Hydrodynamic and thermal evaluation of nanofluids for heat exchangers and solar applications
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Abstract
This doctoral research presents a thermal and hydrodynamic experimental evaluation of water-based nanofluids in a coiled flow inverter heat exchanger (CFI-HE) and solar thermal applications. Aluminum oxide (Al2O3) and titanium dioxide (TiO2) nanoparticles were used to prepare samples from 1% to 3% volume concentrations (% v/v). The experimental analysis is for laminar and turbulent flow under steady state. The performance evaluation criteria (PEC) based on the Nusselt number and the Fanning friction factor is used to evaluate the CFI-HE, multitube HE, and coiled HE. According to PEC values, the results show that all nanofluids over perform the base fluid. The 3% v/v Al2O3/H2O and TiO2/H2O water-based nanofluids achieved maximum increases of 53% and 59% under turbulent flow conditions, respectively. CFI-HE presented higher PEC values and better stability of nanofluids compare to coiled HE and multitube HE. Moreover, Nusselt number and Fanning friction factor correlations based on the experiments are proposed in this investigation.
The CFI-HE using Al2O3/H2O and TiO2/H2O water-based nanofluids was incorporated to a salt gradient solar pond (SGSP) for heat extraction, in which the thermal efficiency of the SGSP is 15% and 25% higher compared to base fluid, with 3% v/v Al2O3/H2O and TiO2/H2O, respectively. Furthermore, Al2O3/H2O nanofluids were evaluated in a parabolic trough solar collector (PTSC) and the maximum efficiency was obtained for Al2O3/H2O 1% v/v reaching to 58% at the smallest incidence angle, finding that the efficiency had a strong dependence on the incidence angle. Long-term stability of nanofluids, lowering the cost of manufacturing nanoparticles, and optimizing operational parameters are areas of opportunity that require attention to obtain high-potential nanofluids. It is conclusive that, thermal and hydrodynamics results for heat exchange and solar thermal applications demonstrates the strength of nanofluids to enhance the performance in heat transfer applications.