CFD study of fluid flow in an all-glass evacuated tube solar water heater
Ai Ning1, Fan Jianhua2, Li Yumin3*
1. College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310032, China;
2. Dept. of Civil Engineering,Technical University of Denmark, Copenhagen;
3. College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310032, China
The all-glass evacuated tube solar water heater is one of the most widely used solar thermal technologies. The aim of the paper is to investigate fluid flow in the solar water heater by means of the computational fluid dynamics (CFD). The investigation was carried out with a focus on the convective heat transfer in the tube. The buoyancy induced flow circulation in different parts of the tube was analyzed. It is shown that fluid flow becomes stochastic and turbulent if fluid temperature is high enough. The flow instability leads to mixing of the warm uprising flow and the cold downward flow, which decreases efficiency of the heat exchange process. A baffle in the tube can prevent the flow instability and secure the flow circulation in the tube. The results of the investigation provide a helpful guidance for further investigation of the mechanism of heat transfer processes and a reference for future system optimization.