Calculation Of The Exhaust Volume Of An Underground Garage And Simulation On Pollutant Dispersion Process

In order to ensure the air quality in a garage to meet the hygiene standard as well as to save energy,it is very important to determine a reasonable ventilation rate and to choose a proper air distribution mode of mechanical ventilation system.It is important to acknowledge the dispersion characteristics of exhausted pollutants while cars idling and cold starting process of the car.It may help to use natural ventilation feasibly or to arrange the air inlets and outlets more properly.However,research on the pollutants dispersion characteristics under idling condition of vehicles are far from enough.To this end,how to determine proper ventilation volume and grasp the dispersion characteristics of pollutants while car idling in a garage were studied in this paper.Firstly,five empirical formulas currently used to calculate the ventilation flow rate of an underground garage were compared based on the calculation result of a garage in Xi'an.It reveals that there are significant differences exist between the five results from 5 formulas due to different value of the coefficient adopted in different formula.The result obtained from No.3 formula is more feasible.It has a simple form and the physical meaning of each item is clear.Thus,it is suggested to be used in practical projectThen,a garage in size of 45m×45m×3m was chosen as the computational domain. The transient dispersion process of the exhaust fume of a car idling in the garage was simulated by solving the standardκ-εmodel together with the control equations. Dynamic mesh technology was adopted.Analyses were conducted on the static pressure fields and CO concentration fields around the car moving in an airtight,naturally ventilated or mechanically ventilated garage.Results show that negative pressure zones form on the left and right of car shoulder and the pressure distribution are symmetrical along the center line of the cars,the symmetry axis of symmetry.The exhaust fume of the car disperses to the surrounding environment under the buoyant force and the small discharging momentum.And then the pollutant dispersion processes were also simulated under the cases of two-car parallel and cross idling.It shows that a lower pressure formed in the zone between two vehicles.And the exhaust fumes interfere with each other and several eddies appear in this zone,which makes CO accumulate in this part and the air quality deteriorate.However,it has little impact on dispersion characteristics of CO in the main stream.