Flow boiling and pressure drop in parallel flow microchannels

Abstract

The use of microchannels for advanced heat transfer applications has quickly become commonplace. They are found in automotive applications, fuel cells, and even electronics cooling. However, there are fundamental issues still unresolved with heat transfer and fluid mechanics and the application of microchannels. Researchers have reported microchannel data using very different hydraulic diameters, sometimes as much as 2 orders of magnitude. An experimental investigation of the heat transfer, pressure drop, and flow boiling in microchannels is performed. A new channel size classification has been developed based upon the manufacturing techniques as well as the underlying fluid mechanics and heat transfer theory. Six parallel channels with a hydraulic diameter of 207 micrometers is manufactured and tested. Flow boiling patterns have been observed in the channels. Observations suggest that the conventional flow boiling patterns also occur in microchannels. This suggests that there is no difference in the theory used for conventional channels. Therefore, a microchannel can be model in the conventional manor. Heat fluxes of up to 930 kW/m2 have been maintained in the microchannel. The local heat transfer coefficient and quality has been measured. The largest heat transfer coefficient achieved is 192 kW/m2K. In addition, the highest quality achieved is 1.0. Dry-out was also observed during experimentation.