Non-intrusive diagnostics of differentially-heated two-component immiscible fluid layer with phase change

Abstract

Experiments on buoyancy-driven convective phenomena in a differentially-heated two component immiscible fluid layer with phase change phenomena have been reported. The real-time mapping of the transients associated with the process has been affected in a complete non-intrusive manner using rainbow schlieren deflectometry. Experiments have been performed for varying heat flux levels supplied to the lower horizontal surface of the cavity and for different heights of the secondary fluid layer. The two-component immiscible fluid mixture comprises of water as the (lighter) primary fluid layer and dichloromethane (DCM) as the (heavier) secondary fluid component. The supplied heat flux levels are sufficient enough to induce phase change in the secondary fluid layer through nucleate pool boiling. In addition to the real-time mapping of the buoyancy-induced convection in both the fluid layers, the process of vapor bubble inception, their growth and departure from the lower heated wall of the cavity have been recorded in the form of time-lapsed schlieren images. Conditions under which the continued interaction of the vapor phase of DCM with the interface leads to interface deformation and its final breakage have been investigated. Based on the force balance analysis, the critical volume of the DCM vapor phase required for interface breakage has been determined. Dependence of parameters such as neck breakage height, time required for interface breakage etc. on the supplied heat flux level and height of the secondary fluid has been investigated. The experimental observations revealed the importance of vapor bubbles-induced fluid agitation in the otherwise stagnant primary fluid layer, disruption of the thermal boundary layer in a completely passive manner as the upward rising vapor volume condenses at the top horizontal surface of the differentially-heated cavity and their implications in possible heat transfer enhancement.