Lattice Boltzmann Numerical Investigation of Inner Cylindrical Pin-fins Configuration on Nanofluid Natural Convective Heat Transfer in Porous Enclosure

Concerning the geometrical effect of inner cylindrical hot pins, the natural convective heat transfer of nanofluid in a homogenous porous medium in a squared enclosure is numerically studied, using lattice Boltzmann method (LBM). In order to investigate the arrangement of inner cylinders for better heat transfer performance, five different configurations (including one, three, and four pins) were compared, while the total heat transfer area of inner pins were held fixed. Squared cavity walls and inner cylinder's surfaces were constantly held at cold and warm temperatures, respectively. In our simulation, Brinkman and Forchheimer-extended Darcy models were utilized for isothermal incompressible flow in porous media. The flow and temperature fields were simulated using coupled flow and temperature distribution functions. The effect of porous media was added as a source term in flow distribution functions. The results were validated using previous creditable data, showing relatively good agreements. After brief study of copper nano-particles volume fraction effects, five cases of interest were compared for different values of porosity and Rayleigh number by means of averaged Nusselt number of hot and cold walls; and also local Nusselt number of enclosure walls. Comparison of different cases shows the geometrical dependence of overall heat transfer performance via the average Nusselt number of hot pins strongly depending on their position. The four pin case with diamond arrangement shows the best performance in the light of enclosure walls' average Nusselt number (heat transfer to cold walls). However, the case with three pins and downward triangular arrangement surprisingly gives promising heat transfer performance. In addition, the results show that natural convective heat transfer and flow field is intensified with increasing Rayleigh number, Darcy number, and porosity.