Given the global increase in energy prices, the optimal use of available energy is an undeniable requirement for competition in today's world. One of the key equipment to save energy is high-efficiency heat exchangers. There are different ways to increase heat transfer in heat exchangers. The use of porous materials is one of the passive methods that has received special attention in heat transfer processes in recent decades. The porous medium significantly increases heat transfer due to the increased contact surface with the fluid and having a higher thermal conductivity than the fluid, but will also increase the pressure drop. In the present numerical study, the porous material is located within the range of sinusoidal tube exchangers with different dimensions, and in this case, fluid flow and heat transfer have been investigated. In the present study, the incompressible and stable flow equations in the turbulent flow regime are discretized using the finite volume method and solved with the coupled algorithm in Fluent software. The k-ω SST turbulence model is used to simulate turbulent flow. Also, the local thermal equilibrium model is used for the energy equation and the Darcy-Brinkman-Forchheimer model is used for the momentum equation in a porous medium. The porous material is homogeneous and isotropic and its porosity coefficient is considered equal to 0.95. In this study, the fluid is air and the boundary condition of a constant temperature of 373 K on the tube's wall and a temperature of 300 K at the inlet of the tube is established. In this study, heat transfer coefficient, Nusselt number, friction factor, and performance eva‎luation criteria for three geometric parameters (L*) have been calculated equal to 11, 19, and 25. L* is the ratio of the wavelength to half the sine amplitude and determines the degree of waviness of the tube. In this study, the effect of two parameters of Darcy number and porous medium thickness on heat transfer and pressure drop in turbulent flow inside the tube has been investigated. Observing the results, it is found that by adding a porous medium to divergent sections of the sinusoidal tube, the hot temperature front in these areas has increased, which has led to an increase in the outlet temperature of the transducer. inserting the porous material in the divergent sections of the sinusoidal tubes will have a positive effect on reducing the pressure drop caused by the porous medium. The results show that in all three cases mentioned for the geometric structure of the sinusoidal tube, in a fixed Darcy number, with increasing the thickness of the porous medium, the heat transfer, pressure drop, and performance eva‎luation criteria increase. As the thickness of the porous medium increases, the ratio of increase in heat transfer to pressure drop in large Darcy numbers will be greater than in small Darcy numbers, while the rate of increase in heat transfer and pressure drop in small Darcy numbers will be greater than in large Darcy numbers. The results showed that with decreasing particle size of the porous medium, heat transfer and pressure drop increase and performance eva‎luation criteria decreases. Also, the most changes in heat transfer, pressure drop, and performance eva‎luation criteria in the Darcy range are 10^-3 to 10^-5. Among the studied cases, in geometric parameter 25 and Darcy number 0.01, with increasing the thickness of porous medium, the performance eva‎luation criteria reaches the highest value in this research. In this case, the Nusselt number and friction factor increase by 58% and 180%, respectively, compared to a tube without a porous material.

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احمد سوهانكار، محمود اشرفي زاده