Nanofluids effect on the overall transfer coefficients change mechanism analysis

The understanding of the enhanced thermal conductivity mechanism in nanofluids remains elusive, underscoring the necessity for investigating their influence on heat conduction. A comparative analysis was carried out on the overall heat transfer coefficients of SiO 2 , TiO 2 , MgO, ZrO 2 , CeO 2 , Al 2 O 3 , and Fe 3 O 4 , yielding 346.5, 442.9, 569.2, 465.6, 663.2, 562.4, and 706.2 W/m 2 K, respectively. Our investigation further extended to the differential impacts of various nanofluids on heat transfer conduction coefficients, with Fe 3 O 4 nanofluids demonstrating the greatest, and SiO 2 the least, heat transfer coefficients. Importantly, these nanofluids play a cooperative role in enhancing heat transfer coefficients. Previous studies have largely concentrated on the effects of individual and mixed nanofluids on overall heat transfer coefficients, neglecting the combined effects of different nanofluids. Moreover, the mechanisms underlying these effects remain vague, with insufficient corresponding characterizations. Our study seeks to address these limitations. We also studied the impact of nanofluid concentration, pH, and temperature on heat conduction. Our results suggest that the overall heat transfer coefficient escalates with increasing nanofluid concentration and temperature. For example, the overall heat transfer coefficients for SiO 2 nanofluids surged from 346.5 W/m 2 K at 25°C to 369.4 W/m 2 K at 35°C, 411.4 W/m 2 K at 45°C, and 427.6 W/m 2 K at 55°C. A rise in pH also led to an increase in overall heat transfer coefficients up to a certain point, after which they started decreasing. The zeta potentials of the aforementioned nanofluids were −12.1, −24.8, −28.6, −23.2, −35.9, −31.3, and −40.4 mV, respectively, and these potentials dwindled with an increase in pH. The influence of nanofluids on overall heat transfer may have implications for the enhanced oil recovery effect.