Heat transfer enhancement and pressure drop of Fe3O4 -water nanofluid in a double tube counter flow heat exchanger with internal longitudinal fins

Use of internal fins in tubes of heat exchangers is a good practice for heat transfer enhancement. This paper reports an experimental study of forced convective heat transfer in a double tube counter flow heat exchanger with multiple internal longitudinal fins using Fe3O4 -water nanofluid. The convective heat transfer enhancement and pressure drop are investigated for the nanofluid flowing in a horizontal circular tube with internal longitudinal fins under turbulent conditions (5300 < Re < 49,200) and the volumetric concentration of Fe3O4 nanoparticles are in the range of 0 < φ < 0.4%. Results indicates that the heat transfer rate is 80-90% more in finned tube heat exchanger compared to the plain tube heat exchanger for the higher volumetric concentration of nanofluid. Nusselt number ratio of Fe3O4- water nanofluid with base fluid (water) increases with the Reynolds number. Friction factor decreases with the increase in Reynolds number and pressure drop is more in finned tube heat exchanger compared to the plain tube heat exchanger due to the effect of fin geometry which offers resistance to the flow. Wilson plot method is used to develop the Nusselt number correlation for the flow of Fe3O4- water nanofluid through the finned tube heat exchanger.