Exergy analysis of parabolic trough solar collectors using Al_2O_3/synthetic oil nanofluid

摘要

Parabolic trough solar collector (PTC) is one of the most mature and widely used type of solar energy harnessing devices. Therefore, investigation of the effect of various operational conditions on the overall efficiency of these devices has been topic of substantial interest in the recent decade. Moreover, utilization of nanoparticles as a useful additive to the working fluid should be examined thoroughly to optimize the collector's outputs.To do so, in the present study, energy and exergy efficiencies of a typical PTC as a function of several involving parameters are numerically calculated. These parameters are nanoparticle volume fraction (from 0 to 5 percent), environment wind speed (from still air to speed of 10 m/s) and the normalized HTF's inlet temperature.It was seen that the thermal efficiency is reduced by increasing the HTF inlet temperature, but the exergy efficiency variations have a different behavior compared to the thermal efficiency. Also, the negative effect of the higher inlet temperatures in decreasing the efficiency is more obvious for the higher NP volume fractions. For no wind condition, the maximum reduction of the thermal efficiency is about 10% for the highest HTF inlet temperature with 5% of NP volume fraction and this value is minimum (3%) for the lowest inlet temperature for the pure base fluid. As the wind speed increases, the variation trends of both exergy and thermal efficiencies remain almost the same. According to the results, for the highest simulated wind speed (at 10 m/s), the thermal efficiency reduction in comparison to the still air case is between 7% (for pure fluid at lowest inlet temperature) and 22% (for HTF with %5 NPs volume fraction content at highest simulated temperature). Also, addition of 5% nanoparticles will increase the relative exergy efficiency about 19%.