Research On A Natural Smoke Exhaust Device Using Venturi Effect To Improve Exhaust Performance Under External Wind

Natural smoke exhaust is widely used in large space public buildings because of its simple operation,installation and cost saving.It depends on the thermal pressure generated by the fire itself to exhaust the fire smoke.However,in practical application,external wind could interfere with the natural smoke exhaust and affect the smoke exhaust efficiency and even fail to extract the smoke timely and effectively.In this paper,on the basis of Venturi effect in natural ventilation,a Venturi-shaped device using the Venturi effect has been designed to improve the natural smoke exhaust performance under wind conditions.Theoretical,numerical and experimental research on natural smoke exhaust process for this device under wind conditions are carried out.It may provide reference and data support for the design of natural smoke exhaust system and the improvement of relevant norms.Firstly,based on the two-zone fire model,a brief theoretical analysis of Venturishaped device under wind conditions is made.The mass flow rate through the exhaust is taken as the evaluation index of natural smoke exhaust effect.The effectiveness of Venturi-shaped device is proved theoretically.As the main research method of this paper,Computational fluid dynamics(CFD)simulation has been carried out on the following works:(1)An orthogonal test design is used to determine the optimal combination of the primary structural parameters of Venturi-shaped device.(2)The comparison between the Venturi-shaped ventilator and the traditional ventilator indicates that the former performed better,with a maximum increment of 180% on the mass flow rate.(3)The influences of wind speed(0.5m/s~10m/s)on the mass flow rate through the roof vent are evaluated.It shows that the larger the wind speed,the greater is the increase in the velocity and hence the negative pressure above the vent,thus the increment percentage of the mass flow rate through the Venturi vent to that through the traditional vent increases with wind speed.So the effect of enhancing exhaust air is more significant with increasing wind speed.(4)The influences of the heat source power(0~200kW)on the mass flow rate through the roof opening are evaluated.It shows that the increment percentage of the mass flow rate through the Venturi vent compared to the traditional vent was decreased significantly,but the former is always better than the latter.Finally,the reduced-scale wind tunnel experiment is performed to study the performance of the ventrui-shaped device under different external wind speeds.It shows that the Venturi vent is better than traditional vent under typical external wind conditions;the performance of the Venturi-shaped device increased with wind speed.It also verifies the validity of the conclusions obtained by CFD simulation to a certain extent.