Search

Heat transfer enhancement in thermal systems is one of the most important efforts of researchers. Adding nanoparticles to circulating fluid is an effective way to increase the heat transfer rate, while its effect on pressure drop may be positive or negative in various cases. In this paper, both thermal and hydrodynamic aspects of flowing a TiO2/water nanofluid were considered with concentrations of 0.05, 0.1, 0.2, 0.5, and 1 mass percentages. The nanofluid was streamed through a helical coiled path, under a constant heat flux and different flow rates. The thermal characteristics are followed by calculations of Nusselt number (Nu), convective heat transfer coefficient, and heat transfer enhancement (HTE%). Accordingly, the utmost increase in Nusselt number was found as 29.8 and 36.5% for the concentration of 1 mass%, in laminar and turbulent flows, respectively. The pressure drop was assessed by means of friction factor and drag reduction percentage (DR%), so that in the lowest concentration and the lowest Reynolds number, the maximum DR% occurred as 6.4%. To have a better understanding of the system, the pumping power is reported against HTE% amounts. [ABSTRACT FROM AUTHOR]

Nowadays, photovoltaic technology has been recognized as a popular energy source in most parts of the world. The temperature rise in photovoltaic cells is one of the major weak points of this technology which impacts on its electricity generation. Using nanofluid circulation as the coolant of photovoltaic modules, is one of the methods concerned by scholars. In this paper, using carbon black nano particles in water was investigated experimentally, and the concentration range of 0–0.4 wt% were tested. Results showed an unexpected cooling behavior of carbon black/water nanofluid. So that, the concentration of 0.21 wt% was found to be the best case. This concentration led to produce 7% more output power in comparison with pure water as coolant and 54% more output power in compare with the conventional photovoltaic module. In order to precisely calculate the electrical energy efficiency, the consumed pumping power was considered, too. The exergy assessment is another investigated matter in this paper and a modified method for exergy efficiency calculation is presented. Accordingly, the overall exergy efficiency rises 15.2% and the entropy generation depresses 1.4% compared with the conventional module, for the best case. [ABSTRACT FROM AUTHOR]