Research On Natural Smoke Exhaust Technology In Thin And Tall Atriums

With the growing atriums in building construction,the research on atrium smoke control has highlighted its importance.When the fire occurs in an atrium,the burning fuel source provides the initial upward force for the plume,and the smoke spreads inside the atrium due to buoyancy force.The thermal barrier effect is formed when the temperature of the upper atrium is higher than that in the lower region.The early stage of the fire is influenced by the thermal barrier effect,which the rising speed of the plume flow is postponed,causing the time of detection of the smoke to be later than the scheduled time.With the fire grow,the influence of thermal barrier effect is gradually weakened.At the same time,the temperature inside the atrium keeps rising,causing the temperature difference to increase gradually between inside and outside the building,due to which the chimney effect will enlarge as well.The chimney effect inside buildings will accelerate the diffusion rate of smoke,and the rational use of stack effect will be conducive to the discharge of smoke.At present,a small size model,such as a shaft,is used as a research object for the study of the smoke spread.The verification test of the theoretical model is only in a small size building structure,and the correction coefficient is also based on these experimental results.When it comes to a large-scale building structure,such as the atrium,the cold wall will let the smoke settle down,and the axial plume will be rewinding and rising again at a certain height,so the plume temperature is not only different in the vertical direction,but also in the same plane.There is a certain difference between the movement of smoke diffusion in the atrium and the shaft.In this case,whether the correction coefficient of the theoretical formula is still the same,whether the existing research results can be directly applied to the atrium is still doubtful.Therefore,the spread characteristics of the large-scale interior buoyancy plume mainly studied in this paper are discussed in this field.It is hoped that this study can not only verify the applicability of the theoretical results,but also give a valuable reference method in the design of the atrium smoke exhaust.From the basic conservation formula,this paper derives the equation for the axial temperature rise,the axial velocity,the diffusion radius of the plume and the maximum rising height in the stable thermal stratification.Environmental factor is proposed novelty to reflect the the thermal barrier effect,the chimney effect,the atrium shape.Innovatively put forward the coefficient of fire source to reflect the combustion characteristics synthetically.To analyze the influence of different boundary conditions on the environmental coefficient and the fire coefficient,hot smoke test was carried out inside the atrium of a hotel building and the numerical simulation of the computational fluid dynamics was carried out as well.Through the hot smoke test and computational simulation,it is proved that the theoretical model is applicable to plume spreading.The simulation results confirm that the theoretical model is also applicable to the calculation of natural smoke exhaust.The effects of six factors,such as temperature difference in indoor and outdoor,the area of vent,the size of the atrium,the shape of the atrium,the temperature gradient inside the atrium and the power of the fire source,are discussed respectively,from which the influence of variables on the coefficient is obtained.The atrium with a shape ratio of less than 0.1 is defined as a super thin high atrium in this thesis.In this type of atrium,plume will contacts with the wall when it rises.According to the research results,the corresponding formulas for atrium with different shape coefficients,different power sources and different thermal stratification frequencies are established respectively.Based on the results of the simulation data,the influence of the interaction of different boundary conditions on the environmental coefficient and the fire coefficient in the natural smoke exhaust theory model of the atrium is discussed by using the classical statistical method.Through statistical analysis,the shape factor and the thermal stratification frequency are the two main factors that affect the design of natural smoke exhaust in atrium.The research of this subject belongs to the research on the combination of theory and application in the field of smoke prevention and exhaust.The development of this topic has practical and guiding significance to the smoke control design to the thin and tall atrium.