Effects of Design Parameters on the Fluid Flow and the Efficiency of Single Ended Evacuated Tubular Solar Thermal Collectors via FEM Modelling and Experimentation

This work is about assessment of the single-ended evacuated tubular solar thermal collectors which are widely used in solar heating applications. Exchange and transfer of heat are accomplished by a thermosyphon process. The flow pattern of the working fluid within the collector is determined by a combination of gravity forces and the fluid's buoyancy forces which are due to varying density at varying temperature. This paper reports on a finite element method (FEM) based numerical study of the dependence of the working fluid flow pattern on the collector's design parameters such as inclination angles and collector length-to-diameter ratio. This fluid flow pattern determines the heat exchange between the working fluid and the selective coating and thus the efficiency of the collector. A model of this process has been implemented in a simulator built via COMSOL FEM software package. A physical solar water heating system made with five commercial evacuated tubular collectors was also built and tested to verify the simulation results. Public access to the simulator is provided here