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Abstract- In the present paper, three different samples of alumina used as nanoparticles in the ethylene glycol suspension of alumina with volumetric concentration in the range . These samples have different surface properties, shape and size. The use of Al2O3/EG nanofluids as coolants in a double-tube heat exchanger has been studied under laminar flow conditions. The hot solvent inlet heat exchanger must be cooled down with a specified amount. At first, heat transfer relations between hot solvent and nanofluids as coolants have been investigated theoretically. Subsequently, heat transfer area and flow rate of coolant are optimized by using the nanofluids. In the present paper, heat transfer coefficient, overall heat transfer coefficient, friction factor, pressure drop and pumping power for Al2O3/EG nanofluids calculated.

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In present study, heat transfer in double-tube heat exchanger filled with metal porous material has been investigated. In contrast to the most of previous studies, fluid flow is considered turbulent in heat exchanger which is in a good agreement with the practical performance of these exchangers in the industry. Fluid flow and heat transfer equations have been discretized on a collocated grid by the means of finite volume method with simple algorithm. Discretized equations are solved with a numerical program in FORTRAN language in order to study the effect of porous material parameters and Reynolds of fluid flow on the heat transfer in double-tube heat exchanger. According to the results and analysis of porosity in the range of 0.8 to 0.95 as well as pore diameter of 1 mm up to 6 mm and diverse types of porous material, it is observed that the decrease in porosity, the increase in pore diameter and use of copper porous material (with high heat conduction coefficient), increase heat transfer. In the best case, overall heat transfer coefficient enhances up to 7 times. Moreover, the results reveal that the heat transfer enhancement ratio have no distinct difference with changing Reynolds number of turbulent flow in the range of 10000 to 80000. Performance evaluation criteria, which investigate the effects of pump lost power and thermal power, depicts that with using porous material the value of the pump lost power is of major importance which can be decrease by increasing the porous pore diameter.