Heat transfer behavior and turbulence flow statistics for subcooled pool boiling on earth and ISS gravity conditions based on CFD Direct Numerical Simulations.*

Subcooled pool boiling defines a system where the temperature of the bulk liquid is lower than the saturation temperature of the considered fluid. In engineering applications, the effect of subcooled pool boiling on heat transfer nucleate boiling is generally considered to be negligible. However, some research emphasizes an impact in shifting the boiling curve. The present work is based on CFD high-fidelity computing results using an in-house DNS solver to solve the Navier-Stokes equations for incompressible flow, coupled to mass, momentum and energy equations. A level set technique is used to track the interface liquid-vapor. Time advancement is achieved using a fractional step method. Sharp jumps are implemented in velocity, temperature, and pressure. A dynamic contact angle is considered. Simulations have been conducted on both earth gravity and International Space Station (ISS) gravity for different subcooling levels. 

Our computations show a decrease in the heat flux while subcooling increases until it reaches a minimum point after which an increase in heat flux is observed. Before reaching the local minima point, the decrease of the heat flux is due to flow turbulence governed by bubble departure, while after reaching this minimum point, the increase is due to shrinking and coalescence of the bubbles. The present results will be focusing on the turbulence statistics overview. We will provide qualitative analysis based on isotropy, vorticity, velocity, Reynolds stresses, turbulent kinetic energy, and turbulent heat flux.