Steady state hydrothermal analysis of the absorber tubes used in Linear Fresnel Reflector solar thermal system

Linear Fresnel Reflector (LFR) solar thermal system is a promising technology in solar thermal applications. In LFR system, parallel absorber tubes (usually 8–16) are located inside a trapezoidal cavity, which receives reflected solar flux from the mirrors situated below it. The fluid (usually water) inside the tubes undergoes phase change due to the incident solar flux. The focus of this paper is to carry out hydrothermal analysis in an absorber tube of a Linear Fresnel Reflector (LFR) solar thermal system. In the present work, a generic methodology to deal with steady state hydrothermal analysis of the absorber tubes has been discussed. The single phase regions as well as the two-phase region of the absorber tube have been analyzed. A one dimensional model has been used for the analysis for both the regions. In the two-phase region analysis is carried out under the assumption that the homogeneous equilibrium model is valid. For this hydrothermal analysis, the radiative and convective heat losses from the surface of the tube to the atmosphere are obviously needed. To obtain the heat losses, the computational analysis of the heat transfer in the trapezoidal cavity is carried out. The present model can be used to predict the variation of bulk fluid temperature, variation of heat transfer coefficient, pressure loss along the length under different mass flux and different solar flux, in single phase region. Similarly, variation of dryness fraction, local boiling two phase flow coefficient, and total pressure drop can be predicted for two phase region. This model can be used to understand and design for a better LFR system.

► 1D model has been used for hydrothermal analysis in LFR absorber tubes.
► Variable net heat flux has been considered for this hydrothermal analysis in the tubes.
► CFD model of cavity is used to estimate heat losses from the absorber tube.