Flow And Heat Transfer Characteristics Of Fluid Mixtures In Silicon Microchannels

Recently, it was found that flow and heat transfer characteristics in microchannels are quite different from conventional channels.The study on flow and heat transfer in microchannels is of great practical and scientific values, more and more researchers begin to focus on this subject. As to the design of heat sink, it is very important to choose proper working fluid for flow and heat transfer in microchannels. Most of previous researches in silicon microchannels took water as working fluid instead of fluid mixtures.In this thesis, we carried out a series of experiments to investigate the flow and heat transfer characteristics of water/ethanol mixtures through 5 silicon microchannels with different geometrical parameters. The experimental correlations of flow friction and heat transfer were obtained according to the results of the study. The effect of the geometrical parameters on the flow and heat transfer in silicon microchannels is remarkable. The friction factor is the same with different working fluids but the Nusselt number is not. It was also found that entrance effect is notable to both flow and heat transfer in microchannels.Furthermore, two-phase flow patterns of water/ethanol mixtures in silicon microchannels with different geometrical parameters were also studied by taking CCD images of boiling working fluid in the microchannels. According to the CCD images of flow patterns, the possible causes were discussed and the differences of the flow patterns through the two given channels were compared. It was found that the flow patterns of mixtures are quite different from the pure fluid in silicon microchannels because of mass transfer. Layered flow and oscillating flow were observed in the larger channel and echo flow of vapor core in the smaller one. The experimental research laid a solid foundation for further study on two-phase flow through microchannels.