Due to the lack of energy sources, improving energy conversion efficiency in heat exchangers is an important subject. Also increasing the heat transfer in systems that are related to the energy consumption could reduce the environment pollution. Different ways were suggested for enhancing the heat transfer in heat exchangers, among them convective heat transfer in systems including porous plug-ins attract many researchers due to the wide applications of these systems in engineering processes and equipment like geothermal energy recovery, air heaters, drying processes, electronics cooling, solid matrix heat exchangers, decreasing size of heat exchangers for aerial industries, etc. By using porous media, the space and material needed for heat exchanger would be reduced effectively. The aim of this thesis is to achieve improved alignment and optimal longitudinal distribution of porous material segments in the tube, to enhance heat transfer with appropriate and controllable pressure drop. Ratio between heat transfer and pressure for tube with porous media should be higher than tube without porous material. Laminar and forced flow regime with the input speed of 5.0 meters per second is considered. Volume ratio of porous material fixed to the tube at all times is considered as much as 18% of total volume of tube which is a critical quantity for porous material in tube. Indicating degrees of freedom are the number of blocks of porous material, distance between the blocks and size of them. Simulation was done using FLUENT software. Wall boundary conditions in two different modes of constant heat flux and a constant temperature of the wall are taken into account. A performance evaluation criteria (PEC), which is the ratio of Nu number to pressure loss in tube with porous material in compare to tube without porous media, is defined to find best mode of porous media arrangement. As the number of pieces of porous material increased, the heat transfer in tube increased too. Moreover, order of segments is from biggest to smallest in arrangement with highest PEC. It is determined that three blocks of porous media could effectively increase heat transfer in compare with one and two segments geometry. After determining the optimal geometry of the problem, the impact of other porous material parameters such as porosity, Darcy number and the effective thermal conductivity of porous media was studied in fluid and porous region. In optimized circumstances, PEC increases 66% for constant heat flux boundary condition and Nu number increase 95%. For constant temperature at the wall, PEC is determined 62.9% higher than tube without porous media. Moreover, Nu number increases 95% for constant wall temperature boundary condition in tube. Finally, all the simulations that assume local thermal equilibrium as a model to simulate heat transfer in porous media were compared with the Local thermal non-equilibrium assumption and it was concluded that thermal coefficient ratio less than 10, these two models match very good. However, for thermal coefficient ratio higher than these two models shows huge difference. For TKR number higher than 30, it is determined that average Nu number difference is higher than . Keywords: Heat transfer, Porous media, Convective heat transfer, Performance evaluation criteria, Local thermal equilibrium, Local thermal non-equilibrium.
