Critical Heat Flux of Natural Circulation Boiling in a Vertical Tube : Effect of Oscillation and Circulation on CHF

Abstract

An experimental study has been made to elucidate an effect of oscillated flow induced near critical heat flux and natural circulated flow of vapor and liquid in a vertical tube on the critical heat flux. The experiment has been carried out for the condition of heated tube length of L=100 to 1000 mm, tube diameter of D=4 to 9 mm and the CHF was measured under the condition that the exit of the unheated tube connecting the heated tube was extruded into a vapor chamber to prevent a liquid flowing into the heated tube from the top of the tube. The experiment reveals that the CHF for D=7 and 9 mm and any tube length from 100 to 1000 mm becomes identical to that for the case of the tube top being in the liquid, while the CHF for D=4 and 5 mm is smaller than that for the case of the tube top being in the liquid due to no liquid supply from the top. It is found that the oscillation induced near the CHF increases the CHF.