Comparison of the induced flow obtained with 2D and 3D CFD simulations of a solar chimney at different width-to-gap ratios

Solar chimneys are among the most common methods for natural ventilation of buildings. Computational Fluid Dynamics (CFD) has been widely applied in research and design of solar chimneys. Most of the previous studies are based on 2D CFD models which ignore the effects of the width (the third dimension) of the air channel. In addition, the applicability of 2D models for the solar chimneys with a low width-to-gap ratio is still questionable. This study investigates both 2D and 3D CFD models for window-sized vertical solar chimneys. The 2D model is applied to the domain comprising the central plane of the channel gap ( G) and height ( H) while the 3D model is applied to the domain consisting of the channel gap, height, and width ( W). The flow fields, flow rates and thermal efficiencies computed with the 2D and 3D models at different heights, gaps, and widths are compared. The results show that W/ G is the most crucial factor. The effects of the side walls are significant at a low W/ G but gradually diminishes as W/ G increases. At W/ G = 15, the side wall effects are confined to a region of about 2.6% W. Particularly, for W/ G>8, the differences between the 2D and 3D flow rates and thermal efficiencies are within ±5%. These findings offer a reference for researchers and engineers to select between 2D and 3D CFD models for a specific solar chimney.