Investigation Of The Optical And Thermal Performance Of Parabolic Trough Collectors With The Novel Cavity Receiver

This paper proposed a novel cavity receiver for parabolic trough collectors.Based on the in-depth investigation of the optical and heat transfer models,the optical and thermal performance of parabolic trough collectors with the novel cavity receiver were studied by combination of theoretical modeling and experimental research,the details were as follows:(1)Due to the deficiencies of a single optical model,four different optical models were established in this paper based on the ray tracing method,combined with the Monte Carlo method,finite volume method,and change photon energy method in the optical simulation.The running time,computation effort,fluctuation of the results,etc.of the four optical models were compared quantitatively.On the basis of the comparison and summary,a novel optical simulation algorithm was presented,combining the advantages of different optical models.It was suited to carrying out a mass of optical simulations in the process of optical design and optimization accurately and rapidly.(2)Due to the shortage of quantitative comparison and applicability analysis of heat transfer models with different complexities for parabolic trough collectors,the simulated values of models with different complexities and experimental results were compared in this paper.It was concluded that the accuracies of one-dimensional and three-dimensional heat transfer model both could meet the requirement of the engineering calculation if the outlet temperature was required to be calculated to evaluate its thermal performance of the parabolic trough collectors.Furthermore,the applicabilities of different heat transfer models in collector design,optimization,performance evaluation,etc.were presented,according to the modeling processes and characteristics of simulation results of the models with different complexities,which provided the theoretical basis for the heat transfer models selection.(3)A novel cavity receiver for the parabolic trough collectors was proposed.A single tube was adopted as the heat transfer fluid flow channel,which could withstand the high pressure.It was convenient to connect in series and with the system pipeline.The absorber consisted of a center tube and two inclined fins.The insulation materials were filled between the absorber and the shell,and a glass plate was covered on the cavity aperture to reduce the heat loss.A movable cover was designed at the cavity aperture creatively,which could be used for reducing the heat loss effectively under non-collecting solar energy conditions.The heat loss reduction rate was 6.36%～13.55%under the same environmental conditions if it was turned off.Additionally,it could be used for overheating protection when the system was overheated.Its optical performance was analyzed qualitatively and quantitatively.The orthogonal test was applied to investigate the heat loss of the cavity receiver.(4)A thermal performance test system of parabolic trough collectors was built.The heat loss test,collector efficiency test of continuously tracking the sun around two axes and horizontal east-west axis,and overheating protection test were performed for parabolic trough collectors with the proposed novel cavity receiver.The thermal performance of the collector was evaluated and the heat transfer models were validated by the test results.On this basis,the effects of the environmental and physical parameters on the thermal performance of the collector were investigated.The annual thermal performance of the collector was simulated in different climatic regions according to solar energy distribution and building thermal design in China.