Analysis of the critical heat flux of subcooled flow boiling in microgravity

There is a significant decrease in flow boiling CHF when the inertial force of the fluid is not large enough in microgravity, but this tendency decreases with the increase of the inertial force. In the present study, the critical heat flux (CHF) of subcooled flow boiling at different gravity levels on smooth silicon surfaces was investigated. The working fluid is FC-72, with the subcooling of 15 K. The flow boiling heat transfer characteristics, including the CHF, wall temperatures and bubble behavior were studied. The effects of the heater length, channel height and flow velocity on the CHF were studied. It was found that the CHF increases with the increase of the channel height and flow velocity, but decreases with the increase of the heater length. A similar tendency was found for the ratio of the CHF in microgravity to that in normal gravity (q(CHF-mu g)/q(CHF-1g)). The relation of the flow velocity, heater length, channel geometrical parameters, and q(CHF)(-mu g)/q(CHF-1g) was studied by the dimensionless analysis. Finally, a correlation for the prediction of q(CHF-mu g)/q(CHF-1g) was developed based on the dimensionless analysis and the prediction results agree quite well with the experimental data within +/- 10%.