Simulations and experiments of heat loss from a parabolic trough absorber tube over a range of pressures and gas compositions in the vacuum chamber

A new simulation tool aimed at characterizing the thermal behavior of parabolic trough collectors over a wide range of pressures and gas mixtures in the vacuum chamber is presented in this study. The model is able to accurately predict overall efficiency and heat losses obtained in a number of experimental sources based on both on-sun and off-sun testing, with vacuum in the annulus and no hydrogen. Excellent agreement of the simulations with experiments including different gas compositions, especially with high hydrogen concentrations, is achieved through the use of molecular dynamics results for the determination of the accommodation coefficient of the mixture. Additional experiments were carried out to validate the accuracy of the model over a range of pressures between 10-4 and 130 mbar. The accurate modelling of rarefied gas dynamics presented here also leads to an excellent agreement between simulations and experiments over the whole pressure range. An accurate determination of the performance in such extreme conditions is critical for an adequate Operation & Maintenance strategy, as well as the development of effective predictive and preventives plans.
QC 20160519