Heat Transfer And Flow Research Of Internally Pin-finned Parabolic Trough Collector

The outer wall of an operated parabolic trough solar collector(PTC)tube is heated in the circumferential direction by the non-uniform solar heat flux,the resulting thermal strain may cause the collector tube to fail.Pin-fin array is a commonly used heat transfer enhancement structure,but relevant research about its application on PTC tube is few.In order to reduce the failure of collector tube,the pin-fin array is introduced into the inner surface of the collector tube to achieve the effects of enhancing the heat transfer and homogenizing the temperature field.The main research method is numerical simulation.Firstly,the pre-processing of simulation calculation is introduced,including the research object selection,meshing and grid independence analysis.Then the calculation settings of numerical simulation are verified,mainly including the standard k-?turbulence model simulating the heat transfer oil flow in the collector tube and the composite thermal boundary conditions imposed on the outer wall of collector tube.Based on previous work,the effects of Reynolds number,section shape and height-to-diameter ratio of pin-fin element and row number on the flow performance,heat transfer performance,heat transfer enhancement performance and circumferential section temperature difference of PTC tube are studied.The following conclusions are obtained:(1)the standard k-?turbulence model and the composite thermal boundary conditions can simulate the flow and heat transfer of the collector tube respectively.Further,the Reynolds number,the long axis to short axis ratio and the height-to-diameter ratio of the pin-fin element have a great influence on the flow performance,heat transfer performance,heat transfer enhancement and circumferential section temperature difference of the collector tube while the row number of pin-fin array has little effect.(2)In the current research context,one pin-fin array structure with good comprehensive performance is obtained through the study of this paper:the pin-fin element has an elliptical section with a long axis to short axis ratio of 2.56 and has a height-to-diameter ratio of 2,the array has five rows and the five elements of each row are distributed uniformly on the absorber tube lower section part whose circumferential angle varies from-135°to-45°.When the Reynolds number increases from 1.40?10~5 to7.67?10~5,compared to smooth PTC,the circumferential temperature difference of the absorber tube of the PTC inserted with the mentioned above pin-fin array is decreased by8.60%~17.57%,the range of the corresponding Nusselt number increment and pressure drop increment are 4.15%~41.26%,41.27%~92.73%respectively,and the heat transfer enhancement factor ranges from 0.92 to 1.14.