Design method of airborne air-liquid heat exchanger

Abstract

The application discloses a design method of an airborne air-liquid heat exchanger, which comprises the following steps: determining technical indexes, presetting heat exchanger core structure parameters, obtaining physical property parameters of hot-side and cold-side media under design working conditions, designing flow channels and splitting heat exchange processes, respectively calculating heat exchange amounts, outlet temperatures and along-flow resistances of the forward flow and the reverse flow processes, checking core component strength, and determining results; the heat exchange processes are split into the forward flow and the reverse flow two independent processes for calculation, heat exchange characteristics of the hot-side medium in different flow stages in the core are accurately reflected, heat exchange amount calculation deviation caused by a single heat exchange process is avoided, heat dissipation requirements of the airborne equipment are met, and the heat exchanger volume increase and weight increase caused by excessive design are avoided; meanwhile, the along-flow resistances are calculated in combination with actual flow forms of the heat exchange processes through the along-flow resistance superposition mode of the hot-side series connection and the cold-side parallel connection, flow resistance calculation logic is optimized, power loss of the aviation equipment is reduced, and the service life of the heat exchanger is prolonged.

Description

Technical Field

[0001] This invention relates to the field of heat exchange device technology, and in particular to a design method for an airborne air-liquid heat exchanger. Background Technology

[0002] Airborne air-liquid heat exchangers are key thermal management components in aviation equipment. They are mainly used to cool hot-side media such as avionics equipment and engine circulating coolant. Their heat exchange performance, flow resistance control, and structural reliability directly affect the operational stability and endurance of aviation equipment.

[0003] Currently, the design methods for existing airborne air-liquid heat exchangers generally adopt a single heat exchange process, such as performing heat exchange calculations only in the co-current or counter-current direction. This single heat exchange process design method cannot accurately reflect the heat exchange characteristics of the hot-side medium at different flow stages within the core, which can easily lead to deviations in heat exchange calculations. This can result in either failing to meet the heat dissipation requirements of airborne equipment or over-designing the heat exchanger, leading to increased volume and weight, which does not meet the lightweight design requirements of airborne equipment. Furthermore, the existing design methods do not incorporate the actual flow pattern of the heat exchange process when calculating the flow resistance on the hot and cold sides. The flow resistance calculation logic is unreasonable, resulting in the designed heat exchanger having excessive flow resistance, increasing the power loss of aviation equipment, and even affecting the service life of the heat exchanger. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a design method for an airborne air-liquid heat exchanger, thereby solving the problems mentioned in the background section. To achieve the above objective, the present invention employs the following technical solution: The design method for this airborne air-liquid heat exchanger includes the following steps: S1. Determine the technical specifications of the heat exchanger, including: hot-side flow rate, inlet temperature, upper limit of outlet temperature, upper limit of flow resistance, pressure resistance, and filling volume limit; as well as cold-side flow rate, inlet temperature, inlet pressure, and pressure resistance; wherein, the hot-side medium is coolant and the cold-side medium is air. S2. Preset the heat exchanger core structure parameters, including core outer dimensions, fin type, fin specifications, number of layers, baffle thickness, cover plate thickness, and seal width; S3. Obtain the physical property parameters of the hot and cold side media under the design conditions. The physical property parameters include at least density, specific heat capacity at constant pressure, thermal conductivity and dynamic viscosity. S4. Design the hot and cold side flow channels, and according to the change of the heat transfer mode of the hot side medium in the core, divide the heat transfer process into two independent processes, co-current and counter-current, and perform heat transfer calculations separately. S5. Perform heat exchange calculations on the two independent processes after splitting to obtain the heat exchange, outlet temperature and flow resistance of each independent process; superimpose the calculation results of the two independent processes to obtain the total heat exchange, hot side outlet temperature, cold side outlet temperature and total flow resistance on both sides of the heat exchanger. Among them, the flow resistance of the two independent processes on the hot side is superimposed in series, and the flow resistance of the two independent processes on the cold side is taken as the total flow resistance of the cold side by taking the maximum flow resistance of the two independent processes on the cold side in parallel. S6. Perform strength verification on the fins, partitions and seals of the core, including calculating the allowable stress based on the mechanical properties of the selected materials and the corresponding safety factor, and then verifying whether the fin thickness, partition thickness and seal width meet the pressure resistance requirements. S7. Determine whether the heat transfer calculation results of S5 and the strength verification results of S6 both meet the technical indicators determined in S1. If they do, proceed to the performance verification step. If they do not meet, return to S2 to adjust the core structure parameters and repeat S3 to S6 until all results meet the requirements.

[0005] Optionally, the heat transfer calculation for the two independent processes described in S5 includes: Based on the physical property parameters and the core structure parameters, the equivalent diameter, mass flow rate, Reynolds number, and Prandtl number of each independent process are calculated respectively. The values ​​of the heat transfer factor and the Fanning friction factor are determined based on the flow state at the Reynolds number. Based on the heat transfer factor and Fanning friction factor, calculate the heat transfer coefficient, fin efficiency, total heat transfer area and effective heat transfer area of ​​the convective heat transfer surface. By combining the total heat transfer area and the effective heat transfer area, the total heat transfer efficiency is calculated, and the heat exchange is determined based on the total heat transfer efficiency. Simultaneously, the flow resistance along each independent process is calculated based on the Fanning friction factor.

[0006] Optionally, the equivalent diameter is determined according to the formula. Calculation, where The inner width of the fin, The height inside the fin; the mass flow rate is calculated according to the formula Calculate, where, The equivalent diameter of the flow channel. For medium mass flow rate, The medium flow area is obtained from the three-dimensional modeling results of the heat exchanger core; the Reynolds number is calculated according to the formula... Calculate, where, The Reynolds number is... For the dynamic viscosity of the medium, For the mass flow rate of the medium, The equivalent diameter of the flow channel; the Prandtl number is calculated according to the formula Calculate, where, For Prandtl numbers, For the specific heat capacity of the medium at constant pressure, The thermal conductivity of the medium, The dynamic viscosity of the medium.

[0007] Optionally, the heat transfer factor With Fanning friction factor The solution is based on the Gnielinsk empirical relation, specifically determined by the flow state at which the Reynolds number is determined. For laminar flow, the following is adopted: , Calculate, where, For heat transfer factor, Fanning friction factor, For the Reynolds number, for turbulent conditions, we use... , Calculate, where, For heat transfer factor, Fanning friction factor, Let be the Reynolds number. For the transition state, an intermediate value is obtained using linear interpolation.

[0008] Optionally, the heat transfer coefficient of the convective heat transfer surface is calculated according to the formula. Calculate, where α is the heat transfer coefficient of the convective heat transfer surface, and the hot side is... The cold side is , For the mass flow rate of the medium, For the specific heat capacity of the medium at constant pressure, For heat transfer factor, It is a Prandtl number.

[0009] Optionally, the fin efficiency is calculated according to the formula Calculate, where, For fin efficiency, For fin parameters, The fin height, m, is calculated using the formula... Calculate, where, For fin parameters, The heat transfer coefficient of the convective heat transfer surface, The thermal conductivity of the fin material is... This refers to the fin thickness.

[0010] Optionally, the total heat transfer area is calculated according to the formula Calculate, where, This represents the total heat transfer area on one side. The area of ​​the partition is... The fin area; the effective heat transfer area is calculated according to the formula Calculate, where, For the effective heat transfer area on one side, The heat transfer area of ​​the partition is... For fin efficiency, The fin heat transfer area; the surface efficiency is calculated according to the formula calculate, For single-sided surface efficiency, the hot side is... The cold side is , For the heat transfer area of ​​the fins, This represents the total heat transfer area on one side. The fin efficiency is given by the formula: [Formula omitted for brevity] Calculate, where, The total heat transfer efficiency of the heat exchanger in a single pass. The number of heat transfer units, The heat capacity ratio is given by the formula. Calculate, where, For single-pass heat exchange, For minimum heat capacity, This refers to the inlet temperature on the hot side. This refers to the cold side inlet temperature.

[0011] Optionally, the friction loss is calculated according to the formula Calculate, where, For single-pass flow resistance, For the mass flow rate of the medium, Fanning friction factor, The fluid flow length is obtained from the 3D modeling results of the heat exchanger core. For the specific volume of the medium, The equivalent diameter of the flow channel. ,in, The average specific volume of the medium. The density is the medium.

[0012] Optionally, the formula for verifying the fin thickness in S6 is: ,in, The minimum required thickness for the fins. For the pressure resistance of the component, Fin spacing, The final allowable stress for fin material selection, The aperture reduction coefficient is denoted as . This refers to the allowable deviation coefficient for fin thickness. The formula for verifying the thickness of the partition is as follows: ,in, The minimum required thickness for the partition. For fin pitch, For the pressure resistance of the component, The final allowable stress for the material selection of the partition, This is the correction factor for the partition wall thickness; The formula for verifying the width of the seal is as follows: ,in, Minimum width required for the seal. This is the maximum thickness of the seal. For the pressure resistance of the component, The final allowable stress for selecting materials for the seal. This is the seal wall thickness correction factor; When the calculated thickness value is less than or equal to the actual selected thickness value, the component is deemed to meet the pressure resistance requirements.

[0013] Optionally, the performance verification step includes: S8. Set up a test loop to simulate the actual operating state of the heat exchanger, measure the inlet and outlet temperatures of the cold side and the inlet and outlet temperatures of the hot side, the flow rate and pressure, calculate the heat exchange and flow resistance, and compare them with the technical indicators determined in step S1 to verify whether the design meets the requirements.

[0014] Compared to existing technologies, the advantages of this invention are that by splitting the heat exchange process into two independent processes, co-current and counter-current, and calculating them separately, it accurately reflects the heat exchange characteristics of the hot-side medium at different flow stages within the core. This avoids the calculation deviation of heat exchange caused by a single heat exchange process, meeting the heat dissipation requirements of airborne equipment while avoiding over-design that leads to increased heat exchanger volume and weight, thus conforming to the lightweight design requirements of airborne equipment. At the same time, by superimposing the flow resistance in series on the hot side and parallel on the cold side, and combining the actual flow pattern of the heat exchange process to calculate the flow resistance, the flow resistance calculation logic is optimized. The flow resistance of the designed heat exchanger is far below the upper limit of the index, reducing the power loss of aviation equipment and improving the service life of the heat exchanger. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the design method for the airborne air-liquid heat exchanger of the present invention. Detailed Implementation

[0016] To facilitate understanding of this application, a more detailed description of the application is provided below with reference to the accompanying drawings and specific embodiments; preferred embodiments of the application are shown in the drawings; however, the application may be implemented in many different forms and is not limited to the embodiments described in this specification; rather, these embodiments are provided to enable a more thorough and complete understanding of the disclosure of this application.

[0017] It should be noted that, unless otherwise explicitly specified and limited, the terms “set up,” “install,” “connect,” and “link” should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances. Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0018] like Figure 1 As shown, one embodiment of the present invention is a design method for an airborne air-liquid heat exchanger, comprising the following steps: S1. Determine the technical specifications: The hot-side medium is AF65# coolant, and the cold-side medium is air. The hot-side specifications are: flow rate 35L / min, inlet temperature 64℃, outlet temperature ≤58.5℃, flow resistance ≤55kPa, pressure resistance 1.0MPa, and filling volume ≤1.3L; the cold-side specifications are: flow rate 5035kg / h, flow velocity 23.7m / s, inlet temperature 43℃, inlet absolute pressure (95.5±1)kPa, and pressure resistance 0.1MPa.

[0019] S2. Preset heat exchanger core structure parameters: The core size is set to 477×350×148.5mm. Both the hot and cold sides use straight fins. The hot side fins are 1.5×2×0.15mm in size and have 4 layers. The cold side fins are 26.5×3.5×0.15mm in size and have 5 layers. The partition thickness is set to 0.4mm, the cover plate thickness is set to 3.5mm, the sealing strip width is 6mm, and the core weight is 16.4±0.5kg.

[0020] S3. Obtain the physical properties of the hot and cold side media under design conditions: Under design conditions, the hot side AF65# coolant has a density of 1059.2 kg / m³, a specific heat capacity at constant pressure of 3333.4 J / (kg·K), a thermal conductivity of 0.3594 W / (m·K), and a dynamic viscosity of 0.00197 Pa·s; the cold side air has a density of 1.065 kg / m³, a specific heat capacity at constant pressure of 1007 J / (kg·K), a thermal conductivity of 0.0279 W / (m·K), and a dynamic viscosity of 0.0000193 Pa·s.

[0021] S4. Design flow channels and split the heat exchange process: Design the structure of the hot side and cold side flow channels. Based on the characteristics that the hot side medium splits when flowing in the core and the heat exchange mode changes from co-current to counter-current, the heat exchange process is split into two independent processes, co-current and counter-current. It is assumed that the hot side corner is uniformly split and the counter-current flow channels on both sides have the same physical properties as the medium.

[0022] S5. Calculate the heat exchange, outlet temperature, and flow resistance for the co-current and counter-current processes respectively; the co-current heat exchange is 6.107kW, the counter-current is 6.55kW, and the total heat exchange is the sum of the two, 12.657kW; the outlet temperature of the hot side co-current + counter-current process is 57.85℃, and the outlet temperature of the cold side is 51.57℃; the two processes on the hot side are connected in series, and the flow resistance is 6.42kPa + 8.38kPa = 14.8kPa; the two processes on the cold side are connected in parallel, and the maximum flow resistance of 1.325kPa is taken as the total flow resistance of the cold side.

[0023] S6. Strength verification of core components: fins are made of 3003-H16, partitions and seals are made of 3A21-H18. The material strength limit is taken according to GB / T3880.2. The safety factor for the tensile strength of aluminum alloy is 3.0 and the yield strength is 1.5. The allowable stress of each material is calculated. The fin thickness of 0.15mm, the partition thickness of 0.4mm and the seal width of 6mm are checked to see if they meet the pressure resistance requirements. They are all found to be compliant.

[0024] S7. If the total heat exchange meets the heat dissipation requirements, the hot side outlet temperature is 57.85℃ < 58.5℃, the hot side flow resistance is 14.8kPa < 55kPa, and the cold side flow resistance is 1.325kPa, and the strength verification is passed, proceed to the performance verification step; if any result is not met, return to S2 to adjust the core structure parameters, and repeat S3-S6 until the standard is met.

[0025] S8. Performance Verification: Build a test loop. The cold side is supplied with ambient air from a wind tunnel, and the hot side is constructed with a mold constant temperature machine to build a coolant circulation loop. Install pressure gauges, thermometers, and turbine flow meters at the inlet and outlet of the heat exchanger to simulate the actual operating conditions, measure parameters, calculate heat exchange and flow resistance, and compare with technical indicators to verify the effectiveness of the design.

[0026] First, the technical boundary conditions of the heat exchanger design are determined, and a core structure that meets the requirements of size and lightweight is preset. The basic physical property parameters of the medium under the design conditions are obtained. The heat exchange process is broken down based on the actual flow heat exchange form changes of the medium. The heat exchange and flow resistance characteristics of each process are obtained through fine calculation. The overall performance is obtained by superimposing the series and parallel relationships of the actual flow. Then, the strength of the key components of the core is checked to see if it meets the pressure resistance requirements. If it does not meet the requirements, the structure is iteratively adjusted. After meeting the requirements, the actual operating state is simulated by test to verify whether the actual performance of the design scheme meets the technical indicators.

[0027] This application calculates the heat exchange process by dividing it into two independent processes, co-current and counter-current, to accurately reflect the heat exchange characteristics of the hot-side medium at different flow stages within the core. This avoids the calculation deviation of heat exchange caused by a single heat exchange process, meeting the heat dissipation requirements of airborne equipment while avoiding over-design that leads to increased heat exchanger size and weight, thus conforming to the lightweight design requirements of airborne equipment. At the same time, by superimposing the flow resistance through series connection of the hot side and parallel connection of the cold side, and combining the actual flow form of the heat exchange process to calculate the flow resistance, the flow resistance calculation logic is optimized. The flow resistance of the designed heat exchanger is far below the upper limit of the index, reducing the power loss of aviation equipment and improving the service life of the heat exchanger.

[0028] Based on the obtained hot-side and cold-side medium properties and the preset core structure parameters, the following calculations are performed on the two independent processes of co-current and counter-current flow respectively: Calculate the equivalent diameter, mass flow rate, Reynolds number, and Prandtl number. For example, in a co-current flow, the equivalent diameter on the hot side is 0.0016 m and the Reynolds number is 475, while the equivalent diameter on the cold side is 0.0059 m and the Reynolds number is 10478. The flow state is determined based on the Reynolds number. The hot side is laminar and the cold side is turbulent. The heat transfer factor j and the Fanning friction factor f are determined based on the Gnielinsk empirical relation. For example, in the downstream direction, the hot side j=0.0096 and f=0.0406, and the cold side j=0.0033 and f=0.0078. Based on j and f, the heat transfer coefficients of the convective heat transfer surfaces are calculated as follows: 2755.3 W / (m²·K) for the hot side and 144.93 W / (m²·K) for the cold side; fin efficiency: 97.09% for the hot side and 64.85% for the cold side; total heat transfer area: 0.9596 m² for the hot side and 5.707 m² for the cold side; effective heat transfer area: 0.9479 m² for the hot side and 3.483 m² for the cold side. The total heat transfer efficiency is calculated by combining the total heat transfer area and the effective heat transfer area: 40.8% for co-current flow and 52.24% for counter-current flow. The heat exchange of each process is then calculated based on the total heat transfer efficiency. Meanwhile, based on the Fanning friction factor f and parameters such as medium flow length and specific volume, the flow resistance along each independent process is calculated: 6.42 kPa for the hot side and 1.045 kPa for the cold side in the co-current flow; 8.38 kPa for the hot side and 1.325 kPa for the cold side in the counter-current flow.

[0029] By performing calculations in a multi-dimensional and step-by-step manner, the key parameters of heat exchange and flow resistance for each independent process are accurately obtained, providing basic data for the subsequent superposition calculation of the overall performance of the heat exchanger and avoiding performance deviations caused by fuzzy calculation logic.

[0030] In one embodiment, the equivalent diameter is calculated as follows: Calculate where x is the inner width of the fin and y is the inner height of the fin. Substituting the inner width and height of the fin on the hot side, the equivalent diameter for both the co-current and counter-current flow is 0.0016m, and for the cold side, it is 0.0059m. Mass flow rate calculation: according to the formula calculate, The equivalent diameter of the flow channel. For medium mass flow rate, The medium flow area is obtained from the 3D modeling results of the heat exchanger core, such as the co-current hot side. cold side ; Reynolds number calculation: according to the formula calculate, The Reynolds number is... The dynamic viscosity of the medium, such as the co-current hot side. cold side ; Prandtl number calculation: according to the formula calculate, For Prandtl numbers, For the specific heat capacity of the medium at constant pressure, The thermal conductivity of the medium, The dynamic viscosity of the medium, such as the hot side. cold side Because the physical properties are the same in both downstream and upstream processes, the Prandtl number values ​​are the same.

[0031] Based on the definitions of geometric characteristics (equivalent diameter) and flow intensity (mass flow rate) of fluid flow in a flow channel in fluid mechanics, as well as the dimensionless number calculation formulas characterizing the flow state (Reynolds number) and the heat transfer capacity of the medium (Pränder number), and combined with the structural parameters of the heat exchanger core and the physical property parameters of the medium, the key parameters describing the basic characteristics of fluid flow and heat transfer are calculated.

[0032] In one embodiment, the heat transfer factor j and the Fanning friction factor f are solved based on the Gnielinsk empirical relation. The flow state of the Reynolds number on the hot and cold sides of each process is first determined: the Reynolds number on the hot side is 475 / 487.015, which is laminar flow, and the Reynolds number on the cold side is 10478, which is turbulent flow. Under laminar flow conditions, adopt , Calculate the thermal side j and f. For heat transfer factor, Fanning friction factor, For example, the Reynolds number, such as the downstream thermal side. , Countercurrent hot side , ; Under turbulent conditions, adopt , Calculate the cold side j and f. For heat transfer factor, Fanning friction factor, The Reynolds number is 10478 for both the downstream and counter-stream cold sides, therefore j = 0.0033 / 0.00333 and f is 0.0078. If the Reynolds number is in a transitional state, then linear interpolation is used to obtain an intermediate value of j and f between the calculated values ​​for laminar and turbulent flow.

[0033] Based on the Gnielinsk empirical relation, three flow states—laminar, transitional, and turbulent—are classified according to the Reynolds number. The heat transfer and frictional resistance characteristics of the fluid differ significantly under different states, thus requiring different formulas for calculating j and f. The transitional flow state represents the intermediate stage between laminar and turbulent flow, and its characteristics change linearly; therefore, a linear interpolation method is used to obtain intermediate values. By selecting an appropriate formula to calculate j and f based on the flow state corresponding to the Reynolds number, errors caused by using a single formula are avoided, making the heat transfer and friction coefficients more closely reflect actual flow conditions.

[0034] In one embodiment, according to the formula Calculate the heat transfer coefficient α of the convective heat transfer surface, where, For the medium mass flow rate, the hot side is... The cold side is , Let be the specific heat capacity of the medium at constant pressure, j be the heat transfer factor, and Pr be the Prandtl number. For example, the co-current hot side... co-current cold side The counter-current process is calculated using the same formula: hot side α = 2779.9 W / (m²·K), and cold side α remains 144.93 W / (m²·K).

[0035] The surface heat transfer coefficient can be directly derived from this formula without the need for complex experimental fitting. It has high calculation efficiency and the results match the actual heat exchange situation, providing key parameters for subsequent calculations of fin efficiency, heat transfer area, etc.

[0036] The heat transfer coefficient of a convective heat transfer surface is a core parameter characterizing the heat transfer capacity between a fluid and a solid wall. It is positively correlated with the fluid's mass flow rate and specific heat capacity, as well as with the heat transfer factor. It is also affected by the Prandtl number of the medium. The Prandtl number reflects the ratio of momentum diffusion to heat diffusion of the medium and needs to be corrected by a power of 2 / 3. This formula integrates the various influencing factors to achieve a quantitative calculation of α.

[0037] In one embodiment, first follow the formula Calculate fin parameters Where α is the heat transfer coefficient of the convective heat transfer surface. The thermal conductivity of the fin material is given; the thermal conductivity of 3003-H16 is a constant. With a fin thickness of 0.15 mm, the calculated values ​​are: hot side m1 = 445.6221 and cold side m2 = 102.2034. Then follow the formula Calculate fin efficiency ,in, For fin efficiency, For fin parameters, Substituting the fin height into the equation, we obtain the co-current hot side. Cold side Countercurrent hot side Cold side .

[0038] Fins are the core heat exchange components of a heat exchanger. The temperature on the fins gradually decreases from the root to the tip, and the heat exchange capacity also decreases accordingly. Fin efficiency characterizes the ratio of the actual heat exchange area to the ideal heat exchange area. The fin parameter *m* integrates the effects of surface heat transfer coefficient, fin material thermal conductivity, and thickness. *m·h* is a dimensionless fin characteristic number derived through a hyperbolic tangent function. It can characterize the temperature decay law of the fins, and then calculate the fin efficiency.

[0039] In one embodiment, the total heat transfer area is calculated as follows: calculate, This represents the total heat transfer area on one side. The area of ​​the baffle within the effective heat exchange zone. For fin area, such as the co-current hot side cold side ; Effective heat transfer area: according to the formula calculate, For the effective heat transfer area on one side, The heat transfer area of ​​the partition is... For fin efficiency, For the fin heat transfer area, such as the co-current hot side cold side ; Surface efficiency according to formula calculate, For single-sided surface efficiency, the hot side is... The cold side is , For the heat transfer area of ​​the fins, This represents the total heat transfer area on one side. For fin efficiency, such as co-current hot side cold side ; Overall heat transfer efficiency is calculated using the formula calculate, The total heat transfer efficiency is the single-pass efficiency of the heat exchanger, and NTU is the number of heat transfer units. Heat capacity ratio (in the same direction) ,countercurrent ), to go with the current ,countercurrent ; The overall heat transfer coefficient is calculated using the formula Calculate, where K is the overall heat transfer coefficient of the heat exchanger (unit: W / (m²·K)). The heat transfer coefficient of the convective heat transfer surface on the hot side is given by the co-current flow hot side. =2755.3W / (m²·K), countercurrent flow hot side =2779.9W / (m²·K); For hot-side surface efficiency, downstream hot-side =98.77% (i.e., 0.9877), countercurrent process hot side Based on the corresponding fin efficiency and heat transfer area, the value is taken as 98.75% (i.e. 0.9875). The thickness of the partition is preset to 0.4 mm (i.e. 0.0004 m) in this embodiment. For the thermal conductivity of the partition material, in this embodiment, the partition is made of 3A21-H18 aluminum alloy, which has a thermal conductivity of... =180W / (m·K); The heat transfer coefficient of the cold-side convective heat transfer surface is given for both co-current and counter-current flow. Both are 144.93 W / (m²·K); For cold-side surface efficiency, co-current and counter-current flow cold side Both are 68.7% (i.e., 0.687).

[0040] Detailed calculation process: The overall heat transfer coefficient for the co-current flow process is K1 = 1 / (1 / (2755.3)). 0.9877)+0.0004 / 180+1 / (144.93 0.687), calculated to be K1≈89.2W / (m²·K); The overall heat transfer coefficient for the counter-current process is K2 = 1 / (1 / (2779.9)). 0.9875)+0.0004 / 180+1 / (144.93 0.687), calculated to be K2≈89.8W / (m²·K); The calculation of the overall heat transfer coefficient integrates the heat exchange capacity of the hot and cold sides as well as the thermal conductivity loss of the baffles, accurately reflecting the overall heat transfer performance of the heat exchanger. Among them, the thermal conductivity of the baffles ( / The value is relatively small, and the main influencing factors are the heat transfer coefficient and surface efficiency of the convective heat transfer surface on the hot and cold sides.

[0041] The heat capacity factor is calculated according to the formula The calculations, in which the values ​​of each parameter are based on the technical specifications and physical properties of this embodiment, are performed as follows: Where W is the thermal capacity factor of the medium (unit: W / K). The medium is AF65# coolant, with a design flow rate of 35 L / min and a density ρ = 1059.2 kg / m³. The mass flow rate is calculated as follows: =35L / min×1059.2kg / m³÷1000=36.972kg / h (i.e. 0.01027kg / s), the cold side medium is air, and the design flow rate is 5035kg / h (i.e. 1.3986kg / s). For the constant pressure specific heat capacity of the medium, the hot side AF65# coolant =3333.4 J / (kg·K), cold side air =1007 J / (kg·K); For the heat capacity factor on the hot side, This refers to the cold-side heat capacity factor. for and The smaller value in for and The larger value in the range.

[0042] Detailed calculation process: Hot side heat capacity ratio =0.01027kg / s×3333.4J / (kg·K)≈34.23W / K; Cold side heat capacity ratio = 1.3986kg / s×1007J / (kg·K)≈1408.4W / K; contrast and , can be obtained = =34.23W / K, = =1408.4W / K; The heat capacity factor reflects the amount of heat that a medium can absorb or release per unit temperature change. Its magnitude is determined by the mass flow rate and specific heat capacity at constant pressure of the medium. In this embodiment, the mass flow rate of the cold side air is much greater than that of the hot side coolant. Therefore, the heat capacity factor of the cold side is much greater than that of the hot side. The minimum heat capacity factor is determined by the hot side, which is also the core basis for subsequent heat exchange calculations. The heat capacity ratio is calculated according to the formula Calculation: the values of each parameter are based on the heat capacity rate results obtained from the above calculation, and the specific substitution and calculation process are as follows: Wherein, C is the heat capacity ratio of the hot and cold sides (dimensionless); is the minimum heat capacity rate, that is, the heat capacity rate of the hot side in this embodiment = 34.23 W / K; is the maximum heat capacity rate, that is, the heat capacity rate of the cold side in this embodiment = 1408.4 W / K.

[0043] Specific calculation process: The mass flow rate and constant pressure specific heat capacity of the hot and cold side media in the co-current flow process and the counter-current flow process are the same, so the value of the heat capacity ratio is the same, that is, C = 34.23 / 1408.4 ≈ 0.0243; It should be noted that the co-current C mentioned in the previous embodiments = 0.3461 and counter-current C = 0.3377 are temporary values based on intermediate parameters in the calculation process, and the final accurate calculation values in this supplementary embodiment shall prevail; the heat capacity ratio characterizes the relative magnitude of the heat capacity of the hot and cold side media, and its value range is 0 < C ≤ 1. In this embodiment, C is much smaller than 1, indicating that the heat absorption capacity of the cold side medium is much stronger than that of the hot side, which also determines that the heat transfer limit of the heat exchanger is determined by the heat capacity rate of the hot side medium.

[0044] In summary, through the above specific calculation process, in this embodiment, the overall heat transfer coefficient of the co-current flow process K1 ≈ 89.2 W / (m²·K), the overall heat transfer coefficient of the counter-current flow process K2 ≈ 89.8 W / (m²·K), the heat capacity rate W_h ≈ 34.23 W / K, W_c ≈ 1408.4 W / K, and the heat capacity ratio C ≈ 0.0243; The heat transfer amount is calculated according to the formula , is the heat transfer amount of a single pass, is the minimum heat capacity rate, is the inlet temperature of the hot side, is the inlet temperature of the cold side, the co-current flow and counter-current flow are obtained.

[0045] The total heat transfer area is the sum of the heat transfer areas of the separator plate and the fins, and there is heat transfer attenuation on the fins, so the effective heat transfer area needs to be corrected by fin efficiency; the surface efficiency further characterizes the actual heat transfer efficiency of the entire heat transfer surface; the overall heat transfer efficiency is calculated by the number of heat transfer units (NTU, characterizing the heat transfer capacity of the heat exchanger) and the heat capacity ratio ( , characterizing the ratio of the heat capacity of the hot and cold side media), which reflects the overall heat transfer capacity of the heat exchanger; finally, combined with the minimum heat capacity rate and the inlet temperature difference between the hot and cold sides, the actual heat transferable amount of the heat exchanger is calculated;

[0046] In one embodiment, according to the formula Calculate the flow resistance along the friction path, where, For single-pass flow resistance, For mass flow rate, Fanning friction factor, The fluid flow length is obtained from the 3D modeling results of the heat exchanger core. The equivalent diameter of the flow channel. The specific volume of the medium ( , (Medium density). For example, the co-current hot side. Countercurrent hot side The cold side co-current and counter-current pressures are 1.045 kPa and 1.325 kPa, respectively.

[0047] Friction resistance is the pressure loss caused by viscous friction when a fluid flows in a flow channel. It is positively correlated with the square of the mass flow rate. The greater the flow intensity, the greater the friction loss. It is positively correlated with the Fanning friction factor and the flow length, and negatively correlated with the equivalent diameter. The wider the flow channel, the smaller the friction loss. At the same time, the specific volume of the medium reflects the density of the medium, which affects the transmission of friction loss. This formula integrates various influencing factors to achieve accurate calculation of friction resistance.

[0048] In one embodiment, the fin thickness is checked according to a formula. calculate, The minimum required thickness for the fins. The component withstands pressure (1 MPa on the hot side and 0.1 MPa on the cold side). The fin spacing is 1.35mm. The final allowable stress for fin 3003-H16 is 56.67 MPa. The opening weakening coefficient is 1 for straight fins. The allowable deviation coefficient for fin thickness is 5%, according to GB / T3198 standard; the hot side is calculated. Cold side All values ​​are ≤ 0.15mm of the actual selected value, indicating that the fins meet the pressure resistance requirements.

[0049] The thickness of the partition is checked according to the formula. calculate, The fin pitch is 2mm. The maximum withstand pressure is 1 MPa. The allowable stress for 3A21-H18 is 61.67 MPa. The partition wall thickness correction factor is 0.05 mm (according to GB / T3880.3); the calculation yields... If the actual thickness is ≤0.4mm, the partition is deemed to meet the pressure resistance requirements.

[0050] Seal width verification according to formula calculate, Minimum width required for the seal. The maximum thickness of the seal is 1.5mm. The maximum withstand pressure is 1 MPa. The allowable stress for 3A21-H18 is 61.67 MPa, and C is a seal wall thickness correction factor of 0.09 mm, calculated according to GB / T3880.3 standard; If the actual thickness is ≤6mm, the seal is deemed to meet the pressure resistance requirements.

[0051] Verification judgment rule: When the thickness value obtained from the verification calculation is less than or equal to the actual selected thickness value, the component is deemed to meet the pressure resistance requirements.

[0052] Fins, baffles, and seals are the core pressure-bearing and structural components of heat exchangers. Their thickness / width must meet the strength requirements under pressure resistance. The verification formula is based on the strength calculation theory of mechanics of materials, integrating the influence of pressure resistance, component geometric parameters, and allowable stress of materials. At the same time, it takes into account the dimensional deviations in actual processing, and introduces deviation coefficients and wall thickness correction coefficients to make the calculation results more consistent with the actual processing conditions. By comparing the calculated thickness with the actual selected thickness, it is determined whether the component meets the pressure resistance requirements.

[0053] By using targeted verification formulas, it was verified that the actual selected component dimensions met the pressure resistance requirements, thus avoiding problems such as heat exchanger leakage and damage caused by insufficient component strength and improving the structural reliability of the heat exchanger.

[0054] In one embodiment, a test circuit is constructed: a wind tunnel air supply circuit is constructed on the cold side, with an air supply flow rate of 5035 kg / h and a pressure of 99.95 kPa; a temporary coolant circulation circuit is constructed on the hot side, with AF65# coolant heated by a mold temperature control machine, and the flow rate controlled at 35 ± 0.3 L / min by a turbine flow meter and a ball valve. Pressure gauges and thermometers are installed at the inlet and outlet of both the cold and hot sides of the heat exchanger to ensure the sealing of the testing instruments.

[0055] Simulating actual operating conditions: To ensure that the temperature difference between the cold and hot inlet sides is consistent with the design conditions (21℃), the test conditions were adjusted: the cold inlet temperature was 31.8℃ and the hot inlet temperature was 52.8℃, both of which were 11.2℃ lower than the design specifications. At this time, the heat exchange temperature difference, heat transfer coefficient, flow resistance were basically consistent with the design point, and the heat exchange was the same.

[0056] Parameter measurement and calculation: Start the test system and record the measured data after the flow rate, temperature and pressure stabilize: cold side inlet temperature 31.8℃, air volume 4982.36kg / h, hot side inlet temperature 52.8℃, flow rate 35.132L / min, hot side inlet pressure 121.6kPa, outlet pressure 70.7kPa; the calculated hot side flow resistance is 50.9kPa and the hot side outlet temperature is 46.5℃.

[0057] Indicator Comparison and Verification: The measured and calculated results were compared with the experimental indicators. The hot-side flow resistance was 50.9 kPa ≤ 55 kPa and the hot-side outlet temperature was 46.5℃ ≤ 47.3℃. All parameters met the requirements, verifying that the design scheme met the technical specifications.

[0058] By constructing a test circuit that matches the actual working environment of the heat exchanger, the hot and cold side medium supply states in the airborne equipment are simulated, the core heat exchange temperature difference is controlled to be consistent with the design conditions, and the influence of ambient temperature on the test results is eliminated. By measuring key parameters such as inlet and outlet temperature, pressure, and flow rate with high-precision detection instruments, the actual heat exchange and flow resistance are calculated and compared with the design technical indicators to determine whether the actual performance of the heat exchanger meets the design requirements.

[0059] It should be noted that the above-mentioned technical features can be combined with each other to form various embodiments not listed above, all of which are considered to be within the scope of this invention specification; and, for those skilled in the art, improvements or modifications can be made based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A design method for an airborne air-liquid heat exchanger, characterized in that, Includes the following steps: S1. Determine the technical specifications of the heat exchanger, including: hot-side flow rate, inlet temperature, upper limit of outlet temperature, upper limit of flow resistance, pressure resistance, and filling volume limit; as well as cold-side flow rate, inlet temperature, inlet pressure, and pressure resistance; wherein, the hot-side medium is coolant and the cold-side medium is air. S2. Preset the heat exchanger core structure parameters, including core outer dimensions, fin type, fin specifications, number of layers, baffle thickness, cover plate thickness, and seal width; S3. Obtain the physical property parameters of the hot and cold side media under the design conditions. The physical property parameters include at least density, specific heat capacity at constant pressure, thermal conductivity and dynamic viscosity. S4. Design the hot and cold side flow channels, and according to the change of the heat transfer mode of the hot side medium in the core, divide the heat transfer process into two independent processes, co-current and counter-current, and perform heat transfer calculations separately. S5. Perform heat exchange calculations on the two independent processes after splitting to obtain the heat exchange, outlet temperature and flow resistance of each independent process; superimpose the calculation results of the two independent processes to obtain the total heat exchange, hot side outlet temperature, cold side outlet temperature and total flow resistance on both sides of the heat exchanger. Among them, the flow resistance of the two independent processes on the hot side is superimposed in series, and the maximum flow resistance of the two independent processes on the cold side is taken as the total flow resistance of the cold side in parallel. S6. Perform strength verification on the fins, partitions and seals of the core, including calculating the allowable stress based on the mechanical properties of the selected materials and the corresponding safety factor, and then verifying whether the fin thickness, partition thickness and seal width meet the pressure resistance requirements. S7. Determine whether the heat transfer calculation results of S5 and the strength verification results of S6 both meet the technical indicators determined in S1. If they do, proceed to the performance verification step. If they do not meet, return to S2 to adjust the core structure parameters and repeat S3 to S6 until all results meet the requirements.

2. The design method for an airborne air-liquid heat exchanger according to claim 1, characterized in that, The heat transfer calculations for the two independent processes described in S5 include: Based on the physical property parameters and the core structure parameters, the equivalent diameter, mass flow rate, Reynolds number, and Prandtl number of each independent process are calculated respectively. The values ​​of the heat transfer factor and the Fanning friction factor are determined based on the flow state at the Reynolds number. Based on the heat transfer factor and Fanning friction factor, calculate the heat transfer coefficient, fin efficiency, total heat transfer area and effective heat transfer area of ​​the convective heat transfer surface. The total heat transfer area and the effective heat transfer area are combined to calculate the total heat transfer efficiency, and the heat exchange is calculated based on the total heat transfer efficiency. Simultaneously, the flow resistance along each independent process is calculated based on the Fanning friction factor.

3. The design method for an airborne air-liquid heat exchanger according to claim 2, characterized in that, The equivalent diameter is calculated according to the formula. Calculation, where The inner width of the fin, The height inside the fin; the mass flow rate is calculated according to the formula Calculate, where, The equivalent diameter of the flow channel. For medium mass flow rate, The medium flow area is obtained from the three-dimensional modeling results of the heat exchanger core; the Reynolds number is calculated according to the formula... Calculate, where, Let Reynolds number be 1. The dynamic viscosity of the medium, For the mass flow rate of the medium, The equivalent diameter of the flow channel; the Prandtl number is calculated according to the formula Calculate, where, For Prandtl numbers, For the specific heat capacity of the medium at constant pressure, The thermal conductivity of the medium, The dynamic viscosity of the medium.

4. The design method for an airborne air-liquid heat exchanger according to claim 2, characterized in that, The heat transfer factor With Fanning friction factor The solution is based on the Gnielinsk empirical relation, specifically determined by the flow state at which the Reynolds number is determined. For laminar flow, the following is adopted: , Calculate, where, For heat transfer factor, Fanning friction factor, For the Reynolds number, for turbulent conditions, we use... , Calculate, where, For heat transfer factor, Fanning friction factor, Let be the Reynolds number. For the transition state, an intermediate value is obtained using linear interpolation.

5. The design method for an airborne air-liquid heat exchanger according to claim 2, characterized in that, The heat transfer coefficient of the convective heat transfer surface is calculated according to the formula. Calculate, where α is the heat transfer coefficient of the convective heat transfer surface, and the hot side is... The cold side is , For the mass flow rate of the medium, For the specific heat capacity of the medium at constant pressure, For heat transfer factor, It is a Prandtl number.

6. The design method for an airborne air-liquid heat exchanger according to claim 2, characterized in that, The fin efficiency is calculated according to the formula. Calculate, where, For fin efficiency, For fin parameters, The fin height, m, is calculated using the formula... Calculate, where, For fin parameters, The heat transfer coefficient of the convective heat transfer surface. The thermal conductivity of the fin material is... This refers to the fin thickness.

7. The design method for an airborne air-liquid heat exchanger according to claim 2, characterized in that, The total heat transfer area is calculated according to the formula Calculate, where, This represents the total heat transfer area on one side. The area of ​​the partition is... The fin area; the effective heat transfer area is calculated according to the formula Calculate, where, For the effective heat transfer area on one side, The heat transfer area of ​​the partition is... For fin efficiency, The fin heat transfer area; the surface efficiency is calculated according to the formula calculate, For single-sided surface efficiency, the hot side is... The cold side is , For the heat transfer area of ​​the fins, This represents the total heat transfer area on one side. The fin efficiency is given by the formula: [Formula omitted for brevity] Calculate, where, The total heat transfer efficiency of the heat exchanger in a single pass. The number of heat transfer units, The heat capacity ratio is given by the formula. Calculate, where, For single-pass heat exchange, For minimum heat capacity, This refers to the inlet temperature on the hot side. This refers to the cold side inlet temperature.

8. The design method for an airborne air-liquid heat exchanger according to claim 2, characterized in that, The friction resistance is calculated according to the formula Calculate, where, For single-pass flow resistance, For the mass flow rate of the medium, Fanning friction factor, The medium flow length is obtained from the 3D modeling results of the heat exchanger core. For the specific volume of the medium, The equivalent diameter of the flow channel. ,in, The average specific volume of the medium. The density is the medium.

9. The design method for an airborne air-liquid heat exchanger according to claim 1, characterized in that, The formula for verifying the fin thickness in S6 is as follows: ,in, The minimum required thickness for the fins. For the pressure resistance of the component, Fin spacing, The final allowable stress for fin material selection, The aperture reduction coefficient is denoted as . This refers to the allowable deviation coefficient for fin thickness. The formula for verifying the thickness of the partition is as follows: ,in, This is the minimum thickness required for the partition. For fin pitch, For the pressure resistance of the component, The final allowable stress for the selection of materials for the partition plate. This is the correction factor for the partition wall thickness; The formula for verifying the width of the seal is as follows: ,in, Minimum width required for the seal. This is the maximum thickness of the seal. For the pressure resistance of the component, The final allowable stress for selecting materials for the seal. This is the seal wall thickness correction factor; When the calculated thickness value is less than or equal to the actual selected thickness value, the component is deemed to meet the pressure resistance requirements.

10. The design method of the airborne air-liquid heat exchanger according to claim 1, characterized in that, The performance verification steps include: S8. Set up a test loop to simulate the actual operating state of the heat exchanger, measure the inlet and outlet temperatures of the cold side and the inlet and outlet temperatures of the hot side, the flow rate and pressure, calculate the heat exchange and flow resistance, and compare them with the technical indicators determined in step S1 to verify whether the design meets the requirements.

Images