Wu Zhibo

Bio: Wu Zhibo is an academic researcher from University of Science and Technology of China. The author has contributed to research in topics: Ignition system & Heat flux. The author has an hindex of 4, co-authored 10 publications receiving 52 citations.

Prediction of Three-Dimensional Downward Flame Spread Characteristics over Poly(methyl methacrylate) Slabs in Different Pressure Environments

Abstract: The present study is aimed at predicting downward flame spread characteristics over poly(methyl methacrylate) (PMMA) with different sample dimensions in different pressure environments. Three-dimensional (3-D) downward flame spread experiments on free PMMA slabs were conducted at five locations with different altitudes, which provide different pressures. Pressure effects on the flame spread rate, profile of pyrolysis front and flame height were analyzed at all altitudes. The flame spread rate in the steady-state stage was calculated based on the balance on the fuel surface and fuel properties. Results show that flame spread rate increases exponentially with pressure, and the exponent of pressure further shows an increasing trend with the thickness of the sample. The angle of the pyrolysis front emerged on sample residue in the width direction, which indicates a steady-burning stage, varies clearly with sample thicknesses and ambient pressures. A global non-dimensional equation was proposed to predict the variation tendency of the angle of the pyrolysis front with pressure and was found to fit well with the measured results. In addition, the dependence of average flame height on mass burning rate, sample dimension and pressure was proposed based on laminar diffusion flame theory. The fitted exponent of experimental data is 1.11, which is close to the theoretical value.

Width effects on downward flame spread over poly(methyl methacrylate) sheets

Abstract: The experiments of downward flame spread over poly(methyl methacrylate) sheets with different dimensions were conducted in this study. In comparison with flame spread over samples under infinite wi...

Experimental and Numerical Study on Effect of Sample Orientation on Auto-Ignition and Piloted Ignition of Poly(methyl methacrylate).

Abstract: In this work, the effect of seven different sample orientations from 0° to 90° on pilot and non-pilot ignition of PMMA (poly(methyl methacrylate)) exposed to radiation has been studied with experimental and numerical methods. Some new and significant conclusions are drawn from the study, including a U-shape curve of ignition time and critical mass flux as sample angle increases for pilot ignition conditions. However, in auto-ignition, the ignition time and critical mass flux increases with sample angle α. Furthermore, a computational fluid dynamic model have been built based on the Fire Dynamics Simulator (FDS6) code to investigate the mechanisms controlling the dependence on sample orientation of the ignition of PMMA under external radiant heating. The results of theoretical analysis and modeling results indicate the decrease of total incident heat flux at sample surface plays the dominant role during the ignition processes of auto-ignition, but the volatiles gas flow has greater influence for piloted ignition conditions.

Investigation on the dependence of flash point of diesel on the reduced pressure at high altitudes

Abstract: The high altitudes of the plateau areas lead to a decreasing flash point temperature of liquid fuels due to the reduced ambient pressure It indicates that liquid fuels suffer greater fire and explosion hazards at high altitudes To reveal the dependence of flash point on reduced pressure at high altitudes, a series of field flash point determinations are performed at six different altitudes on the Qinghai–Tibet Plateau The results show that flash point decreases nonlinearly with the reduced pressure, which is inconsistent with the current standards of flash point determination, where adopt a linear correction for the pressure effect on flash point Taking diesel as an example, two methods, the Clausius–Clapeyron relation method and the LCR method, are proposed to predict the flash point of diesel under different pressures The results show that the predictive accuracy of the two methods is similar, and both of the two methods give more accurate predictive flash point than the linear relationship The Clausius–Clapeyron relation is validated to be able to expound the dependence of flash point of liquid fuels on reduced pressure These two methods can complement each other The Clausius–Clapeyron relation method is recommended when the accurate the phase-transition enthalpy is known, the LCR model is an available method when the phase-transition enthalpy is unknown or uncertain, especially for the complicated fuel mixtures

Ignition and burning behaviors of automobile oil in engine compartment

Abstract: Accidental leakage of automobile oils is of great inclination to initiate pool fires in engine compartment, with threats to induce the flashover of other components and flame penetration into the passenger compartment. This paper presents experimental results of the ignition and burning behaviors of a kind of automobile oils (automatic transmission oil) using a cone calorimeter. Measurements of oil temperature, ignition time, mass loss and heat release rate are performed at different external heat fluxes and initial fuel depths. The comparison between experimental and numerical oil temperature evolutions shows that the variations of the ignition time at different experimental conditions depend on the heat dissipation process inside the liquid phase. The steady mass burning rate is nearly independent of initial fuel depth and has a linear relation with external heat fluxes. In addition, the results indicate an increase in peak heat release rate by a large margin initially, followed by a relatively small margin under thicker initial fuel depths, while its variations are proportional to external heat fluxes. Correlations are also developed to determine the peak heat release rate as a function of the initial fuel depth.

Convection Heat Transfer

Abstract: Geometry: shape, size, aspect ratio and orientation Flow Type: forced, natural, laminar, turbulent, internal, external Boundary: isothermal (Tw = constant) or isoflux (q̇w = constant) Fluid Type: viscous oil, water, gases or liquid metals Properties: all properties determined at film temperature Tf = (Tw + T∞)/2 Note: ρ and ν ∝ 1/Patm ⇒ see Q12-40 density: ρ ((kg/m) specific heat: Cp (J/kg ·K) dynamic viscosity: μ, (N · s/m) kinematic viscosity: ν ≡ μ/ρ (m/s) thermal conductivity: k, (W/m ·K) thermal diffusivity: α, ≡ k/(ρ · Cp) (m/s) Prandtl number: Pr, ≡ ν/α (−−) volumetric compressibility: β, (1/K)

Influence of vertical channel on downward flame spread over extruded polystyrene foam

Abstract: The influence of vertical channel with various structure factors (α) on downward flame spread over extruded polystyrene (XPS) foam is investigated. The flame shape, flame height (Hf), temperature in the channel (Tv) and on the curtain wall surface (Tc), flame spread rate (Vf), and induced air flow (Q) are obtained. Hf first drops and then increases as α rises, attributing to similar changing trends of induced airflow rate and Froude number. Concerning the temperature history, Tc > Tv at the initial stage while Tc T c ‾ (average value) and T v ‾ drop as α rises, and T v ‾ > T c ‾ under most conditions. A model is established to predict the total, convective and radiative heat fluxes transferred to preheating zone. The convective heat flux is more dominant than the radiative heat feedback from the curtain wall. Vf first rises and then drops as α increases. For α

Experimental and theoretical study on downward flame spread over uninhibited PMMA slabs under different pressure environments

Abstract: This paper presents an experimental and theoretical study of side-edge effects on downward flame spread over two parallel polymethyl methacrylate (PMMA) slabs under different pressure environments. Identical experiments of downward flame spread over thin PMMA slabs with side-edges unrestrained were conducted at different altitudes in Hefei (102 kPa), Geermu (73.2 kPa) and Lhasa (66.3 kPa). Experimental results show that the flame spread rate is controlled by ignition along the side-edge, rather than at the center of the samples, for experiments with both single and two parallel slabs. Based on these results, a thermal model is developed which describes flame spread along the edge and quantitatively agrees with experimental results. In the parallel-slab case, convective heating appears to influence the spread rate only when the separation distance is very small, with radiative heating playing a more important role as separation distance increases. The angle of the pyrolysis front, formed between the faster side-edge spread and slower center-region spread, hardly changes with pressure, but changes significantly with separation distance, due to differing modes of heat transfer between the side-edge and center region. In addition, variations of flame height with pressure and separation distance are reasonably interpreted from diffusion flame theory.

A state-of-the-art review of fire safety of photovoltaic systems in buildings

Abstract: Considering that the buildings sector consumes a significant amount of energy and consequently emits greenhouse gases, reducing energy consumption and demand in buildings by employing advanced clean and energy efficient technologies is a vital worldwide commitment. This is why green building and energy efficient technologies, especially photovoltaic (PV) systems, have been widely applied in new and existing constructions. They can, however, cause a new intractable challenge, i.e., fire safety. This paper presents a state-of-the-art review of the increasing number of scientific studies on photovoltaic system fire safety. Real fire incidents and faults in PV systems are briefly discussed, more particularly, original fire scenarios and victim fire scenarios. Moreover, studies on fire characteristics of photovoltaic systems and the suggested mitigation strategies are summarized. Hence, the focus of this paper is on fire safety of the system which is not only limited to surveying the existing literature but also detecting the research gaps. The analysis reveals that a PV fire incident is a complex and multi-faceted topic that cannot be simplified to a single variable causing a single outcome. This calls for stronger integration of all aspects while studying the cause of the fire and the resulting combustion products. Overall, this paper is envisioned to assist the researchers in the field of PV systems by mapping the fire characteristics of photovoltaic and helps to develop fire prevention strategies for building designers and decision-making authorities.

Experimental study on the burning rates of Ethanol-Gasoline blends pool fires under low ambient pressure

Abstract: Ethanol-Gasoline has been used as vehicles fuel in areas widely in world, especially in China with areas from plain to high altitude. The addition of ethanol in gasoline will change the physicochemical properties of pure fuels, and then affect the burning behaviors. In this study, the burning rates of blending fuels were mainly investigated in a full-scale cargo compartment with ambient pressure of 40 kPa, 61 kPa, 80 kPa, 101 kPa. A 20 cm round pool filled with fuels at ethanol ratio of 0%, 10%, 20%, 50%, 80% and 100% by volume was employed. Mass burning rate, flame temperature, fuel temperature as well as flame images were measured and analyzed. The results indicate that as ambient pressure decreases, the burning rate decreases, and flame height increases significantly, but only the temperature at the flame base region is affected obviously. With increasing ethanol ratio, the burning rate shows a non-monotonic variation with a peak value, and the maximum value occurs at a certain ethanol ratio varied with pressure; but the maximum value of flame height and flame temperature occurs at ethanol ratio of about 20% and ambient pressure of 40 kPa, and shows a monotonic decrease at relative large pressure. A simple empirical correlation for burning rate data is developed based on ambient pressure, stoichiometric ratio and the ratio of the heat of combustion to the heat of vaporization, which shows a good agreement with 15% deviation.