A CFD study of air leakage through door assemblies for smoke control
煙氣控制中門組件遮煙性的 CFD 研究
Student thesis: Master's Thesis
Many building codes stipulate the need for the fire-rated doors to be closely fitted around their edges to impede the passage of smoke and flame. To ensure the smooth opening of the doors, gaps between the door panels and the walls and floor cannot be totally eliminated. Depending on the country where the building code is enforced, the maximum permissible door gap requirement varies substantially. The presence of these gaps permits the passage of large amount of smoke. With the increased attention now being given to the design of buildings to control smoke movement and to maintain smoke-free areas of refuge, better information on the flow of air and smoke-air mixtures through closed door assemblies is needed. The quantitative leakage data would aid in understanding the effectiveness of interior doors as barriers to smoke flow and the prediction of untenable condition in building fire safety engineering design. There are many studies on the leakage performance of door assemblies. However, most of them were the record of test procedure and result data, according to the standard test methods, aiming to rate the door’s capacity of preventing smoke. Only limited theoretical and numerical studies have been conducted. This paper made an attempt to reproduce the experiments of leakage test using CFD method, and thereby with the aid of CFD to investigate the influence of pressure difference and dimensions of door gap on the leakage flow rate. Several models were selected to carry out simulations. The Shear Stress Transport (SST) model exhibited good performance on the prediction of the fluid field. Compared to the theoretical quadratic equation, the simulation results showed a better approximation to the previous experimental data. The inherent inaccuracy of theoretical quadratic equation tended to under-estimate the leakage flow rate. Then a series of simulation were performed in respect of doors with different geometries, which were widely used in the construction of buildings. The computed results indicated that the leakage flow rate increased with the increase of gap height, but decreased with the growth of gap depth. The flow per unit width through a gap of width was independent of gap width. The leakage flow rate was found to be strongly influenced by the height of gap. It was not sensitive to the change of width of the door panel. The mathematic derivation verified the relationship between the flow rate and with of the door panel. Finally, curves were fitted to the data using regression analysis. The mathematic properties of the relationship between leakage flow rate and the pressure difference was described using quadratic and power law equations. The coefficients of regression fits were summarized in a table, to facilitate the prediction of leakage flow rate through door assemblies.
- Smoke prevention, Fire doors