Bubble dynamics and heat transfer associated with pool nucleate boiling under microgravity conditions

Abstract

A building block type approach is used to investigate mechanisms associated with nucleate boiling heat transfer and vapor removal under microgravity conditions. In this approach, starting with a single bubble, the complexity of the experiments is increased to include merger of neighboring bubbles. Key processes of interest are the heat transfer rates associated with micro/macrolayer evaporation and bubble dynamics. The bubble dynamics includes bubble growth and departure. The bubble growth is influenced by heat transfer, whereas, the forces acting on the bubble determine the bubble diameter at departure and bubble growth period. In microgravity, buoyancy force is practically non-existent. As such, forces (e.g. lift) that are insignificant at earth normal gravity become important at zero gravity and determine the bubble departure diameter. Experiments using single and multiple cavities microfabricated in silicon wafers have been performed at normal gravity and in the parabolic flight of the KC135. The experimental results of bubble dynamics and heat transfer have been validated with 2-D and 3-D numerical simulations of the process. Based on the scaling of the effect of gravitational acceleration, the requirements for space flight experiments are developed. The hardware used in the experiments will