Thermal and power performance analysis for heat transfer applications of nanofluids in flows around cylinder

Nanofluids are fluid suspensions of nanoparticles and extensive studies have been conducted on nano fluid applications in heat transfer processes. In this paper, we examine the thermal and power performances of nanofluid flows around a circular cylinder using empirical relations, and compare them to those from the flowrate approach, by which the flowrate of the base fluid is increased to improve the heat transfer efficiency. A critical concentration is defined to separate the favorability of nanofluid and flow rate approaches. The maximum thermal efficiency state for nanofluids with particle concentration higher than the critical concentration should not be pursued, since the simple flowrate approach can serve the thermal improvement purpose better at the same power consumption as the nanofluid approach. Effects of nanoparticle size, concentration, material properties, temperature, and flow Reynolds number are also investigated. Our results suggest that the application of nanofluids in the heat transfer systems studied here is more preferable in low Reynolds number and high temperature situations with finer nanoparticles. By comparing the performances of CuO and Al2O3 nanofluids, we find that the nanoparticle density plays a more significant role than the thermal conductivity in determine the thermal performances. In spite of the simplicity of the model and methods used here, this study reviews further the complexity of nanofluid behaviors, and caution should be executed when considering nanofluids for heat applications. The nanofluid vs. flowrate assessment criterion and the results and analysis could also be useful for nanofluid design and applications. (C) 2016 Elsevier Ltd. All rights reserved.