INVESTIGATION ON THE EFFECT OF THE CHIMNEY CUP ON THE NATURAL UPWARD DRAFTING

Increasing interest is obvious nowadays on natural ventilation system which has been left out since 1970s due to the development of the mechanical ventilation systems. The potential benefits in terms of operational cost, energy requirement and carbon dioxide emission have raised more interest than ever in the passive ventilation systems. A significant amount of research work has been done on the solar chimney since the 1990s. Most of the studies focused on the effects of geometry and inclination angle on the ventilation performance of a solar chimney. Computational Fluid Dynamics (CFD) technique, which has been adopted as investigation tool in the present research, has also attracted considerable amount of interest due to the ability to compute numerical modeling of solar chimney. However, published studies showed that the natural passive ventilation has not been fully understood. The understanding is that the drafting force of the chimney is mainly due to the wind velocity at the top of the chimney and the thermal gradient. The geometry of the chimney cup could be another factor in creating a greater upward drafting force; hence, four different cup configurations have been investigated.
In addition to the CFD analysis, an experiment set up has been designed, fabricated and used to investigate different geometries of chimney cup in order to find out the optimum design conditions. The CFD analysis using ANSYS- FLUENT version 14 software has been validated by comparing with the experimental measurements. Some cases have shown large discrepancy and it is contributed to the measuring instrument installation. In many cases, reasonable agreement was achieved. Increased outlet surface of the chimney cup showed a decrease in the outlet pressure and thus resulted in greater pressure difference, and eventually a greater upward drafting force or higher air flow velocity.