THE UPFLOW AND DOWNFLOW CRITICAL HEAT FLUX OF WATER AND FREON IN A VERTICAL TUBE AND ITS FLOW DIRECTION FACTOR

The upflow and down flow critical heat flux (CHF) experimental data of fluid water and freonin vertical tube are analyzed. It shows that under certain conditions, the flow direction has a evidentaffect on CHF. The total rms of comparison of upflow and downflow data and predicting downflow datausing upflow CHF correlation are in range of 6%--14%. The CHF for upflow are regualarlygreater than those for downflow, but it becomes to reverse in the range of low critical quality. A flowdirection factor, C = bl·(X_1)~(b2)·(R_(el))~(b3)·(ρ _l/ρ_s)~(b4) is proposed on the basis of mechanism of the CHFdifference between upflow and downflow. It has a wide parameter range and is not only suitable forfluid water, but also for fluid freon treated by modeling transformation. The total rms of calculationalvalue of CHF, by use of proposed flow direction factor is reduced by 20% to 46%, and the maximumerrors and 95% error band are also decreased to a certain extent.