Fundamental insights into enhancing supercritical heat transfer via pulsating flow: Interaction between wave and pseudo-interface

Abstract

Heat transfer at supercritical pressure (SCP) transiting from liquid-like (LL) to gas-like (GL) state is a compressible flow featured by a nonuniform density field. Pulsating flow has been confirmed as an effective approach to enhance heat transfer. However, pulsating flow introduces pressure waves, the interaction of which with the nonuniform density field remains an open question. This paper numerically studies a fundamental interaction problem to bridge the research gap. The physical model is a round GL fluid surrounded by LL fluid, forming a circular pseudo-interface for ${\mathrm{CO}}_2$ at an SCP of 7.6 MPa. A compression wave is introduced into the domain by the sudden moving of an imaginary piston at 1 m/s. The compression wave induces a complex wave system after interacting with the pseudo-interface. The nonuniform acceleration by the compression wave results in a higher velocity in the GL region than in the LL one. Due to the Kelvin–Helmholtz instability, decomposition and mixing of the GL region then take place. Overall, the uniformity of density and temperature is improved on the microsecond timescale, manifesting that heat transfer is enhanced. This paper reveals nonuniform acceleration and Kelvin–Helmholtz instability as fundamental mechanisms for enhancing heat transfer at supercritical pressures via pulsating flow.