Heat transfer performance matching simulation method for cooling system of new energy commercial vehicle

Abstract

The invention relates to the technical field of new energy commercial vehicle cooling system performance matching, and discloses a new energy commercial vehicle cooling system heat transfer performance matching simulation method comprising the following steps: installing a to-be-tested fan matched with a radiator on a test bench, and carrying out running-in; adjusting the rotating speed of the to-be-tested fan, and establishing stable 0PA static pressure difference and air inlet temperature on the air inlet side and the air outlet side of the to-be-tested fan until the working state is stable; rotating speed-air volume data of the fan to be measured are measured, a curve is drawn, and a rotating speed-air volume mathematical model formula is fitted; a to-be-tested fan, a radiator and an engine are integrally installed in a profiling mode; and performing a cooling system performance test. According to the heat transfer performance matching simulation method for the cooling system of the new energy commercial vehicle, the heat transfer performance and the flowing performance of the cooling system of the new energy commercial vehicle are simulated and tested.

Description

Technical Field

[0001] The present invention relates to the technical field of performance matching of a cooling system of a new energy commercial vehicle, and in particular to a heat transfer performance matching simulation method for a cooling system of a new energy commercial vehicle. Background Art

[0002] The radiators used for traditional commercial vehicle internal combustion engines generally operate under conditions of large water flow and large air volume, so the flow form is mostly violent turbulent flow. Compared with traditional internal combustion engines, current new energy commercial vehicles are generally equipped with fuel cell engines. The operating temperature of fuel cell engines is relatively low, and the water flow rate in the radiator is relatively small, which is affected by the large front area of ​​the radiator and the relatively small upper limit of the air volume on the air side. The flow forms on the liquid side and air side of the radiator used in new energy commercial vehicles are mostly relatively stable laminar flows. There are differences in the heat transfer performance and matching of the cooling system and the radiator of the traditional commercial vehicle internal combustion engine.

[0003] Unlike traditional internal combustion engine radiators, new energy commercial vehicle radiators mostly work under conditions of small coolant flow, low wind speed and high heat dissipation demand. Therefore, a simulation method for matching the heat transfer performance of the cooling system of new energy commercial vehicles is urgently needed. By establishing the corresponding heat transfer simulation process and the appropriate heat transfer characteristic model equation, the heat transfer performance simulation and test of the cooling system of new energy commercial vehicles can be carried out in the design stage. Summary of the invention

[0004] The purpose of the present invention is to address the deficiencies of the above-mentioned technologies and provide a simulation method for matching the heat transfer performance of a cooling system of a new energy commercial vehicle, so as to simulate and test the heat transfer and flow performance of a cooling system of a new energy commercial vehicle.

[0005] To achieve the above purpose, the heat transfer performance matching simulation method of the cooling system of a new energy commercial vehicle designed by the present invention comprises the following steps:

[0006] A) Install the fan to be tested that matches the radiator on the test bench and run it in;

[0007] B) Adjust the speed of the fan to be tested, and establish a stable 0PA static pressure difference and inlet temperature on the air inlet and air outlet sides of the fan to be tested until the working state is stable;

[0008] C) measuring the speed-air volume data of the fan to be tested, drawing a curve, and fitting a speed-air volume mathematical model formula;

[0009] D) Install the fan, radiator and engine to be tested as a whole, and install the geometric relationship between the components according to the actual vehicle status;

[0010] E) Conduct cooling system performance test, combine the speed-air volume mathematical model formula of the fan to be tested, stably control the inlet air temperature, liquid side flow rate and outlet water temperature, adjust the cold air side air volume until the inlet water temperature of the radiator meets the heat load control requirements for heat dissipation, and obtain the test data of the cooling system.

[0011] Preferably, the test data of the cooling system includes geometrical parameters of the radiator, flow and heat transfer characteristics of the coolant side of the radiator, flow and heat transfer characteristics of the cold air side of the radiator and the heat release of the radiator as a whole.

[0012] Preferably, in step E), the water inlet temperature of the radiator The unit is ℃, where T 2w is the outlet water temperature of the radiator, in °C, Q w The load required for the vehicle to dissipate heat, in KW, C pw is the specific heat of the coolant, M w is the coolant mass flow rate, in KG / S, M w =G w / 60*ρ mw , G w is the coolant volume flow rate, unit L / MIN, ρ mw is the coolant density.

[0013] Preferably, in step E), the geometrical structural parameters of the radiator include the heat dissipation belt side and the heat dissipation pipe side. On the heat dissipation belt side, the heat dissipation belt hydraulic diameter D f is the hydraulic diameter of the heat dissipation zone, in MM, h f is the wave height of the heat dissipation zone, in MM, t f is the wave distance of the heat dissipation zone, in MM, l f is the length of the single-wave heat dissipation belt, in MM, and the side surface area of ​​the heat dissipation belt F2 = 2l f *n sf *B core *n tf *10 ；6 , unit is MM 2 , n sf is the wave number of a single heat dissipation belt, dimensionless, B core is the thickness of the radiator core, in MM, n tf is the number of heat sink belts, dimensionless;

[0014] On the heat pipe side, the outer circumference of the heat pipe is l to =2*(t lf -t sf )+π*t sf , unit is MM, t lf is the length of the heat pipe along its long axis, in MM, tsf is the short axis length of the heat pipe, in MM, and the wetted perimeter of the heat pipe l toi =2*(t lf -t sf )+π*(t sf -2δ t ), unit is MM, δ t is the wall thickness of the heat pipe, in mm, and the cross-sectional area of ​​a single heat pipe is s tt =(t lf -t sf )*(t sf -2δ t )+π*(t sf -2δ t ), unit is MM 2 ;

[0015] On the heat pipe side, the heat pipe hydraulic diameter The unit is MM, the tube side surface area F1 = 2l toi *H core *(n tf -1)*10 ；6 , unit is MM 2 , H core is the height of the radiator core, in mm, the total heat dissipation area of ​​the radiator is F = F1 + F2, in mm 2 .

[0016] Preferably, in step E), the flow and heat transfer characteristics of the coolant side of the radiator are calculated, and the mass flow rate of the coolant in the tube is The unit is KG / M 2 *S, the Prandtl number of the coolant is defined by dimensionless, u w is the kinematic viscosity of the coolant, in M 2 .S, Λ w is the thermal conductivity of the coolant, in units of W / (M*℃);

[0017] Reynolds number in the tube Dimensionless, for the inside of the tube, the Nusselt number on the tube side is calculated using the Schidt & Tate formula in laminar flow conditions Dimensionless, L is the flow length, numerically equal to H core , unit MM, is the ratio of the coolant mainstream and wall kinematic viscosities, dimensionless;

[0018] Heat release coefficient inside the heat pipe Unit: W / (M 2 *℃).

[0019] Preferably, in step E), the flow and heat transfer characteristics of the cold air side of the radiator are calculated, and the air volume of the air side of the radiator is calculated. Unit M 3 / S,T 2a is the radiator outlet temperature, in °C, T 1a is the radiator inlet air temperature, in °C, PA is the cold air density, C pa The specific heat of cold air is adjusted according to the customer's input to find the most demanding working point, and the corresponding radiator outlet temperature And ask T 2a ≤T 2W Otherwise, the air volume needs to be recalculated again until it meets the requirements. If the radiator core is a single-row tube structure, calculate the flow and heat transfer characteristics of the cold air side of the radiator, and the Reynolds number on the air side Dimensionless, Vef is the air velocity of the radiator, unit: M / S; D f is the hydraulic diameter of the heat dissipation zone, in MM, γef is the kinematic viscosity of air, in PA*S, and the convective heat transfer of the fluid across the cylinder is calculated using the Rukauskas correlation. The Rukauskas correlation is derived from a circular tube. If the heat dissipation tube is a flat tube, it is derived using the equivalent diameter. C is the constant coefficient of the characteristic correlation, dimensionless. Pr is the air Prandtl number, dimensionless. is the ratio of the dynamic viscosity in the center of the radiator tube to the dynamic viscosity of the tube wall, dimensionless, m is the Reynolds number power exponential constant, dimensionless, n is the Prandtl power exponential constant, dimensionless;

[0020] Heat dissipation coefficient of the outer surface of the heat pipe The unit is W / (M2*℃), ΛA is the thermal conductivity of cold air, the unit is W / M·℃, and the actual heat release coefficient of the outer surface of the radiator heat pipe is a af =η af *a a , unit W / (M2*℃), η af is the heat dissipation efficiency, l is the heat transfer height of the heat dissipation belt, which is half of the wave height of the heat dissipation belt, in MM. S is the fin constant, unit is M -1 ,λ f is the thermal conductivity of the heat dissipation belt, the unit is W / (M*℃), δ f is the thickness of the heat dissipation belt material, in M. th(sl) is a super function.

[0021] Preferably, in step E), the overall heat release of the radiator includes the heat transfer coefficient of the radiator, the logarithmic mean temperature difference of the radiator and the theoretical heat dissipation of the radiator. The unit is W / (M2 *℃), R f is the fouling coefficient;

[0022] Radiator logarithmic mean temperature difference The unit is ℃, △T min =T 1w -T 2a , unit is ℃, △T max =T 2w -T 1a , unit is ℃, △T ln According to the pure countercurrent calculation, the actual flow of the radiator fluid is a cross flow, and the fluids do not mix with each other, so correction is needed. For the cross-flow type, single-flow tube-belt water radiator, there is a radiator logarithmic mean correction temperature difference ΔT m = E·ΔT ln , unit is ℃, E is the temperature coefficient, dimensionless, R is the liquid-temperature difference ratio, dimensionless, ΔT w is the temperature difference between the inlet and outlet of the coolant, in °C, Δt a is the difference between the radiator air side outlet temperature and the ambient air temperature, in °C. P is the liquid side heat dissipation efficiency, dimensionless;

[0023] Theoretical heat dissipation of the radiator Q nf =K*△T m *F*10 ；3 , the unit is KW, if Q nf ≥Q w This indicates that the design is effective, otherwise the radiator needs to be redesigned.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. The present invention takes into account the many characteristics of the radiator of the cooling system of new energy commercial vehicles, such as being used in working environments with high load and low speed, large air volume but low wind speed, and small coolant flow rate. For the first time, the present invention proposes a method for describing the heat transfer characteristics of the liquid side and the air side of the radiator of new energy commercial vehicles respectively using the Sid & Tate model and the Rukauskas model;

[0026] 2. The heat transfer and flow performance of the cooling system (radiator + high-pressure fan) of new energy commercial vehicles were simulated and tested, and the rationality of the model was verified by the test results. The deviation between the theoretically calculated heat dissipation and the actual test results was less than 8%, and the deviation between the corresponding matched test air volume and the theoretical calculated value was less than 2%, proving that the model used meets the working characteristics of the radiator used for radiator cooling of new energy commercial vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The air volume curve when the fan speed to be tested is 25 in the simulation method for matching the heat transfer performance of the cooling system of new energy commercial vehicles;

[0028] Figure 2 The air volume curve when the fan speed to be tested is 40 in the simulation method for matching the heat transfer performance of the cooling system of new energy commercial vehicles;

[0029] Figure 3 It is the air volume curve when the fan speed to be tested is 45 in the simulation method of heat transfer performance matching of the cooling system of new energy commercial vehicles. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] A simulation method for matching heat transfer performance of a cooling system of a new energy commercial vehicle comprises the following steps:

[0032] A) Install the fan to be tested that matches the radiator on the test bench and run it in;

[0033] B) Adjust the speed of the fan to be tested, and establish a stable 0PA static pressure difference and inlet temperature on the air inlet and air outlet sides of the fan to be tested until the working state is stable;

[0034] C) measuring the speed-air volume data of the fan to be tested, drawing a curve, and fitting a speed-air volume mathematical model formula;

[0035] D) Install the fan, radiator and engine to be tested as a whole, and install the geometric relationship between the components according to the actual vehicle status;

[0036] E) Conduct cooling system performance test, combine the speed-air volume mathematical model formula of the fan to be tested, stably control the inlet air temperature, liquid side flow rate and outlet water temperature, adjust the cold air side air volume until the inlet water temperature of the radiator meets the heat load control requirements for heat dissipation, and obtain the test data of the cooling system.

[0037] The test data of the cooling system include the geometric parameters of the radiator, the flow and heat transfer characteristics of the coolant side of the radiator, the flow and heat transfer characteristics of the cold air side of the radiator and the overall heat release of the radiator.

[0038] In addition, in step E), the water inlet temperature of the radiator The unit is ℃, where T 2w is the outlet water temperature of the radiator, in °C, Q w The load required for the vehicle to dissipate heat, in KW, C pw is the specific heat of the coolant, M w is the coolant mass flow rate, in KG / S, M w =Gw / 60*ρ mw , G w is the coolant volume flow rate, unit L / MIN, ρ mw is the coolant density.

[0039] Specifically, in step E), the geometric structural parameters of the radiator include the heat dissipation belt side and the heat dissipation pipe side. On the heat dissipation belt side, the heat dissipation belt hydraulic diameter is D f is the hydraulic diameter of the heat dissipation zone, in MM, h f is the wave height of the heat dissipation zone, in MM, t f is the wave distance of the heat dissipation zone, in MM, l f is the length of the single-wave heat dissipation belt, in MM, and the side surface area of ​​the heat dissipation belt F2 = 2l f *n sf *B core *n tf *10 ；6 , unit is MM 2 , n sf is the wave number of a single heat dissipation belt, dimensionless, B core is the thickness of the radiator core, in MM, n tf is the number of heat sink belts, dimensionless;

[0040] On the heat pipe side, the outer circumference of the heat pipe is l to =2*(t lf -t sf )+π*t sf , unit is MM, t lf is the length of the heat pipe along its long axis, in MM, t sf is the short axis length of the heat pipe, in MM, and the wetted perimeter of the heat pipe l toi =2*(t lf -t sf )+π*(t sf -2δ t ), unit is MM, δ t is the wall thickness of the heat pipe, in mm, and the cross-sectional area of ​​a single heat pipe is s tt =(t lf -t sf )*(t sf -2δ t )+π*(t sf -2δ t ), unit is MM 2 ;

[0041] On the heat pipe side, the heat pipe hydraulic diameter The unit is MM, the tube side surface area F1 = 2l toi *H core*(n tf -1)*10 ；6 , unit is MM 2 , H core is the height of the radiator core, in mm, the total heat dissipation area of ​​the radiator is F = F1 + F2, in mm 2 .

[0042] In step E), the flow and heat transfer characteristics of the coolant side of the radiator are calculated, and the mass flow rate of the coolant in the tube The unit is KG / M 2 *S, the Prandtl number of the coolant is defined by Dimensionless, u w is the kinematic viscosity of the coolant, in M 2 .S, Λ w is the thermal conductivity of the coolant, in units of W / (M*℃);

[0043] Reynolds number in the tube Dimensionless, for the inside of the tube, the Nusselt number on the tube side is calculated using the Schidt & Tate formula in laminar flow conditions Dimensionless, L is the flow length, numerically equal to H core , unit MM, is the ratio of the coolant mainstream and wall kinematic viscosities, dimensionless;

[0044] Heat release coefficient inside the heat pipe Unit: W / (M 2 *℃).

[0045] In step E), the flow and heat transfer characteristics of the cold air side of the radiator are calculated, and the air volume on the air side of the radiator is calculated. Unit M 3 / S,T 2a is the radiator outlet temperature, in °C, T 1a is the radiator inlet air temperature, in °C, PA is the cold air density, C pa The specific heat of cold air is adjusted according to the customer's input to find the most demanding working point, and the corresponding radiator outlet temperature And ask T 2a ≤T 2W Otherwise, the air volume needs to be recalculated again until it meets the requirements. If the radiator core is a single-row tube structure, calculate the flow and heat transfer characteristics of the cold air side of the radiator, and the Reynolds number on the air side Dimensionless, Vef is the air velocity of the radiator, unit: M / S; D f is the hydraulic diameter of the heat dissipation zone, in MM, γef is the kinematic viscosity of air, in PA*S, and the convective heat transfer of the fluid across the cylinder is calculated using the Rukauskas correlation. The Rukauskas correlation is derived from a circular tube. If the heat dissipation tube is a flat tube, it is derived using the equivalent diameter. C is the constant coefficient of the characteristic correlation, dimensionless. Pr is the air Prandtl number, dimensionless. is the ratio of the dynamic viscosity in the center of the radiator tube to the dynamic viscosity of the tube wall, dimensionless, m is the Reynolds number power exponential constant, dimensionless, n is the Prandtl power exponential constant, dimensionless;

[0046] Heat dissipation coefficient of the outer surface of the heat pipe The unit is W / (M2*℃), ΛA is the thermal conductivity of cold air, the unit is W / M·℃, and the actual heat release coefficient of the outer surface of the radiator heat pipe is a af =η af *a a , unit W / (M2*℃), η af is the heat dissipation efficiency, l is the heat transfer height of the heat dissipation belt, which is half of the wave height of the heat dissipation belt, in MM. λ f is the thermal conductivity of the heat dissipation zone, δ f is the thickness of the heat dissipation belt material, in M. th(sl) is a super function.

[0047] In step E), the overall heat release of the radiator includes the heat transfer coefficient of the radiator, the logarithmic mean temperature difference of the radiator and the theoretical heat dissipation of the radiator. The unit is W / (M 2 *℃), R f is the fouling coefficient;

[0048] Radiator logarithmic mean temperature difference The unit is ℃, △T min =T 1w -T 2a , unit is ℃, △T max =T 2w -T 1a , unit is ℃, △T ln According to the pure countercurrent calculation, the actual flow of the radiator fluid is a cross flow, and the fluids do not mix with each other, so correction is needed. For the cross-flow type, single-flow tube-belt water radiator, there is a radiator logarithmic mean correction temperature difference ΔT m = E·ΔT ln , unit is ℃, E is the temperature coefficient, dimensionless, R is the liquid-temperature difference ratio, dimensionless, ΔT w is the temperature difference between the inlet and outlet of the coolant, in °C, Δt a is the difference between the radiator air side outlet temperature and the ambient air temperature, in °C. P is the liquid side heat dissipation efficiency, dimensionless;

[0049] Theoretical heat dissipation of the radiator Q nf =K*△T m *F*10 ；3 , the unit is KW, if Q nf ≥Q w This indicates that the design is effective, otherwise the radiator needs to be redesigned.

[0050] Taking a new energy commercial vehicle cooling system as an example, the customer input is as follows:

[0051] 1) Inlet air temperature (℃): 25, 40, 45

[0052] 2) Coolant flow (L / MIN): 90

[0053] 3) Test medium: 50% water 50% ethylene glycol

[0054] 4) Key working point heat dissipation load (KW): 26, 32, 46, 65KW

[0055] 5) Radiator water outlet temperature (℃): 60 -1

[0056] Design the radiator based on the above input and verify the design.

[0057] The theoretical water inlet temperature and heat transfer qualitative temperature of the radiator are calculated based on the customer input. The heat transfer qualitative temperature is the average of the theoretical water inlet and outlet temperatures of the radiator. The calculation results are shown in Table 1:

[0058] Table 1: Inlet water temperature calculation table

[0059]

[0060] The maximum allowable outlet temperature of engine cooling water is between 64 and 71°C, and the cooling constant is between 20 and 25°C. The cooling constant of traditional fuel vehicles is 60°C. The heat dissipation requirement is three times that of traditional fuel vehicles. The most demanding working conditions are an inlet air temperature of 45°C and a heat dissipation load of 65KW. Therefore, this point is selected as the rated point in the following theoretical calculation process.

[0061] The structural selection of the radiator is first determined based on experience. The core front area S ≥ 0.011 * QW = 0.011 * 65 = 0.715 M 2 , select the tube-belt aluminum welded radiator, and preliminarily determine the geometric structure of the radiator:

[0062] External dimensions of the core assembly: core width L CORE =925.8MM, core height HCORE =780MM, core thickness B CORE =42MM, single row tube, the front area of ​​the radiator core S = 0.722124M 2 .

[0063] The heat dissipation belt is made of rust-proof aluminum according to EN AW3003. The structural dimensions are: wave height H F =7.8MM, wave distance T F =3.34MM, width L FF =42MM, heat dissipation belt skylight angle Θ F =26°, the distance between adjacent skylights is 0.9MM, and the length of the single-wave heat dissipation belt is L F =16.88MM, material thickness Δ F =0.1MM, single heat dissipation belt wave number N SF There are 229 heat sinks. TF There are 103 pieces. The key dimension characteristics of the heat sink include the hydraulic diameter of the heat sink and the side surface area of ​​the heat sink.

[0064] Calculation of hydraulic diameter of heat dissipation belt:

[0065]

[0066] Calculation of the side surface area of ​​the heat sink:

[0067] F2=2l f *n sf *B core *n tf *10 ；6 =2*16.88*229*42*103=33.44m 2

[0068] Heat pipe short axis length T SF =1.2MM, heat pipe long axis length T LF =42MM, radiator heat pipe material thickness Δ T =0.3MM, heat pipe T TF The number is 102. Since the heat pipe is a flat pipe and its length is much greater than its width in its cross section, it can be approximately considered that its inner and outer surface areas are equal. The calculation of the key dimensional features of the radiator includes the wetted perimeter of the heat pipe, the cross-sectional area of ​​a single pipe, the hydraulic diameter of the heat pipe and the side surface area of ​​the heat pipe:

[0069] Calculation of the outer circumference of the heat pipe:

[0070] l to =2*(t lf -t sf )+π*t sf =85.368mm

[0071] Calculation of the wetted perimeter of the heat pipe:

[0072] l toi =2*(t lf -t sf )+π*(t sf -2δ t )=83.484mm

[0073] Calculation of the cross-sectional area of ​​a single heat pipe:

[0074] s tt =(t lf -t sf )*(t sf -2δ t )+π*(t sf -2δ t )*(t sf -2δ t ) / 4=24.7626mm 2

[0075] Calculation of hydraulic diameter of heat pipe:

[0076]

[0077] Calculation of the side surface area of ​​the heat pipe:

[0078] F1=2l to *H core *t tf *10 ；6 =2*85.638*780*102*10 ；6 =13.6m 2

[0079] Calculation of the total heat dissipation area of ​​the radiator:

[0080] F=F1+F2=33.44+13.6=47m 2

[0081] Calculation of coolant flow and heat transfer in the heat pipe, including the calculation of coolant mass flow rate in the pipe:

[0082]

[0083] The kinematic viscosity, dynamic viscosity and thermal conductivity of the coolant are obtained from the reference book, and then the Prandtl number of the coolant is calculated according to the definition of the Prandtl number. The values ​​are shown in Table 2:

[0084]

[0085] Table 2: Calculation of coolant Prandtl number (applicable to the interval value in this example)

[0086]

[0087] The physical parameters, Prandtl number and Reynolds number of the coolant at the qualitative temperature are determined by linear interpolation. The Reynolds number of the coolant suitable for this example is calculated according to the definition, and the values ​​are shown in Table 3:

[0088]

[0089] Table 3: Coolant viscosity, thermal conductivity, Prandtl number and Reynolds number at qualitative temperature

[0090]

[0091] R et =543~581<2300, the coolant in the radiator tube is in a laminar state.

[0092] For the inside of the tube, the Nusselt number N is calculated using the Schidt & Tate formula in laminar flow conditions. ut

[0093]

[0094] Note: Because the temperature difference in this example is very small, Can be processed as value 1.

[0095] Calculation of heat release coefficient inside the heat pipe:

[0096]

[0097] Nusselt number on the coolant side N ut and the heat release coefficient a inside the radiator tube w See Table 4:

[0098] Table 4: Nusselt number of coolant and heat release coefficient in tube at qualitative temperature

[0099]

[0100]

[0101] Regarding the flow and heat transfer calculation of cold air outside the radiator tube,

[0102] Since the heat transfer efficiency in heat transfer cannot be greater than 1, we must first ensure that the air outlet temperature of the radiator air side will not be greater than the radiator liquid outlet temperature, that is, it cannot be greater than the 60°C input by the customer, otherwise the system matching will fail. The calculated radiator air side air volume is shown in Table 6:

[0103] Table 6: Preliminary determination of radiator air side air volume

[0104]

[0105] The most demanding working point in Table 6 is that the inlet air temperature is 45℃, the simulated load is 65KW, and the cold air density is 1.2KG / M 3 At this time, the calculated volumetric air volume is 3.59M 3 / S. Take the safety factor as 1.2, 1.2*M a =4.308M 3 / S=15508M 3 / H.

[0106] Verification calculation of the air outlet temperature of the radiator air side corresponding to the most demanding working point:

[0107]

[0108] The requirements are met, so the corresponding volumetric air volume and radiator air side outlet temperature can be applied to the first theoretical trial calculation.

[0109] In this example, the radiator core structure is a single-row tube, so it is treated as a single-tube state with air sweeping outward. When the air sweeps outward in a single tube, the air viscosity is found in the table to be γef = 17.91*10 -6 PA*S, calculation of the air side Reynolds number of the radiator, Laminar flow.

[0110] The convective heat transfer of fluid across a single tube is calculated using the Rukauskas correlation. The Rukauskas correlation is derived for round tubes. In this example, the heat dissipation tube is a flat tube, so the equivalent diameter, D, is used. f =3.09MM. Considering that the temperature gradient of the air wall temperature of the radiator is very small, the correlation formula It can be approximated to 1. The values ​​of C, m and n are selected from Table 10-2 of "Thermal Engineering Foundation" (Zhang Xuexue). It can be seen that when R ef =10 3 ~2*10 5 , C=0.26, m=0.6, n=0.36.

[0111]

[0112] Thermal conductivity of cold air A =2.78×10 -2 W / M·℃, calculate the heat release coefficient a of the outer surface of the heat pipe a :

[0113]

[0114] Fin efficiency is used as an indicator to measure the effectiveness of fin heat transfer. The heat dissipation belt is used to expand the heat dissipation area and increase the heat dissipation capacity, but the heat dissipation belt has a height. As the height increases, the heat dissipation capacity of the heat dissipation belt will gradually decrease. At this time, the efficiency of the heat dissipation belt needs to be considered, as follows:

[0115]

[0116] th(sl) is a super function, calculated as follows:

[0117] sl=115.3*3.9*10 ；3 =0.4497

[0118]

[0119] Where: l is the heat exchange height, half of the wave height, L = 7.8 / 2 = 3.9*10 -3 MM,λ f is the thermal conductivity of the heat sink, and the aluminum alloy takes λ f =200W / M·℃

[0120] δ f is the thickness of the heat dissipation belt material, δ f =0.1×10 -3 MS is the fin efficiency constant coefficient, unit: M -1

[0121] The heat sink efficiency is calculated using the formula for straight ribs with equal cross-section:

[0122]

[0123] Then a af =η af *a a =0.938*132.46=124.25W / M2·℃

[0124] Write the heat transfer coefficient K of the radiator based on the cold air side

[0125]

[0126] Combined with the known conditions calculated previously, the logarithmic mean temperature difference △T is calculated according to pure countercurrent ln , known conditions include T 1w =71.39℃, T 2w =60℃, T 1a =45℃, T 2a =57.86℃, we get:

[0127] △T min =T 1w -T 2a=71.39-57.57=13.82℃

[0128] △T max =T 2w -T 1a =60-45=15℃

[0129]

[0130] The actual flow of the radiator fluid is a cross flow, and the fluids do not mix with each other. The logarithmic mean temperature difference calculated according to pure counterflow needs to be corrected by the temperature coefficient E: For a cross-flow type, single-flow tube-type water radiator, the average temperature difference calculation process is as follows:

[0131]

[0132] ΔT m =ε·ΔT ln =13.363℃

[0133] In the formula, Δt w is the temperature difference between the inlet and outlet of the coolant, Δt a It is the difference between the radiator air side outlet temperature and the ambient air temperature.

[0134] Calculate the heat dissipation capacity Q of the entire radiator n =K*△T m *F*10 -3 =112.76*13.363*47*0.001=70.8kW>65kW

[0135] From the perspective of theoretical calculation, the design and selection of the radiator are appropriate, but test results are still needed to verify the rationality of the theoretical calculation.

[0136] 650MM high pressure fan (with cooling module) speed-air volume data see Table 7, curve see Figure 1 to Figure 3 In this case, a 650MM diameter high-pressure fan is selected to match the cooling module of the new energy commercial vehicle, and the single performance test of the high-pressure fan is completed on the corresponding test equipment. From the test results, it can be preliminarily determined that under the most demanding working conditions, that is, the air volume is 15508M 3 / S, the operating speed of the high pressure fan is between 3000 and 3500RPM.

[0137] Table 7: Speed-flow data of high pressure fan

[0138]

[0139] The fan, radiator and engine to be tested are installed as a whole according to the actual vehicle status, and then the cooling system performance test is carried out. When the inlet air temperature is adjusted to 25, 40, and 45°C, the outlet water temperature is adjusted to 60 -1 ℃, the heat load is constant (26, 32, 46, 65) ± 0.5KW for control, and the peripheral data of the cooling system - fan and radiator are measured. The test results are shown in Table 8:

[0140] Table 8: New energy commercial vehicle cooling system performance matching test

[0141]

[0142] Combined with the speed-air volume curve of the 650MM high-pressure fan, the fan speed at each working point is matched, see Table 9:

[0143] Table 9: Performance matching example of fan-cooling module for new energy commercial vehicles

[0144]

[0145]

Claims

1. A simulation method for heat transfer performance matching of a cooling system of a new energy commercial vehicle, comprising the following steps: A) Install the fan to be tested that matches the radiator on the test bench and run it in; B) Adjust the speed of the fan to be tested, and establish a stable 0PA static pressure difference and inlet temperature on the air inlet and air outlet sides of the fan to be tested until the working state is stable; C) measuring the speed-air volume data of the fan to be tested, drawing a curve, and fitting a speed-air volume mathematical model formula; D) Install the fan, radiator and engine to be tested as a whole, and install the geometric relationship between the components according to the actual vehicle status; E) Conduct cooling system performance test, combine the speed-air volume mathematical model formula of the fan to be tested, stably control the inlet air temperature, liquid side flow rate and outlet water temperature, adjust the cold air side air volume until the inlet water temperature of the radiator meets the heat load control requirements for heat dissipation, and obtain the test data of the cooling system.

2. The heat transfer performance matching simulation method of the cooling system of a new energy commercial vehicle according to claim 1 is characterized in that: The test data of the cooling system includes the geometric parameters of the radiator, the flow and heat transfer characteristics of the coolant side of the radiator, the flow and heat transfer characteristics of the cold air side of the radiator, and the overall heat release of the radiator.

3. The method for simulating the heat transfer performance matching of the cooling system of a new energy commercial vehicle according to claim 2 is characterized in that: In step E), the water inlet temperature of the radiator The unit is ℃, where T 2w is the outlet water temperature of the radiator, in °C, Q w The heat dissipation load required by the vehicle, in KW, C pw is the specific heat of the coolant, M w is the coolant mass flow rate, in KG / S, M w =G w / 60*ρ mw , G w is the coolant volume flow rate, unit L / MIN, ρ mw is the coolant density.

4. The method for simulating the heat transfer performance matching of the cooling system of a new energy commercial vehicle according to claim 3 is characterized in that: In the step E), the geometrical structural parameters of the radiator include the heat dissipation belt side and the heat dissipation pipe side. On the heat dissipation belt side, the heat dissipation belt hydraulic diameter D f is the hydraulic diameter of the heat dissipation zone, in MM, h f is the wave height of the heat dissipation zone, in MM, t f is the wave distance of the heat dissipation zone, in MM, l f is the length of the single-wave heat dissipation belt, in MM, and the side surface area of ​​the heat dissipation belt F2 = 2l f *n sf *B core *n tf *10 -6 , unit is MM 2 , n sf is the wave number of a single heat dissipation belt, dimensionless, B core is the thickness of the radiator core, in MM, n tf is the number of heat sink belts, dimensionless; On the heat pipe side, the outer circumference of the heat pipe is l to =2*(t lf -t sf )+π*t sf , unit is MM, t lf is the length of the heat pipe along its long axis, in MM, t sf is the short axis length of the heat pipe, in MM, and the wetted perimeter of the heat pipe l toi =2*(t lf -t sf )+π*(t sf -2δ t ), unit is MM, δ t is the wall thickness of the heat pipe, in mm, and the cross-sectional area of ​​a single heat pipe is s tt =(t lf -t sf )*(t sf -2δ t )+π*(t sf -2δ t ), unit is MM 2 ; On the heat pipe side, the heat pipe hydraulic diameter The unit is MM, the tube side surface area F1 = 2l toi *H core *(n tf -1)*10 -6 , unit is MM 2 , H core is the height of the radiator core, in mm, the total heat dissipation area of ​​the radiator is F = F1 + F2, in mm 2 .

5. The method for simulating the heat transfer performance matching of the cooling system of a new energy commercial vehicle according to claim 4 is characterized in that: In step E), the flow and heat transfer characteristics of the coolant side of the radiator are calculated, and the mass flow rate of the coolant in the tube The unit is KG / M 2 *S, the Prandtl number of the coolant is defined by Dimensionless, u w is the kinematic viscosity of the coolant, in M 2 .S, Λ w is the thermal conductivity of the coolant, in units of W / (M*℃); Reynolds number in the tube Dimensionless, for the inside of the tube, the Nusselt number on the tube side is calculated using the Schidt & Tate formula in laminar flow conditions Dimensionless, L is the flow length, numerically equal to H core , unit MM, is the ratio of the coolant mainstream and wall kinematic viscosities, dimensionless; Heat release coefficient inside the heat pipe Unit: W / (M 2 *℃).

6. The method for simulating the heat transfer performance matching of the cooling system of a new energy commercial vehicle according to claim 5 is characterized in that: In step E), the flow and heat transfer characteristics of the cold air side of the radiator and the air volume of the air side of the radiator are calculated. Unit M 3 / S,T 2a is the radiator outlet temperature, in °C, T 1a is the radiator inlet air temperature, in °C, PA is the cold air density, C pa The specific heat of cold air is adjusted according to the customer's input to find the most demanding working point, and the corresponding radiator outlet temperature And ask T 2a ≤T 2W Otherwise, the air volume needs to be recalculated again until it meets the requirements. If the radiator core is a single-row tube structure, calculate the flow and heat transfer characteristics of the cold air side of the radiator, and the Reynolds number on the air side Dimensionless, Vef is the air velocity of the radiator, unit: M / S; D f is the hydraulic diameter of the heat dissipation zone, in MM, γef is the kinematic viscosity of air, in PA*S, and the convective heat transfer of the fluid across the cylinder is calculated using the Rukauskas correlation. The Rukauskas correlation is derived from a circular tube. If the heat dissipation tube is a flat tube, it is derived using the equivalent diameter. C is the constant coefficient of the characteristic correlation, dimensionless. Pr is the air Prandtl number, dimensionless. is the ratio of the dynamic viscosity in the center of the radiator tube to the dynamic viscosity of the tube wall, dimensionless, m is the Reynolds number power exponential constant, dimensionless, n is the Prandtl power exponential constant, dimensionless; Heat dissipation coefficient of the outer surface of the heat pipe The unit is W / (M2*℃), ΛA is the thermal conductivity of cold air, the unit is W / M·℃, and the actual heat release coefficient of the outer surface of the radiator heat pipe is a af =η af *a a , unit W / (M2*℃), η af is the heat dissipation efficiency, l is the heat transfer height of the heat dissipation belt, which is half of the wave height of the heat dissipation belt, in MM. λ f is the thermal conductivity of the heat dissipation zone, δ f is the thickness of the heat dissipation belt material, in M. th(sl) is a super function.

7. The method for simulating the heat transfer performance matching of the cooling system of a new energy commercial vehicle according to claim 6 is characterized in that: In step E), the overall heat release of the radiator includes the heat transfer coefficient of the radiator, the logarithmic mean temperature difference of the radiator and the theoretical heat dissipation of the radiator. The unit is W / (M 2 *℃), R f is the fouling coefficient; Radiator logarithmic mean temperature difference The unit is ℃, △T min =T 1w -T 2a , unit is ℃, △T max =T 2w -T 1a , unit is ℃, △T ln According to the pure countercurrent calculation, the actual flow of the radiator fluid is a cross flow, and the fluids do not mix with each other, so correction is needed. For the cross-flow type, single-flow tube-belt water radiator, there is a radiator logarithmic mean correction temperature difference ΔT m = E·ΔT ln , unit is ℃, E is the temperature coefficient, dimensionless, R is the liquid-temperature difference ratio, dimensionless, ΔT w is the temperature difference between the inlet and outlet of the coolant, in °C, Δt a is the difference between the radiator air side outlet temperature and the ambient air temperature, in °C. P is the liquid side heat dissipation efficiency, dimensionless; Theoretical heat dissipation of the radiator Q nf =K*△T m *F*10 -3 , the unit is KW, if Q nf ≥Q w This indicates that the design is effective, otherwise the radiator needs to be redesigned.

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