Heat transfer mode shift to adiabatic thermalization in near-critical carbon dioxide with flow boiling in a microchannel

Abstract

Heat transfer via acoustic waves, known as adiabatic thermalization or the piston effect, was previously studied in enclosures under microgravity and terrestrial conditions with carbon dioxide (CO2). Here we report on the importance of the piston effect with flow boiling in a microchannel. It is shown that because of large density variations, and asymptotical behavior of specific heats ratio, the piston effect enhances heat transfer near the critical condition. Critical opalescence temperature measurements of CO2 were compared to calculated temperature rise associated with the piston effect, and it was revealed that a substantial shift in thermalization modes from vaporization to acoustic waves occurs for near-critical flow boiling of CO2, The results from both methods were found to be in a good agreement, and it is suggested that the contribution of the piston's effect increased from 4.3% to 77.6% when the reduced pressure increased from 0.86 to 0.99. Revealing the nature of the piston effect pertinent to enhanced heat transfer will advance copious technological fields like space exploration, fusion reactors, data centers, electronic devices, and sensing technology.