Study On Smoke Movement And Ventilation Control Method For Temperature Inversion Environment In Underground Large Space

This paper is focused on the smoke plume motion characteristics and exhaust ventilation control method for underground space with reverse vertical temperature distribution. Based on the large space model of underground plant, experiment and numerical simulation is carried out to put forward methods of smoke exhaust ventilation scheme for underground large space.1. Theoretical research on smoke motion characteristics in large space. The parcel method is applied to study the motion characteristics of smoke in the inversion environment. Based on the existing maximum height formula for axisymmetric plume, with the principle of hydrodynamic images, the maximum height formula is modified for wall plume.2. 2D-PIV measurement technology is used to achieve the smoke motion characteristic with different fire plume location. The results show that, in the environment with inversion temperature, the smoke plume will stop rising and hang at upper part of the space, as the buoyancy force decreases. In the experiment, when the sandalwood(smoke) is placed at the central position of the bottom with 433 ℃ of surface temperature, the maximum height of the rising smoke is 840 mm. When the sandalwood(smoke source) is placed by the side wall with 312 ℃ of surface temperature, the maximum height of the rising smoke is 820 mm.3. Based on the model of underground hydro-power plant, motion of smoke with different fire position and heat release rate are studied by numerical method. the results show that, the maximum height of the rising smoke increases with the heat release rate. Scenario 1: fire is at the center of the generator floor. When the heat release rate is 1 k W, the maximum height is 14 m. When the heat release rate is 20 k W, the maximum height is 20 m. However, when the heat release rate is 40 k W, the smoke will reach the top of the space without hanging. Scenario 2: fire is by the side wall on the generator floor. Because of the Coanda effect, the critical heat release rate for reaching top drops in 10 k W~20 k W. Scenario 3: is at the center of the busbar floor. Since the space of the generator floor is much larger than the busbar floor, the velocity and temperature of smoke reduces a lot when entering the generator floor. With the same heat release rate, the maximum height of this condition is higher. The critical heat release rate for reaching top drops in 60 k W~80 k W.4. Based on the model of underground hydro-power plant, the influence of the exhaust air volume, the exhaust vents location, the air-supplement area on the effect of the smoke extraction. The results show that, when the actual exhaust air volume is half of the based condition, with reducing to the same level of carbon monoxide concentration, 1.7 times of extracting time is needed. When the actual exhaust air volume is 1.5 times of the based condition, with reducing to the same level of carbon monoxide concentration, 0.64 times of extracting time is needed. Exhausting vents with different height can adapt to more situations.