Study On The Optical And Thermal Characteristic Of The Flat-plate Solar Collector With A V-corrugated Absorber

Owing advantages of good security and easy combination with buildings,flat-plate solar collectors(FPCs)are increasingly applied in China year by year.In this study,a new V-corrugated absorber with multi-channels was proposed and applied in the flat-plate solar collector(VFPC).The optical and thermal characteristic of the VFPC were studied simulatedly and experimentally,and the main findings were reported as follows:(i)A new V-corrugated absorber with multi-channels was proposed and applied in the flat-plate solar collector.The absorber was extruded with aluminum and specific triangular channels were directly formed,which made the absorber own advantages of convenient processing and high reliability,and to be cost-effective.When the inlet temperature of heat transfer fluid was in the range of 33.1-69.2 oC,the thermal efficiency of the VFPC was in the range of 80.8%-42.6%.Besides,a movable cover was designed at the aperture of the glazing cover,which could be used for the overheating protection when the VFPC was overheated,and for the heat preservation when the VFPC was non-operated,and the coefficient of overheating protection and rate of heat loss reduction were-3.6 and 20.5%-34.1%,respectively.(ii)The Monte Carlo Ray Tracing(MCRT)method has been widely used in the optical simulation of solar collectors but its simulation results fluctuated in multiple runs.The influencing parameters were analyzed,which included the way of random number generation,running times,ray numbers,grid numbers and random number generation times.On these bases,an optimized MCRT method was proposed by combining the MCRT method with the iteration method,where the minimum and maximum running times were introduced.The proposed method was beneficial to mitigate the fluctuation,improve the accuracy and reduce the runtime,and it could be used for the optical simulation of various kinds of solar collectors.(iii)The dynamic thermal performance prediction models(including the quasi-dynamic test model,transfer function model and dynamic heat transfer model)for the VFPC were built.It was found that with the model building process being more complicated,the prediction results of the transient thermal performance were more accurate,while the differences in the prediction results of long-term thermal performance were slight.Furthermore,the applicability of different models in different thermal performance analysis tasks,such as the collector design,performance optimization and evaluation,were compared and summarized,which provided a theoretical basis for the selection of dynamic thermal performance prediction models.(iv)An outdoor thermal performance experimental system was built,and it was used for the test of steady-state and dynamic-state thermal performance,overheating protection and heat preservation performance of the VFPC.According to the experimental results,the thermal performance of the VFPC was analyzed,the coefficients of the dynamic test model were regressed,and the heat transfer models and dynamic test models were verified.On these bases,the thermal performance of the VFPC under different operating and environmental parameters were quantitatively evaluated,and compared with that of the sheet-and-tube flat-plate solar collector,which showed that the thermal performance of the VFPC was better.Besides,the influence of structural and physical parameters on the thermal performance of the VFPC were quantitatively evaluated,and the optimal design was conducted with the orthogonal and grey correlation analysis.Finally,taken Tianjin as an example,the annual performance of the VFPC was analyzed to offer theoretical support for its wide application.