Research On The Influence Of Spiral And Sinusoidal Corrugation Characteristics On The Performance Of Parabolic Trough Solar Collector

Solar energy has gradually become the most valuable energy source,in the context of sustainable development in modern society.Parabolic trough solar collectors(PTC)has broad prospects for the development of solar thermal applications due to its simple structure,safety and high reliability.However,the low energy density of solar energy limits the operating efficiency of the collector and restricts further engineering application.Aiming at the problem of low conversion efficiency of the collector,this paper uses numerical calculation methods to study the heat transfer and flow characteristics of heat transfer fluid in the collector.From the perspective of changing the surface structure of absorber tube,the collector was optimized and the effect of spiral characteristics and sinusoidal-corrugation characteristics on the collector performance was explored.Firstly,the physical model of parabolic trough solar collector was established,and the finite volume method(FVM)was used to numerically calculate the flow and heat transfer process of the fluid in collector.The temperature and turbulent kinetic energy distribution were analyzed and the influence of operating conditions on the flow and heat transfer characteristics of fluid.The defined parameters mainly include the average Nu,Nu_x/Nu_s,the friction factor f,and the system comprehensive heat transfer factorη.Secondly,in order to effectively promote the overall performance of the parabolic trough solar collector,the helically corrugated tube and sinusoidal corrugated tube with a sine curve as the corrugated profile have been established successively.Compared with traditional smooth absorber tube,the flow and heat transfer characteristics of the fluid in the two new absorber tubes are studied and the mechanism of the influence of the new structures on the collector performance was explored.Moreover,the influence of various structural parameters of the heat absorption tube on the comprehensive heat transfer performance of the system is considered.For helically corrugated tube,increasing the corrugation height,reducing the corrugation spacing and reducing the fillet radius can simultaneously rise the heat transfer performance and flow resistance of the working fluid,and then affects the overall performance of the system.Taking the change of corrugation height as an example,when the corrugation height is increased from 2mm to 5mm,the maximum heat transfer enhancement effect rises from 17%to 19.3%,and the friction factor increases from 21.6%to 70.9%.The maximum comprehensive heat transfer factor obtained by changing the corrugation height and the flow Re is 1.32.For the sinusoidal corrugated absorber tube,the comprehensive heat transfer performance is increased by 35%at most compared with the smooth tube within the parameter range of this study.Finally,the heat transfer and flow characteristics of the fluid in the two enhanced tubes were compared with those of ordinary corrugated tube.The helically corrugated tube with any flow condition has a better effect of enhancing the heat transfer of the fluid,but the energy loss caused by the flow resistance is obvious.The sinusoidal feature has relatively little improvement in heat transfer effect but can maintain low flow resistance.In order to obtain higher heat transfer performance while suppressing the increase of flow resistance,a helically sinusoidal corrugated tube combining the structural characteristics of spiral and sinusoidal corrugation was established,and a parametric analyzes of the performance was carried out.For the helically sinusoidal corrugated absorber tube,decreasing the sine amplitude,increasing the period of sine curve,increasing the corrugation spacing and increasing the fillet radius have a positive impact improving the overall performance.For example,when the corrugation spacing is 70mm,100mm,and 130mm,the comprehensive heat transfer factors are 1.09,1.162,and 1.214 respectively with the condition of Re=43200.That is,the comprehensive performance of the system rises with the increase of the pitch.The maximum comprehensive heat transfer factors obtained by varying the structural parameters are 1.298,1.235,1.238 and 1.23,respectively.