Numerical simulation of condensation in horizontal circular and square minichannels using R134a

doi:10.11949/j.issn.0438-1157.20151306

Abstract

Abstract:

Heat transfer and pressure drop characteristics of condensation for R134a at saturation temperature of 320 K inside horizontal circular and square minichannels were investigated numerically. The results indicated that the heat transfer coefficients and frictional pressure drop gradients increased with mass flux and vapor quality, while the pressure drops decreased with increasing vapor quality at x>0.85. Compared with the circular tube, the square channel with the same perimeter as the corresponding circular tubes can enhance heat transfer coefficients and increase the pressure losses. The numerical results agreed well with the well-known empirical correlations for condensation. A thicker liquid film was obtained at the bottom of the round tube, while the liquid film for the square channel accumulated at the bottom and the middle top of the channels at lower vapor quality. The proportion of the thinner liquid film region, which corresponded to a higher heat transfer coefficient, increased with increasing vapor quality, leading to a higher heat transfer coefficient at higher vapor quality. The liquid film thicknesses in square channels were lower than that in circular channels, thus enhancing the heat transfer.

Key words: condensation, minichannels, numerical simulation, heat transfer, pressure drop

摘要：

利用数值模拟研究了水平圆形与方形微小通道内R134a的冷凝换热阻力特性,制冷剂饱和温度为320 K。结果表明:传热系数与摩擦压降梯度随着质量流量、干度的升高而升高,而干度大于0.85时,摩擦压降梯度随着干度的升高而降低。方形通道的换热与阻力均高于圆形通道,数值结果与文献冷凝换热、阻力公式吻合较好。圆形通道内冷凝液膜集聚在通道下部,而方形通道内液膜集中在角落区域。薄液膜区域所占的比例随着干度的增大而增大,方形通道内的液膜厚度要小于圆形通道,换热效果优于圆形通道。

关键词: 凝结, 微小通道, 数值模拟, 传热, 压降

CLC Number:

TK124

ZHANG Jingzhi, LI Wei. Numerical simulation of condensation in horizontal circular and square minichannels using R134a[J]. CIESC Journal, 2016, 67(5): 1748-1754.

张井志, 李蔚. 水平圆形与方形微小通道内R134a冷凝数值模拟[J]. 化工学报, 2016, 67(5): 1748-1754.

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