Study on the heat exhaust coefficient and smoke flow characteristics under lateral smoke exhaust in tunnel fires

Abstract

Summary The heat exhaust coefficient and smoke flow characteristics under lateral smoke exhaust in tunnel fires were studied in this paper. Through the dimensional analysis, the dimensionless relationship between the heat exhaust coefficient, heat release rate, exhaust vent size, and exhaust velocity was obtained. In addition, this paper also studied the effect of the lateral exhaust vent on the smoke flow field. Results showed that the lateral smoke exhaust caused strong air entrainment on the downstream of the exhaust vent and boundary layer separation on the upstream of the exhaust vent. As the exhaust velocity increased, the degree of air entrainment gradually increased, and the smoke layer near the exhaust vent gradually became thinning and plug‐holing phenomenon occurred; meanwhile, the boundary layer separation would be suppressed or disappear, but the increase of the heat release rate would enhance the boundary layer separation. As the exhaust vent got narrower, the air entrainment downstream of the exhaust vent was reduced, and the boundary layer separation also got weaker.

Transport and Depositing Characteristics of Exhaling Aerosols from Inside of the Human Respiratory Airway

“…Once inhaled, these virus-loaded aerosols can settle on the inner walls of the respiratory airway, paving the way for viral invasion of the immune system and subsequent infections [6][7][8][9][10][11][12][13][14]. Therefore, the quantity of exhaled aerosols released into the external environment is directly connected to the risk of virus transmission [15][16][17]. Deep investigation of the properties of exhaled aerosols is therefore of great significance in effectively addressing the potential for widespread epidemic transmission in the future.…”

Numerical investigation on the characteristics of lateral smoke extraction in the immersed road tunnel

“…The different actions of suction force in the smoke extraction process show different impacts on the smoke spreading underneath the tunnel ceiling, including the air entrainment. 14 Moreover, under the horizontal suction-force action of lateral smoke extraction, the smoke is drawn into the exhaust vent horizontally and laterally during flowing longitudinally in the tunnel, resulting in more difficulties in the smoke exhaust compared with those traditional ceiling smoke extractions. After all, the buoyancy of smoke induced by density difference is vertical in essence, which is bound to benefit the traditional ceiling smoke exhaust.…”

“…However, as illustrated in Figure 1, the drawn‐force of lateral smoke extraction is horizontal because the exhaust vents are installed on the sidewall of those immersed tunnels, and it acts on the side surface of the smoke layer. The different actions of suction force in the smoke extraction process show different impacts on the smoke spreading underneath the tunnel ceiling, including the air entrainment 14 . Moreover, under the horizontal suction‐force action of lateral smoke extraction, the smoke is drawn into the exhaust vent horizontally and laterally during flowing longitudinally in the tunnel, resulting in more difficulties in the smoke exhaust compared with those traditional ceiling smoke extractions.…”

“…For the lateral smoke extraction in the immersed tunnel, Xu et al 16 addressed the best opening angle of a damper on the sidewall to improve the smoke exhaust efficiency theoretically and experimentally. Fan and Xu 14 pointed out that the lateral smoke exhaustion could cause strong air entrainment in downstream of the exhaust vent, while the smoke layer near the exhaust vent gradually became thinner and plug‐holing phenomenon occurred. Liu et al 17 found that the total volume rate of opening two continuous groups of smoke vents in downstream is higher than that of opening two spaced groups of smoke vents.…”

Experimental study on the effect of lateral concentrated smoke extraction on smoke stratification in the longitudinal ventilated tunnel

“…On the other hand, the smoke contains many toxic gases. Therefore, timely and effective control and extraction of the smoke generated from the tunnel fire is of great significance for evacuation and rescue of personnel 1‐7 …”