FLOW BOILING CRITICAL HEAT FLUX IN A SMALL TUBE FOR FC-72

Flow boiling of FC-72 in a small tube was investigated experimentally. The tube with an inner diameter of 1.8 mm and a length of 129 mm was made from SUS304 stainless steel. The effect of flow velocity and subcooling on critical heat flux (CHF) was measured in this experiment. The flow velocity u was varied from 0.33 to 4.26 m/s, and the inlet subcooling degree was varied from 25 to 36 K. The heat transfer coefficients with the imposed heat flux varying from the non-boiling to the boiling region were then measured. Experimental results showed that CHF increased as flow velocity was raised, but it sharply declined above u = 3.0 m/s because of premature CHF. On the basis of the experimental data, the empirical correlation between the boiling number and the Weber number was obtained. The predicted value of this correlation was in agreement with the measured data within 17%.