© 2020 Elsevier Ltd In this investigation, laminar flow with a hybrid nanofluid as a working fluid in a newly designed double layer microchannel with sinusoidal walls is investigated. The nanofluid is Al2O3-Cu/water hybrid nanofluid. Results indicate that changing the geometry of fluid route (wavelength of the sinusoidal wall), usage of nanofluid and increasing fluid velocity can alter Nusselt number, the maximum temperature distribution in the microchannel, Performance Evaluation Criterion and friction factor. The presence of sinusoidal wavelength across the entire microchannel can improve mixing between surface and fluid, and this mixing happens because of the slow flow of fluid in low Reynolds number (Re = 50) and the average Nusselt number variation is the same for similar wavelengths. For Re = 300, 700 and 1200, the decrease in PEC is the same for the higher volume concentration of solid nanoparticles and the change in the level of curves for each wavelength are close together compared with Re = 50. When the difference temperature between surface and fluid is reduced, the heat transfer value is reduced, and the maximum temperature of the lower layer increases sharply so that for Re = 50 the value of maximum temperature is noticeable compare with Re = 1200.
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