numerical simulation of the flow in a concentric double-pipe heat exchanger with a square inner pipe and a circular outer pipe

Double-pipe heat exchangers are commonly used in various industries, including power plants, solar cells, refineries, and automotive. the double-pipe heat exchanger is one of the most used simple exchangers in the industry. in this study, we employ computational fluid dynamics to investigate the flow characteristics of nanofluids within a double-pipe heat exchanger featuring a square inner tube and a circular outer tube (sc). the simulations are conducted under constant heat flux conditions, exploring laminar and turbulent flow regimes. numerical results for water flow under forced convection are compared with reference results for validation. the results indicate that as the reynolds number increases, particularly in turbulent flow regimes, the nusselt number in nanofluid flow increases more than in water flow. for instance, in the case of aluminum oxide nanofluid flow at a reynolds number of 500, the nusselt number demonstrates a nearly 5% enhancement over water flow. in contrast, at a reynolds number of 20000, this enhancement escalates to approximately 20%. three types of nanoparticles are considered to investigate the effect of nanoparticle type on heat transfer and pressure drop. the results show that the use of nanoparticles has a slight effect on the friction factor while significantly enhancing heat transfer.