Evaluation of Heat Flux Distribution Uniformity around the Receiver Tube of Parabolic Trough Collector based on Six Statistical and Geometrical Indices

摘要

In addition to the total amount of heat flux (HF), its distribution around the receiver tube has an outstanding effect on the outlet temperature (T_0) and thermal efficiency (ηth) of parabolic trough collectors (PTCs). According to former researches, whatever the heat flux around the receiver tube is more uniform, the collector efficiency increases. But no index has yet been provided for the evaluation of HF distribution. In this paper, the quality of HF distribution around the receiver tube of LS-3 PTC is investigated by definition of six statistical and geometrical indices, including S.D, A.E, Int, Avg, Ust, and Bst. To investigate these indices, first, the HF around the receiver tube should be varied by the change of focal length (f) and using Compound Parabolic Concentrator (CPC). Second, the above-mentioned indices are calculated based on the statistical formulations. Third, the receiver tubes affected by the miscellaneous HF distributions (as boundary conditions) are simulated using one validated numerical method. Finally, the correlations between the specified indices and T_0 are investigated. According to the results, the index of Int indicates the number of sun rays hit on the receiver tube. Thus this index can represent optical efficiency η_(opt)). Also, the inverse of both Ust and Bst parameters are introduced as the indices of uniform HF around the receiving tube. In other words, the statistical and circumferential uniformities of HF values are two effective parameters in the definition of the HF uniformity. Meanwhile, the regression expresses the effect of Ust is 84 times more than Bst on T_0 and ηth. Also, the overall efficiency can increase up to 2.61% using the CPC-type reflector.