Modelling and optimization of transparent parabolic trough collector based on gas-phase nanofluids

The Parabolic Trough Collector (PTC) is the most common type of high-temperature solar thermal technology, in which the heat transfer fluid is usually synthetic oil, molten salt or water/steam. Experiences in existing plants have shown some operating problems with all these types of fluid, which limit solar to thermal efficiency and increase power plant costs. To solve such constraints an innovative solar Transparent Parabolic Through Collector (TPTC) working with gas-based nanofluid has been proposed and investigated in the present paper. Transparent receivers combined with gas-based nanofluids were found to be able to directly adsorb solar radiation due to the very high total surface of nanoparticles. The use of directly radiated nanoparticles allows compensating the relatively low heat transfer coefficient typical of gaseous heat transfer fluids with an increase of the exchange surface. Yet to allow a complete absorption of the solar energy within the transparent receiver tube a proper mixture of CuO and Ni nanoparticles has been designed. The proposed solar collector has been modelled by means of a discretized in space model to simplify the description of the behaviour of the physical system under the assumptions of quasi steady state conditions. The above-mentioned model has then been used to run an optimization procedure to define the main geometrical and operational parameters of the TPTC. Simulations have shown that the maximum TPTC solar to thermal efficiency is 62.5%, for a nanofluid outlet temperature of 650 degrees C and a nanoparticles volume concentration of 0.3%. (C) 2013 Elsevier Ltd. All rights reserved.