Ruowen Zong

Preparation and thermal stability of polypropylene/montmorillonite nanocomposites

Two different methods were used to prepare polypropylene/clay nanocomposites. One was from pristine montmorillonite and a reactive compatibilizer hexadecyl trimethyl ammonium bromide (C6); the other is from different organophilic montmorillonites (OMT). The nanocomposites structures are demonstrated by X-ray diffraction (XRD) and transmission electron microscopy (TEM); The thermal properties of the nanocomposites were investigated by thermogravimetric analysis (TGA). It is shown that different methods and organophilic montmorillonites influence the morphology and thermal stability of polypropylene/clay nanocomposites.

Halogen-free flame retardation and silane crosslinking of polyethylenes

Halogen-free flame-retarded and silane crosslinkable polyethylenes have been prepared by a melt process using magnesium hydroxide (MH) as a flame retardant. The effects of silane concentration, peroxide concentration, etc. on the silane grafting on linear low density polyethylenes were investigated. The thermal analysis of the silane crosslinked polyethylenes was performed by thermogravimetry (TG), and its results show that silane crosslinking provides an increase in the thermal stability of polyethylenes. The combustion characteristics of the silane crosslinked polyethylenes containing MH have also been studied using limiting oxygen index (LOI) and the Cone Calorimeter. The rate of heat release and smoke emission of the silane crosslinked polyethylenes decrease, and LOI, the time to ignition and the residue after combustion increase as MH content increases.

Preparation and characterization of polystyrene/graphite oxide nanocomposite by emulsion polymerization

Polystyrene intercalated graphite oxide (GO) nanocomposite was prepared by emulsion polymerization reaction and characterized by X-ray diffraction (XRD), high resolution electron microscopy (HREM), and thermogravimetric analysis (TGA). It was shown that polystyrene can be intercalated into the interlayer space of GO and form exfoliated and intercalated nanocomposites. The thermal analysis demonstrated that the presence of GO enhances the char residue of the nanocomposite.

Classification and identification of soot source with principal component analysis and back-propagation neural network

Identification of soot sources is significant in fire investigation and forensic science. In this paper, principal component analysis (PCA) and a back-propagation (BP) neural network model have been used to classify and identify the soot samples from three different kinds of combustible material. Diesel, polystyrene and acrylonitrile butadiene styrene were burnt under the controlled combustion conditions in small-scale burn tests. Based on the matrix data from the GC-MS analysis data, two principal components have been obtained from PCA analysis with the cumulative energy content of 90.21%. Three different kinds of soot sample can be classified with 100% accuracy. A BP neural network model for predicting and identifying the soot source has been further developed. Accurate identification of the unknown samples has been achieved with this trained BP model. This pilot study indicates that PCA and BP neural network methods have potential in the analysis of soot to identify its principle pre-combustion source material.

Effect of Different Fuels on Confined Compartment Fire

Experimental simulations of confined compartment fires are conducted in a reduced-scale compartment. Different areas of fire source and different types of fuel are considered in order to investigate the fire growth process and critical condition for flashover according to the changeable fire source characteristics. For these experimental cases, profiles of mean upper layer temperatures and temperature fluctuations are measured. The mass flow rate out from two vents is extensively discussed. A dimensionless model of this compartment fire growth is developed based on the nonlinear dynamics model. The critical criterion for flashover to occur is revised later, which shows that the energy gain rate and loss rate intersect at the turning point of fuel controlled fire and ventilation controlled fire. Finally, the simulation results of the model are compared with experimental data and the critical boundary between flashover and nonflashover is illustrated to show that the theoretical prediction reasonably agreed with experimental results except for polyethylene, where a higher value of fuel property number, , existed.Experimental simulations of confined compartment fires are conducted in a reduced-scale compartment. Different areas of fire source and different types of fuel are considered in order to investigate the fire growth process and critical condition for flashover according to the changeable fire source characteristics. For these experimental cases, profiles of mean upper layer temperatures and temperature fluctuations are measured. The mass flow rate out from two vents is extensively discussed. A dimensionless model of this compartment fire growth is developed based on the nonlinear dynamics model. The critical criterion for flashover to occur is revised later, which shows that the energy gain rate and loss rate intersect at the turning point of fuel controlled fire and ventilation controlled fire. Finally, the simulation results of the model are compared with experimental data and the critical boundary between flashover and nonflashover is illustrated to show that the theoretical prediction reasonably agreed with experimental results except for polyethylene, where a higher value of fuel property number, δ, existed.

Study on multi-section, nonlinear model of flashover in a long–narrow confined space

The particularity in building structures of long–narrow spaces makes it different from the study of flashover model from the conventional theory. In this article, based on the nonlinear dynamics theory, a multi-section model was proposed to analyze the phenomenon of flashover. In this model, long–narrow confined space was divided into several sections, and each section was further divided into two zones, as hot smoke layer and cold air layer. The continuity equation and energy equation for each control volume defined from thermal smoke layer were established. The critical radius for the onset of flashover has been determined theoretically. In this article, a comparison with experiment for a multi-section, nonlinear model of flashover is presented, and the modeling results are compared with the experimental data which were obtained through a batch of fire tests in a reduced scale, long–narrow confined space. The theoretical calculation results agree reasonably well with measured results, in which the critical temperature and fire radius of flashover can be predicted. In general, for the polypropylene cribs, the predicted results are broadly consistent with the experimental results when the fire radius is below this critical value, but for heptane and wood cribs, the predicted value is a little higher. However, the model is useful in predicting the critical fire radius and temperature for flashover. In this article, the relationship between the characteristic parameters of fuel and the critical radius of fire source has also been investigated, which is linear growth.

Experimental Study on Pyrolysis of Black Non-Charring Polymers in the Reduced-Pressure Environment

A series of experiments on a black non-charring polymer in the low-pressure chamber is conducted under different external heat fluxes. The surface and bottom temperatures and the mass loss of the sample are measured. A parameter Tp is introduced to describe the impact of pressure on the surface temperature. There is a loose layer of the char residue left with significant pyrolysis bubbles under the low heat flux, and the bubble size decreases with pressure. The parameter Tp is found to exhibit a significant decline trend with increasing pressure, and the mass loss rate of the sample decreases apparently as the pressure increases. However, under a high heat flux, the char residue is denser, and the pyrolysis bubbles are not observed. The value of Tp and the mass loss rate of the sample have no obvious relationship with pressure. The average pyrolysis rate is linearly proportional to pa.

Experimental Study and Model Analysis of Flashover in Confined Compartments

Catastrophe analysis of flashover has been studied based on a series of fire experiment in three different scales of compartment. The experimental data have been compared with the theoretical values predicted by a nonlinear fire growth model, which were in reasonable agreement with the theoretical bifurcation curves. Several critical conditions for flashover to occur have been also investigated, including the ceiling height, the fire radius, and the compartment scale size. The results showed that fire radius played the dominating role in the occurrence of flashover, and the characteristic value of fuel, χH c /H vap , could be regarded as the dominating factor for the width of unstable range at the theoretical curves. And the scaling correlation between the compartment size and the critical fire radius appeared to be \( {R}_f\propto {L}_c^{3/4} \) from the tests.

Influence of fire accelerant on the thermal degradation and ignition of wood chip

It is important in fire investigation and forensic science to understand how a fire accelerant can influence the combustible material in the fire process. In this paper, thermogravimetric analysis and burning tests have been conducted to study the effect of gasoline on the decomposition and ignition of camphorwood. The results have shown that the major effect of gasoline during the woods decomposition takes place in the stage of dehydration (30~150℃) and major decomposition reaction (250~400℃). The Coats-Redfern integral method has been applied for the degradation in nitrogen, indicating the overall activation energy for the degradation has been decreased with the addition of gasoline to wood. The ignition time has been shortened and the ignition temperature has been reduced with the increase of gasoline volume, and the largest reduced range is 86.3% and 69.5% respectively, but with a limit for saturation. The ignition temperatures dropped with the increase of heat flux for wood with 1 mL of gasoline and, at the lower value of heat flux, the change of ignition temperature and time is more sensitive. The results could help better understand of the effect of fire accelerants in investigations into the cause of fires.

Experimental and Numerical Study of Ceiling Jet Fire in a Confined Reduced-scale Corridor

Safety evaluation and assessment becomes an important topic in the design and operation of tunnels and other underground corridors nowadays. The computational fluid dynamics (CFD) model is an indispensable tool in this process, which can predict the possible fire scenarios by calculating the temperature, concentration, velocity and heat transfer in the domain of concern. In this paper, a validation study for a newly developed CFD code SIMTEC is presented, and the modeling results are compared with experimental data which were obtained through a batch of fire tests in a reduced-scale corridor. The simulations agree reasonably well with measured results. In general, the CFD model predicts the hot layer temperature and CO2 concentration with good accuracy, especially at the position closer to the end of the corridor. The CO concentration close to the fire source is also well captured in the simulation. However, the CO concentration prediction downstream, far away from fire source, is poor. In this study, the effect of corridor fire intensity was also investigated, by varying the fire source size while with other parameters fixed. Both the measurements and the simulation indicate that the average hot layer temperature near the fire source did not change obviously despite the increase in the fire source size.