Evacuated Tube Collectors - Influence of thermophysical properties in numerical simulations by CFD

Solar liquid heating systems using evacuated tube collectors currently have a better performance than flat plate collectors for high temperature operation. This is due to reduced heat losses by convection, as a result of the vacuum layer over the inner tube. The solar collectors with vacuum tubes are a novelty in Brazil, in addition, its use on a commercial scale is less than 10 years and there are many questions to be answered about their use and efficiency. To get a better understanding of the operation of this equipment, it has started a program of study through a collaboration between the NETE - UNISINOS (Study Center Thermal and Energy of University of Vale do Rio dos Sinos) and LABSOL-UFRGS (Solar Energy Laboratory of Federal University of Rio Grande do Sul). The methodology consists in the numerical simulation by CFD (Computer Fluid Dynamics) and validate the methodology through numerical and experimental results. The results of velocity fields and mean temperature indicate that the methodology is quite adequate.