The Research Of Fluid Flow And Heat Transfer In Rectangular Microchannels With Fractal Structure

Via experiments and numerical simulations in rectangular microchannels with fractalstructure, this research aims at analyzing the fluid flow and heat transfer characteristics ofdeionized water. The adopted hydraulic diameters are125μm,166.67μm and187.5μm,including branches from0to2. And the Reynolds Number is less than2300.Firstly the rectangular microchannels with zero branches are investigated and theobtained flow friction factors f aree in consistent with the theoretic calculated values. Butthe Poiseuille Number Po is not constant so that the aspect ratio is no longer the onlydeterminate factor. Regarding with the heat transfer, the criterion numeral Nu graduallyrises with the increase of Reynolds Number. However the experimental heat transferperformance of the above microchannels is different from the prediction of Dittus-Boelterand Shah empirical correlations.And then comparing the experimental results and simulations of fractal microchannelswith one branch and two branches, both of them show the same trend that the pressure dropslightly increases when the mass flow rate raises. But in high Reynolds Number region, thediscrepancies increase due to the flow resistance at the corner. At the same time, along withthe mass flow rate rises, the proportion of frictional pressure loss to the total pressure lossgradually decreases. What’s more, the experimental results also show that the influence ofaspect ratio on pressure drop is deeper than that of branch number.Similarly, related with the heat exchange performance, the influence of them isdifferent. When the branch number is fixed, the effect of vortices appears nonlinearly onheat enhancing. On the other hand, once the total length of microchannels is constant,choosing more branches can’t obviously improve the heat exchange performance. In thisstudy, the effect of branch number is larger than that of aspect ratio on the heat exchangeperformance.Finally through the numerical simulation method, the effect of T-shape bifurcationstructure and L-shape elbow structures is indicated how they do contributions to the fluidflow and heat transfer. Since the flow direction suddenly changes, the centrifugal force at corners leads to the pressure rising. Meanwhile the generated symmetric vortices destroythe detention behavior near the wall. And brought with the secondary flow, the central coldfluid fully exchanges the heat with the high temperature fluid so that the heat transfer issignificantly strengthened.