R. Huo

Experimental and Numerical Studies on Longitudinal Smoke Temperature Distribution Upstream and Downstream from the Fire in a Road Tunnel

Four full-scale tests are conducted in a real road tunnel, with ceiling jet temperature distributions measured 200 m upstream and downstream from the fire. Two sizes of pool fires, 1.8 and 3.2 MW, with two different fire surface heights, 0.2 and 1.7 m from the floor level, are considered. Longitudinal ventilation velocities are also varied. The experimental data obtained in these four tunnel fire tests are used for validation of FDS 4.0 parallel simulation on tunnel fires. The ceiling jet temperature distributions upstream and downstream, and thus the back-layering length are compared. Results show that the temperatures predicted by FDS 4.0 are near to the measured data. In near fire regions, for instance, not more than 40–80 m away from the fire, the temperature predicted is very close to the full-scale data. There is a deviation between the predicted value and the measured one, shown to be mainly less than 4–5 C, at positions further away. The back-layering length predicted by FDS 4.0 also seems to agree fairly well with that deduced from the full-scale experiments.

Large eddy simulation of fire-induced buoyancy driven plume dispersion in an urban street canyon under perpendicular wind flow

The dispersion of fire-induced buoyancy driven plume in and above an idealized street canyon of 18 m (width) x 18 m (height) x 40 m (length) with a wind flow perpendicular to its axis was investigated by Fire Dynamics Simulator (FDS), Large Eddy Simulation (LES). Former studies, such as that by Oka [T.R. Oke, Street design and urban canopy layer climate, Energy Build. 11 (1988) 103-113], Gayev and Savory [Y.A. Gayev, E. Savory, Influence of street obstructions on flow processes within street canyons. J. Wind Eng. Ind. Aerodyn. 82 (1999) 89-103], Xie et al. [S. Xie, Y. Zhang, L. Qi, X. Tang, Spatial distribution of traffic-related pollutant concentrations in street canyons. Atmos. Environ. 37 (2003) 3213-3224], Baker et al. [J. Baker, H. L. Walker, X. M. Cai, A study of the dispersion and transport of reactive pollutants in and above street canyons--a large eddy simulation, Atmos. Environ. 38 (2004) 6883-6892] and Baik et al. [J.-J. Baik, Y.-S. Kang, J.-J. Kim, Modeling reactive pollutant dispersion in an urban street canyon, Atmos. Environ. 41 (2007) 934-949], focus on the flow pattern and pollutant dispersion in the street canyon with no buoyancy effect. Results showed that with the increase of the wind flow velocity, the dispersion pattern of a buoyant plume fell into four regimes. When the wind flow velocity increased up to a certain critical level, the buoyancy driven upward rising plume was re-entrained back into the street canyon. This is a dangerous situation as the harmful fire smoke will accumulate to pollute the environment and thus threaten the safety of the people in the street canyon. This critical re-entrainment wind velocity, as an important parameter to be concerned, was further revealed to increase asymptotically with the heat/buoyancy release rate of the fire.

Decay of Buoyant Smoke Layer Temperature Along the Longitudinal Direction in Tunnel Fires

A simple model was reported to predict the longitudinal distribution of temperature rise for the smoke layer along a tunnel. The longitudinal decay of excess smoke layer temperature in dimensionless form was studied by including convective and radiative heat transfer to the boundary. An expression was derived to relate to the dimensions of the cross-section of the tunnel, the depth and the velocity of the smoke layer to the temperature. A series of full-scale tests was conducted in three vehicular tunnels to verify the model. There, temperature field and smoke layer traveling velocity were measured downstream the fire source. The decay factors for longitudinal smoke layer excess temperature distributions were predicted from the model based on the smoke layer velocities and the dimensions of the vehicular tunnel. Results are then compared with those deduced directly from the measured temperature data. Good agreement was achieved. Language: en

Experimental Studies on the Rise-Time of Buoyant Fire Plume Fronts Induced by Pool Fires

Experimental studies were conducted in the PolyU/USTC Atrium to investigate the rise-time of buoyant plume front induced by pool fires. Through a series of full-scale burning tests, three semi-empirical equations were derived to predict the rise-time of buoyant plume front induced by a fire at three positions. These three positions are at the centre, near a wall and in the corner of the atrium floor respectively. The rise-time in dimensionless form and the plume radius equation are analyzed based on the measured data.

Experimental investigation on drag effect of sprinkler spray to adjacent horizontal natural smoke venting

Discharge rate of a horizontal adjacent smoke vent under sprinkler spray is experimentally investigated. Temperature of smoke layer and velocity of smoke venting were measured, under different sprinkler operating pressures and smoke venting areas. CO concentration at the smoke vent center and velocity of vent flow with fresh air outside were recorded in tests under different smoke venting conditions. Experimental results have shown that efficiency of smoke venting is controlled by a combination of smoke buoyancy and drag force of sprinkler spray. Only when buoyancy is greater than drag force the smoke could be extracted by venting. Velocity of smoke venting has shown to decrease as the operating pressure increases. Smoke venting logging, which represents the failure of smoke venting, was experimentally found from certain operating pressure called initial logging pressure. The CO concentration was found to increase after sprinkler was operated as the smoke is constrained in the spray region with horizontal momentum decreased. Negative pressure difference is caused at the vent when there is smoke venting logging, which might practically bring the exterior fresh air into the fire building. Additionally, experiments results have shown that the venting area has little influence on smoke flow under smoke venting logging.

PolyU/USTC Atrium: A Full-Scale Burning Facility -- Preliminary Experiments

The PolyU/USTC Atrium, a full-scale burning facility for atrium fire studies has been constructed at the University of Science and Technology of China (USTC). The atrium will be managed by USTC and the Hong Kong Polytechnic University (PolyU). The construction features of the facility are reported briefly, and further studies using this facility are outlined. Typical use of the facility is demonstrated by several smoke filling tests. The results on the smoke layer interface height were analyzed and compared with those predicted by zone models. It is observed that a zone model can give quite accurate prediction on smoke filling during most of the burning period. Language: en

Experimental Studies on Stability of Smoke Layer with a Sprinkler Water Spray

Abstract The adverse effects of a sprinkler on smoke exhaust systems used to be debated in designing fire safety provisions. However, very few experimental studies on the interaction of a sprinkler with the smoke layer have been reported; therefore, this study investigates and reports on the interaction of a smoke layer with a sprinkler water spray by a specially designed rig with 25 tests. Smoke spreading from a fire chamber was collected in an adjacent hall. The stability of the smoke layer was then studied by the discharged water spray. The ratio of spray drag to smoke buoyancy is proposed to determine smoke stability.

Full Scale Experiments on Studying Smoke Spread in a Road Tunnel

Three full scale tests were conducted in a road tunnel to study the smoke spread with different fire sizes and wind speed conditions. The smoke temperature under the ceiling, the smoke layer height distribution and the travel of the smoke front in a 1000 m long domain along the road tunnel were measured. Results showed that wind speed had much influence on the spread of smoke in the tunnel. When wind speed was such low as less than 1 m/s, a smoke layer could form and stabilize all along the tunnel. But when the wind speed was such high as more than 2 m/s, smoke layer could only be maintained in a distance of about 400 m in the downstream. The slowdown of the traveling of the smoke front in the downstream along the tunnel was more obvious when the wind speed was smaller. All these full scale data presented here can be used for further study on the verification or improvement of existing fire models for enhancing their applicability to such long tunnels.

An Empirical Equation to Predict the Growth Coefficient of Burning Rate of Wood Cribs in a Linear Growth Model

A series of bench scale experiments are carried out to study the growth characteristics of cubic wood cribs burning. A comparison among linear fitting, power-law fitting, and exponential fitting shows that linear growth model seems to be the best to describe the growth of wood crib fires. An empirical linear model is also achieved to predict the linear growing burning speeds of wood cribs with different stick spacing conditions based on the experimental data obtained.

Stability of Smoke Layer Under Sprinkler Water Spray

Stability of smoke layer induced by a fire will be studied in this paper. A series of full-scale burning tests were carried out to study the interaction of the hot smoke layer with a sprinkler water spray. A new rig was built to give a smoke layer. The results show that the stability of a smoke layer will be disturbed by the discharged water spray. The operating pressure of the sprinkler system is a key point. When the smoke layer lost its stability, the dragging force acting on the smoke layer was found to be less than the buoyancy.Copyright