An analytical model of heat and mass transfer through non-adiabatic high-rise shafts during fires

Abstract

Fire protection in high-rise buildings requires a good understanding of the physics of smoke spread so that control measures can be properly undertaken. The problem is often complicated by the coupled heat and mass transfer phenomena, especially when smoke spread through vertical shafts far from a fire origin. Numerical analysis is often challenging due to limited computer resources for such large structures. This study aims to develop an analytical model of the smoke movement through a high-rise shaft under two ventilation conditions: the shaft with a given constant smoke flow rate, and with the smoke purely driven by stack effect. A hand-calculation procedure is proposed to obtain the solution to the analytical model, and demonstrated in a case of a 40-storey building with a fire located at the 1st floor. The accuracy of the analytical model is confirmed by comparisons to a numerical simulation and three experiments in the literature. It was found that the calculated profiles of smoke temperatures and shaft wall temperatures depend on the temperature attenuation coefficient α, a non-dimensional parameter associated with the geometrical and thermal properties of the smoke and the shaft. The analytical solutions of the smoke temperatures and smoke flow rates were plotted at different fire floor temperatures in non-dimensional forms, which can be used for the design of shaft smoke controls. The effect of radiation heat transfer on the calculation results was also discussed through a sensitivity study of the analytical model. It was found that the calculated smoke and shaft wall temperatures seem not quite sensitive to the radiation heat transfer in the case being studied.