Enhancement of heat transfer in shell and tube heat exchanger using mini-channels and nanofluids: An experimental study

Abstract

This study aimed to experimentally investigate the effects of Al2O3-water nanofluids with six different volume concentrations (0.02%, 0.1%, 0.2%, 0.4%, 0.6%, and 0.8%) instead of water as working fluid on heat transfer and pressure drop on the tube side of a mini-channel shell and tube heat exchanger (MC-STHE). The shell-side hot fluid flow rate was kept constant at 180 L/h, while the flow rate of the tube-side cold fluids ranged from 125 to 600 L/h. The convective heat transfer coefficient (CHTC) of the nanofluids increased in the transition and turbulent regions. The nanofluids also extended the transition region. The nanofluids had higher friction factors than water. The nanofluids had an optimal volumetric concentration and a flow rate of 0.4% and 375 L/h, respectively, at which the CHTC enhanced by 49%, while the friction factor increased by 21% compared to water. Compared to macrotube heat exchangers, the CHTC enhanced 3 to 7 times with the combined effect of the mini-channels and nanofluids in the shell-and-tube heat exchanger (STHE). Consistent with earlier studies (maximum TEF of 1.8), the thermal enhancement factor (TEF) for the optimal volumetric concentration Al2O3- water nanofluid in the MC-STHE was 1.6 at most under the same hydrodynamic conditions. The performance evaluation criterion (PEC) and the efficiency evaluation criterion (EEC) showed that there was no point (not enhancement) in using nanofluids instead of the base fluid (water) in the MC-STHE.