Increased heat transfer in thermal equipment such as heat exchangers is a subject on which extensive studies have been conducted. Various methods have been studied by the researchers for increasing the heat transfer in heat exchangers. Using fins is one of the methods used to increase the heat exchange surface in equipmeant. It also increases heat transfer and pressure losses within the exchangers. The method that has received much attention in recent years is the use of porous medium in the heat exchangers. Using porous medium enhances heat transfer and pressure drop. In this study, longitudinal porous fins are used to increase heat transfer in double pipe heat exchangers. Using porous longitudinal fins in heat exchangers is a new aspect about which, no comprehensive research has been published. To do so, the analysis of flow and heat transfer has been carried out using numerical simulations with Fluent software. The fluid in inner tube is liquid water with constant properties, and the fluid within the outer tube (annular space between the two tubes) is air. The flow in tubes is assumed to be turbulent with a constant Reynolds number of 10000. Darcy-Brinkman-Forchheimer model was used to simulate porous medium, k-? model was used for simulation of turbulent flow, for the momentum equation, and the two-equation model or local thermal non equilibrium has been used for the energy equation. The input flow is a fully developed hydrodynamic one. All the thermodynamic properties of solid phase (porous material) and the fluid are independent of temperature. The porous material is assumed to be completely homogeneous and isotropic. Current project examines the effects of porous environment parameters and optimization of porous fin. To optimize the porous fin, a fixed amount of porous material is used so that the ratio of porous material volume to the heat exchanger volume remains constant. The use of porous longitudinal fin increase heat transfer and pressure drop, therefore, optimized geometry of porous fin is challenged to achieve maximum heat transfer and minimal pressure drothat performance evaluation criterion has been used to optimize the geometry of porous fin. The results show that at a constant thickness of fin, by reducing the height of the fin (increasing the number of fins) the overall heat transfer of heat exchanger and pressure drop are decreased. The highest performance evaluation standard is obtained for the case where the porous fin has the least height. The effect of Darcy number or permeability in terms of Nusselt number and the criteria for performance evaluation have been studied. The results show that by reducing the Darcy number or permeability, due to increased interaction between the fluid and porous material, the heat transfer and pressure drop are increased. It was also observed that by reducing the Darcy number, performance evaluation criteria is increased. In fact, higher Darcy numbers have less energy recovery rates compared to the energy loss. Furthermore, the effect of porosity coefficient has been studied in terms of Nusselt number and performance evaluation criterion. The results show that by increasing porosity coefficient, the heat transfer is increased. It was also observed that by increasing porosity coefficient, performance evaluation criterion is increased. Performance evaluation criterion is increased due to constant pressure drop and increased heat transfer due to increased porosity. Keywords: heat transfer, heat exchanger, fin, porous material, performance evaluation criterion, local thermal non equilibrium.