Research On Flow Resistance Of Nano-fluids In Rectangular Microchannels

Microchannels were widely used in Micro-electro mechanical systems, micro-electronics, biology, making flow and heat transfer in microchannel become one of the hottest spot in science and industrial field. The study on micro heat and mass transfer is a complicated subject, but with extensive value. Many experimental data and analysis showed that flow performances in microchannel were different from that of in conventional channel. Experiments on flow resistance of single-phase and two-phase are conducted in aluminium rectangular microchannels with Al2O3/water nanofluid as working fluid. All the heights are uniformly 2mm, and the width is 2mm, 1mm and 0.6mm respectively.Firstly, experiments on single phase flow was conducted in aluminium rectangular microchannels with nanofluids with two various volume fractions as working fluid. It was found that, the pressure drop increases with the increase of the Re, the pressure drop of high volume fraction nano-fluid is bigger than that of low volume fraction nano-fluid. The frictional resistance coefficient decreases with the increase of the Re and it is biggest in 0.6mm microchannel, smallest in 2mm microchannel. According to the experimental data, the product of f Re is const and higher than classical theory prediction. The product of f Re in two various volume fractions of nanofluid have little difference in the same microchannel.Secondly, experiments on two-phase flow were studied and contrasted. The experimental results showed that: two-phase frictional pressure drop increases with the increase of dryness of outlet and heat flux. The dryness of outlet at high volume fraction nano-fluid is higher than that of at low volume fraction nano-fluid. The size of microchannel had a great impact on two-phase friction pressure drop. Two-phase friction pressure drop was increasing as the size was decreasing. As the heat flux increases, irregular and more severe cyclical pressure drop fluctuation was observed. Finally, Values between experiment and L-M model were compared. The results showed that the two-phase frictional multiplier increases with the increase of the dryness of outlet and the heat flux, decrease with the increase of mass flux. The volume of L-M model is obviously smaller than that of the experiment, So, L-M model couldn't predict very well in this experiment.