Investigating Bubble Frequency Changes in Pool Boiling in Pure Solutions and on a Stainless Steel Cylinder

Bubble dynamics is the most important sub-phenomenon, which basically affects the nucleate pool boiling heat transfer coefficient which includes bubble departure frequency, bubble diameter and nucleation site density. In this research, bubble departure frequency values were experimentally measured for heat fluxes up to ۱۲۰ kW.m-۲. Experiments were carried out for pool boiling of pure liquids, including water, ethanol and methanol on a horizontal smoothed cylinder, at atmospheric pressure. A high-speed digital video camera was applied to capture the dynamics of the bubble nucleation process. For ethanol and methanol, rigid spherical bubbles with small contact area were observed. The spherical shapes seem to be because of small diameters. For all test fluids, experimental results show that the bubble frequency increase with increasing heat flux. Increase in the rate of bubble generation, reduction in the waiting time and growth time can be the causes of this phenomenon. Also, experimental results show, Heat transfer coefficient increases with increasing heat flux for all test fluids at the experimental condition.