Two-Phase Fluid Flow in Microchannels: An Experimental Study

An extensive experimental two-phase flow study has been carried out on two single round microtubes for refrigerants. First of all, an optical measurement method for two-phase flow pattern characterization in microtubes was developed to determine the frequency of bubbles exiting a micro-evaporator, their coalescence rates and lengths as well as their mean two-phase vapor velocity. Based on the bubble frequency results and CHF (Critical Heat Flux) measurements made on the micro-evaporator (predicted with a new microchannel version of the Katto-Ohno correlation), a new type of flow pattern map for evaporating flow in microchannels was proposed. This flow pattern map may in the future be used as the starting point for the development of heat transfer and pressure drop models and the thermal design of micro-evaporators. In addition, an extensive new two-phase pressure drop database was obtained.