Augmentation of heat transfer in equipment, such as heat exchangers, is an important issue for saving energy, extensive studies has been done on this issue. Many methods of increasing the heat transfer of heat exchangers investigated. These equipment are used in power generation industry, process industry, Chemical industry, electronic equipment, geothermal energy recovery, air heaters, manufacturing, air conditioning, space applications and etc. The method that is more considered by researchers is using porous media in heat exchangers by many ways of inserts of porous media. Also metal foams with high conductivity attracts researchers as a porous media. Using metal foams in heat exchangers enhance the heat transfer and pressure drop, so optimizing these parameters is the cause of many investigation on ways of inserting the metal foams in heat exchangers for reaching the best layout that is maximum heat transfer and minimum pressure drop. Porous media are used in electronic parts, drying processes, heat pipes, geothermal systems, extraction of oil resources, insulating, storage of nuclear waste, filters, energy systems such as heat exchangers, chemical reactors, cooling parts, solar collectors and etc. In the present work, a numerical study of flow and heat transfer characteristics is made in a counter flow and double pipe heat exchanger with porous structures inserted in both pipes of heat exchanger. In fact our purpose in this work is achieving a layout for metal foam that has the maximum heat transfer and minimum pressure drop with constractual design with constant volume of metal foam. So we used the "Performance Evaluation Criteria" or PEC number for achieving the best layout. The momentum equation modelled by Darcy model and energy equation is modelled by two equation model or Local Thermal Equilibrium (LTE) method. The Fluent software is used to solve the governing equations. We used a constant volume of metal foam for inserting in the heat exchanger that is occupy twenty percent of the whole volume of the heat exchanger. The fluid is water so the Prandtl number is equal to 7. The porosity, the Reynolds number and thermal conductivity of the solid to fluid are set fixed at 0.95, 100 and 100 respectively. The flow is axisymmetric, two-dimensional and in steady state with no internal heat generation. The thermo-physical properties of the porous matrix and the fluid are assumed to be constant and the porous medium is considered homogeneous, isotropic and in local thermal equilibrium with the fluid. The pipes are made of stainless steel. The results showed that increasing the partition number of the metal foam enhanced heat transfer and no sensitive effect on pressure drop because of the constant volume of porous media, so the partition number equal to 4 chosen as the best layout for porous media. Effect of Darcy number on Nusselt number and PEC number investigated. The results showed that decreasing the Darcy number enhanced the heat transfer because of increasing the fluid and solid interaction and increased pressure drop. Also the increasing of percentage of the pressure drop of the heat exchanger with metal foam to heat exchanger without metal foam is more than increasing of percentage of the heat transfer with decreasing the Darcy number, so increasing the Darcy number enhanced the PEC number. Keywords: Heat transfer, Pressure drop, Heat exchanger, Porous media, Metal foam, Performance evaluation criteria, Local thermal equilibrium.