In this paper, laminar forced convection of CuO nanofluid is numerically investigated\nin sudden expansion microchannel with isotherm walls and different\nexpansion ratios (ER). An Eulerian two-fluid model is considered to simulate\nthe nanofluid flow inside the microchannel and the governing mass,\nmomentum and energy equations for both phases are solved using the finite\nvolume method. Eulerian-Eulerian two-phase model is very efficient because\nof considering the relative velocity and temperature of the phases and the nanoparticle\nconcentration distribution. In solving the flow equations for both\nphases, the SIMPLE algorithm is modified for the coupling of the velocity and\npressure and the continuity equations for both phases are combined in order\nto create the pressure correction equations. However, the Eulerian-Eulerian\nmodeling results show higher heat transfer enhancement in comparison to\npure water, so that for a 2% copper-water nanofluid, it has been observed a\n35% increase of the heat transfer. The heat transfer enhancement increases\nwith increase in Reynolds number and nanoparticle volume concentration,\nwhile the pressure drop increases only slightly. An investigation of the expansion\nratio of microchannel shows that the average Nusselt number increases\nwith decrease in expansion ratio as well as with increase in Reynolds number.\nAlso, the Bifurcation has been occurred in higher Reynolds number that is\ndifferent for each expansion ratio of the microchannel.
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