Linhe Zhang

Experimental Study on Cross-ventilation Compartment Fire in the Wind Environment

When fire occurs in the rooms of high-rise buildings, the strong ambient wind will play an important role in fire spread and smoke movement behavior. However, wind effect on compartment fire in cross ventilation condition has not been fully studied so far. In the present study, an effort has been made to study crossventilation compartment fire in the wind environment through experimental investigations. The experimental fire was generated by 250ml (10cm×10cm tray burner) or 500ml (20cm×20cm tray burner) nheptane on the floor of a cube enclosure with two opposite vents on the walls. The inside and outside gas temperature profiles at different vertical and horizontal locations were recorded by two thermocouple matrixes. The ambient wind velocity was set to zero, 1.5m/s and 3m/s. It is observed that the ambient wind has two contradictory effects on the compartment fire: promoting fire severity by more oxygen supplying and cooling the fire by heat removing and combustible gases diluting. The spilled-out flame/plume extends horizontally farther with the increase of wind speed. It is found that the compartment fire with 500ml fuel reaches post-flashover stage while that with 250ml doesn’t. The wind effect is obviously observed in larger fires while not significant in smaller fires.

An experimental study on thermal radiation of fire whirl

Fire whirl is frequently observed in wildland fires, and may cause serious difficulty in firefighting owing to its significant turbulent flow. In this paper, the radiation of fire whirl is investigated through experiments using a fire whirl facility made up of an air curtain apparatus, with five different sizes of n-heptane pools (25, 30, 35, 40 and 45 cm). The flame contour was extracted by image processing. By using infrared methods, the flame emissivity of fire whirl at different heights for different pool diameters was measured, and thereby a correlation was developed between the flame emissivity and the flame diameter. The soot volume fraction in the luminous flame is estimated to range within 2.5 × 10−6 to 4.0 × 10−6, much higher than that of general heptane pool fires, which provides an explanation of the higher flame emissivity of fire whirl. The emissive power profile v. normalised height is deduced from flame emissivity and flame temperature data. A multizone flame model (in which each zone is assumed as a grey body) is used, based on the measured data of flame emissivity, to predict the radiation of fire whirl. Comparison between the predicted and measured data of radiative flux shows good agreement.

Neutral Plane and Length Scale of Spill Fire Plume Considering the Effects of Cross-Ventilation

This study sought to explore the neutral plane and length scale of spill fire plume considering the effect of cross-ventilation. The neutral plane heights for the downwind and upwind openings were firstly formulated, which suggested that the neutral plane heights vary monotonically with the crosswind velocity. The formulation was verified using the experimental data by two different methods. It was verified that with increasing crosswind velocity, the decrease of neutral plane height will induce rapid increase in the burning intensity of spill fire plume, as well as the convective heat flow rate, the flame length, and the original temperature. A new mathematical model consisting of a new length scale was developed as an extension from the models in literature for no-wind cases to cover the cases with various cross-ventilation conditions. It was indicated that the new length scale can be used to correlate the axial temperature data of spill fire plume under various cross-ventilation conditions.

Flame length of non-buoyant turbulent slot flame

Abstract This work presents a modeling and experimental analysis on the flame length of buoyant turbulent slot diffusion flame. An approximate predictive correlation of flame length is derived based on the governing equations. The role of initial momentum and buoyancy on flame length is quantitatively described by a modified Froude number Frm. The physical model indicates that the flame length of a turbulent slot flame is proportional to (Frm)1/3 and (Frm)0 respectively when the flame is buoyancy-dominated and momentum-dominated. The results, for the first time, give a physical verification on the previous scaling laws on buoyant turbulent slot flame in literature. Slot flame tests are conducted using two burners (for which the width W and length L are respectively 0.9 mm × 20.5 mm and 5.5 mm × 86 mm) and four kinds of high-purity hydrocarbon gas fuels (methane, acetylene, ethane and propane). Experimental data show that the radial temperature profiles of buoyant turbulent slot flames can be well described by a Gaussian function normalized by the temperature radius, which is independent of axial position and flame scale. Moreover, experimental data verify that the physical model applies for different fuel supply rates, types of fuels and flame scales. Additionally, the results indicate that the turbulent slot flame is buoyancy-dominated when Frm   107. Finally, it is indicated that the scale effect of turbulent slot flame is closely associated with the flame temperature under different flame scales.