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

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 ver-tical 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 dis-tribution information could be used for building boiling models in future works.

Automated summary

Previous studies have focused more on the upward-facing or vertical surface bubble behavior, and the studies on downward-facing bubble behavior are relatively scarce. In this experiment, the bubble moving speed and expanding speed were investigated under different heat flux and mass flux conditions. The results showed that the bubble moving speed followed a normal distribution and was close to the liquid velocity. The bubble expanding speed increased with the heat flux and remained constant for each bubble. A parameter called the heater factor was proposed and found to be relatively constant under different conditions, potentially following a lognormal distribution. These findings provide valuable insights for future development of boiling models.