TWO PHASE BOILING AND FLOW INSTABILITIES IN A MICROCHANNEL

摘要

Boiling in microchannels is a very efficient mode of heat transfer. High heat and mass transfer coefficients are achieved. Evaporation of the liquid meniscus is the main contributor to the high heat fluxes achieved due to phase change at thin liquid films in a microchannel. The microscale hydrodynamic motion and the mechanisms at the immediate vicinity of the moving contact line are still not fully comprehended. There are several flow instabilities during boiling in microchannels. These instabilities need to be well understood and predicted due to their adverse effects on the heat transfer. It is hoped to understand particular flow instabilities, such as flow reversal, through experimental research at the contact line. A simultaneous visualisation and measurement experiment was carried out to investigate these flow instabilities in microchannels. Boiling has been induced in a microchannel (d_h 570 μm), stabilising just one liquid-vapour interface, and observing its progression through various microchannel geometries. Images and video sequences have been achieved with both a high speed camera and an infra red camera. Analysis of these images allow the application of several existing models to be fitted to our flow instability observations, namely flow reversal and its possible mechanism of vapour recoil, at the moving contact line.