Experimental investigation of heat transfer performance of Al2O3 nanofluids in a compact plate heat exchanger

This study experimentally investigates the performance of a compact gasketed plate heat exchanger (PHE) employing Al2O3 nanofluids prepared for several low concentrations of Al2O3 (0.01, 0.05, 0.10, 0.15 and 0.20 vol %) and base fluids of distilled water (DW) and its mixture with ethylene glycol (15% and 30% of EG) for several flow rates (0.03-0.093 l/s). The main thermophysical properties of those nanofluid samples were experimentally measured. The prepared nanofluids showed a Newtonian rheological behaviour and an increase in viscosity up to 7.5% for 0.2 vol%. The enhancements in the thermal conductivity were significant and the values were 7.3 %, 8.4% and 9.1% for Al2O3 nanofluids at 0.2 vol% compared to the base fluids DW, 15% EG and 30% EG, respectively. A newly developed experimental setup is used to run the nanofluids through the PHE under particular conditions for heating purposes (mainly high temperature), and their performance is evaluated in comparison with the conventional heat transfer fluids (the base fluids). Nusselt number, pressure drop, and energy efficiency factor were determined for the nanofluids and base fluids. The results indicated a heat transfer enhancement with the increase of the nanoparticles' concentration reaching the maximum value of 27% at 0.2 vol% for DW based Al2O3 nanofluid and was accompanied by an increase in pressure drop of 8%. The heat transfer enhancement became lower with the increase of the EG percentage such as 19.1% at 0.2 vol% for 30% of EG based Al2O3 nanofluid. In addition, the energy efficiency factor increased by the addition of Al2O3 nano -particles to the base fluids and with the increase of flow rates up to the value of 1.3 at the highest particles concentrations. This work provides an important step concerning the performance of particular design of Al2O3 nanofluids and operation conditions in compact PHEs towards the development of thermal management systems under the current industry's trends for optimizing energy use and minimizing equipment size.