Helmholzt振荡腔对光滑圆管换热的强化实验

气流通过Helmholzt振荡腔产生脉动气流.实验固定振荡腔进出口直径和振荡腔直径, 在改变振荡腔腔长的情况下, 在圆管进口Re为22000到82000范围内对等热流加热条件下的圆管换热实验进行了研究.实验将脉动气流所产生的圆管换热效果与定常气流产生的换热效果进行对比.结果表明:气流流经Helmholzt振荡腔后对圆管换热有强化作用, 其强化作用主要集中在沿圆管轴向前10倍直径的长度上, 强化比约为1.1-1.9.随着距离增大换热强化比迅速减小.振荡腔腔长对换热效果有较强的影响. 

An experimental study of the effects of air flow through Helmholzt cavity on heat transfer within a smooth round tube

When the air flows through the Helmholzt oscillation cavity,it will be pulsing.The inlet and outlet diameters of Helmholzt cavity remain const,but the length of cavity is changed so that,the Reynolds number at the inlet changes from 22 000 to 82 000.The experimental investigation was conducted under equiflux conditions.Comparison was made between the heat transfer coefficient of steady air flow and unsteady air flow.The results show that: The pulse air flow can increase the heat transfer,but the enhancement of heat transfer takes place mainly at the distance of 10 times of the diameter along the axial direction of the round tube.The ratio of enhancement lies between 1.1 to 1.9.This ratio decreaser significantly as the distance becomes longer.Beyond the distance of 10 times of the diameter,the ratio of enhancement fluctuates slightly as the Reynolds number increases.The experimeotal investigation also shows that the heat conduction coefficient is influenced by the length of the Helmholzt cavity.