Abstract
Heat exchangers serve as pivotal components in industries. Enhancement in the performance of heat exchangers has been the focus of researchers in the recent past. The aim of this study was to numerically investigate the improvement in thermal performance of heat exchangers by combining two passive techniques, i.e., use of nanofluids and coiled tubes. Thermohydraulic performance of a shell and helical coil tube heat exchanger was evaluated at 0.1%, 0.3% and 0.5% volume concentrations of MWCNT/water nanofluid and at coil Reynolds numbers of 9000-15,000. The numerical simulations were performed considering the cold-fluid (water) flows through the shell, whereas the hot fluid (water and nanofluid) flows through the helical coil in a counter-current flow direction. The RNG k-epsilon model with enhanced wall treatment was applied. The results illustrate that the Nusselt number of the fluid flowing through the coil increased as coil Reynolds number and nanofluid volume concentration increased. When multiwall carbon nanotube/water nanofluid with a volume concentration of 0.5% was used at a coil Reynolds number of 15,000, the highest improvement in Nusselt number was observed i.e., 31.5% and the highest pressure drop of 47.35% was noted at the same conditions The maximum decline of 40.5% in the effectiveness of the heat exchanger was found when Reynolds number increased from 9000 to 15,000 at 0.5% volume concentration of nanofluid. The thermal performance factor, which serves as an index for heat exchanger performance was also calculated.