Aims: This study focused on investigating the thermal behaviour of a water-in-glass evacuated solar heater experimentally and numerically. Study Design: The study was carried out in three parts: numerical modelling, experimentation and validation of the numerical modelling results. Place and Duration of Study: The study was carried out in six month at Thermophysics Institute of Northeastern University in Shenyang, China. Methodology: A lab-scale experimental model was developed using two full scale evacuated tubes inclined 45° to the vertical and coupled to a rectangular water storage tank. Thermo resistors were connected to multi-channel data logger to record both spatial and temporal temperature distribution of the system. A three-dimensional numerical model was developed using a Computational Fluid Dynamics (CFD) package, Fluent 6.1 to investigate temperature and flow fields. This model interprets exactly the geometry of the lab-scale experimental model so that it can be validated against experimental results. A user defined function was developed to take into account the variation of incident angle with daily and seasonal movement of the sun which affects the amount of heat flux incident on the tube collector. Results: The numerical model showed that flow in the tube is bi-filamental with the hot stream moving up the tube on the top side and the cold stream moving down the tube from the storage tank on the lower side. It also showed that the maximum temperature reached by the water in the system depends upon the amount of incident radiation. Conclusion: The numerical model can be used for predicting temperatures in the water-in-glass solar water heaters.
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