Heat transfer in nucleate pool boiling under microgravity condition

Experiments on nucleate pool boiling were conducted under microgravity conditions created along a trajectory of the ballistic rocket TR-1A No.5 launched by NASDA. Surface temperature distribution and microlayer thickness underneath bubbles were measured by thin film sensors coated directly on the glass substrate with transparent heaters. The structure enabled to relate local heat transfer coefficient to the liquid-vapor behavior observed from underneath. From the experiments by using ethanol at almost constant temperature from 25 to 30 degrees C under pressure from 0.01 to 0.48MPa, information about the structure of a coalesced bubble and liquid-vapor behavior at the bubble base, CHF condition, and feasibility of steady state heat transfer in microgravity was obtained. To clarify the heat transfer mechanisms, a new model to predict the surface heat flux from the measured microlayer thickness and surface superheat was proposed. The prediction reproduced well the value calculated independently from the heat conduction across the glass substrate.