加热上升混合对流传热实验研究

Experimental Research of Heated Upward Mixed Convective Heat Transfer

在加热上升混合对流中,浮升力的存在显著改变了速度分布和切压力分布,使边界层趋于层流化和充分发展湍流起始点的延后,并使传热系数表现出由弱化、恢复再强化的过程。本研究在中压下不同直径的竖直加热圆管上进行了纯蒸汽的强迫对流传热实验,也在超临界压力下不同直径的加热圆管上进行水的强迫对流和自然循环传热实验。研究表明:随着浮升力参数的增大,传热逐渐弱化;在浮升力参数达到一定值时传热系数达到最小值,随后逐渐恢复,并最终出现强化。在实验数据基础上提出了加热上升混合对流的传热关系式。

In the heated upward mixed convection, the distributions of velocity and shear-stress vary significantly due to the existing of buoyancy force, leading to the laminarization of boundary layer and the delay of the onset of fully developed turbulent convection, and the heat transfer coefficient experiences a process from the deterioration, recovery and enhancement. The present investigation deals with the experiments in tubes of different diameters for the forced convection of pure steam and the forced convection and natural circulation of supercritical water. The research indicates that as the buoyancy force increases, the heat transfer deteriorates and reaches a minimum at a certain value of buoyancy force, then it turns to recovery and enhancement finally. The present investigation presents a correlation of heat transfer coefficients based on the experimental data for heated upward flow.