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Wang X.,Hefei University of Technology | Wang X.,Collaborative Innovation Center for Urban Public Safety | Zhu P.,Hefei University of Technology | Li Y.,Hefei University of Technology | And 2 more authors.
Experimental Thermal and Fluid Science | Year: 2015

To investigate the effect of low ambient air pressure on the characteristics of water mist which was injected into a low pressure (<0.1MPa) environment, the sizes and velocities of the water droplets were measured using Shadowgraph technique. A stainless steel vessel with a diameter of 600mm and height of 800mm was designed for simulating low ambient air pressure conditions using a vacuum pump. Ambient air pressures of 0.1, 0.08, 0.06, 0.04, 0.02MPa, and working pressures of the water mist system of 1.0, 3.0, 4.0MPa were considered. The results show that, under each certain pressure of water mist system, both of the Sauter mean diameter (d32) and the arithmetic mean diameter (d10) of water mist droplets decrease with decrease of the ambient air pressure from 0.10 to 0.02MPa. An empirical formula has been developed to express the influence of ambient air pressure on Sauter mean diameter of water mist. In addition, the axial velocities of water mist droplets generated with working pressure of 3.0MPa and 4.0MPa decrease following a decrease in ambient air pressure, while there is no obvious variation to the tested results of the cases with 1.0MPa working pressure. © 2015 Elsevier Inc. Source

Zhang T.,Hefei University of Technology | Zhou X.,Hefei University of Technology | Yang L.,Hefei University of Technology | Yang L.,Collaborative Innovation Center for Urban Public Safety
Materials | Year: 2016

This work investigated experimentally and theoretically the fire hazards of thermal-insulation materials used in diesel locomotives under different radiation heat fluxes. Based on the experimental results, the critical heat flux for ignition was determined to be 6.15 kW/m2 and 16.39 kW/m2 for pure polyurethane and aluminum-polyurethane respectively. A theoretical model was established for both to predict the fire behaviors under different circumstances. The fire behavior of the materials was evaluated based on the flashover and the total heat release rate (HRR). The fire hazards levels were classified based on different experimental results. It was found that the fire resistance performance of aluminum-polyurethane is much better than that of pure-polyurethane under various external heat fluxes. The concentration of toxic pyrolysis volatiles generated from aluminum-polyurethane materials is much higher than that of pure polyurethane materials, especially when the heat flux is below 50 kW/m2. The hazard index HI during peak width time was proposed based on the comprehensive impact of time and concentrations. The predicted HI in this model coincides with the existed N-gas and FED models which are generally used to evaluate the fire gas hazard in previous researches. The integrated model named HNF was proposed as well to estimate the fire hazards of materials by interpolation and weighted average calculation. © 2016 by the authors. Source

Yang H.-Y.,Anhui University of Science and Technology | Zhou X.-D.,Anhui University of Science and Technology | Yang L.-Z.,Anhui University of Science and Technology | Yang L.-Z.,Collaborative Innovation Center for Urban Public Safety | Zhang T.-L.,Anhui University of Science and Technology
Materials | Year: 2015

Many of the photovoltaic (PV) systems on buildings are of sufficiently high voltages, with potential to cause or promote fires. However, research about photovoltaic fires is insufficient. This paper focuses on the flammability and fire hazards of photovoltaic modules. Bench-scale experiments based on polycrystalline silicon PV modules have been conducted using a cone calorimeter. Several parameters including ignition time (tig), mass loss, heat release rate (HRR), carbon monoxide (CO) and carbon dioxide (CO2) concentration, were investigated. The fire behaviours, fire hazards and toxicity of gases released by PV modules are assessed based on experimental results. The results show that PV modules under tests are inflammable with the critical heat flux of 26 kW/m2. This work will lead to better understanding on photovoltaic fires and how to help authorities determine the appropriate fire safety provisions for controlling photovoltaic fires. © 2015 by the authors. Source

He S.,Anhui University of Science and Technology | Li Z.,Anhui University of Science and Technology | Shi X.,Anhui University of Science and Technology | Yang H.,Anhui University of Science and Technology | And 3 more authors.
Advanced Powder Technology | Year: 2015

In this study, we tried to synthesize ultralow density and super hydrophobic silica aerogel with extra high specific surface area, by using absolutely cost effective processing from sodium silicate. Hydrosol was obtained through ion exchange. To reduce the processing time, the gels were mechanically agitated to granules before solvent exchange. N,N-Dimethylformamide (DMF), serving as drying control chemical additive (DCCA), was introduced to reduce shrinkage. When the molar ratio of Si in sodium silicate to DMF is 0.31, the pore size distribution is the narrowest. Before dried under ambient pressure, the gels were surface modified by Trimethylchlorosilane (TMCS) in order to make sure the aerogels are hydrophobic. And the proper molar ratio of TMCS to pore water is 0.0233 which is much lower than that in previous experiments. The resulting aerogels have well-developed mesoporous structure with extremely high specific surface area (817 m2/g) and super hydrophobicity (contact angle of 165°). © 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. Source

Peng F.,Anhui University of Science and Technology | Zhou X.-D.,Anhui University of Science and Technology | Zhao K.,Anhui University of Science and Technology | Wu Z.-B.,Anhui University of Science and Technology | And 2 more authors.
Materials | Year: 2015

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. © 2015 by the authors. Source

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