Effect of shielding rates on upward flame spread over extruded polystyrene foam in vertical channel and heat transfer mechanism

Fire hazard of extruded polystyrene (XPS) thermal insulation materials has aroused public concern. In order to develop flame spread theory and the guideline for fire risk assessment of XPS, an experimental study on upward flame spread behavior and heat transfer mechanism of XPS in a vertical channel with different frontal shielding rates was conducted. Maximum temperature at the place 2 cm from XPS surface and at the center of channel first increase and then decrease as the shielding rate rises. The former is higher than the latter. Experimental value of average flame height rises as the shielding rate increases. A model for predicting the flame height is built, and the predicted results are consistent with the experimental results. Moreover, the relation between flame height and pyrolysis height under different shielding rates is obtained. The flame spread rate rises as the shielding rate increases. A prediction model of flame spread rate is established, and its prediction results are more accurate compared with those from previous models. The model also predicts that radiative heat transfer is the dominant heat transfer mode, accounting for 93% of the total heat transfer. This work is beneficial for fire risk assessment and fire safety design of building façade.     

Inhibition of counterflow methane/air diffusion flame by water mist with varying mist diameter

In the present study, the effect of fine water mist on extinguishment of a methane–air counterflow diffusion flame was investigated to understand the underlying physics of fire extinguishment of highly stretched diffusion flame by water mist. Twin-fluid atomizers were used to generate polydisperse water mist of which Sauter mean diameters were 10, 20, 40, and 60 μm. When water mist is not added, the critical stretch rate at extinguishment is 439 s⁻¹ as compared to the theoretical value of 460 s⁻¹. For the case with water mist addition, when the stretch rate is small enough, almost all the water mist evaporates within the flame zone. On the other hand, for high stretch rate case, large mist droplets pass through the flame zone and can reach the stagnation plane. However, no oscillatory motion was found around the stagnation plane. Critical stretch rate at extinguishment decreases monotonously with the mass fraction of water mist independently of the mist diameter within the range of D₃₂ from 10 μm to 60 μm. On the other hand, with increase in the surface area parameter, the critical stretch rate at extinguishment decreases rapidly and becomes less sensitive at large surface area parameter, of which tendency is qualitatively in good agreement with theoretical predictions. For a constant surface area parameter, the critical stretch rate decreases with mist diameter because the mass fraction of water mist should increase in proportion to the mist diameter to keep the surface area parameter constant. When the water mist evaporates completely in the flame zone as in the present study, the mass fraction of the water mist is the dominant factor for fire extinguishment, rather than the surface area parameter. Therefore, an appropriate combination of stretch rate and water mist mass fraction should be provided to suppress effectively a given fire with a small amount of water mist.     

Characterization of a plasma polymer coating from an organophosphorus silane deposited at atmospheric pressure for fire-retardant purposes

Protective coatings from diethylphosphatoethyltriethoxysilane (DEPETS) have been deposited on different polymer substrates in a plasma discharge operated at atmospheric pressure. Plasma polymer chemistry and structure were characterized by means of Fourier transform infrared spectroscopy (FTIR), laser desorption ionization-mass spectrometry (LDI-MS), nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). A chemical structure of the plasma polymer has been proposed based on the coating molecular characterization. Coatings were deposited on polycarbonate (PC) and polyamide 6 (PA6) substrates. The flame retardant properties of coated substrate samples were assessed using cone calorimetry and compared to those of bare substrates. A significant increase in the time to ignition (TTI), up to +143%, was recorded after coating deposition due to the formation of a high-performance barrier layer at the surface of both polymer substrates.     

纸芯片-敞开式质谱法分析减肥保健品的3种常见非法添加剂

目的 建立纸芯片与敞开式质谱联合法检测减肥保健品中3种常见非法添加剂的分析技术。方法 依据酸刻蚀法制备通道型纸芯片, 分别考察纸芯片的几何通道尺寸、不同比例有机喷雾溶剂所需的通道疏水坝宽度和喷雾电压对目标物的分析响应影响。将纸芯片与敞开式质谱联合, 分析减肥保健品中西布曲明、安非他酮和氟西汀的成分。结果 在正离子模式和3.5 kV电压下, 以甲醇/水为溶剂, 3种目标物在0.25~50.00 μg/mL表现出良好的线性关系, r2均大于0.99, 检出限为0.1 μg/mL, 回收率为89.9%~107.4%, 3种目标物在纸芯片喷雾纸上的相对强度与普通三角形喷雾纸增强了1.11~2.15倍, 线性关系也略有提高, 且检出限降低了2.75~3.5倍。25批次的实际样品中有19批次样品检测出了1种或多种违禁添加剂成分。结论 纸芯片结合敞开式质谱法可用于减肥类保健品中违禁添加剂的快速筛查手段。     

Experimental study on the propagation characteristics of hydrogen/methane/air premixed flames in a narrow channel

This work is focused on the explosion characteristics of premixed gas containing different volume fractions of hydrogen in a narrow channel (1000 mm × 50 mm × 10 mm) under the circumstance of stoichiometric ratio. The ignition positions were set in the closed end and the middle of the pipeline respectively. The results showed that when the gas was ignited at the pipeline closed end, the propagating flame was tulip structure for different premixed gas. When the hydrogen volume fraction was less than 40%, the flame propagation speed increased significantly with the rise of hydrogen volume fraction, and the overpressure peak also appeared obviously in advance. However, when the volume fraction of hydrogen was more than 40%, the increase of flame propagation speed and the overpressure peak occurrence time varied slightly. Furthermore, when the ignition position was placed in the middle of the pipeline, the flame propagation speed propagating to the opening end was much faster than that propagating to the closing end, and there was no tulip shape when the flame propagates to the opening end. The flame propagating to the closed end appeared tulip shape under the influence of airflow, and high-frequency flame oscillation occurred during the propagation. This work shows that the hydrogen volume fraction and ignition position significantly affected the flame structure, flame front speed, and explosion overpressure.     

Numerical investigation on the effects of reaction orders on the flame propagation dynamic behaviors for premixed gas in a closed tube

In this paper, the premixed flame propagation in a closed tube is surveyed using Computational Fluid Dynamics. The propagation characteristics of premixed flame are obtained coupling a single-step reaction mechanism with a laminar flame model. Three single-step reaction mechanisms are established with different reaction orders for hydrocarbon fuels. This study is to establish a wider range of reaction mechanisms and represent actual experimental conditions better. The numerical simulation results demonstrate that reaction orders can affect the tulip flame development. As the flame spreads, the tulip flame fronts become wrinkled. When the reaction order is 2, there are more wrinkles in the flame front and the degree of wrinkles is more obvious. Reaction orders also affect the flame tip velocity and the flame skirt velocity. The main reason is that laminar flame speeds are significantly different. When the reaction orders are 1.5 and 2, laminar flame speeds are mainly affected by temperature, which respectively increase by about 25% and 75%. When the reaction order is 1, the pressure is crucial for the variation of laminar flame speed. The laminar flame speed decreases by about 33%.     

Experimental study on the effect of diluent gas on H2/CO/air mixture turbulent premixed flame

To study the effects of different diluents on the propagation characteristics of H₂/CO/air mixture turbulent premixed flames, a series of experiments were carried out in a turbulent premixed flame experimental system. The effects of turbulence intensity (0.49–1.31 m/s), dilution gas content (10%, 20%, and 30%), hydrogen fraction (50%, 70%, and 90%), and equivalence ratio (0.6, 0.8, and 1.0) on the turbulent premixed flame were studied. The results show that with the increase in hydrogen fraction or turbulence intensity or equivalence ratio, the S_T and u_t increase at the same radius. Compared with N₂ dilution, CO₂ dilution showed a more obvious inhibition effect on S_T. With the increase of Ka, S_T;35mm/u’ gradually decreased, and the extent of S_T;35mm/u’ decrease gradually became smaller. As the intensity of turbulence increases or the hydrogen fraction increases, the slope of S_T,35mm/u’ with Da/Le gradually decreases. In the turbulence intensity range of this experiment, the u_t,35mm/μ_l under nitrogen dilution condition has a larger floating range. The growth rate of u_t,35mm/μ_l at a low equivalence ratio is significantly higher than that at a high equivalence ratio.     

Flame characteristics of premixed H2-air mixtures explosion venting in a spherical container through a duct

The explosion venting duct can effectively reduce the hazard degree of a gas explosion and conduct the venting energy to the safe area. To investigate the flame quantitative propagation law of explosion venting with a duct, the effects of hydrogen fraction and explosion venting duct length on jet flame propagation characteristics of premixed H₂-air mixtures were analyzed through experiment and simulation. The experiment results under initial conditions of room temperature and 1 atm show that when hydrogen fraction was high enough, part of the unburned hydrogen was mixed with air again to reach an ignitable concentration, resulting in the secondary combustion was easier produced and the duration of the secondary flame increased. With the increase of venting duct length, the flame front distance and propagation velocity increased. Meanwhile, the spatial distribution of pressure field and temperature field, and the propagation process and mechanism of the flame venting with a duct were analyzed using FLUENT software. The variation of the pressure wave and the pressure reflection oscillation law in the explosion venting duct was captured. Therefore, in the industrial explosion venting design with a duct, the hazard caused by the coupling of venting pressure and venting flame under different fractions should be considered comprehensively.     

Fabrication and characterization of MnO2 based composite sheets for development of flexible energy storage electrodes

Development of cost efficient, flexible and light weight paper electrodes for high-tech applications is high in demand in era of modern disposable technology. In this study α-MnO₂ nanorods were fabricated through hydrothermal method by varying growth time and further combined with lignocelluloses fibers extracted from self growing plant, Monochoria Vaginalis. Crystal structure, morphology and thermal properties of MnO₂ nanorods were characterized by X. Ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM) and Thermogravimetric Analysis (TGA), respectively. FESEM image analysis revealed the highest aspect ratio of 48.016 for 4?h treated MnO₂ sample and high purity level was confirmed by XRD. MnO₂ sample with high aspect ratio, relatively pure and larger yield was selected for incorporation of lignocelluloses fibers to fabricate flexible, light-weight and environmentally safe LC/MnO₂ composite paper sheet. Furthermore, LC/MnO₂ composite sheet was employed as working electrode in 2?M sodium sulfate electrolyte for cyclic voltammetry measurements. Presented LC/MnO₂ composite sheet revealed specific capacitances 117, 59, 39, 25 and 23?F/g at scan rates of 5, 10, 20, 50 and 100?mV/s, respectively. Incorporation of LC fibers within MnO₂ nanorods as binders will open the possibilities to fabricate the flexible paper electrode for application in supercapacitors and batteries due to facile synthesis, light-weight and environmentally friendly aspects.     

Synthesis of ZnO rod arrays on aluminum recyclable paper and effect of the rod size on power density of eco-friendly nanogenerators

In this work, we demonstrated a novel and effective approach on the use of low-cost electrodes, an eco-friendly substrate and zinc oxide (ZnO) micro or nanorods (MRs or NRs, respectively) for building triboelectric devices (TENGs). The reported strategy focuses on using low-cost materials and fabrication processes. For the first time and without any pre-treatment, an aluminum recyclable paper from the milk carton (named ARP) was used as a substrate and TENG bottom electrode. A systematic study on the growing of ZnO structures on ARP by chemical bath deposition has been carried out. We found that the ZnO rods size, and resistivity of the TENG upper electrode considerably influence the power density of the device. Such sustainable, low-priced ZnO-based TENGs can produce up to 1.6μW/cm² output power density when operated at 50?Hz. The fabrication of an eco-friendly nanogenerator demonstrates the possibility of manufacturing low-cost, flexible, and large-area energy harvesting devices for future applications.