Coupled optical and thermal analyses of a new type of solar water heaters using parabolic trough reflectors

Abstract

A new type of solar water heating system using an array of parabolic trough collectors (PTCs) was investigated. A coupled simulation technique was used to solve the complex radiation, convection, and conduction heat transfer problem inside the system. The realistic non-uniform heat flux at the walls of the receiver pipe was obtained by optical analysis and was used simultaneously in thermal modeling. A comprehensive model by considering thermal losses under the non-uniformity of heat flux was proposed and verified with experimental data. In the experiments, the water with different inlet temperatures and flow rates was tested. The obtained results demonstrate that the location of the receiver pipe relative to the PTCs significantly affects the system's thermal efficiency. For the system under study, the best position of the absorber pipe was found at the d/f ratio of 0.8. At the optimal position of absorber pipe, the average daily system's thermal efficiency is about 70%, and for an absorber pipe located at the focal line of the collectors, it is less than 60%. It can be concluded that the thermal efficiency of the current system is higher than that of conventional systems under the same conditions.