Critical boiling heat flux in inclined small tubes at zero inlet flow

An experimental study was carried out to investigate the nucleate boiling characteristics and the Critical Heat Flux (CHF) of countercurrent boiling in the inclined small tubes at zero inlet flow. Both saturated water and R-113 were used as working liquids. The inner diameters of the tested tubes ranged from 2.1 mm to 4.0 mm, the tube lengths changed from 100 mm to 300 mm, the inclination angles varied from 90° to 0°. The experimental results show that CHF decreases with the decrease of the inclination angle. A semi-theoretical correlation for the CHF of countercurrent boiling in the vertical tube with sealed bottom was modified for considering the effect of the inclined angle. The modified correlation can reasonably well predict the CHF for the inclined tube.