L.H. Hu

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.

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 Study on the Burning Characteristics of Wood Cribs in a Confined Space

A series of experiments were conducted to study the burning characteristics of wood cribs in a confined space. The results show that burning conditions of wood cribs in a confined space fall into two regimes: the smaller porosity factor burning regime and the larger porosity factor burning regime. The scaled steady mass loss rates of wood cribs burning in the larger porosity factor regime linearly increases with the increase of the porosity factor in a confined space. The concentrations of CO, CO2 and O2 in combustion products, the flame temperature and the mass loss rate exhibit different time-variations or relationships with the porosity factor for wood cribs burning in these two different regimes.

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.

Tracking a Ceiling Jet Front for Hot Smoke Tests in Tunnels

There are difficulties in tracking the ceiling jet front while carrying out hot smoke tests in long tunnels with a small fire. In this study, an experimental method using infrared beams is suggested. The arrival time of the hot ceiling jet front to a designated position is measured by the abrupt attenuation of the infrared beam intensity. Field measurements are carried out in an underground tunnel of length 88 m. Diesel pool fires up to 1.5 MW are studied. The results on tracking the ceiling jet front are compared with the measurements by using the thermocouples, thermal resistors, and visual observations. This method is demonstrated to be useful for tracking the ceiling jet front at positions further away from the fire. Therefore, the method is suitable for studying the ceiling jet in hot smoke tests for evaluating smoke management systems in long tunnels.

Smoke Filling Simulation in a Boarding-Arrival Passage of an Airport Terminal using Multicell Concept

A multicell concept, which first divides the total space into subspaces and then uses the traditional two-layer zone model in each subspace, is performed in this paper to simulate the smoke filling process in a domestic boarding–arrival passage, with an aspect ratio of about 52.3, of an international airport terminal by using CFAST version 4.0.2. Results show that the impingement of ceiling jet upon the passage ends is a critical time for the evacuation of people near these ends. Some comparisons are also presented to show that more reasonable results about the smoke temperature field and the smoke layer interface height are achieved using this method than using the traditional two-layer zone model. Further, results through different subspace dividing technology and using FDS version 3.0, a CFD model, are also achieved and compared on simulating the smoke filling process in a simplified passage, for the purpose of studying the prediction of impingement time, the smoke temperature distribution, and the smoke layer interface height development pattern before and after the impingement. The limitations of this modeling technology and future research topics are also discussed.

Study of the Transitional State between Two Wood Crib Burning Regimes by CO Concentration in a Confined Space

Traditionally, the burning of wood cribs has been divided into a surface area controlled regime, and a porosity controlled regime according to mass loss rate. In the two regimes, the concentration of CO produced should also have different characteristics. In this paper, the variation of concentration of CO produced by burning wood cribs is studied. A series of experiments with different wood crib structures are conducted. The mass loss rate and the concentration of CO are measured. It has been found that the concentration of CO has an obvious transitional state, and the corresponding transitional value of porosity factor for dividing the two burning regimes according to the concentration of CO is exactly the same as that according to the mass loss rate.