Numerical Investigation Of Heat Transfer And Fluid Flow In A Solar Air Heater Duct With Multi V-shaped Rib With Non-contour On The Absorber Plate

In recent years, haze phenomena all over the country raises energy concerns. The positive development and utilization of renewable clean energy is the most effective way to improve the current environmental problems. Solar air collector is the basic tool to convert solar energy into thermal energy and it is widely used in all fields of our life. Absorber plate is the main structure of solar collector and setting the ribs on it can enhance heat transfer. The rib structure has a great impact on the photo-thermal conversion efficiency, therefore optimize the rib structure is an important way to improve the efficiency of solar energy utilization.In this dissertation, V-shaped ribs with non-contour on solar collector are chosen for the research object. Numerical simulation is used to analyze the heat transfer and flow characteristics. Meshing the model, grid quality and independence checks, and the effectiveness analysis are conducted for the numerical simulation. When Reynolds number ranges from 7000 to 16000, the impacts of rib shapes e1-e2-e1(e1 is the height of front rib, e2 is the height of end rib), rib pitch(P), angle of attack (a) and relative width ratio (W/w) on the Nu number, friction factor, and thermo performance factor of the solar collector are studied and analyzed.In the study of heat transfer characteristics, the comparison between non-contoured ribs with contoured ribs of different shapes shows that the maximum value of thermo performance factor occurs when the non-contoured rib shape e1-e2-e1 is 1-3-1. Thermo performance factor decreases with the increase of rib pitch p and the maximum value of thermo performance factor occurs for P=mm. Thermo performance factor decreases with the increase of rib inclination angle a, and the maximum value of thermo performance factor occurs for a=30° while the least value occurs for a=75°. Thermo performance factor decreases first and then increases with the increase of relative width ratio W/w, and the maximum value of thermo performance factor occurs for W/w=6 while the least value occurs for W/w=2.Rib structure determines the fluid flow which has an influence on the heat transfer effect. In the study of the flow characteristics, compared with different rib shapes, it shows that a lower height of front rib allows fluid more easily across the rib. On the one hand, it can develop vertexes with small diameter and high turbulence intensity. On the other hand, it can have an intense impingement on the leeward wall area and the next upwind area of the rib. Therefore, the heat transfer coefficient is enhanced. The number of times of mainstream cold fluid contact with the thermal fluid near the heating surface increase and the cold and hot fluid mixing more uniformity when the angle of attack and rib pitch is small. At the same time, The vortex diameter is small, but the turbulence intensity is high. Therefore, the heat transfer efficiency is improved.