Synthesis and application of ZnO rod-shaped nanoparticles for the optimal operation of the plate heat exchanger

Abstract

ZnO nanoparticles with tunable morphology exhibit attractive behaviors in transport phenomena, which make them valuable for thermal applications. The present study focuses on the synthesis and application of ZnO nanoparticles with two different shapes for the preparation of the working heat transfer nanofluid. First, the rod-shaped and spherical-shaped nanoparticles were synthesized by simple chemical methods and then ultrasonically dispersed in pure water to prepare a set of stable nanofluids with concentrations between 0.2% and 1% of nanoparticles. The nanofluid samples were analyzed thermo-physically to obtain the optimal nanoparticles volume fraction for presenting the best thermal properties. In the following, a brazed plate heat exchanger was examined to evaluate the heat transfer characteristics of the selected nanofluids as a coolant fluid at flow rates between 1 and 3.5 l/min. The experimental results showed that the lowest Prandtl number appeared at the volume fraction of 0.4%. This concentration was considered the operating basis of the heat exchanger. ZnO nanoparticles had the considerable effect on the thermal characteristics of water as a working fluid. The maximum growth in the heat transfer rate was found for the nanofluid with the rod-shaped nanoparticles at the lowest flow rate (1 l/min), which were 29.2% more than pure water and 7.5% higher than the nanofluid with spherical-shaped nanoparticles. Additionally, due to the exponential increase in the pumping power, there was a flow rate range (less than 2 l/min) in which the energetic performance of the nanofluids was higher than water.