Thermal and hydraulic characteristics of a hybrid nanofluid containing graphene sheets decorated with platinum through a new wavy cylindrical microchannel

One approach to improve cooling efficiency of cylindrical microchannel heat sinks (CMCHS) is increasing the total wetted surface through cylindrical geometries instead of using flat configurations. In addition, the wavy structures using advanced working fluids is a novel technique to enhance the heat transfer in CMCHS. In this study, by using a graphene-platinum/water hybrid nanofluid as the working fluid, the effect of wavy-shaped fins on hydro-thermal performance of a cylindrical CMCHS is investigated numerically. Three-dimensional, steady, laminar flow is simulated using the finite volume method. The sinusoidal fins form the secondary flows in the channel, which disturb the boundary layer leading to intensification in heat transfer. Increasing the amplitude, concentration, and Reynolds number decrease the thermal resistance and facilitate heat transfer. The maximum value of the average heat transfer coefficient is calculated as 13387 W/m(2)K, while the highest pumping power and lowest thermal resistance are calculated to be 0.6 W and 0.031 K/W, respectively. A comparison between the wavy and straight CMCHSs shows that wavy fins can improve the heat transfer coefficient by up to 75%. The maximum performance evaluation criterion (PEC) is obtained at a concentration of 0.02% and Reynolds number of 600 for all amplitudes. Finally, multi-objective optimization is performed to find the optimal states that yield the highest heat transfer coefficient, lowest thermal resistance, and lowest pumping power regarding the designers' demands. Optimization is conducted using genetic algorithm and the compromise programming method. The results obtained from the optimization indicate that nanoparticle concentration profoundly affects pumping power, while amplitude has severer influence on the thermal attributes. The main novelties of this work are to employ wavy fins in a CMCHS, as well as to use multi-objective optimization with regard to the relative importance of heat transfer and pumping power in this configuration.