Effect of Magnetic Stirrer Action and Concentration of Iron Oxide Nanofluid on Stability and Thermal Energy Performance of Solar-Based Heat Exchanger

Abstract The nanofluid-integrated evacuated tube solar collector (ETSC) exhibits significant properties and is utilized in solar-based heat exchanger applications. However, the agglomeration of nanoparticles influences the heat transfer performance, and variations in solar radiation limit the overall performance of the heat exchanger. To address the research gap and enhance the thermal performance of ETSC, we investigated different wt% of iron oxide (Fe3O4) nanofluids operated at a flowrate of 0.03 kg/s, utilizing paraffin phase change material (PCM) to absorb excessive heat energy. The nanofluid was subjected to magnetic stirrer action at a stir speed of 500 rpm for 60 min, with a frequency of 40 kHz. The influence of magnetic stirrer action on the stability behavior of nanofluids was evaluated through zeta potential analysis, which revealed improved stability behavior for long-term operation. The study examines the impact of Fe3O4 concentration and PCM on thermal properties. The results show that the ETSC operating with 0.5 wt% Fe3O4 nanofluid integrated with PCM exhibits optimum thermal performance. Specifically, an enhanced thermal conductivity of 0.975 W/m · K at 75 °C, a higher fluid outlet temperature of 82.1 °C recorded at a solar radiation of 706.9 W/m2, a superior heat transfer coefficient of 456 W/m2 · K, a moderate pressure drop of 0.624 kPa, an increased thermal efficiency of 72.1%, and a reduced heat loss of 401.3 W were achieved.