Pool Boiling in Earth and micro-gravity during sub-cooling temperatures

Pool boiling simulations are carried out to study the effects of gravity, sub-cooling and super-heating. The purpose is to explore how the sub-cooling and super-heating in varying environments affects the bubble dynamics: bubble formation, bubble departure, sliding and coalescence bubbles; and the heat transfer statistical analysis. Direct Numerical Simulations of pool boiling were performed using our in-house high fidelity solver, where the liquid-vapor interface is tracked with a level set formulation. The gorening equations are advanced in time with a fractional step method. The ghost-fluid formulation is used to take into account sharp jumps in pressure, velocity and temperature across the multiphase boundary, and the interface is represented using the level set technique. A mathematical model based on Halton sequence is used to construct nucleation sites density, and ski Python package is used to track bubbles and determine their properties. Microgravity two-dimensional simulations indicate that the bubble departure size increases with decrease in gravity due to the buoyancy effects. In very low gravity, a central bubble remains attached to the surface due to lack of equilibrium between buoyant force and wall adhesion force. Heat transfer temporal variations in space averaged heat flux indicate that the time to reach steady state increases when gravity decreases. Sub-cooling studies indicate that heat transfer decreases when increasing the degree of sub-cooling. Besides, bubble departure becomes too slow when the sub-cooling degree increases. The time to reach steady state is constant for all sub-cooling cases.