垂直矩形通道内混合对流的实验研究

EXPERIMENTAL INVESTIGATION ON THE MIXED CONVECTION IN A VERTICAL RECTANGULAR DUCT

通过实验研究了内置均匀加热板的垂直矩形通道入口段混合对流换热的温度场和阻力特性。实验分别针对同向流动和反向流动两种情况进行了研究,其中Re=329-5565,Gr=9．7×105-7．7×106。通过实验得到了矩形通道内混和对流换热的总体平均Nusselt数和压力损失的变化规律。实验表明固体壁面的导热对总体换热具有非常重要的作用。平均Nusselt数随Re的增加而增加; Re<1000时反向流动的Nusselt数大于同向流动时Nusselt数,Re>1800时二者相差很小。压力损失与Re近似为乘幂关系,且随热流密度变化很小。

The mixed convection heat transfer of the entrance region in a vertical rectangular duct with a uniformly heated plate was experimentally investigated when the forced air flowed upward and downward. The temperature distributions and pressure drops were measured when the Reynolds number ranged from 329 to 5565 and Grashof number from 9.7×10^5 to 7.7×10^6. The heat conduction through the duct walls in the experiment effectively influenced the characteristic of the convection. The experimental results showed that the average Nusselt number increased with the Reynolds number. For Re 〈1000, the average Nusselt number of downward flow was larger than that of upward flow. But when the Reynolds number increased up to 1800, the both Nusselt numbers were closely equal. The pressure drop was approximately in the power function of the Reynolds number and changed little with the heat flux.