Thermal performance evaluation and enhancement of a parabolic trough collector

Abstract

In this article, the effect of concentration technology on the thermal performance of a solar water heating system is investigated. A three-dimensional numerical simulation of a parabolic trough collector (PTC) is carried out using the commercial software ANSYS. The performance of a line-focus concentration system is compared to that of an integrated collector storage solar water heater. The PTC provides more useful heat but has higher nighttime thermal losses. It is proposed to reduce nighttime energy loss by insulating the PTC storage tank. The effects of the insulation coverage strategy and medium are discussed. Numerical results show that the thermal insulation material significantly influences heat transfer. Indeed, addition of glass wool reduces heat collection during the day and improves heat preservation at night, while adding an air-filled glass tube increases heat transfer during the day and reduces nighttime thermal losses. The effect of tank insulation coverage is also investigated. This solar system performs best when the upper half of the tank is insulated. The maximum water temperature is 360.5 K, the overall thermal loss coefficient is 9.38 W/m2 K, and the nighttime thermal loss coefficient is 6.2 W/m K. The optimum PTC configuration is one in which the upper half of the tank is insulated by a 0.01 m-thick layer of air that is held in place by glass. This optimized system provides 29% more useful heat, a lower overall heat loss coefficient of 14.9%, and a lower nighttime heat loss coefficient of 62% than the non-insulated-tank-based PTC.