Heat Transfer Fluids

The choice of heat transfer fluids has significant effects on the performance, cost and reliability of solar thermal systems.In this chapter, we evaluate existing heat transfer fluids such as oils and molten salts based on a new figure of merit capturing the combined effects of thermal storage capacity, convective heat transfer characteristics and hydraulic performance of the fluids.Thermal stability, freezing point and safety issues are also discussed.Through a comparative analysis, we examine alternative options for solar thermal heat transfer fluids including watersteam mixtures (direct steam), ionic liquids/melts and suspensions of nanoparticles (nanofluids), focusing on the benefits and technical challenges.