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Cong H.Y.,Hefei University of Technology | Wang X.S.,Hefei University of Technology | Wang X.S.,Collaborative Innovation Center for Urban Public Safety | Zhu P.,Hefei University of Technology | And 2 more authors.
Applied Thermal Engineering | Year: 2017

This study investigated the smoke extraction process by natural ventilation through a vertical shaft. In addition, the factors restricting smoke exhaust, such as plug-holing and boundary layer separation are discussed. Accordingly, a new concept (board-coupled shaft) is introduced to solve the dilemma. By installing a thin board under the shaft, the negative effect of plug-holing can be eliminated, leading to higher smoke-extraction efficiency in the shaft. Numerical simulations were performed using the Fire Dynamic Simulation (Version 6.1.2). The influences of board location and fire heat release rate on smoke extraction were investigated. Furthermore, the validity of this model was proved, and the results indicate that the distance between the board and shaft should be properly selected. In addition, a new empirical model was deduced to predict the mass flow rate inside the shaft, which agrees well with the experimental data. © 2017 Elsevier Ltd


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.


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.


Yan J.,Hefei University of Technology | Wang Q.,Hefei University of Technology | Wang Q.,Collaborative Innovation Center for Urban Public Safety | Wang Q.,CAS Hefei Key Laboratory of Materials for Energy Conversion | And 3 more authors.
Applied Thermal Engineering | Year: 2016

One kind of composite board based battery thermal management system (BTMS) is proposed and a three-dimension battery thermal model is proposed in this work. The composite board consists of three parts with a sandwich structure, which contains a heat conducting shell, an insulation panel and phase change material (PCM). Then four different modes are compared in detail to verify the thermal performance of the composite board under normal operating condition and thermal abuse condition. The results show that the composite board can effectively improve the heat dissipation capability and the uniformity of the temperature, meanwhile it can enhance the heat-insulation capability of the battery pack to prevent the thermal runaway propagation. In addition, increasing the latent heat of PCM can greatly improve the thermal performance of the composite board, thus the PCM with a latent heat of 1125 kJ/kg and the phase change temperature between 303.15 K and 323.15 K are recommend to be used in the battery thermal management. © 2016 Elsevier Ltd


Wang Y.,Hefei University of Technology | Wang Y.,City University of Hong Kong | Wang Q.,Hefei University of Technology | Wang Q.,Collaborative Innovation Center for Urban Public Safety | And 3 more authors.
Applied Thermal Engineering | Year: 2016

The breakage and fallout of glass façades may easily occur and significantly affect the enclosed fire dynamics. However, little is known about the effect of fire location on the glass thermal response. In particular, due to large size and various installation forms, glass façades perform differently when fire location alters. The different glass thermal performances, resulting from fire location changing from glass edge to center, are simulated using finite element method. Frame supported and point supported glass panes are employed. The glass stress distribution, breaking time, crack initiation and propagation are presented. It is established that fire location has a notable influence on thermal behavior of glass. Frame supported glass façades are more prone to breakage when fire located in the center of a pane. If the fire is positioned close to the fixing points, point supported glass façades will be more prone to breaking. For the purpose of comparison, relevant full-scale experimental results are presented. It is intended the results will provide useful knowledge for the fire resistance optimization of glass façades. © 2016 Elsevier Ltd


Ping P.,Hefei University of Technology | Ping P.,China University of Petroleum - East China | Wang Q.,Hefei University of Technology | Wang Q.,Collaborative Innovation Center for Urban Public Safety | And 5 more authors.
Journal of Power Sources | Year: 2015

Abstract A full-scale burning test is conducted to evaluate the safety of large-size and high-energy 50 Ah lithium-iron phosphate/graphite battery pack, which is composed of five 10 Ah single cells. The complex fire hazards associated with the combustion process of the battery are presented. The battery combustion behavior can be summarized into the following stages: battery expansion, jet flame, stable combustion, a second cycle of a jet flame followed by stable combustion, a third cycle of a jet flame followed by stable combustion, abatement and extinguishment. The multiple jets of flame indicate serious consequences for the battery and pose a challenge for battery safety. The battery ignites when the battery temperature reaches approximately 175-180 C. This critical temperature is related to an internal short circuit of the battery, which results from the melting of the separator. The maximum temperature of the flame can reach 1500 C. The heat release rate (HRR) varies based on the oxygen generated by the battery and the Joule effect of the internal short circuit. The HRR and heat of combustion can reach 49.4 kW and 18,195.1 kJ, respectively. The state of charge of the battery has a significant effect on the maximum HRR, the overall heat generation and the mass loss of the battery. © Elsevier Inc. All Rights reserved.


Tang F.,Hefei University of Technology | Tang F.,Anhui University of Science and Technology | Hu L.H.,Anhui University of Science and Technology | Hu L.H.,Collaborative Innovation Center for Urban Public Safety | And 3 more authors.
Energy and Buildings | Year: 2015

This paper compares the heat flux profile upon building external facade due to ejected thermal plume from window in a subatmospheric pressure (64 kPa, Lhasa, Tibet, altitude: 3650 m) with that in normal pressure (100 kPa, Hefei, altitude: 50 m) and proposes a global correlation for these two pressures. A set of experiments is carried out in a 0.4 m cubic scale room model with a facade wall attached and a window of various geometries in these two altitudes to study the influence of the ambient pressure on the heat flux profile upon external facade due to ejected thermal plume from the room. Water-cooled heat flux gage arrays are employed to measure the vertical heat flux profile upon the facade wall. It is found that the heat flux profile upon the facade wall in the vicinity of window is much higher in the subatmospheric pressure than that in the normal pressure. A new global correlation is proposed to characterize the vertical profile of the heat flux upon external facade in the thermal plume region by accounting for relative entrainment change in these two pressures. © 2015 Elsevier B.V. All rights reserved.


Sun Q.,Hefei University of Technology | Wang Q.,Hefei University of Technology | Wang Q.,Collaborative Innovation Center for Urban Public Safety | Wang Q.,CAS Hefei Key Laboratory of Materials for Energy Conversion | And 3 more authors.
Energy Conversion and Management | Year: 2015

To analyze the thermal behavior of 945 mA h lithium titanate battery during charging and discharging processes, the experimental and numerical studies are performed in this work. The cathode and anode of the 945 mA h lithium titanate soft package battery are the lithium nickel-cobalt-manganese-oxide and lithium titanate, respectively. In the experiment, an Accelerating Rate Calorimeter combined with battery cycler is employed to investigate the electrochemical-thermal behavior during charge-discharge cycling under the adiabatic condition. In numerical simulation, one electrochemical-thermal model is adopted to predict the thermal response and validated with the experimental results. From both experimental and simulated results, the profile of potential and current, the heat generation, the temperature, the temperature changing rate and the temperature distribution in the cell are obtained and thermal runaway is predicted. The analysis of the electrochemical and thermal behavior is beneficial for the commercial application of lithium titanate battery in the fields of electric vehicles and hybrid electric vehicles. © 2014 Elsevier Ltd. All rights reserved.


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.


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.

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