Numerical study of implemented eco-friendly nanofluid in the pinfin-equipped heatsinks with novel C-shaped and V-shaped patterns

Abstract

In the current study, three cross-sections including circular, square, and triangular cross sections have been selected based on their higher efficiency in enhancing the heat transfer rate while having low-pressure drop. The two added patterns (namely C-shaped and V-shaped) for the arrangement of these pinfins in the present study, is a novel idea that has not been studied before in microchannel studies. Additionally, the nanofluid type has been chosen based on previously conducted experiments. On the whole 72 simulations have been carried out in ANSYS-Fluent commercial code. The mesh independency study (based on the defined patterns and types of cross sections) was conducted based on the resulting pressure drop of the microchannel and the predicted average temperature of the heated plate. The achieved mesh designs were compiled among these and have satisfactory performance in predicting the desired physical quantities. A steady state analysis was carried out for the conducted analysis where the laminar flow regime was perhaps dominant because of the very low characteristic dimensions in considered flows. Consequently, the laminar flow model was applied. The energy equation for observing the temperature variation at different locations through the solid and liquid layers was requisite for these analyses. The applied material for the microchannel walls was aluminum and water was defined as the main fluid in these investigations. Due to applying the specific nanofluid named green graphene-based nanofluid at different concentrations, the User Defined Function (UDF) was written in C programming language in which the thermal conductivity and the viscosity parameters of nanofluid were varied based on the local temperature value of the corresponding cell in the present finite volume discretization method based commercial code. The polynomial model for density variation of water in mass, momentum, and energy conservation equations is implemented. Consequently, the density of water is defined as the function of the local temperature. The constant value of the 400000 Wm-2 heat flux was defined as the boundary condition in these simulations. For the inlet of the channel, the velocity inlet boundary condition was considered where the pressure outlet was defined along the outlet boundary. Three distinct values of velocity were selected. The parameters which have been calculated in these simulations were pressure drop, mean temperature of the heated plate, minimum temperature of the heated plate, the maximum temperature of the heated plate, and outlet temperature of the channel. The SIMPLE algorithm has been selected as the scheme in these studies where the least square cell-based model was selected as the spatial discretization scheme. The second-order accurate upwind method was defined for the momentum, pressure, and temperature fields, respectively. The residual thresholds for momentum and energy equations were 10-5 and 10-6, respectively. After applying the aforementioned configurations, the simulations were conducted until reaching the convergence point based on the previously defined values of residuals. Based on gathered data from the simulations, the parameters including heat transfer coefficient, thermal resistance, temperature distribution uniformity, Figure of Merit (FoM), and pumping power were extracted for the given velocity and concentration of the nanofluid for the 72 cases of studies. In the analysis conducted for investigating the the temperature uniformity index, the least value was achieved for the triangular cross-sectioned pinfins with C-shaped pattern. Additionally it was concluded that this parameter declines by increasing the velocity and the concentration for various defined configurations. For the heat transfer coefficient parameter which was defined, this conclusion is revealed that by increasing the particle fraction of nanofluids, the heat transfer coefficient enhances. Moreover, It was resulted that by increasing the flow rate value, the heat transfer coefficient increases as well. Among the tested comparison, the triangular cross-sectioned pinfin with the C-shaped pattern has reached the pinnacle of this investigated parameter. Thermal resistance, as another studied parameter, was evaluated for the defined configurations where increasing the particle fraction and velocity lead to reduction of thermal resistance. In the conducted comparison based on this parameter, the triangular cross-sectioned pinfin with C-shaped pattern achieved the least value of thermal resistance with respect to other studied configurations. The FoM parameter was defined in order of making balance between the enhancement of heat transfer coefficient and pressure drop where increasing the concentration lead to enhancement of FoM at constant defined velocity of 15 ms−1 for the C-shaped pattern. The same procedure was followed for the V-shaped pattern as well. Having higher than unity value of FoM revealed the higher growth of heat transfer coefficient over the pressure drop for the cases including the nanofluids in comparison with pure water cases of studies. Pumping power, as the parameter represents the required power of forcing fluid flow into the channel, was evaluated as various concentrations and the results indicated that by increasing the concentrations, this parameters augmented due to enhancing the value of viscosity. The achieved results approved that the square and circular cross-sectioned pinfins possess the highest and lowest value of this parameter for the C-shaped pattern respectively.