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Chen X.,Wuhan University of Technology | Zhang H.,Wuhan University of Technology | Liu X.,Key Laboratory of Building Fire Protection Engineering and Technology of MPS | Niu Y.,Wuhan University of Technology | And 2 more authors.
Journal of Loss Prevention in the Process Industries | Year: 2017

The inert powder of sodium bicarbonate with different particle size distribution in certain proportion was employed to study its suppressing effect on dust explosion and flame propagation. A certain proportion of combustible aluminum dust was mixed with different granular sodium bicarbonate powder with single-diameter particle or different granulometric distribution. The explosion experiment was performed in a vertical pipe experimental platform. The ionic current and flame propagation behavior and flame temperature were obtained to evaluate the inhibitory effects of inert powder on dust explosion flame. The experimental results showed that the sodium bicarbonate with different granulomertic distribution made suppression effect on the flame of aluminum dust explosion. The inert inhibition powder with different granulomertic distribution led to flame structure change and reduced the thickness of the preheat zone during flame propagation. Meanwhile, the flame propagation velocity and flame temperature were reduced. Furthermore, an optimum proportion of sodium bicarbonate was obtained for the best inhibition effect on the aluminum dust explosion. Results show that the suppression effect on the flame combustion reaction zone was the critical factor for dust explosion mitigation. © 2017 Elsevier Ltd.


Tan W.,Tianjin University | Du H.,Tianjin University | Liu L.,Tianjin University | Su T.,Tianjin University | Liu X.,Key Laboratory of Building Fire Protection Engineering and Technology of MPS
Journal of Loss Prevention in the Process Industries | Year: 2017

With the widespread use of ammonia in the industrial fields, more and more accidents are caused by ammonia leakage and dispersion. To study the dispersion law of ammonia in a food factory, small scale wind tunnel experiments were designed. Different initial conditions such as release flow rate, wind speed, release height and the heights of concentration sensors were considered. Ammonia concentration was measured near release source, obstacles and far from release source, respectively. The law of ammonia dispersion is determined by its physical properties, release source conditions and atmospheric environment. Ammonia concentrated in the axial direction and showed an upward movement near the source as ammonia's density is lower than the air. We obtained the law of ammonia dispersion in a food factory through experiments indicating that the concentration of each measuring point is proportional to the flow rate. With the increase of wind speed, the concentration of ammonia at different points first increased and then decreased. The results showed that the effect of ammonia dispersion was more obvious under the influence of the wind field. The maximum concentration can be reached under the wind speed range of 0.8–1.2 m/s. Changing the height of source and measuring point will make a great difference in the concentration of the measuring point. In the simulation work, RNG k-ε model represents better agreement with the experimental data. Ammonia movement has a strong concentration gradient and the horizontal wind field streamlined ammonia movement. © 2017


Li L.J.,Hefei University of Technology | Tang F.,Hefei University of Technology | Tang F.,Key Laboratory of Building Fire Protection Engineering and Technology of MPS | Dong M.S.,Hefei University of Technology | Tao C.F.,Hefei University of Technology
Applied Thermal Engineering | Year: 2016

Poisonous and harmful smoke is one of the most important factors in the life-threatening in tunnel fires. In the event of fire, the effective control of fire growth and smoke sinking is crucial for personnel security in tunnel. The aim of this work is to study the smoke thermal stratification with ceiling extraction in a longitudinal ventilated tunnel. A series of experiments were carried out in a 1/6 scale model tunnel [72 m (length) × 1.5 m (width) × 1.3 m (height)]. Four thermocouple trees are used to measure vertical temperature profile. The heat release rate, ceiling extraction velocity and longitudinal forced air flow velocity were considered. It was found that: (a) the smoke temperature below the tunnel ceiling decreased and the thermal stratification stability reduced with the increasing of ceiling extraction velocity; (b) the measured temperatures ratios ΔTcf/ΔTh versus ΔTcf/ΔTavg with and without ceiling extraction are in good agreement with Nyman and Ingason's work; (c) with the coupling effect of ceiling extraction and longitudinal forced air flow, a modified Froude number was proposed to describe the influence of ceiling extraction, and the relation between the smoke thermal stratification and the modified Froude number agree well with Nyman and Ingason's model. © 2016 Elsevier Ltd


Zhang G.,China University of Mining and Technology | Zhang G.,Key Laboratory of Building Fire Protection Engineering and Technology of MPS | Zhang G.,China Mobile | Zhu G.,China University of Mining and Technology | And 3 more authors.
Safety Science | Year: 2016

A risk assessment method was proposed to evaluate the evacuation safety in the collapse of a large steel-structured gymnasium caused by localized fire. The criterion for safety evacuation was that the available evacuation time was greater than the required evacuation time, which could be determined by a proposed steel-temperature rise model and a proposed evacuation model, respectively. In the proposed steel-temperature rise model, not only the effects of smoke thermal radiation and convection, but also the effects of flame thermal radiation on steel components were considered. In the evacuation model, the required evacuation time was determined mainly by the following factors: distance from the farthest point to the safety exit, personnel evacuation speed, width of evacuation exit, and density of personnel. All these results and experimental data obtained in this study provide valuable references to fire simulation, hazard assessment, and fire protection design. © 2016 Elsevier Ltd.


Gao Z.H.,Hefei University of Technology | Ji J.,Hefei University of Technology | Ji J.,Key Laboratory of Building Fire Protection Engineering and Technology of MPS | Fan C.G.,Hefei University of Technology | And 2 more authors.
Tunnelling and Underground Space Technology | Year: 2016

Smoke layer interface height is an important parameter in fire safety science. In this paper, a series of experiments were conducted in a 1/6th scale model tunnel for determining the smoke layer interface height in medium scale tunnel fire scenarios. The commonly used approaches, including visual observation, N-percentage rule and integral method are reviewed firstly. Then, considering the subjectivity and empiricism of previous approaches, a buoyancy frequency method is put forward based on the vertical temperature distribution in tunnel, which has definite physical meaning and eliminates the subjectivity of previous methods. The smoke layer thicknesses determined by buoyancy frequency method are compared with the results of visual observation, N-percentage rule (N = 10, 20, 30) and integral ratio method, respectively. The comparison results reveal that the smoke layer thicknesses determined by buoyancy frequency method fit best with the visual values for all the experimental conditions. While the calculated values by integral ratio method are lower than the visual values. In addition, the selection of optimum N values for the N-percentage rule in different cases is also discussed. © 2016 Elsevier Ltd.


Ji J.,Anhui University of Science and Technology | Wan H.,Anhui University of Science and Technology | Li K.,Anhui University of Science and Technology | Li K.,Wuhan University of Science and Technology | And 3 more authors.
International Journal of Heat and Mass Transfer | Year: 2015

Numerical simulations were carried out to study the smoke behaviors induced by fires in inclined tunnels with different slopes and the upstream maximum temperatures along the tunnel centerline were specifically focused. The simulation results show that the longitudinal centerline peak temperature occurs at the downstream region of fire source rather than right above the fire source. Two typical behaviors were found during the quasi-steady state: the upstream smoke layer interface is almost parallel to horizontal level while the downstream smoke layer interface is parallel to the inclined tunnel ceiling. The upstream maximum temperature under the ceiling remain approximately constant near the fire sources and then drop progressively with increasing distance to fire source due to the existence of vortexes, which is fairly different from the downstream maximum temperature distribution. Hence, an empirical correlation is developed by taking into account the tunnel slope, heat release rate and the upstream maximum temperature and using dimensional analysis. The correlation indicates that the dimensionless upstream maximum temperature decreases as the distance from fire source increases and it is proportional to 0.56 power of the dimensionless heat release rate and its relationship with tunnel slope is nonlinear and non-monotonous. © 2015 Elsevier Ltd. All rights reserved.


Chen C.-K.,Hunan Institute of Technology | Chen C.-K.,Key Laboratory of Building Fire Protection Engineering and Technology of MPS | Zhu C.-X.,Hunan Institute of Technology | Liu X.-Y.,Key Laboratory of Building Fire Protection Engineering and Technology of MPS | And 3 more authors.
Tunnelling and Underground Space Technology | Year: 2016

A set of experiments was carried out in a 1/9 reduced-scale single-track railway tunnel to investigate the effect of fuel area size on the temperature distribution and behavior of fires in a tunnel with natural ventilation. Methanol pool fires with four different fuel areas 0.6×0.3m2 (1 pan), 1.2×0.3m2 (2 pans), 2.4×0.3m2 (4 pans) and 3.6×0.3m2 (6 pans), were used in these experiments. Data were collected on temperatures, radiative heat flux and mass loss rates. The temperature distribution and smoke layer in the tunnel, along with overflow dimensions and radiant heat at the tunnel entrance were analyzed. The results show that as the fuel area enlarges, the fire gradually becomes ventilation-controlled and the ceiling temperature over the center of fire source declines. Burning at the central region of fire source is depressed due to lack of oxygen. This makes the temperature distribution along the tunnel ceiling change from a typical inverted V-shape to an M-shape. As observed in the experiments, a jet flame appeared at tunnel entrances and both the size and temperature of the flame increased with the enlargement of fuel area leading to a great threat to firefighters and evacuees in actual tunnel fires. © 2015 Elsevier Ltd.


Chen C.-K.,Hunan Institute of Technology | Zhu C.-X.,Hunan Institute of Technology | Liu X.-Y.,Key Laboratory of Building Fire Protection Engineering and Technology of MPS | Yu N.-H.,Key Laboratory of Building Fire Protection Engineering and Technology of MPS
International Journal of Heat and Mass Transfer | Year: 2016

Sealing the tunnel entrance is a common tactic for tunnel fire fighting, while it is not easy to seal the two entrances synchronously in actual tunnel fire-fighting process. A set of reduced experiments were then conducted to investigate the effect of asymmetrical sealing of tunnel entrances on tunnel fire behavior and temperature distribution. The data of temperature, radiative heat flux and mass loss rate, etc. were acquired. The results demonstrate that hot smoke region shifts to the side not completely sealed, and burning at the side with less sealing ratio is more violent with higher smoke temperature and longer hot smoke plume. Plume temperature at the tunnel entrance could reach to 300°C as measured in the experiments and jet flame was observed at the end not completely sealed. These would lead to great danger to fire fighters in actual tunnel fire fighting. © 2015 Elsevier Ltd. All rights reserved.


Chen C.-K.,University of South China | Chen C.-K.,Key Laboratory of Building Fire Protection Engineering and Technology of MPS | Zeng J.-W.,University of South China | Shen B.-Y.,University of South China
Journal of Central South University | Year: 2015

Twenty tests were conducted to investigate the efficiency of the intumescent coating designed to protect steel plate at the elevated temperature, by means of electrical furnace. And the factors of the initial thickness of coating and temperature of electrical furnace were considered. The high temperature response behavior of the intumescent coating was observed. And the expansion form of ultrathin intumescent coating and the temperature of the steel plate (TS) were obtained. Besides, the heat flux from expansion layer to steel plate versus time was analyzed in order to evaluate the heat transfer effect of intumescent coating on steel plate. The experimental results show that the response behaviors of the coating subjected to fire could be divided into four phases: stabilization phase, foaming expansion phase, carbonization-consumption phase and inorganic layer phase. And the net heat flux to the steel plate decreased observably in the foaming expansion phase, while the surplus white inorganic substance, which is the residue of the intumesced char layer in the inorganic layer phase under the condition of the temperature of the electrical furnace (TEF) beyond 700 °C over 1 h, has little effect on fire protection for the steel plate. © 2015, Central South University Press and Springer-Verlag Berlin Heidelberg.

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