Critical Heat Flux Enhancement Mechanism by Surface Modification based on Hydrodynamic Instability Model

Abstract

This paper presents surface modifications based on hydrodynamic instability model to enhance critical heat flux (CHF). Experimental observations of the CHF performance based on the surface modifications were performed in a plate pool boiling facility using an FC-72 refrigerant under saturation conditions. Temperature distribution and CHF condition of each heater surface were determined using an infrared thermometry. Four types of heater surfaces were considered: plain, 9 and 64 pillars, and 9 holes. The CHF performance of the plain and 9 and 64 pillars heating surfaces showed similar trend (148 kW/m2). For the 9 holes heating surface, the CHF performance was increased by 20%, compared to other heating surfaces (174 kW/m2). Rayleigh-Taylor (RT) instability observation at the CHF condition for the plain and 9 holes heating surfaces were conducted to show the relation between the RT instability wavelength and the CHF condition. The hot spots for the 9 holes heating surface were isolated in the patterned surfaces before the CHF was reached, while the hot spots of the other surfaces were coalesced at high heat fluxes. The hydrodynamic theory by changing the RT instability wavelength based on the surface modification can explain the CHF enhancement mechanism.