Heat transfer mode shift to adiabatic thermalization in near-critical carbon dioxide under terrestrial conditions

Abstract

\n Heat transfer via acoustic waves is referred to as adiabatic thermalization or the piston effect. Until now, adiabatic thermalization was believed to be a secondary effect that mostly occurs under microgravity conditions and is readily overpowered by mixing due to gravitational forces. However, this work revealed that in microsystems, adiabatic thermalization is a dominant heat transfer mechanism. A substantial shift in thermalization modes from vaporization to acoustic waves was observed through critical opalescence temperature measurements of carbon dioxide (CO2). The contribution of the piston’s effect increased from 4.3–77.6% when the reduced pressure increased from 0.86 to 0.99. The findings are used to explain the observed heat transfer enhancement that occurred concurrently with the reduction in the void fraction. Revealing the nature of the piston effect to enhance heat transfer will advance copious technological fields like space exploration, fusion reactors, data centers, electronic devices, and sensing technology.