Experimental study on condensation heat transfer of R134a in mini channel with micro diamond fins

doi:10.11949/0438-1157.20221047

Abstract

Abstract:

An experimental system of condensation heat transfer using air jet impinged cooling method was established to investigate the condensation heat transfer characteristics of R134a in mini channel with micro diamond fins. The experiments were performed at vapor quality between 0 and 1, saturation pressure between 0.50 MPa and 1.50 MPa, mass flux of refrigerant between 160 kg/(m²·s) and 380 kg/(m²·s), and heat flux between 10.1 kW/m² and 59.8 kW/m². The local condensation heat transfer coefficient of the channel under different working conditions was obtained, and the influences of vapor quality, saturation pressure, mass flux and heat flux on the condensation heat transfer were analyzed. The experimental results show that, in condensation process, the local condensation heat transfer coefficient decreases with the decrease of vapor quality, mass flux and heat flux, and increases with the decrease of saturation pressure. Based on the experimental data, a calculation formula of condensation heat transfer suitable for the tiny diamond-shaped discrete rib channels in this experiment is proposed.

Key words: condensation, microscale, heat transfer, jet impingement, two-phase flow

摘要：

建立了采用空气射流冲击冷却方法的冷凝换热实验系统，对R134a在铝质微小菱形离散肋通道中的冷凝换热特性进行了实验研究。实验工况范围为制冷剂干度0~1、饱和压力0.50~1.50 MPa、制冷剂质量流率160~380 kg/(m²·s)、热通量10.1~59.8 kW/m²。实验获得了不同工况下的通道局部冷凝传热系数，分析了干度、饱和压力、质量流率以及热通量对冷凝换热的影响规律。实验结果表明：局部冷凝传热系数随干度、质量流率和局部热通量的减小而减小，随饱和压力的降低而增大，其中在干度x>0.4的区域内质量流率对于冷凝传热系数的影响效果更为明显。基于实验数据，提出了一个适用于本实验中微小菱形离散肋通道的冷凝换热计算公式。

关键词: 冷凝, 微尺度, 传热, 射流冲击, 两相流

CLC Number:

TK 124

Ran LIU, Jie LI, Yubing WANG, Hongbo ZHAN, Dalin ZHANG. Experimental study on condensation heat transfer of R134a in mini channel with micro diamond fins[J]. CIESC Journal, 2022, 73(11): 4938-4947.

刘冉, 李杰, 王玉兵, 詹洪波, 张大林. 微小菱形离散肋通道中R134a的冷凝换热实验研究[J]. 化工学报, 2022, 73(11): 4938-4947.

Figures/Tables 18

Fig.1 The test piece of mini channel with micro diamond fins

Fig.2 Internal structure of mini channel with micro diamond fins

Table 1 Structure size of mini channel with micro diamond fins

θ/(°)	S_L/mm	S_T/mm	S_g/mm	W_f/mm	L_f/mm
60	1.73	2.00	1.00	1.00	1.73

Fig.3 Condensing heat transfer experimental system

Fig.4 Physical drawing of jet device

Table 2 Range of condensation experimental working conditions

G_R134a/(kg/(m²·s))	P_sat/kPa	q/(kW/m²)
160	500,700,900,1100,1300,1500	9.3~42.1
210	500,700,900,1100,1300,1500	9.6~46.5
260	500,700,900,1100,1300,1500	10.1~55.1
310	500,700,900,1100,1300,1500	10.3~56.8
360	500,700,900,1100,1300,1500	10.4~59.8

Fig.5 Comparison between experimental values and calculated values by empirical formula of jet impingement heat transfer coefficient

Fig.6 Schematic of the calculation method of heat exchange of jet impingement

Fig.7 Analysis of condensation heat balance

Table 3 Measuring range and precision of data measuring equipment

设备	测量范围	精度
科里奥利质量流量计(制冷剂)	0~50 kg/h	0.0025
科里奥利质量流量计(空气)	0~500 kg/h	0.0025
绝对压力传感器	0~16 bar	0.2%FS
压差传感器	0~60 kPa	0.2%FS
T型热电偶	-200~350℃	±0.2℃

Table 4 Calculation method and results of uncertainty of calculation parameters

计算参数	不确定度计算公式	计算结果
干度 $x k$	$δ x k x k = ∂ x k ∂ G δ G 2 + ∂ x k ∂ α a i r δ α a i r 2 + ∂ x ∂ t w δ t w 2 + ∂ x ∂ t a i r δ t a i r 2$	1.60%
局部热通量 $q w, k$	$δ q w q w = ∂ q w ∂ t w δ t w 2 + ∂ q w ∂ t a i r δ t a i r 2 + ∂ q w ∂ α a i r δ α a i r 2$	3.20%
局部冷凝传热系数 $α w, k$	$δ α w α w = ∂ α w ∂ q w δ q w 2 + ∂ α w ∂ t s a t δ t s a t 2 + ∂ α w ∂ t w δ t w 2$	10.10%

Table 4 Calculation method and results of uncertainty of calculation parameters

计算参数	不确定度计算公式	计算结果
干度 $x k$	$δ x k x k = ∂ x k ∂ G δ G 2 + ∂ x k ∂ α a i r δ α a i r 2 + ∂ x ∂ t w δ t w 2 + ∂ x ∂ t a i r δ t a i r 2$	1.60%
局部热通量 $q w, k$	$δ q w q w = ∂ q w ∂ t w δ t w 2 + ∂ q w ∂ t a i r δ t a i r 2 + ∂ q w ∂ α a i r δ α a i r 2$	3.20%
局部冷凝传热系数 $α w, k$	$δ α w α w = ∂ α w ∂ q w δ q w 2 + ∂ α w ∂ t s a t δ t s a t 2 + ∂ α w ∂ t w δ t w 2$	10.10%

Fig.8 Distribution of vapor quality, saturation temperature, saturation pressure, wall temperature, heat flux and condensation heat transfer coefficient in flow direction

Fig.9 Influence of vapor quality on local condensation heat transfer coefficients

Fig.10 Influence of mass flux on local condensation heat transfer coefficients

Fig.11 Influence of saturation pressure on local condensation heat transfer coefficients

Fig.12 Influence of heat flux on local condensation heat transfer coefficients

Fig.13 Comparison between experimental values of condensation heat transfer coefficient and calculated values by empirical formula

Fig.14 Comparison of condensation heat transfer effect of various microchannels

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