A Novel Infrared-Based Experimental Technique to Detect Phase Dynamics on Boiling Surfaces

Abstract

Heat transfer in nucleate boiling is strongly affected by the liquid and vapor phase distribution on the boiling surface. A novel experimental technique for the detection of phases on boiling surfaces is presented. The technique is based on high-speed infrared (IR) thermometry through an IR-transparent silicon wafer heater; hence the name DEPIcT, or DEtection of Phase by Infrared Thermometry. Where the heater surface is wet, the IR camera measures the temperature of the hot water in contact with the heater. On the other hand, where vapor (whose IR absorptivity is very low) is in contact with the heater, the IR light comes from the cooler water beyond the vapor. The resulting IR image appears dark (cold) in dry spots and bright (hot) in wetted area. Using the contrast between the dark and bright areas, we can visualize the distribution of the liquid and gas phases in contact with the heater surface, and thus identify also the liquid-vapor-solid contact line. DEPIcT is able to detect thin liquid layers, through the analysis of interference patterns. Finally, the technique is applied to nucleate boiling of water at atmospheric pressure to gain insight into the surface micro-hydrodynamics at high heat fluxes, all the way up to CHF.