Experimental Analysis of Bubble Behavior and Critical Heat Flux During Pool Boiling on Vertical Circular Tubes

The heat transfer during pool boiling incorporates a higher rate of heat dissipation capability at low-temperature differences. This technique is widely used in the nuclear industry for thermal management. In this study, the effect of tube diameter and length on critical heat flux (CHat atmospheric conditions in saturated water during pool boiling) is analyzed. The tubes of SS 304 are kept in the vertical orientation. The diameter of the tubes ranges from 1.2 mm to 9 mm. The experiments are performed with tubes having lengths varying from 50 mm to 1000 mm. It has been noted that tubes of smaller diameter show a greater magnitude of critical heat flux (CHF) for the given length. Compared to other tubes, the magnitude of CHF for a 1.2 mm diameter is higher. For a given diameter, a longer tube is found to have lower CHF than the ones having lesser length. The variation in the CHF magnitude is negligible for tubes with a diameter of more than 2.5 mm beyond a length of 200 mm. The location of occurrence of CHF is near the bottom end of the vertical tube. The study illustrates the behavior of bubble nucleation for various tube dimensions and heat fluxes. The inception and detachment of bubbles for different tubes are analyzed. The pool boiling regime is categorized and studied basing the behavior of the incepted and departed bubble while maintaining uniform heat flux. A mathematical relation that empirically accounts for the effect of tube dimensions , i.e., length and diameter on pool boiling CHF is proposed. The experimental CHF data obtained during pool boiling are tabulated toward contributing to the CHF databank.