3D Thermal-structural Analysis of an Absorber Tube of a Parabolic Trough Collector and the Effect of Tube Deflection on Optical Efficiency

Abstract

In this paper deformation rate of an absorber tube of a parabolic trough collector due to a 3D solar flux density distribution is studied theoretically. Three dimensional temperature distribution and tube thermal expansion due to non-uniform solar flux over the tube are determined numerically. The local concentration ratio for the parabolic trough collectors, which is a key boundary condition in the thermal analysis is computed by Monte Carlo Ray Tracing method for different conditions. The governing equations of thermo-elastic constitutive are solved in three dimensions for steady state thermal and static structural analysis with appropriate boundary condition using Finite Volume and Finite Element numerical codes. Thermal stresses and strain are determined for two types of collectors; first one is a constructed collector and second one is under construction at Shiraz (Iran) solar thermal power plant. Results of the local concentration ratio, flux density, temperature distribution and thermal expansions are determined for the designed conditions. Appropriate flow rate and convection coefficient for each season are found in order to decrease tube bending, prevent optical efficiency drop of collectors, keep high factor of safety, and reduce cyclic daily amplitude motion which lead to longer life time of absorber tube.