Thermal-hydraulic and thermodynamic performances of liquid metal based nanofluid in parabolic trough solar receiver tube

Abstract

Parabolic trough collectors (PTCs) are widely applied in concentrated solar energy utilization, and the further improvement of PTC's efficiency is usually restricted by heat transfer performance of parabolic trough solar receiver (PTR) tube. With the aim to enhance the heat transfer performance of PTR tube, liquid metal based nanofluid (i.e. the suspension of nano-scale powders in liquid metal) is proposed as working fluid due to its superior thermal transport properties. The thermal-hydraulic and thermodynamic performances of two types of liquid metal based nanofluids including gallium (Ga)-copper (Cu) and Ga-carbon nanotube (CNT) in PTR tube are numerically investigated. Monte Carlo Ray-Trace Method is used to obtain actual distribution of non-uniform heat flux on receiver tube wall, and four parameter turbulence model is adopted considering the low Prandtl number of liquid metal based nanofluid. The numerical method is validated by the experimental data. The results show that the presence of Cu and CNT can enhance the forced convection heat transfer of pure Ga in PTR tube, and the average enhancement degrees can reach up to 34.5% and 45.2% respectively under present conditions. Also, the frictional pressure drops of Ga–Cu and Ga-CNT nanofluids are larger than that of pure Ga at the same Reynolds number. With the increase of nano-powder concentration, the total entropy generation decreases and the exergetic efficiency increases. The thermodynamic performance of Ga-CNT nanofluid is better than that of Ga–Cu nanofluid under the same condition.