Hydrodynamics and heat transfer during flow boiling instabilities in a single microchannel

Boiling in microchannels is widely considered as one of the front runners in process intensification heat removal. Flow boiling heat transfer in microchannel geometry and the associated flow instabilities are not well understood, further research is necessary into the flow instabilities adverse effect on heat transfer. Boiling is induced in microchannel geometry (hydraulic diameter 727 mu m) to investigate several flow instabilities. A transparent, metallic, conductive deposit has been developed on the exterior of rectangular microchannels, allowing simultaneous heating and visualisation. Presented in this paper is data for a particular case with a uniform heat flux of 4.26 kW/m(2) applied to the microchannel and inlet liquid mass flowrate, held constant at 1.13 X 10 5 kg/s. In conjunction with obtaining high-speed images, a sensitive infrared camera is used to record the temperature profiles on the exterior wall of the microchannel, and a data acquisition system is used to record the pressure fluctuations over time. Various phenomena are apparent during the flow instabilities; these can be characterised into timescales occurring at 100's seconds, 10's seconds, several seconds and finally milliseconds. Correlation of pressure oscillations with temperature fluctuations as a function of the heat flux applied to the microchannel is possible. From analysis of our results, images and video sequences with the corresponding physical data obtained, it is possible to follow simultaneously particular flow, pressure and temperature conditions leading to nucleate boiling, flow instabilities and transition regimes during flow boiling in a microchannel. The investigation allowed us to quantify and characterise the timescales of various observed instabilities during flow boiling in a microchannel. High speed imaging revealed some of the controlling physical mechanisms responsible for the observed instabilities. (C) 2008 Elsevier Ltd. All rights reserved.