Research On Two-phase Heat Transfer Of Nanofluids Flow Boiling In Microchannel

Microchannels were widely used in Micro-electro mechanical systems, micro-electronics, biology, and with the progress of materials, more and more new materials were introduced in the boiling heat transfer and flow experiment, such as nano-materials, making flow and heat transfer in microchannel become one of the hottest spot in science and industrial field. Many experimental data and analysis showed that flow and heat transfer performances in microchannel were different from that of in conventional channel. And in another hand, the nano-materials have special properties on heat transfer, it had significant size effect. that making nanofluids to become special in the temperature and flow character. And using the nanofluids in the experiments on heat transfer performances can improve the energy exchange. This paper choosed the material Al2O3-water to be the working fluids in the experiment of two-phase are conducted in aluminium rectangular microchannels. All the heights are uniformly 2mm, and the width is 2mm, 1mm and 0.6mm respectively.Firstly, this paper studied the themophysical characters of nonofluids. Experimental and theoretical research on thermal conductivities and viscosity of nanofluids are done. At the beginning, the methods for measuring thermal conductiveities and viscosity of nanofluids are summarised in general. Then, the themophysical characters are calculated according to the theory, which were compared with the result of experimental data of both nanofluids and normal fluids. It was founded that with the addition of nano-particle vulumm, the thermal conductiveities and viscosity of nanofluids became bigger. And the results showed that the themophysical characters of experimental nanofluids were better than that of theory data. And the thermal conductivities of the two different nanofluids were increasing 8.6% and 7.9% respectively.Secondly, By the comparation of experiment data, the impact factors of boiling heat transfer coefficient were researched. The result showed that the heat transfer coefficient related little with mass flux. And it varied with the increasing of flow velocity, but not widely. Hat transfer coefficient slightly increased when mass flux increased, and the higher the heat flux was, the higher the heat transfer coefficient was. The two different density nanofluids share the same trendency. And this paper researched the heat transfer mechanism of nanofluids in microchannels. Heat transfer coefficient of nanofluids was increasing more sharply than that of normal fluids. And it related to heat flux, while had little relations with dryness and mass flux.