This project, conducted as part of NASA-Sponsored Flow Boiling and Condensation Experiment (FBCE), aims to characterize bubble motion in the nucleate boiling regime under microgravity through fundamental force balances. Specifically, the goal is to develop correlations that predict the conditions for bubble departure from the nucleation site and subsequent lift-off from the heated surface. NASA’s recent push for longer manned flights to space requires the optimization of the equipment on board, which includes their cooling systems. The forces acting on bubbles in terrestrial flow boiling experiments were reviewed and compared to microgravity conditions. A comprehensive literature review identified key discrepancies between terrestrial and microgravity flow boiling. Based on these differences, a hypothesized set of governing force balances were proposed to describe bubble motion in space. Preliminary examination suggests the system is dominated by surface tension effects, shearing, and drag forces. Video data from the International Space Station’s (ISS) experiments are currently being processed with the goal of replicating the experiment’s conditions in a COMSOL MultiPhysics simulation to extract the equations governing the bubble’s motion. Model inputs include the bubble’s radius and contact angles which are good predictors for bubble departure and lift-off. Preliminary results indicate terrestrial bubbles need to reach a size smaller than extraterrestrial bubbles to depart and lift off. This research seeks to determine the critical bubble size at which departure and lift-off can occur. The results of the finalized force balance enhance understanding of why the phenomenon of critical heat flux occurs in space-based flow boiling systems and generate new strategies to improve cooling efficiency for future space missions.
