Characteristics of drag reduction in different cross sections of hydrophobic micro pin fins

doi:10.11949/j.issn.0438-1157.20150890

Abstract

Abstract:

The hydrophobic coatings with different properties are coated on the surfaces of micro pin fins with different cross sections of circular, diamond and elliptical to obtain hydrophobic micro pin fins with contact angles of 99.5°, 119.5° and 151.5°, respectively. The reduction coefficient of the pressure drop and the friction resistance are measured experimentally when water flows through the hydrophobic micro pin fins at different flow rates. Experimental results show that the change rate of pressure drop in ellipse and diamond micro pin fins increases gradually, however the change rate of pressure drop in circular micro pin fins increases at first and then decreases when the contact angle changes from 83° (the red copper smooth surface) to 151.5°. With the increase of the flow rate, the change rate of pressure drop in ellipse micro pin fins gradually decreases, while it decreases at first and then almost keeps constant in diamond and circular micro pin fins. The investigation also illustrates that the resistance reduction rates in all of test sections become large with the increase of the contact angle at the same Re. Under the same contact angle conditions, the resistance reduction rate gradually decreases in elliptical micro pin fins with the increase of Re, while it decreases at first and then keeps almost constant in diamond shaped and circular test sections. The minimal resistance reduction rates in diamond shaped and circular micro pin fins are 50.81% and 58.68% at contact angle of 151.5°, respectively.

Key words: hydrophobic micro pin fins, contact angel, friction resistance coefficient, pressure drop, resistance reduction rate

摘要：

采用疏水液处理紫铜微肋阵表面,分别在截面为圆形、菱形和椭圆形微肋阵实验段内形成接触角分别为99.5°、119.5°和151.5°(水为工质)的疏水性表面,实验测试各个工况下流道内流动阻力和压力降,分析了不同截面形状对疏水性微肋阵内减阻特性的影响规律。结果表明,当接触角增大时,压力降变化率在微肋阵内的变化规律随截面形状的改变而发生变化;同一接触角下,椭圆形微肋阵内压力降变化率随流量增加而逐渐减小,而菱形和圆形微肋阵则先减小后保持常数。相同Reynolds数(Re)下,3种截面实验段中减阻率均随接触角的增大而增加。接触角相同时,椭圆形微肋阵内阻力系数变化因子随Re的增大而逐渐减小;菱形和圆形则先减小后保持常数,接触角为151.5°时最小阻力系数变化因子分别为50.81%和58.68%。

关键词: 疏水性微肋阵, 接触角, 摩擦阻力系数, 压力降, 减阻率

CLC Number:

TK124

JIANG Guilin, GUAN Ning, ZHANG Chengwu, LIU Zhigang. Characteristics of drag reduction in different cross sections of hydrophobic micro pin fins[J]. CIESC Journal, 2016, 67(4): 1258-1268.

姜桂林, 管宁, 张承武, 刘志刚. 不同截面疏水性微肋阵内减阻特性[J]. 化工学报, 2016, 67(4): 1258-1268.

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