Computational multifluid-structure interaction study on nucleate boiling under the effect of stationary or oscillating torus

Abstract

The present numerical study characterizes nucleate boiling heat transfer in ethanol from a single nucleation site on a horizontal base plate in the presence of a fluid-immersed solid copper torus. The torus lies above the base plate, with its axis centered along the nucleation site, and it is either kept stationary or subjected to forced oscillations in the vertical direction. A sharp-interface dual grid Level Set method (SI-DGLSM)-based in-house solver is used here, in which a Level Set-based Immersed Boundary Method (LSIBM) is used to impose the boundary condition at the moving solid-fluid interfaces. For nucleate boiling in the presence of a stationary torus, enhancement in Nusselt number is observed due to thinning of the thermal boundary layer under the torus and thickening of the thermal boundary layer near the bubble. In the presence of torus oscillations, a lock-on regime is observed at optimal actuation parameters, for which the frequency of bubble departure synchronizes with the actuation frequency of the torus. A significant increase in Nusselt number is observed within the lock-on regime due to active pumping of superheated liquid towards the nucleating bubble during bubble growth. Analysis of heat flux partitioning shows that the enhancement in Nusselt number may be mainly attributed to higher sensible heat flux in the presence of torus oscillations, especially near the lock-on regime. This work demonstrates a novel way for enhancing heat transfer in the single-bubble nucleate boiling regime via externally actuated solid objects immersed in the liquid.