Effect of structure on the performance of inner condenser for heat pump of EV

doi:10.11949/0438-1157.20201949

Abstract

Abstract:

The inner condenser for electric vehicle (EV) heat pump system of the three heat exchangers type was experimentally studied, it was found that the heat transfer capacity difference between the double-layer four-pass condenser and the single-layer two-pass condenser was as high as 7.9%, under the same overall dimensions, and corresponding pressure drop difference of refrigerant side was 177.6%. A one-dimensional simulation model of the double-layer four-pass inner condenser was established to investigate its thermal-hydraulic performance under different structural parameters with refrigerant R134a as well as R1234yf. The simulation results showed that, pressure drop of refrigerant side decreased significantly when the pass arrangement is 11-12-12-11 when the refrigerant was R134a, while the heat transfer capacity was insensitive to the pass arrangement. When the thickness of the second layer of the double-layer condenser was fixed and the thickness of the first layer increased from 10 mm to 20 mm, the heat transfer rates of R134a can be increased by 10.4%, however, pressure drop can be decreased by 63.6%, under the conditions of high air flow rate. When the total thickness of the double-layer condenser was fixed, two thicknesses combinations of the first layer and the second layer as 16 mm-8 mm and 14 mm-10 mm could achieve better overall thermal-hydraulic performance, and the difference of heat transfer rate can be negligible. Under the airflow rate of 732 m³/h, the condenser of the thickness combination of 14 mm-10 mm reduced the pressure drop by 35.19% for R134a, compared to the one of 10 mm-14 mm. When the refrigerant is R1234yf, the heat exchange and pressure drop are reduced by 8.02% and 47.0% respectively compared with R134a.

Key words: heat pump system for electric vehicle, inner condenser, structural parameter, R1234yf, microchannels, heat transfer, gas-liquid flow

摘要：

以三换热器汽车热泵系统中的内部冷凝器为研究对象，实验研究了迎风面积与厚度相等时单层二流程与双层四流程的性能差别，发现双层冷凝器比单层的换热能力最大可增加7.9%，但压降增加了177.6%。建立了双层四流程冷凝器一维仿真模型，研究了当制冷剂为R134a与R1234yf时其在不同结构下的换热量与制冷剂侧压降。结果表明：不同流程排布的换热量差别较小，排布为11-12-12-11时，各个工况的R134a侧压降都显著减小；固定第二层厚度，第一层厚度从10 mm到20 mm，高风速工况下R134a的换热量最大增加10.4%，压降最大可减小63.6%；固定总厚度，采用不同的两层厚度组合，换热量变化较小，存在性能较优的两层厚度组合16 mm-8 mm与14 mm-10 mm；制冷剂为R1234yf时换热量和压降分别比R134a降低了8.02%和47.0%。

关键词: 车用热泵, 内部冷凝器, 结构参数, R1234yf, 微通道, 传热, 气液两相流

CLC Number:

TK 172

Lanping ZHAO, Bentao GUO, Zhigang YANG. Effect of structure on the performance of inner condenser for heat pump of EV[J]. CIESC Journal, 2021, 72(9): 4616-4628.

赵兰萍, 郭本涛, 杨志刚. 车用热泵内部冷凝器结构对性能的影响[J]. 化工学报, 2021, 72(9): 4616-4628.

Figures/Tables 31

Fig.1 Vehicle heat pump system with three exchangers

Fig.2 Schematic diagram of the inner condenser structure

Table 1 Correlations of the model

项目	关联式
空气侧传热及压降^[29]	$j a = 0.2671 R e a - 0.1944 L a 90 0.257 F p L p - 0.5177 F h L p - 1.9045 L h L p 1.7159 L d L p - 0.2147 δ L p - 0.05$
	$f a = 0.545 R e a - 0.3068 L a 90 0.444 F p L p - 0.9925 F h L p 0.5458 L h L p - 0.2003 L d L p 0.0688$
	$h a = j a ρ a v m c p P r a - 2 / 3$
	$R e a = v m D a μ a$
制冷剂侧传热系数（单相）^[30]	$N u = f p / 8 R e r - 1000 P r r 1 + 1.27 (f p / 8) 0.5 (P r r 2 / 3 - 1) [1 + (D r / L) 2 / 3] P r t P r w 0.11$
制冷剂侧传热系数（单相）^[30]	$f p = (1.82 l g R e r - 1.64) - 2$
制冷剂侧传热系数（两相）^[31]	$N u = 0.023 R e l 0.8 P r l 0.4 1 + 2.22 X t t 0.89$
制冷剂侧传热系数（两相）^[31]	$X t t = ρ g ρ l 0.5 μ g μ l 0.1 1 - x x 0.9$
制冷剂压降（单相）^[27]	Re<2000， $f = 0.3164 R e - 0.25$ ；
制冷剂压降（单相）^[27]	Re>2000， $f = 64 / R e$
制冷剂压降（两相）^[32]	$f f l = 0.435 R e e q 0.12$
	$R e e q = G e q D r μ l$
	$G e q = G 1 - x + x ρ l ρ g 0.5$
空泡系数^[32]	$α = 1 + 1 - x x ρ g ρ l 2 / 3 - 1$
突扩压降（单相）^[33]	$ξ = 1 - F m i n F m a x 2$
突扩压降（单相）^[33]	$? H = ξ v m i n 2 2 g$
突缩压降（单相）^[33]	$ξ = 0.5 1 - F m i n F m a x$
突缩压降（单相）^[33]	$? H = ξ v m i n 2 2 g$
突缩压降（双相）^[34]	$? P = G v c 2 2 ρ t p 1 - σ 2 C c 2 - 2 C c 1 - C c$
	$ρ t p = x ρ g + 1 - x ρ l$
	$C c = 1 - 1 - σ 2.08 1 - σ + 0.5371$

Table 1 Correlations of the model

项目	关联式
空气侧传热及压降^[29]	$j a = 0.2671 R e a - 0.1944 L a 90 0.257 F p L p - 0.5177 F h L p - 1.9045 L h L p 1.7159 L d L p - 0.2147 δ L p - 0.05$
	$f a = 0.545 R e a - 0.3068 L a 90 0.444 F p L p - 0.9925 F h L p 0.5458 L h L p - 0.2003 L d L p 0.0688$
	$h a = j a ρ a v m c p P r a - 2 / 3$
	$R e a = v m D a μ a$
制冷剂侧传热系数（单相）^[30]	$N u = f p / 8 R e r - 1000 P r r 1 + 1.27 (f p / 8) 0.5 (P r r 2 / 3 - 1) [1 + (D r / L) 2 / 3] P r t P r w 0.11$
制冷剂侧传热系数（单相）^[30]	$f p = (1.82 l g R e r - 1.64) - 2$
制冷剂侧传热系数（两相）^[31]	$N u = 0.023 R e l 0.8 P r l 0.4 1 + 2.22 X t t 0.89$
制冷剂侧传热系数（两相）^[31]	$X t t = ρ g ρ l 0.5 μ g μ l 0.1 1 - x x 0.9$
制冷剂压降（单相）^[27]	Re<2000， $f = 0.3164 R e - 0.25$ ；
制冷剂压降（单相）^[27]	Re>2000， $f = 64 / R e$
制冷剂压降（两相）^[32]	$f f l = 0.435 R e e q 0.12$
	$R e e q = G e q D r μ l$
	$G e q = G 1 - x + x ρ l ρ g 0.5$
空泡系数^[32]	$α = 1 + 1 - x x ρ g ρ l 2 / 3 - 1$
突扩压降（单相）^[33]	$ξ = 1 - F m i n F m a x 2$
突扩压降（单相）^[33]	$? H = ξ v m i n 2 2 g$
突缩压降（单相）^[33]	$ξ = 0.5 1 - F m i n F m a x$
突缩压降（单相）^[33]	$? H = ξ v m i n 2 2 g$
突缩压降（双相）^[34]	$? P = G v c 2 2 ρ t p 1 - σ 2 C c 2 - 2 C c 1 - C c$
	$ρ t p = x ρ g + 1 - x ρ l$
	$C c = 1 - 1 - σ 2.08 1 - σ + 0.5371$

Fig.3 Calculation process of 2-layer condenser

Fig.4 Physical comparison of two condensers

Table 2 Structural parameters of the condensers

参数	单层	双层
长×宽×厚/mm×mm×mm	215×226×32	215×226×32
扁管宽度/mm	25.4	12
微通道数	26	12
微通道宽×高/mm×mm	0.7×0.6	0.7×0.6
扁管数	23	46
流程分布	15-8	12-11-11-12
百叶窗间距/mm	1.1	1.1
百叶窗高度/mm	6.7	6.7
百叶窗角度/(°)	27	27

Table 3 Parameters of measuring instruments

测量项目	仪表设备	仪表精度	分辨率
制冷剂温度	热电偶	±0.5℃	<0.2℃
制冷剂压力	压力传感器	0.1%	<30 Pa
空气温度	PT100	±0.2℃	<0.1℃
空气压差	微压差变送器	>0.25%	<10 Pa
大气压力	绝对压力变送器	0.1%	<30 Pa

Fig.5 Heat transfer rate of the 1-layer 2-pass condenser and the 2-layer 4-pass condenser

Fig.6 Pressure drop of the 1-layer 2-pass condenser and the 2-layer 4-pass condenser

Table 4 Pass arrangement

编号	扁管排布
1	9-14-14-9
2	10-13-13-10
3	11-12-12-11
4	12-11-11-12
5	13-10-10-13
6	14-9-9-14

Fig.7 Comparison of heat transfer in each pass arrangement

Fig.8 Quality along the 2-layer condensers

Fig.9 Heat transfer coefficients of 2-layer condensers

Fig.10 Comparison of pressure drop of each pass arrangement

Fig.11 Refrigerant quality under different flat tube width of the 1st-layer

Fig.12 Heat transfer coefficients under different flat tube width of the 1st-layer

Fig.13 Heat transfer under different flat tube width of the 1st-layer

Fig.14 Pressure drop under different flat tube width of the 1st-layer

Fig.15 Heat transfer of each pass under different flat tube width of the 1st-layer (airflow rate 732 m3/h)

Fig.16 Pressure drop of each pass under different flat tube width of the 1st-layer (airflow rate 732 m3/h)

Fig.17 Quality of R134a in different flat tube width combinations

Fig.18 Heat transfer coefficients of R134a in different flat tube width combinations

Fig.19 Comparison of heat transfer under different flat tube width of the 1st-layer

Fig.20 Comparison of pressure drop under different flat tube width of the 1st-layer

Fig.21 Heat transfer of each pass under different flat tube width combinations (airflow rate 732 m3/h)

Fig.22 Pressure drop of each pass under different flat tube width combinations(airflow rate 732 m3/h)

Table 5 Physical properties of the saturated state of R1234yf and R134a

性质	R1234yf	R134a
液体动力黏度/（μPa·s）	113.59	141.77
液体运动黏度/(cm²/s)	0.0011469	0.0012861
蒸发潜热/(kJ/kg)	122.13	151.81
液体密度/(kg/m³)	990.38	1102.3
液体热导率/(mW/（m·K)）	56.130	70.427

Fig.23 Heat transfer coefficients of 2-layer condensers with R134a and R1234yf

Fig.24 Quality of 2-layer condensers with R134a and R1234yf

Fig.25 Heat transfer of 2-layer condensers with R134a and R1234yf

Fig.26 Pressure drop of 2-layer condensers with R134a and R1234yf

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