Experimental investigation on the characteristics of bubble growth and slide on a downward-facing heater surface in flow boiling

Abstract

Previous studies have shown that the bubble behavior has significant influence on boiling phenomena. However, studies of downward-facing bubble behavior were rather scarce compared to that of the upward-facing or vertical surface. In this study, a downward-facing flow boiling experiment was conducted to investigate bubble moving speed and bubble expanding speed under different heat flux and mass flux. A high-speed camera was used to observe the boiling surface conditions, images of which were later processed by a computer vision code written by python. Bubble moving speed and bubble expanding speed were analyzed. In the experiment, bubble moving speed was close to the liquid velocity and prone to follow a normal distribution. Bubble expanding speed increased with heat flux and could be regarded as constant for each bubble in the study regime. A parameter called heater factor was proposed and the average of which was observed to be rather constant under different heat fluxes and mass flux. Moreover, the heater factor was likely to follow a lognormal distribution. The distribution information could be used for building boiling models in future works.