Experimental study of thermal performance factor for double-pipe heat exchanger using ZnO–water nanofluid

Since the notion of dispersing nanoscale particles into the base fluid was first presented in the latter half of twentieth century, the area of nanofluids (NFs) has attracted considerable attention. This is reflected in the growing number of researches published annually on nanofluids. In the current study, an experiment was performed on double-pipe heat exchanger using ZnO–water NF to investigate the thermal performance factor (TPF) and pressure drop. The experiment was conducted for a single-phase fully developed flow in the turbulent region with four different volume fractions (VFs) of 0.005%, 0.02%, 0.04%, and 0.07% in the Reynolds number (Re) range of 5500–15000. During the experiments, it was seen that Brownian motion and thickness of interfacial layer also play a vital role in the enhancement of heat transfer rate along with thermal conductivity. At Re of 5500 for VF of 0.07%, the highest enhancement in Nusselt number was recorded as 55.51% with the penalty of 147.37% increase in friction factor. The highest TPF during the study was recorded as 1.15 for volume fraction of 0.07% at 5500 Reynolds number. For better understanding of nanofluid behavior, characterization of ZnO nanoparticles was performed in the laboratories which includes analysis of XRD, HRTEM, EDS, FTIR, and particle size. Within given range of Reynolds number and particle volume fractions, new correlations were also established for Nusselt number and friction factor.