Experimental and CFD analysis of circular tube heat exchangers with solid-hollow inserts

The study focused on conducting a heat transfer analysis of a circular tube heat exchanger with alternating solid-hollow inserts using the Ansys Fluent software version 19.0 and via experimental setup. The objective was to determine the heat exchanger tube's friction factor, heat transfer, and thermal performance factor (TPF) under steady state conditions. The investigation involved circular-hollow and solid inserts with diameters of 66 mm and 33 mm, respectively. The turbulence simulation was carried out within a Reynolds number range of 11,500-26,500, using air as the working fluid and the k-epsilon model for turbulence simulation. Three different insert arrangements were considered during the simulations. Among the different insert arrangements, the geometry with six inserts in the fluid domain exhibited the highest heat transfer while the geometry with five inserts resulted in the lowest heat transfer. However, the friction factor was minimum while using 5 inserts and increased significantly with the number of inserts increased similar results were found during experimental investigation. Even though the heat transfer was lowest with geometry having 5 inserts it yielded the highest TPF due to substantially less friction factor. Among the different insert arrangements and tested Reynolds numbers, the thermal performance factor was highest while using 5 inserts at Reynolds number 11,669, with a value of 1.421. Reynolds number was always kept equal to or greater than 11,500 to ensure the study under fully developed turbulent flow.