cooling medium. When cooling the battery, the refrigerant absorbs heat and changes from a liquid state to a gas state. The heat transfer coefficient of the phase change process is higher than that of single-phase liquid cooling. For example, patent document CN220934195U discloses a direct-cooling energy storage battery pack, battery cluster, and system. Phase change direct cooling systems, represented by this patent document, typically include a compressor, condenser, regenerator, electronic expansion valve, distributor, and direct cooling plate connected by refrigerant pipelines. The refrigerant circulates within the refrigerant pipelines under the combined action of these components and cools the battery through the direct cooling plate. Compared to traditional liquid cooling solutions, direct cooling introduces the refrigerant directly into the direct cooling plate inside the battery pack. This method has fewer system components, responds quickly to battery temperature, and the volatility of the refrigerant does not pose a threat to the safety of the battery and the system. As a result, it is becoming increasingly widely used.

[0004] As is well known, refrigerant piping and distributors play a crucial role in the uniform distribution and mixing of refrigerant. If the diameter of the refrigerant piping is too large or too small, the refrigerant will not be distributed uniformly. When liquid refrigerant passes through the electronic expansion valve, the valve exerts an isenthalpic throttling (pressure reduction) effect, converting the liquid refrigerant into a two-phase gas-liquid state. If the distributor structure is unreasonable, the two-phase refrigerant will not mix uniformly. However, in this field, when designing the refrigerant piping diameter, technicians only consider the refrigerant's mass flow rate based on the lubricating oil return flow rate requirement. When designing the distributor, they only consider how to distribute the liquid, without considering whether the refrigerant is evenly distributed in the piping and evenly mixed in the distributor. This results in technical problems that affect the overall temperature uniformity of the battery.

[0005] Therefore, how to achieve uniform distribution and mixing of refrigerant by using reasonable pipeline diameter and distributor structure while ensuring the reliability of oil return is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] To address the aforementioned technical problems in the prior art, this invention proposes a phase change direct cooling system. By determining a reasonable pipeline structure and pipe diameter, it achieves uniform distribution of the refrigerant while ensuring reliable oil return, thereby improving the overall temperature uniformity of the battery.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A phase change direct cooling system includes a compressor, a condenser, a regenerator, refrigerant piping, several electronic expansion valves, several distributors, and several direct cooling plates. The refrigerant piping includes a liquid piping arranged between the condenser and each electronic expansion valve via the regenerator, a gas-liquid two-phase piping arranged between the electronic expansion valves and the inlet of the direct cooling plate via the distributors, and a gaseous piping arranged between the outlet of the direct cooling plate and the condenser via the regenerator and the compressor. The final diameter of the refrigerant piping is determined by the following method: a. The theoretical two-phase pipeline diameter is calculated based on the total mass flow rate and mass velocity of the refrigerant. Based on the theoretical two-phase pipeline diameter, the absolute difference between the diameter of each standard model pipe and the theoretical two-phase pipeline diameter is calculated. The standard model pipe with the smallest absolute difference is selected. Then, the minimum standard mass flow rate and standard saturation temperature drop are obtained in combination with the standard model pipe. The minimum standard mass flow rate and standard saturation temperature drop are scored and judged until the final pipe diameter that meets the requirements is obtained. b. The theoretical liquid pipeline diameter is calculated based on the total mass flow rate of the refrigerant, combined with the liquid density of the liquid refrigerant and the design flow rate. Based on the theoretical liquid pipeline diameter, the absolute difference between the diameter of each standard model pipe and the theoretical liquid pipeline diameter is calculated, and the pipe diameter of the standard model pipe with the smallest absolute difference is selected as the final pipe diameter. c. The theoretical gaseous pipeline diameter is calculated based on the total mass flow rate of the refrigerant, combined with the gas density and design flow rate of the gaseous refrigerant. Based on the theoretical gaseous pipeline diameter, the absolute difference between the diameter of each standard model pipe and the theoretical gaseous pipeline diameter is calculated, and the pipe diameter of the standard model pipe with the smallest absolute difference is selected as the final pipe diameter.

[0008] The total mass flow rate of the refrigerant is obtained in the following way: (1) Calculate the rated cooling capacity of the direct cooling unit according to the cooling load demand; determine the evaporation temperature of the direct cooling unit according to the load conditions, and obtain the corresponding saturation pressure according to the evaporation temperature; (2) Based on the evaporation temperature and saturation pressure, and combined with the set refrigerant subcooling at the condenser outlet and refrigerant superheat at the direct cooling plate outlet, determine the specific enthalpy at the inlet and outlet of the direct cooling plate; (3) The total mass flow rate of the refrigerant is calculated based on the rated cooling capacity and the specific enthalpy of the inlet and outlet of the direct cooling plate.

[0009] The formula for calculating the rated cooling capacity of the direct-cooling unit is: P_cool=Q_cool / 4h ; Q_cool=Q_bat_ gen-Q_bat_absorb+Q_envi ; In the formula, P_cool This refers to the rated cooling capacity of the direct-cooling unit; Q_cool For the cooling load of the direct-cooling unit; 4h The charging and discharging time of the battery; Q_bat_ gen The heat generated by the battery during charging and discharging can be obtained by multiplying the heat generated by each individual battery cell by the total number of batteries. Q_bat_absorb The design allows for a battery temperature rise of 10°C to account for the heat absorbed by the battery. This is calculated by multiplying the battery's specific heat capacity by the total mass of the battery by the temperature rise. Q_envi The environmental heat load is calculated as the product of the specific heat capacity of the air inside the battery compartment, the air mass, and the change in air temperature.

[0010] The evaporation temperature is determined based on the heat generation and heat transfer temperature difference of the battery under rated operating conditions. This heat transfer temperature difference is the temperature difference between the battery and the direct cooling plate. The saturation pressure is obtained by referring to the thermophysical property parameter table based on the evaporation temperature.

[0011] The specific enthalpy at the inlet of the direct cooling plate is obtained from the pressure-enthalpy diagram of the system based on the saturation pressure and the set refrigerant subcooling at the condenser outlet; the specific enthalpy at the outlet of the direct cooling plate is obtained from the pressure-enthalpy diagram of the system based on the evaporation temperature and the set refrigerant superheat at the outlet of the direct cooling plate; wherein the refrigerant subcooling is 0 and the refrigerant superheat is ≤1℃.

[0012] The formula for calculating the total mass flow rate of the refrigerant is: Mr=P_cool / (h_evp_out-h_evp_in) ; In the formula, Mr This refers to the total mass flow rate of the refrigerant. h_evp_in Specific enthalpy of the direct-cooling plate inlet; h_evp_out Specific enthalpy of the direct-cooling plate outlet.

[0013] The gas-liquid two-phase pipeline includes a primary two-phase pipeline connecting the electronic expansion valve and each distributor, and a secondary two-phase pipeline connecting the distributor and each direct cooling plate. The final diameters of the primary and secondary two-phase pipelines are obtained as follows: a1. Within the recommended range of refrigerant mass flow rate, select any data point and combine it with the total mass flow rate of the refrigerant to calculate the theoretical two-phase pipe diameter for the first-stage two-phase pipeline and the theoretical two-phase pipe diameter for the second-stage two-phase pipeline. a2. Based on the theoretical two-phase pipe diameters of the primary and secondary two-phase pipelines, select the standard pipe model with the smallest absolute difference. Calculate the standard mass flow rate of the refrigerant in the primary and secondary two-phase pipelines based on the standard pipe model. Obtain the minimum standard mass flow rate by comparing the standard mass flow rates. Then, based on the standard pipe model, obtain the standard saturation temperature drop by referring to a table. Determine whether the minimum standard mass flow rate and standard saturation temperature drop meet the requirements by scoring them. If not, reselect data within the recommended range of refrigerant mass flow rate and repeat steps a1-a2 until the final pipe diameters of the primary and secondary two-phase pipelines that meet the requirements are obtained.

[0014] The formula for calculating the diameter of the theoretical two-phase pipeline is as follows: D_inner_EXV=sqrt(4A_EXV / π) ; D_inner_branch=sqrt(4A_branch / π) ; in, A_EXV=Mr_EXV / G ; A_branch=Mr_branch / G ; Mr_EXV=Mr / n ; Mr_branch=Mr_EXV / m ; In the formula, D_inner_EXV This refers to the theoretical diameter of a first-order two-phase pipeline. D_inner_branch This refers to the theoretical diameter of a two-phase pipeline. A_EXV This represents the cross-sectional area of ​​a first-stage two-phase pipeline. A_branch This represents the cross-sectional area of ​​a two-phase pipeline. G The refrigerant mass flow rate selected within the recommended range; Mr This refers to the total mass flow rate of the refrigerant. Mr_EXV This refers to the mass flow rate of the refrigerant in the first-stage two-phase piping, specifically the mass flow rate of the refrigerant piping downstream of each electronic expansion valve. n The number of electronic expansion valves; Mr_branch This refers to the mass flow rate of the refrigerant in a two-phase pipeline. m for One The number of secondary two-phase pipelines branched off from the primary two-phase pipeline.

[0015] The formula for calculating the standard mass flow rate of the refrigerant in the first-stage two-phase pipeline is as follows: G 标准一级 =Mr_EXV / A 标准一级 ; In the formula, G 标准一级 The standard mass flow rate of the refrigerant in a first-stage two-phase pipeline. Mr_EXV The mass flow rate of the refrigerant in a first-stage two-phase pipeline; A 标准一级 This refers to the cross-sectional area of ​​the standard model pipe corresponding to a first-level two-phase pipeline.

[0016] The formula for calculating the standard mass flow rate of the refrigerant in the two-phase pipeline is as follows: G 标准二级 =Mr_branch / A 标准二级 ; In the formula, G 标准二级 The standard mass flow rate of the refrigerant in a two-phase pipeline is given. Mr_branch This refers to the mass flow rate of the refrigerant in a two-phase pipeline. A 标准二级 This refers to the cross-sectional area of ​​the standard model pipe corresponding to a two-stage two-phase pipeline.

[0017] The minimum standard mass flow rate is the minimum of the standard mass flow rate of the refrigerant in the first-stage two-phase pipeline and the standard mass flow rate of the refrigerant in the second-stage two-phase pipeline.

[0018] The method for determining the standard saturation temperature drop is as follows: Based on the pipe diameter of the standard model pipe, the mass flow rate of the refrigerant, the dryness fraction of the gas-liquid two-phase refrigerant, the designed pipe length, and the pipe material, the standard pressure drop of the first-stage two-phase pipeline and the standard pressure drop of the second-stage two-phase pipeline are obtained by referring to empirical tables; based on the standard pressure drops of the first-stage and second-stage two-phase pipelines, the corresponding saturation temperature drops are obtained by referring to the refrigerant's thermophysical property parameter table, and the summation yields the standard saturation temperature drop. ΔT_sat ,and ΔT_sat≤1℃ .

[0019] The recommended range for the refrigerant mass flow rate is 150 kg / m³. 2 ·s~400kg / m 2 ·s.

[0020] The liquid pipeline includes a primary liquid phase pipeline connecting the condenser and the regenerator, and a secondary liquid phase pipeline connecting the regenerator and each electronic expansion valve. The theoretical liquid phase pipeline diameter is calculated based on the total mass flow rate of the refrigerant, combined with the liquid density of the liquid refrigerant and the design flow rate. The theoretical liquid phase pipeline diameter is calculated based on the theoretical liquid phase pipeline diameter of the primary liquid phase pipeline.

[0021] The formula for calculating the theoretical diameter of the liquid pipeline is as follows: D_liq=sqrt(4*Mr / (π*ρ_l*v_liq)) ; D_liq_branch=D_liq / sqrt(n) ; In the formula, D_liq This is the theoretical diameter of the liquid phase pipeline in the primary liquid phase pipeline. D_liq_branch This is the theoretical diameter of the liquid phase pipeline in the secondary liquid phase pipeline; Mr This refers to the total mass flow rate of the refrigerant. ρ_l The liquid density of the liquid refrigerant is obtained by consulting the refrigerant's thermal property parameter table based on the ambient temperature, subcooling, condensation pressure, and corresponding saturation temperature under the battery's rated operating conditions. v_liq The design flow rate for the liquid refrigerant, v_liq The speed range is 1.0 m / s to 1.5 m / s. n This refers to the number of electronic expansion valves, which is also the number of secondary liquid phase pipelines branching off from the primary liquid phase pipeline.

[0022] The gaseous piping includes a three-stage gas phase piping from the outlet of each direct cooling plate to the junction of individual battery clusters, a two-stage gas phase piping from the junction of individual battery clusters to the junction of all battery clusters, and a first-stage gas phase piping from the junction of all battery clusters to the condenser. The theoretical gas phase piping diameter of the first-stage gas phase piping is calculated based on the total mass flow rate of the refrigerant, combined with the gas density and design flow rate of the gaseous refrigerant. The theoretical gas phase piping diameters of the two-stage and three-stage gas phase piping are calculated based on the theoretical gas phase piping diameter of the first-stage gas phase piping.

[0023] The formula for calculating the theoretical gaseous pipeline diameter is as follows: D_ gas=sqrt(4*Mr / (π*ρ_ g*v_gas)) ; D_ gas_branch=D_ gas / sqrt(a) ; D_ gas_branch_branch=D_ gas_branch / sqrt(b) ; In the formula, D_ gas This is the theoretical gaseous pipe diameter of a primary gas phase pipeline; D_ gas_branch This is the theoretical gaseous pipe diameter for a secondary gas phase pipeline; D_ gas_branch_branch This is the theoretical gaseous pipe diameter for a three-stage gas phase pipeline; Mr This refers to the total mass flow rate of the refrigerant. ρ_ g The gas density of the gaseous refrigerant in the compressor suction state is obtained by consulting the refrigerant's thermal property parameter table based on the evaporation pressure, evaporation temperature, and superheat. v_ gas The design flow rate for the gaseous refrigerant, v_ gas The speed range is 6 m / s to 15 m / s. a The number of secondary gas phase pipelines branched off from the primary gas phase pipeline; b The number of tertiary gas phase pipelines branched off from the secondary gas phase pipeline.

[0024] The distributor has a dispensing chamber with an inlet and multiple dispensing ports. The dispensing chamber has a three-stage mixing structure for the refrigerant to impact and reflect in sequence. The first-stage mixing structure is fixed directly above the inlet and has a guide slit between it and the bottom surface of the dispensing chamber, so that the refrigerant is sprayed out along the guide slit after impact and reflection. The second-stage mixing structure is arranged around the bottom surface of the dispensing chamber, so that the refrigerant flows upward after impact and reflection. The third-stage mixing structure is arranged around the top surface of the dispensing chamber, so that the refrigerant enters the dispensing ports after impact and reflection.

[0025] The first-stage mixing structure is a conical cap fixed in the liquid distribution chamber by an extension rod, and the inner diameter of the opening of the conical cap is larger than the inner diameter of the liquid inlet.

[0026] The second-stage mixing structure is an inclined ring with a right-angled surface on the outer surface and an inclined surface on the inner surface. The two right-angled surfaces of the inclined ring are respectively attached to the side and bottom surfaces of the liquid separation chamber.

[0027] The third-stage mixing structure is an inclined top surface located between the side and top surfaces of the liquid separation chamber, directly above the inclined ring.

[0028] The liquid dispenser includes a detachable and fixed upper cover and a lower cover. The upper cover has an upper groove with an opening facing downwards, and the lower cover has a lower groove with an opening facing upwards. The upper cover and the lower cover are fixed together by threads. After fixing, the lower end of the upper groove abuts against the bottom surface of the lower groove to form a liquid dispensing chamber. The liquid dispensing ports are evenly distributed on the upper cover, and the liquid inlet is distributed on the lower cover.

[0029] Compared with the prior art, the beneficial effects of the present invention are: 1. Gas-liquid two-phase pipelines involve the uniform distribution of gas-liquid two-phase refrigerant, which is more difficult than that of single-phase refrigerant. This is because single-phase refrigerant has only "one fluid, one density, and one resistance curve," while gas-liquid two-phase refrigerant involves the interaction of two completely different fluids in a single pipeline. In branching and parallel pipelines, there is a natural tendency for phase separation and flow deviation, making flow distribution physically more unstable and difficult to control. Therefore, mechanistically speaking, the flow rate of gas-liquid two-phase refrigerant is distributed in a complex environment of "multiphase, multi-parameter, strong nonlinearity, and easy separation." Thus, determining the final pipe diameter to achieve uniform distribution of gas-liquid two-phase refrigerant is currently a challenge in the industry. Based on existing technologies, this invention specifically considers the overall temperature uniformity of the battery and uses a criterion combining minimum standard mass flow rate and standard saturation temperature drop to determine the final pipe diameter. This not only improves the overall temperature uniformity of the pipeline but also balances the battery temperature uniformity and the reliability of the refrigerant direct cooling system's oil return.

[0030] 2. This invention uses different methods to determine the final pipe diameter for liquid pipelines, gas pipelines, and gas-liquid two-phase pipelines, balancing the requirements of reliable oil return mass flow rate and pipeline flow and temperature uniformity. This not only helps to meet the uniform distribution and flow of refrigerant in different states, but also helps to ensure better overall temperature uniformity of the battery.

[0031] 3. This invention designs a three-stage mixing structure for the distributor, where the refrigerant undergoes sequential impact and reflection. This structure allows the gas-liquid two-phase refrigerant entering the distributor chamber to flow from the center of the bottom surface outwards, from the bottom surface outwards to the top surface outwards, and from the top surface outwards towards the distributor outlet. This three-stage impact and reflection mechanism forces the refrigerant to undergo jetting and multi-stage reversal flow within the confined cavity. This forced reflection and reversal increases the turbulence of the fluid, thereby disrupting gas-liquid stratification and ensuring thorough mixing. This reduces gas-liquid distribution deviation, ultimately resulting in a fully mixed refrigerant forming a vortex within the distributor chamber and flowing out uniformly through the distributor outlet.

[0032] 4. The liquid separator of the present invention has a simple structure and is detachable, with low processing precision requirements, and is easy to install and maintain. It avoids the difficulty of disassembling and replacing the existing integrated liquid separator and liquid distribution pipeline when the working conditions change in the later stage, and effectively ensures the cooling effect of the battery while reducing maintenance costs. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 A cross-sectional view of the separator (I); Figure 3 for Figure 2 A cross-sectional view indicating the direction of refrigerant flow; Figure 4 Cross-sectional view of the separator (II); Figure 5 for Figure 4 A cross-sectional view indicating the direction of refrigerant flow.

[0034] The diagram is labeled as follows: 1. Electronic expansion valve, 2. Direct cooling plate, 3. Condenser, 4. Regenerator, 5. Compressor, 6. Distributor, 7. Primary liquid phase pipeline, 8. Secondary liquid phase pipeline, 9. Primary two-phase pipeline, 10. Secondary two-phase pipeline, 11. Primary gas phase pipeline, 12. Secondary gas phase pipeline, 13. Tertiary gas phase pipeline, 14. Battery compartment, 61. Distributor chamber, 62. Liquid inlet, 63. Distributor port, 64. Conical cover, 65. Sloping ring, 66. Sloping top surface, 67. Top cover, 68. Bottom cover; a is the first impact reflection zone of the refrigerant, b is the second impact reflection zone of the refrigerant, and c is the third impact reflection zone of the refrigerant. Detailed Implementation

[0035] Example 1 like Figure 1 As shown, this embodiment provides a phase change direct cooling system, including a battery compartment 14. The battery compartment 14 houses a compressor 5, a condenser 3, a regenerator 4, refrigerant piping, several electronic expansion valves 1, several distributors 6, and several direct cooling plates 2. Batteries are mounted on the direct cooling plates 2 in the form of battery clusters via supports. Each battery cluster includes multiple layers of batteries stacked vertically. In this embodiment, the number of battery clusters can be 6, and the number of layers in each battery cluster can be 8. The refrigerant piping connects the various devices to form a closed-loop circuit for refrigerant circulation. It includes liquid piping arranged between the condenser 3 and each electronic expansion valve 1 via the regenerator 4; gas-liquid two-phase piping arranged between the electronic expansion valves 1 and the inlet of the direct cooling plate 2 via the distributors 6; and gas piping arranged between the outlet of the direct cooling plate 2 and the condenser 3 via the regenerator 4 and the compressor 5.

[0036] To ensure a reliable refrigerant return flow rate and uniform refrigerant distribution within the pipeline, the refrigerant pipeline needs to be optimized for its diameter. Therefore, this embodiment proposes a technique for determining the final refrigerant pipeline diameter by combining the total refrigerant mass flow rate with other parameters, as detailed below: a. For gas-liquid two-phase pipelines, first calculate the theoretical two-phase pipeline diameter based on the total mass flow rate and mass velocity of the refrigerant. Based on the theoretical two-phase pipeline diameter, calculate the absolute difference between the diameter of each standard model pipe and the theoretical two-phase pipeline diameter. Select the standard model pipe with the smallest absolute difference. Then, combine the standard model pipe to obtain the minimum standard mass flow rate and standard saturation temperature drop. By scoring the minimum standard mass flow rate and standard saturation temperature drop, the final pipe diameter that meets the requirements is obtained.

[0037] b. For liquid pipelines, first calculate the theoretical liquid pipeline diameter based on the total mass flow rate of the refrigerant, combined with the liquid density of the liquid refrigerant and the design flow rate. Then, based on the theoretical liquid pipeline diameter, calculate the absolute difference between the diameter of each standard model pipe and the theoretical liquid pipeline diameter, and select the pipe diameter of the standard model pipe with the smallest absolute difference as the final pipe diameter.

[0038] c. For gaseous pipelines, first calculate the theoretical gaseous pipeline diameter based on the total mass flow rate of the refrigerant, combined with the gas density and design flow rate of the gaseous refrigerant. Then, based on the theoretical gaseous pipeline diameter, calculate the absolute difference between the diameter of each standard model pipe and the theoretical gaseous pipeline diameter, and select the pipe diameter of the standard model pipe with the smallest absolute difference as the final pipe diameter.

[0039] It should be noted that when selecting the standard pipe model with the smallest absolute difference, the standard pipe models and their corresponding diameters can be found in the national standard GB / T 17791 "Seamless Copper Tubes for Air Conditioning and Refrigeration". For example, for a gas-liquid two-phase pipeline, the calculated inner diameter of the theoretical two-phase pipeline is 8.50 mm, and the wall thickness is generally 0.8 mm. Therefore, the diameter of the theoretical two-phase pipeline is 8.5 + 1.6 = 10.1 mm. This has the smallest absolute difference from the standard pipe model with an outer diameter of 9.52 mm in the national standard GB / T 17791 "Seamless Copper Tubes for Air Conditioning and Refrigeration". Therefore, the pipe model with an outer diameter of 9.52 mm is selected as the standard pipe model.

[0040] In this embodiment, the total mass flow rate of the refrigerant is obtained in the following way: (1) Calculate the rated cooling capacity of the direct-cooling unit based on the cooling load demand. The calculation formula is as follows: P_cool=Q_cool / 4h ; Q_cool=Q_bat_ gen-Q_bat_absorb+Q_envi ; In the formula, P_cool This refers to the rated cooling capacity of the direct-cooling unit; Q_cool For the cooling load of the direct-cooling unit; 4h The charging and discharging time of the battery; Q_bat_ gen The heat generated by the battery during charging and discharging can be obtained by multiplying the heat generated by each individual battery cell by the total number of batteries. Q_bat_absorb The design allows for a battery temperature rise of 10°C to account for the heat absorbed by the battery. This is calculated by multiplying the battery's specific heat capacity by the total mass of the battery by the temperature rise. Q_envi The environmental heat load is calculated as the product of the specific heat capacity of the air inside the battery compartment 14, the air mass, and the change in air temperature.

[0041] Next, determine the evaporation temperature of the direct-cooling unit based on the load conditions. This evaporation temperature is typically 18℃~22℃, determined by the heat generation and heat transfer temperature difference of the battery under rated operating conditions. The heat transfer temperature difference is the temperature difference between the battery and the direct-cooling plate 2. Then, consult the thermophysical property parameter table based on the evaporation temperature to obtain the corresponding saturation pressure.

[0042] (2) Based on the evaporation temperature and saturation pressure, and combined with the set refrigerant subcooling at the outlet of condenser 3 and refrigerant superheat at the outlet of direct cooling plate 2, determine the specific enthalpy at the inlet and outlet of direct cooling plate 2.

[0043] Specifically, the specific enthalpy at the inlet of the direct cooling plate 2 is obtained from the pressure-enthalpy diagram of the system based on the saturation pressure and the set refrigerant subcooling at the outlet of the condenser 3; the specific enthalpy at the outlet of the direct cooling plate 2 is obtained from the pressure-enthalpy diagram of the system based on the evaporation temperature and the set refrigerant superheat at the outlet of the direct cooling plate 2; the design value of the refrigerant subcooling at the outlet of the condenser 3 is 0℃, and the actual value of the refrigerant subcooling is also around 0℃; the refrigerant superheat at the outlet of the direct cooling plate 2 is generally ≤1℃, in order to reduce the battery temperature difference and improve temperature uniformity.

[0044] (3) Based on the rated cooling capacity and the specific enthalpy of the inlet and outlet of the direct cooling plate 2, the total mass flow rate of the refrigerant is calculated, and the calculation formula is as follows: Mr=P_cool / (h_evp_out-h_evp_in) ; In the formula, Mr This refers to the total mass flow rate of the refrigerant. h_evp_in The specific enthalpy of the inlet of the direct-cooling plate 2; h_evp_out Specific enthalpy of the outlet of the direct cooling plate 2.

[0045] In this embodiment, the gas-liquid two-phase pipeline includes a primary two-phase pipeline 9 connecting the electronic expansion valve 1 and each distributor 6, and a secondary two-phase pipeline 10 connecting the distributor 6 and each direct cooling plate 2. The final pipe diameters of the primary two-phase pipeline 9 and the secondary two-phase pipeline 10 are determined as follows: a1. The recommended range for setting the refrigerant mass flow rate is 150 kg / m³. 2 ·s~400kg / m 2 ·s, arbitrarily select a data point within the recommended range of refrigerant mass flow rate, and combine it with the total mass flow rate of the refrigerant to calculate the theoretical two-phase pipe diameter of the first-stage two-phase pipe 9 and the theoretical two-phase pipe diameter of the second-stage two-phase pipe 10.

[0046] The formula for calculating the diameter of the theoretical two-phase pipeline is as follows: D_inner_EXV=sqrt(4A_EXV / π) ; D_inner_branch=sqrt(4A_branch / π) ; in, A_EXV=Mr_EXV / G ; A_branch=Mr_branch / G ; Mr_EXV=Mr / n ; Mr_branch=Mr_EXV / m ; In the formula, D_inner_EXV The theoretical two-phase pipe diameter for a first-stage two-phase pipeline 9; D_inner_branch The theoretical two-phase pipe diameter for the secondary two-phase pipeline 10; A_EXV The cross-sectional area of ​​the first-stage two-phase pipeline 9; A_ branch The cross-sectional area of ​​the two-phase secondary pipeline 10;G The refrigerant mass flow rate selected within the recommended range; Mr This refers to the total mass flow rate of the refrigerant. Mr_EXV This refers to the mass flow rate of the refrigerant in the first-stage two-phase pipeline 9, which is the mass flow rate of the refrigerant pipeline after each electronic expansion valve 1. n This refers to the number of electronic expansion valves 1, which is also the number of first-stage two-phase pipelines 9; Mr_branch The mass flow rate of the refrigerant in the two-phase pipeline 10 is the mass flow rate of the refrigerant. m The number of secondary two-phase pipelines (10) is derived from the primary two-phase pipeline (9).

[0047] a2. First, based on the theoretical two-phase pipe diameter of the first-stage two-phase pipe 9 and the theoretical two-phase pipe diameter of the second-stage two-phase pipe 10, select the standard model pipe with the smallest absolute difference. Calculate the standard mass flow rate of the refrigerant in the first-stage two-phase pipe 9 and the standard mass flow rate of the refrigerant in the second-stage two-phase pipe 10 based on the standard model pipe, and obtain the minimum standard mass flow rate by comparing the standard mass flow rates.

[0048] The formula for calculating the standard mass flow rate of the refrigerant in the first-stage two-phase pipeline 9 is as follows: G 标准一级 =Mr_EXV / A 标准一级 ; In the formula, G 标准一级 The standard mass flow rate of the refrigerant in the first-stage two-phase pipeline 9 is [missing information]. Mr_EXV The mass flow rate of the refrigerant in the first-stage two-phase pipeline 9; A 标准一级 This refers to the cross-sectional area of ​​the standard model pipe corresponding to the first-level two-phase pipeline 9.

[0049] The formula for calculating the standard mass flow rate of the refrigerant in the secondary two-phase pipeline 10 is as follows: G 标准二级 = Mr_branch / A 标准二级 ; In the formula, G 标准二级 The standard mass flow rate of the refrigerant in the two-phase two-stage pipeline is 10. Mr_branch The mass flow rate of the refrigerant in the two-phase pipeline 10 is the mass flow rate of the refrigerant. A 标准二级 This refers to the cross-sectional area of ​​the standard model pipe corresponding to the two-stage two-phase pipeline 10.

[0050] The above comparison of standard mass flow rate refers to taking the minimum value between the standard mass flow rate of the refrigerant in the first-stage two-phase pipeline 9 and the standard mass flow rate of the refrigerant in the second-stage two-phase pipeline 10.

[0051] Secondly, based on the pipe diameter, refrigerant mass flow rate, dryness fraction of the gas-liquid two-phase refrigerant, pipe design length, and pipe material of the standard model pipe, the standard pressure drop of the first-stage two-phase pipe 9 and the standard pressure drop of the second-stage two-phase pipe 10 are obtained by referring to empirical tables. Based on the standard pressure drops of the first-stage two-phase pipe 9 and the second-stage two-phase pipe 10, the saturation temperature drop corresponding to the standard pressure drop of the first-stage two-phase pipe 9 and the corresponding saturation temperature drop of the second-stage two-phase pipe 10 are obtained by referring to the refrigerant thermophysical property parameter table. Summing the saturation temperature drops of the first-stage two-phase pipe 9 and the second-stage two-phase pipe 10 yields the standard saturation temperature drop. ΔT_sat ,and ΔT_sat≤1℃ .

[0052] For example, this embodiment provides an empirical table commonly used in the art, as shown in Table 1 below: Table 1 Experience Table .

[0053] The aforementioned dryness fraction is approximately equal to the inlet dryness fraction of the direct-cooling plate 2, and can be calculated based on the inlet specific enthalpy of the direct-cooling plate 2, the specific enthalpy of the saturated liquid at the evaporation temperature, and the specific enthalpy of the saturated vapor. In engineering practice, there is no heat exchange in the refrigerant piping section, and the dryness fraction is generally set to 0.3. The aforementioned standard pressure drop can also be calculated using the Lockhart-Martinelli two-correlation formula, which is a conventional technique and will not be elaborated further.

[0054] It should be noted that the first-stage two-phase pipeline 9 consists of multiple parallel lines of varying lengths. When obtaining the standard pressure drop of the first-stage two-phase pipeline 9, the longest pipeline is selected for table lookup.

[0055] Finally, the minimum standard mass flow rate and standard saturation temperature drop are scored to determine whether the requirements are met. If the requirements are met, the pipe diameter of the selected standard model pipe is used as the final pipe diameter of the first-stage two-phase pipeline 9 and the second-stage two-phase pipeline 10. If the requirements are not met, data is reselected within the recommended range of refrigerant mass flow rate, and steps a1-a2 are repeated until the final pipe diameters of the first-stage two-phase pipeline 9 and the second-stage two-phase pipeline 10 that meet the requirements are obtained.

[0056] The above scores can be obtained from Tables 2 and 3 below, as follows: Table 2 Minimum Standard Mass Flow Rate Scoring Table .

[0057] Table 3 Standard Saturation Temperature Drop Scoring Table .

[0058] After obtaining the scores for the minimum standard mass flow rate and the standard saturation temperature drop from Tables 2 and 3 above, their average scores are calculated. The average score is then compared with a preset reference threshold. If the average score is within the reference threshold, the score meets the requirements; if the average score is outside the reference threshold, the score does not meet the requirements. In this embodiment, the reference threshold can be set to 70-90 points.

[0059] In this embodiment, the liquid pipeline further includes a primary liquid phase pipeline 7 connecting the condenser 3 and the regenerator 4, and a secondary liquid phase pipeline 8 connecting the regenerator 4 and each electronic expansion valve 1. The theoretical liquid phase pipeline diameter of the primary liquid phase pipeline 7 is calculated based on the total mass flow rate of the refrigerant, combined with the liquid density and design flow rate of the liquid refrigerant; the theoretical liquid phase pipeline diameter of the secondary liquid phase pipeline 8 is calculated based on the theoretical liquid phase pipeline diameter of the primary liquid phase pipeline 7.

[0060] The formula for calculating the theoretical diameter of the liquid pipeline is as follows: D_liq=sqrt(4*Mr / (π*ρ_l*v_liq)) ; D_liq_branch=D_liq / sqrt(n) ; In the formula, D_liq This is the theoretical liquid pipeline diameter for primary liquid phase pipeline 7; D_liq_branch This is the theoretical liquid pipeline diameter for secondary liquid phase pipeline 8; Mr This refers to the total mass flow rate of the refrigerant. ρ_l The liquid density of the liquid refrigerant is obtained by referring to the refrigerant's thermal property parameter table based on the ambient temperature, subcooling, condensing pressure, and saturation temperature corresponding to the condensing pressure under the battery's rated operating conditions. v_liq The design flow rate for the liquid refrigerant, v_liq The speed range is 1.0 m / s to 1.5 m / s. n This refers to the number of electronic expansion valves 1, which is also the number of secondary liquid phase pipelines 8 branching off from the primary liquid phase pipeline 7.

[0061] In this embodiment, the gaseous pipeline includes a tertiary gas phase pipeline 13 from the outlet of each direct cooling plate 2 to the junction of individual battery clusters, a secondary gas phase pipeline 12 from the junction of individual battery clusters to the junction of all battery clusters, and a primary gas phase pipeline 11 from the junction of all battery clusters to the condenser 3. The theoretical gas phase pipeline diameter of the primary gas phase pipeline 11 is calculated based on the total mass flow rate of the refrigerant, combined with the gas density and design flow rate of the gaseous refrigerant. The theoretical gas phase pipeline diameters of the secondary gas phase pipeline 12 and the tertiary gas phase pipeline 13 are calculated based on the theoretical gas phase pipeline diameter of the primary gas phase pipeline 11.

[0062] The formula for calculating the theoretical gaseous pipeline diameter is as follows: D_ gas=sqrt(4*Mr / (π*ρ_ g*v_gas)) ; D_ gas_branch=D_ gas / sqrt(a) ; D_ gas_branch_branch=D_ gas_branch / sqrt(b) ; In the formula, D_ gas This is the theoretical gaseous pipe diameter of the primary gas phase pipeline 11; D_ gas_branch This is the theoretical gaseous pipe diameter of the secondary gas phase pipeline 12; D_ gas_branch_branch The theoretical gaseous pipe diameter of the three-stage gas phase pipeline 13; Mr This refers to the total mass flow rate of the refrigerant. ρ_ g The gas density of the gaseous refrigerant in the suction state of compressor 5 is obtained by referring to the refrigerant's thermal property parameter table based on the evaporation pressure, evaporation temperature, and superheat; the evaporation pressure is also obtained by referring to the refrigerant's thermal property parameter table based on the evaporation temperature. v_ gas The design flow rate for the gaseous refrigerant, v_ gas The speed range is 6 m / s to 15 m / s. a The number of secondary gas phase pipelines 12 branched off from the primary gas phase pipeline 11; b The number of tertiary gas phase pipelines 13 branched from the secondary gas phase pipeline 12.

[0063] It should be noted that the empirical tables and thermophysical parameter tables in this embodiment are conventional methods in the art. The empirical tables are derived by those skilled in the art through historical engineering data, and the thermophysical parameter tables are well-known technologies in the art and can be directly obtained online. Furthermore, this embodiment does not limit the structure of the distributor 6; a conventional structure is sufficient.

[0064] This embodiment, through the determination of reasonable pipeline structure and pipe diameter, can simultaneously ensure the mass flow rate and distribution uniformity of refrigerant in the pipeline, thereby effectively improving the overall temperature uniformity of the battery while ensuring the reliability of oil return.

[0065] Example 2 Based on Example 1, this example provides the specific structure of the liquid dispenser 6.

[0066] like Figures 2-5As shown, the distributor 6 has a dispensing chamber 61, which is provided with an inlet 62 and multiple dispensing ports 63. The inlet 62 is used to connect to the primary two-phase pipeline 9, and the dispensing ports 63 are respectively connected to each secondary two-phase pipeline 10. The dispensing chamber 61 is also provided with a three-stage mixing structure for the refrigerant to be impacted and reflected in sequence. The first-stage mixing structure is fixed directly above the inlet 62 and has a guide slit between it and the bottom surface of the dispensing chamber 61, so that the refrigerant is sprayed out along the guide slit after impact and reflection. The second-stage mixing structure is arranged around the bottom surface of the dispensing chamber 61, so that the refrigerant flows upward after impact and reflection. The third-stage mixing structure is arranged around the top surface of the dispensing chamber 61, so that the refrigerant generates a vortex after impact and reflection and enters the dispensing ports 63.

[0067] The liquid dispenser 6 includes a detachable and fixed upper cover 67 and a lower cover 68. Both the upper cover 67 and the lower cover 68 are preferably circular. The lower surface of the upper cover 67 has a downward-facing boss integrally formed, and the lower surface of the boss has an upper groove with an opening facing downwards. The upper surface of the lower cover 68 has a lower groove with an opening facing upwards. The inner diameter of the lower groove matches the outer diameter of the boss. Both the inner surface of the lower groove and the outer surface of the boss are threaded. The upper cover 67 and the lower cover 68 are fixed together by threads and a sealing ring to form a detachable sealing structure. After the upper cover 67 and the lower cover 68 are fixed, the lower end of the upper groove abuts against the bottom surface of the lower groove to form a liquid dispensing chamber 61. Liquid dispensing ports 63 are evenly distributed on the upper cover 67, and the liquid inlet 62 is located in the middle of the upper groove on the lower cover 68.

[0068] The first-stage mixing structure is a conical cover 64 suspended and fixed within the dispensing chamber 61 by an extension rod. The inner diameter of the opening of the conical cover 64 is larger than the inner diameter of the inlet 62, and the centerline of the conical cover 64 coincides with the centerline of the inlet 62. The extension rod can be formed by extending upward from the apex of the conical cover 64, and the extension rod can be fixed to the upper cover 67 by threads. The conical cover 64 covers the inlet 62, and there is a flow-guiding gap between it and the bottom surface of the dispensing chamber 61, which facilitates the spraying of the refrigerant after impact reflection into the second-stage mixing structure. In this embodiment, the conical cover 64 is used as the first-stage mixing structure. After the refrigerant enters, it will be broken into tiny droplets under the cutting action of high-speed airflow and low-pressure evaporation, realizing gas-liquid mixing and atomization, and improving the uniform mixing effect after entering the dispensing chamber 61.

[0069] The second-stage mixing structure is an inclined ring 65 with a right-angled surface on the outer surface and an inclined surface on the inner surface. The inclined ring 65 is an independent structure, with its two right-angled surfaces respectively attached to the side and bottom surfaces of the liquid distribution chamber 61. The inclination of its inner surface can be 45 degrees, which is used to allow the refrigerant to flow to the third-stage mixing structure after impact.

[0070] The third-stage mixing structure is an inclined top surface 66 located between the side and top surfaces of the liquid distribution chamber 61. The inclined top surface 66 is located directly above the inclined ring 65 and can be formed by cutting the angle between the side and top surfaces of the upper groove. Its inclination angle can be 45 degrees, which is used to generate vortex flow after the refrigerant impacts.

[0071] Figure 2 The specific structure of a liquid dispenser 6 is shown, consisting of... Figure 2 It can be seen that after the entire liquid separator 6 is installed, a narrow flow guide gap is formed between the conical cover 64 and the bottom surface of the lower tank. Figure 3 A schematic diagram of the refrigerant impact reflection within the distributor 6 is shown. The arrows indicate the refrigerant flow direction, and a, b, and c represent the first, second, and third impact reflection zones, respectively. The designed structure allows the refrigerant to enter the distributor chamber 61 under reduced pressure and acceleration through the pre-set throat channels on the lower cover 68 (connected to the inlet 62 and the first-stage two-phase pipeline 9). It first impacts the inner surface of the conical cover 64, generating a first reflection and direction change at point a. Then, it is ejected through the guide slits, impacting the inclined ring 65, forming a second reflection and upward spray at point b. Finally, it impacts the inclined top surface 66, generating a third reflection at point c. The reflected refrigerant forms a vortex within the distributor chamber 61 and then flows out uniformly through the surrounding distributor ports 63. During the refrigerant flow process, the cooperation of the conical cover 64, the inclined ring 65, and the inclined top surface 66 forces the fluid to undergo jetting and multi-stage reflection and direction change within the limited cavity. This forced reflection reversal increases the turbulence of the fluid, thereby disrupting gas-liquid stratification and allowing for thorough mixing of the gas and liquid to reduce gas-liquid distribution deviation.

[0072] Figure 4 The specific structure of another liquid dispenser 6 is shown. Figure 5 This diagram illustrates another type of refrigerant impact reflection within the distributor 6, compared to... Figure 2 , 3 The difference lies in the opposite inclination direction of the inclined top surface 66. This structure allows the refrigerant to bounce directly towards the liquid distribution port 63 after impacting the inclined top surface 66, thereby achieving uniform mixing and improving flow efficiency.

[0073] In this embodiment, the refrigerant enters through the primary two-phase pipeline 9, where it is uniformly mixed by three impact reflections. Finally, it is evenly distributed to different direct-cooling plates 2 via the distributor 63 and the secondary two-phase pipeline 10. The cooled refrigerant then returns to the compressor 5 and is circulated again by the direct-cooling unit through the distributor 6 and refrigerant pipelines. This circulation effectively reduces battery temperature and minimizes temperature inconsistencies between battery cells.

[0074] Example 3 This embodiment tested Example 1, as detailed below: 1. Pre-experiment conditions: Based on the battery's rated operating heat load and the ambient heat load, the customer's cooling capacity of the direct-cooling unit was calculated as follows: P_cool= 60kW. The rated operating conditions of the direct-cooling unit are set at an ambient temperature (i.e., system condensing temperature) of 45℃ and an evaporating temperature of 20℃. The refrigerant subcooling at the outlet of condenser 3 is 0℃, and the refrigerant superheat at the outlet of direct-cooling plate 2 is 1℃. Based on the characteristics of refrigerant R410A, the condensing pressure is 2725kPa according to the thermophysical property table. The saturation pressure corresponding to the evaporating temperature is 1442kPa. Based on the condensing pressure, saturation pressure, subcooling, and superheat, the pressure-enthalpy diagram of refrigerant R410A is consulted, and the specific enthalpy difference between the inlet and outlet of direct-cooling plate 2 is obtained as follows: h_evp_out-h_evp_in= 277.6-132.5 = 145.1 kJ / kg, then the total mass flow rate of the refrigerant is... Mr=P_cool / ( h_evp_out-h_evp_in ) = 60 / 145.1≈0.4135kg / s.

[0075] 2. For a gas-liquid two-phase pipeline: Assuming the system contains 6 battery clusters, i.e., 6 branches, with one electronic expansion valve 1 in each branch, the mass flow rate of the refrigerant in the first-stage two-phase pipeline 9 is: Mr_EXV=Mr / 6≈0.0689 kg / s. Each cluster consists of 8 packs, then... Mr_branch=Mr_EXV / 8≈0.00861kg / s. Select a mass flow rate within the recommended range. G 300 kg / m 2 The data from ·s are used for calculation. The cross-sectional areas of the primary two-phase pipeline 9 and the secondary two-phase pipeline 10 can be obtained from the total mass flow rate and mass velocity of the refrigerant. A_EXV=Mr_EXV / G= 0.0689 / 300 = 2.297×10 -4 m 2 ; A_branch=Mr_ branch / G= 0.00861 / 300 = 2.870×10 -5 m 2 Therefore, the theoretical two-phase pipe diameters of the first-stage two-phase pipeline 9 and the second-stage two-phase pipeline 10 are obtained respectively: D_inner_EXV=sqrt(4 A_EXV / π)= 17.1mm; D_inner_branch=sqrt(4A_branch / π)= 6.05mm.

[0076] Considering the wall thickness, standard copper pipes with the smallest absolute difference between the two stages of pipeline were selected. The results are as follows: for the first-stage two-phase pipeline (9), the standard pipe has an outer diameter of 19.05 mm, a wall thickness of 1.0 mm, and an inner diameter of 17.05 mm; for the second-stage two-phase pipeline (10), the standard pipe has an outer diameter of 9.52 mm, a wall thickness of 0.8 mm, and an inner diameter of 7.92 mm. Therefore, A 标准一级 = 2.283×10 -4 m 2 , A 标准二级 = 4.934×10 -5 m 2 .

[0077] Then we can deduce the result by working backwards. G 标准一级 =Mr_EXV / A 标准一级 = 301.7 kg / m 2 ·s; G 标准二级 = Mr_branch / A 标准二级 = 174.5 kg / m 2 Based on considering the worst-case scenario of oil return, the final mass flow rate used in the evaluation is the minimum of the two values, i.e., 174.5 kg / m³. 2 •s is used as the minimum standard mass flow rate for scoring, resulting in P_G =64.90. Then, based on the empirical table, the standard pressure drops for the two stages of piping are found to be 9.89 kPa and 5.03 kPa, respectively. Since the primary two-phase piping of each battery cluster is connected in parallel, the longest cluster of piping (6 m) is selected for table lookup; the length of the secondary piping is 2.5 m for each stage. Referring to the physical property table, the saturation temperature drops are found to be 0.346℃ and 0.176℃, respectively. Summing these values, the final standard saturation temperature drop used for scoring is 0.522℃, and the standard saturation temperature drop score is... P_ΔT_sat= 84.41. The final average score for both was 74.66. This final score is between 70 and 80, meeting the engineering requirements. Therefore, the final pipe diameter scheme is as follows: the final outer diameter of the first-stage two-phase pipeline 9 is 19.05 mm, and the final wall thickness is 1.0 mm; the final outer diameter of the second-stage two-phase pipeline 10 is 9.52 mm, and the final wall thickness is 0.8 mm.

[0078] Compared to the pipe diameter of a gas-liquid two-phase pipeline in the background technology that only considers the return oil flow rate, if only the return oil flow rate is considered, the higher the flow rate, the better the return oil reliability. Therefore, a mass flow rate of 400 kg / m³ is selected. 2 Using ·s as the basis for calculation, the final outer diameter of the first-stage two-phase pipeline 9 is 19.05 mm, and the wall thickness is 1.0 mm; the outer diameter of the second-stage two-phase pipeline 10 is 6.35 mm, and the wall thickness is 0.8 mm. The mass flow rates of the first-stage two-phase pipeline 9 and the second-stage two-phase pipeline 10 are 301.7 kg / m³. 2 ·s and 486.8kg / m 2 •s; the saturation temperature drops to 1.739℃. A comparison shows that the determined final pipe diameter does not meet the design requirements.

[0079] 3. For liquid pipelines: Based on the experimental preconditions, the total mass flow rate of the refrigerant. Mr= The flow rate is 0.4135 kg / s, the condensation temperature is 45℃, and the density of the saturated liquid is approximately 1027 kg / m³. 3 The design flow velocity is 1.2 m / s. n =6, meaning there are 6 electronic expansion valves 1. The theoretical liquid pipeline diameter of the primary liquid phase pipeline 7 is calculated. D_liq= 20.68mm, theoretical liquid pipe diameter of secondary liquid phase pipeline 8 D_liq_branch = 8.44mm. Selecting the standard pipe model with the smallest absolute difference, the final outer diameter of the primary liquid phase pipe 7 is 22.23mm, and the final wall thickness is 1.0mm; the final outer diameter of the secondary liquid phase pipe 8 is 9.52mm, and the final wall thickness is 0.8mm. Using these pipe diameters, the actual flow velocities of the liquid refrigerant in the primary liquid phase pipe 7 and the secondary liquid phase pipe 8 are calculated to be 1.248m / s and 1.50m / s, respectively. The actual flow velocities are within the design flow rate range, indicating that the final pipe diameters meet the requirements.

[0080] 4. For gaseous pipelines: Based on the experimental preconditions, the total mass flow rate of the refrigerant. Mr= With a flow rate of 0.4135 kg / s and an evaporation temperature of 20°C, and a superheat of 1°C, the gas density, according to the thermophysical property table of refrigerant R410A, is approximately 65.6 kg / m³. 3 The design flow velocity is 10 m / s, and the secondary gas phase pipeline is 12. a= 6. Three-stage gas phase pipeline 13 is b= 8. The theoretical gaseous pipe diameter of the primary gas phase pipeline 11 was calculated. D_gas= 28.35 mm, theoretical gaseous pipe diameter of secondary gas phase pipeline 12 D_ gas_ branch = 11.57 mm, theoretical gaseous pipe diameter of the three-stage gas phase pipeline 13 D_ gas_branch =4.09 mm. Selecting the standard pipe model with the smallest absolute difference, the final outer diameter of the first-stage gas phase pipe 11 is 31.75 mm, and the final wall thickness is 1.2 mm; the final outer diameter of the second-stage gas phase pipe 12 is 15.88 mm, and the final wall thickness is 1.0 mm; the final outer diameter of the third-stage gas phase pipe 13 is 6.35 mm, and the final wall thickness is 0.8 mm. Using these pipe diameters, the actual flow velocities of the gaseous refrigerant in the first-stage gas phase pipe 11, the second-stage gas phase pipe 12, and the third-stage gas phase pipe 13 are calculated to be 9.29 m / s, 6.94 m / s, and 7.39 m / s, respectively. The obtained actual flow velocities are within the design flow velocity range, indicating that the final pipe diameters meet the requirements.

[0081] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention. Furthermore, various different embodiments of the present invention can be arbitrarily combined, as long as they do not violate the spirit of the present invention, they should also be considered as the content disclosed by the present invention.

Claims

1. A phase change direct cooling system, comprising a compressor (5), a condenser (3), a regenerator (4), refrigerant piping, a plurality of electronic expansion valves (1), a plurality of distributors (6), and a plurality of direct cooling plates (2), characterized in that: The refrigerant piping includes a liquid piping arranged between the condenser (3) and each electronic expansion valve (1) via a regenerator (4), a gas-liquid two-phase piping arranged between the electronic expansion valve (1) and the inlet of the direct cooling plate (2) via a distributor (6), and a gaseous piping arranged between the outlet of the direct cooling plate (2) and the condenser (3) via the regenerator (4) and the compressor (5); and the final diameter of the refrigerant piping is obtained in the following way: a. The theoretical two-phase pipeline diameter is calculated based on the total mass flow rate of the refrigerant and the mass flow rate selected within the recommended range. Based on the theoretical two-phase pipeline diameter, the absolute difference between the diameter of each standard model pipe and the theoretical two-phase pipeline diameter is calculated. The standard model pipe with the smallest absolute difference is selected. Then, the minimum standard mass flow rate and standard saturation temperature drop are obtained in combination with the standard model pipe. The minimum standard mass flow rate and standard saturation temperature drop are scored and judged until the final pipe diameter that meets the requirements is obtained. The total mass flow rate of the refrigerant is obtained in the following way: (1) Calculate the rated cooling capacity of the direct cooling unit according to the cooling load demand; determine the evaporation temperature of the direct cooling unit according to the load conditions, and obtain the corresponding saturation pressure according to the evaporation temperature; (2) Based on the evaporation temperature and saturation pressure, and combined with the set refrigerant subcooling at the outlet of the condenser (3) and the refrigerant superheat at the outlet of the direct cooling plate (2), determine the specific enthalpy at the inlet and outlet of the direct cooling plate (2); (3) Calculate the total mass flow rate of the refrigerant based on the rated cooling capacity and the specific enthalpy of the inlet and outlet of the direct cooling plate (2); b. The theoretical liquid pipeline diameter is calculated based on the total mass flow rate of the refrigerant, combined with the liquid density of the liquid refrigerant and the design flow rate. Based on the theoretical liquid pipeline diameter, the absolute difference between the diameter of each standard model pipe and the theoretical liquid pipeline diameter is calculated, and the pipe diameter of the standard model pipe with the smallest absolute difference is selected as the final pipe diameter. c. The theoretical gaseous pipeline diameter is calculated based on the total mass flow rate of the refrigerant, combined with the gas density and design flow rate of the gaseous refrigerant. Based on the theoretical gaseous pipeline diameter, the absolute difference between the diameter of each standard model pipe and the theoretical gaseous pipeline diameter is calculated, and the pipe diameter of the standard model pipe with the smallest absolute difference is selected as the final pipe diameter.

2. The phase change direct cooling system according to claim 1, characterized in that: The formula for calculating the rated cooling capacity of the direct-cooling unit is: P_cool=Q_cool / 4h ； Q_cool=Q_bat_ gen-Q_bat_absorb+Q_envi ； In the formula, P_cool This refers to the rated cooling capacity of the direct-cooling unit; Q_cool For the cooling load of the direct-cooling unit; 4h The charging and discharging time of the battery; Q_bat_gen The heat generated by the battery during charging and discharging is calculated by multiplying the heat generated by each individual battery cell by the total number of batteries. Q_bat_absorb The design allows for a battery temperature rise of 10°C to account for the heat absorbed by the battery. This is calculated by multiplying the battery's specific heat capacity by the total mass of the battery by the temperature rise. Q_envi The environmental heat load is calculated as the product of the specific heat capacity of the air inside the battery compartment (14), the air mass, and the change in air temperature.

3. The phase change direct cooling system according to claim 1, characterized in that: The evaporation temperature is determined based on the heat generation and heat transfer temperature difference of the battery under rated operating conditions. The heat transfer temperature difference is the temperature difference between the battery and the direct cooling plate (2). The saturation pressure is obtained by consulting the thermophysical parameter table based on the evaporation temperature.

4. The phase change direct cooling system according to claim 1, characterized in that: The specific enthalpy at the inlet of the direct cooling plate (2) is obtained from the pressure-enthalpy diagram of the system based on the saturation pressure and the set refrigerant subcooling at the outlet of the condenser (3); the specific enthalpy at the outlet of the direct cooling plate (2) is obtained from the pressure-enthalpy diagram of the system based on the evaporation temperature and the set refrigerant superheat at the outlet of the direct cooling plate (2).

5. A phase change direct cooling system according to claim 2, characterized in that: The formula for calculating the total mass flow rate of the refrigerant is: Mr=P_cool / (h_evp_out-h_evp_in) ； In the formula, Mr This refers to the total mass flow rate of the refrigerant. h_evp_in The specific enthalpy of the inlet of the direct-cooling plate (2); h_evp_out The specific enthalpy of the outlet of the direct cooling plate (2).

6. A phase change direct cooling system according to any one of claims 1-5, characterized in that: The gas-liquid two-phase pipeline includes a primary two-phase pipeline (9) connecting the electronic expansion valve (1) and each distributor (6) and a secondary two-phase pipeline (10) connecting the distributor (6) and each direct cooling plate (2). The final diameters of the primary two-phase pipeline (9) and the secondary two-phase pipeline (10) are obtained in the following manner: a1. Select any data within the recommended range of refrigerant mass flow rate, and calculate the theoretical two-phase pipe diameter of the first-stage two-phase pipe (9) and the theoretical two-phase pipe diameter of the second-stage two-phase pipe (10) in combination with the total mass flow rate of the refrigerant. a2. Based on the theoretical two-phase pipe diameter of the first-stage two-phase pipeline and the theoretical two-phase pipe diameter of the second-stage two-phase pipeline, select the standard model pipe with the smallest absolute difference. Calculate the standard mass flow rate of the refrigerant in the first-stage two-phase pipeline (9) and the standard mass flow rate of the refrigerant in the second-stage two-phase pipeline (10) based on the standard model pipe. Obtain the minimum standard mass flow rate by comparing the standard mass flow rates. Then, obtain the standard saturation temperature drop by looking up the table based on the standard model pipe. Judge whether the minimum standard mass flow rate and the standard saturation temperature drop meet the requirements by scoring them. If not, reselect the data within the recommended range of refrigerant mass flow rate and repeat steps a1-a2 until the final pipe diameter of the first-stage two-phase pipeline (9) and the final pipe diameter of the second-stage two-phase pipeline (10) that meet the requirements are obtained.

7. A phase change direct cooling system according to claim 6, characterized in that: The formula for calculating the diameter of the theoretical two-phase pipeline is as follows: D_inner_EXV=sqrt(4A_EXV / π) ； D_inner_branch=sqrt(4A_branch / π) ； in, A_EXV=Mr_EXV / G ； A_branch=Mr_branch / G ； Mr_EXV=Mr / n ； Mr_branch=Mr_EXV / m ； In the formula, D_inner_EXV The theoretical two-phase pipe diameter of the first-stage two-phase pipeline (9); D_inner_branch The theoretical two-phase pipe diameter of the secondary two-phase pipeline (10); A_EXV The cross-sectional area of ​​the first-stage two-phase pipeline (9); A_ branch The cross-sectional area of ​​the two-phase pipeline (10) is given. G The refrigerant mass flow rate selected within the recommended range; Mr This refers to the total mass flow rate of the refrigerant. Mr_EXV The mass flow rate of the refrigerant in the first-stage two-phase pipeline (9) is the mass flow rate of the refrigerant pipeline after each electronic expansion valve (1). n The number of electronic expansion valves (1); Mr_branch The mass flow rate of the refrigerant in the two-phase pipeline (10) is the mass flow rate of the refrigerant. m for Two-phase pipeline (9) The number of secondary two-phase pipelines (10) is determined.

8. A phase change direct cooling system according to claim 7, characterized in that: The formula for calculating the standard mass flow rate of the refrigerant in the first-stage two-phase pipeline (9) is as follows: G 标准一级 =Mr_EXV / A 标准一级 ； In the formula, G 标准一级 The standard mass flow rate of the refrigerant in a first-stage two-phase pipeline (9) is given. Mr_EXV The mass flow rate of the refrigerant in the first-stage two-phase pipeline (9); A 标准一级 The cross-sectional area of ​​the standard model pipe corresponding to the first-level two-phase pipeline (9).

9. A phase change direct cooling system according to claim 7, characterized in that: The formula for calculating the standard mass flow rate of the refrigerant in the secondary two-phase pipeline (10) is as follows: G 标准二级 =Mr_branch / A 标准二级 ； In the formula, G 标准二级 The standard mass flow rate of the refrigerant in the two-phase pipeline (10) is given. Mr_branch The mass flow rate of the refrigerant in the two-phase pipeline (10) is the mass flow rate of the refrigerant. A 标准二级 The cross-sectional area of ​​the standard model pipe corresponding to the two-phase pipeline (10) is given.

10. A phase change direct cooling system according to claim 6, characterized in that: The method for determining the standard saturation temperature drop is as follows: Based on the pipe diameter of the standard model pipe, the mass flow rate of the refrigerant, the dryness of the gas-liquid two-phase refrigerant, the design length of the pipeline, and the pipeline material, the standard pressure drop of the first-stage two-phase pipeline (9) and the standard pressure drop of the second-stage two-phase pipeline (10) are obtained by referring to the empirical table; Based on the standard pressure drop of the first-stage two-phase pipeline (9) and the standard pressure drop of the second-stage two-phase pipeline (10), the corresponding saturation temperature drop is obtained by referring to the thermophysical property parameter table of the refrigerant, and the summation yields the standard saturation temperature drop. ΔT_sat ,and Δ T_sat≤1℃ .

11. A phase change direct cooling system according to claim 6, characterized in that: The recommended range for the refrigerant mass flow rate is 150 kg / m³. 2 ·s~400kg / m 2 ·s.

12. A phase change direct cooling system according to any one of claims 1-5, characterized in that: The liquid pipeline includes a primary liquid phase pipeline (7) connecting the condenser (3) and the regenerator (4) and a secondary liquid phase pipeline (8) connecting the regenerator (4) and each electronic expansion valve (1). The theoretical liquid pipeline diameter of the primary liquid phase pipeline (7) is calculated based on the total mass flow rate of the refrigerant, combined with the liquid density and design flow rate of the liquid refrigerant. The theoretical liquid pipeline diameter of the secondary liquid phase pipeline (8) is calculated based on the theoretical liquid pipeline diameter of the primary liquid phase pipeline (7).

13. A phase change direct cooling system according to claim 12, characterized in that: The formula for calculating the theoretical diameter of the liquid pipeline is as follows: D_liq=sqrt(4*Mr / (π*ρ_l*v_liq)) ； D_liq_branch = D_liq / sqrt(n) ； In the formula, D_liq The theoretical liquid pipeline diameter of the primary liquid phase pipeline (7); D_liq_branch The theoretical liquid pipeline diameter of the secondary liquid phase pipeline (8); Mr This refers to the total mass flow rate of the refrigerant. ρ_l The liquid density of the liquid refrigerant is obtained by consulting the refrigerant's thermal property parameter table based on the ambient temperature, subcooling, condensation pressure, and corresponding saturation temperature under the battery's rated operating conditions. v_liq The design flow rate for the liquid refrigerant, v_liq The speed range is 1.0 m / s to 1.5 m / s. n The number of electronic expansion valves (1).

14. A phase change direct cooling system according to any one of claims 1-5, characterized in that: The gaseous pipeline includes a three-stage gas phase pipeline (13) from the outlet of each direct cooling plate (2) to the junction of individual battery clusters, a two-stage gas phase pipeline (12) from the junction of individual battery clusters to the junction of all battery clusters, and a first-stage gas phase pipeline (11) from the junction of all battery clusters to the condenser (3). The theoretical gas phase pipeline diameter of the first-stage gas phase pipeline (11) is calculated based on the total mass flow rate of the refrigerant, combined with the gas density and design flow rate of the gaseous refrigerant. The theoretical gas phase pipeline diameters of the two-stage gas phase pipeline (12) and the three-stage gas phase pipeline (13) are calculated based on the theoretical gas phase pipeline diameter of the first-stage gas phase pipeline (11).

15. A phase change direct cooling system according to claim 14, characterized in that: The formula for calculating the theoretical gaseous pipeline diameter is as follows: D_ gas=sqrt(4*Mr / (π*ρ_ g*v_gas)) ； D_gas_branch=D_gas / sqrt(a) ； D_ gas_branch_branch=D_ gas_branch / sqrt(b) ； In the formula, D_ gas The theoretical gaseous pipe diameter of the primary gas phase pipeline (11); D_ gas_branch The theoretical gaseous pipe diameter of the secondary gas phase pipeline (12); D_ gas_branch_branch The theoretical gaseous pipe diameter of the three-stage gas phase pipeline (13); Mr This refers to the total mass flow rate of the refrigerant. ρ_g The gas density of the gaseous refrigerant in the suction state of the compressor (5) is obtained by consulting the refrigerant's thermal property parameter table based on the evaporation pressure, evaporation temperature and superheat. v_ gas The design flow rate for the gaseous refrigerant, v_ gas The speed range is 6 m / s to 15 m / s. a The number of secondary gas phase pipelines (12) branched off from the primary gas phase pipeline (11); b The number of tertiary gas phase pipelines (13) branched from the secondary gas phase pipeline (12).

16. A phase change direct cooling system according to claim 1, characterized in that: The distributor (6) has a dispensing chamber (61), which is provided with an inlet (62) and multiple dispensing ports (63). The dispensing chamber (61) is provided with a three-stage mixing structure for the refrigerant to be impacted and reflected in sequence. The first-stage mixing structure is fixed directly above the inlet (62) and has a flow guide gap between it and the bottom surface of the dispensing chamber (61) so that the refrigerant can be sprayed out along the flow guide gap after impact and reflection. The second-stage mixing structure is set around the bottom surface of the dispensing chamber (61) so that the refrigerant can flow upward after impact and reflection. The third-stage mixing structure is set around the top surface of the dispensing chamber (61) so that the refrigerant can enter the dispensing port (63) after impact and reflection.

17. A phase change direct cooling system according to claim 16, characterized in that: The first-stage mixing structure is a conical cover (64) fixed in the liquid distribution chamber (61) by an extension rod. The inner diameter of the opening of the conical cover (64) is larger than the inner diameter of the liquid inlet (62).

18. A phase change direct cooling system according to claim 16, characterized in that: The second-stage mixing structure is an inclined ring (65) with a right-angled surface on the outer surface and an inclined surface on the inner surface. The two right-angled surfaces of the inclined ring (65) are respectively attached to the side and bottom surfaces of the liquid separation chamber (61).

19. A phase change direct cooling system according to claim 16, characterized in that: The third-stage mixing structure is an inclined top surface (66) located between the side and top surfaces of the liquid separation chamber (61), which is directly above the inclined ring (65).

20. A phase change direct cooling system according to any one of claims 16-19, characterized in that: The liquid dispenser (6) includes a detachable and fixed upper cover (67) and a lower cover (68). The upper cover (67) has an upper groove with an opening facing downwards, and the lower cover (68) has a lower groove with an opening facing upwards. The upper cover (67) and the lower cover (68) are fixed together by threads. After fixing, the lower end of the upper groove abuts against the bottom surface of the lower groove to form a liquid dispensing chamber (61). The liquid dispensing ports (63) are evenly arranged on the upper cover (67), and the liquid inlet (62) is arranged on the lower cover (68).

Images