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当换热设备表面温度发生快速变化时,换热过程属于瞬态换热,这种瞬态过程有可能会导致换热效果降低、热应力增大等结果,甚至可能最终导致机械故障.采用实验和数值模拟,对指数状减流条件下扭转平板发热体表面的瞬态强制对流换热过程进行研究.扭转平板上加指数状热源Q=Q_0exp(t/τ)(t为时间,τ为周期),铂金平板扭转180°为1个扭矩,3根长度分别为26.8,67.8,106.4 mm的铂金平板分别扭转了1,3,5个扭矩.通过对实验数据的分析发现,平均换热系数将在无量纲周期τ*(τ*=τU/L,U为速度,L为有效长度)大于100后趋于准静态,换热系数随着平板长度的增加而减小.对指数状发热率下扭转平板瞬态对流换热过程进行数值计算,其结果和实验结果吻合.数值计算给出了沿长度方向分布的换热系数曲线,分析了换热系数的长度效应.
Abstract：The behavior of heat transfer devices during transient processes with fast temperature changes may produce some undesirable results such as reduced thermal performance and thermal stress with eventual mechanical failure. In this research, forced convection transient heat transfer for helium gas flowing over a twisted plate with different length was experimentally and theoretically studied. The heat generation rate of the twisted plate was increased with a function of Q= Q0 exp(t/τ)(where t is time, τ is period). The plates were twisted with the same helical pitch of 20 mm,and length of 26. 8, 67. 8 and 106. 4 mm(pitch numbers of 1, 3 and 5), respectively. Based on the experimental data, it was found that the average heat transfer coefficient approaches the quasi-steady-state value when the dimensionless period τ*(τ*= τU/L, U is flow velocity, and L is effective length) is larger than about 100 and it becomes higher when τ~*is small. The heat transfer coefficient decreases with the increase of twisted plate length. Numerical simulation results were obtained for average surface temperature difference, heat flux and heat transfer coefficient of the twisted plates with different length and showed reasonable agreement with experimental data. Based on the numerical simulation, mechanism of local heat transfer coefficient distribution was clarified.
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基本信息:
中图分类号:TK124
引用信息:
[1]王丽,赵舟,刘秋生,等.氦气流过不同长度扭转平板的瞬态对流换热研究（英文）[J].南通大学学报(自然科学版),2017,16(04):48-57.
2017-12-20
2017-12-20