Characteristics of enhanced heat transfer of twisted elements with varying twist ratio

doi:10.11949/j.issn.0438-1157.20160493

Abstract

Abstract:

The purpose of this paper is to investigate the heat transfer performance of the tubes with twisted elements at different twist ratio variation Tv. On the constant wall temperature boundary condition, the characteristics of heat transfer and pressure drop are investigated experimentally and numerically. Tv are within the scope of -5-5 and water is used as working fluid．The comprehensive heat transfer and heat enhancement mechanism are analyzed at different Tv. The results show that the condition of Tv>0 along the flow direction is superior to the condition of Tv=0. The average heat transfer enhancement ratio of Tv=2.5 is 5.0% higher than that of Tv=0. However，the heat transfer effect of Tv<0 is inferior to Tv=0, and thus the layout should be avoided. The flow field structures are altered by the change of the twist ratio of the elements. For the case of Tv>0, the vorticity and the action range of the detour-flow vortex within more than half of the element area are improved significantly with the increase of Tv. At the same time the coordination of pressure, velocity and temperature fields is improved and heat transfer is enhanced accordingly.

Key words: twisted element, twist ratio variation, numerical simulation, heat transfer enhancement, fields coordination

摘要：

为探究扭旋叶片的结构参数——扭率变化率Tv对管道换热的影响，以水为介质，在Tv=-5~5范围内，采用实验和数值模拟方法研究了恒壁温条件下流体的传热和阻力特性，并分析了综合传热性能及强化传热机理。结果表明，沿流动方向Tv>0的扭旋叶片安装方式强化传热效果优于Tv=0，研究范围内Tv=2.5时综合强化传热比最高，相对Tv=0平均提高5.0%。而Tv<0时强化传热效果劣于Tv=0，应避免此种叶片安装方式。扭率的变化影响了流场结构，当Tv>0时，在近1/2流动区域内绕流旋涡的涡量和影响区域明显增加，同时，在绕流旋涡流动区域，压力、速度和温度的三场协同程度得到提高，进而强化了换热管道的传热效果。

关键词: 扭旋叶片, 扭率变化率, 数值模拟, 强化传热, 场协同

CLC Number:

TK124

ZHANG Jing, MI Haiying, LI Yaxia, ZHANG Ping, WU Jianhua. Characteristics of enhanced heat transfer of twisted elements with varying twist ratio[J]. CIESC Journal, 2016, 67(12): 4951-4958.

张静, 米海英, 李雅侠, 张平, 吴剑华. 变扭率扭旋叶片强化传热特性[J]. 化工学报, 2016, 67(12): 4951-4958.

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