加热热通量对微柱群通道内强迫对流换热的影响

Influence of heat flux on forced convective heat transfer in duct with micro-cylinder-group

以去离子水为工质,流经宽度3.5mm、长度40mm的叉排微柱群板,微柱群由直径500μm,高度分别为500、750、1000μm的微柱组成。实验研究微柱群内部加热热通量对换热特性的影响。采用电加热棒进行加热,测量微柱群板Reynolds数在100～1000之间时的进出口温度与流量,进而获得微柱群内部Nusselt数。研究结果表明,加热热通量对微柱群换热特性有重要影响。一方面,加热热通量的增大导致工质平均温度升高,工质Prandtl数降低,削弱了工质的换热能力;另一方面,加热热通量的增大降低了工质黏度,加剧了工质热运动,扰动增强,强化了工质的换热能力。当Re较低时,加热热通量的增大由于削弱了端壁面效应对换热的不利影响,同时增加了壁面与工质之间的温差,从而导致换热强化;随着Re的增大,端壁面效应减弱,因而加热热通量的增大对微柱群内部换热的影响减弱。

Deionized water,used as working fluid,flows through a staggered array micro-cylinders-group with 3.5 mm width and 40 mm length,which are made of micro-cylinders with hydraulic diameter of 500 μm and heights of 500 μm,750 μm and 1000 μm.An experimental study is performed on the influence of heat flux on forced convective heat transfer in the micro-cylinders-group heated by an electricity heater.The flow rate and the temperature difference between the inlet and the outlet of micro-cylinder-group are measured and the Nusselt numbers are obtained over Reynolds numbers ranging from 100 to 1000.The experimental results indicate that heat flux has a significant effect on the convective heat transfer in the micro-cylinders-group.As the heat flux increases,the average temperature of the working fluid increases apparently,which decreases the Prandtl number,so that the convective heat transfer of the working fluid is weakened.On the other hand,the viscosity of the working fluid is lower at higher heat flux,which intensifies the molecular thermal motion and strengthens the flow disturbance,enhancing the heat transfer.As the heat flux increases at low Re,the adverse effects of the end-wall effect on convective heat transfer is weakened,and the temperature difference between the wall and the working fluid is increased,further enhancing the heat transfer.With the increase of Re,the influence of heat flux increment on the convective heat transfer decreases due to the weakness of end-wall effect.