Explosion-venting is crucial for ensuring the safe operation of utility tunnels. This study introduces internal explosion-venting protection measures specifically designed for utility tunnels. The study investigated flame propagation and pressure changes under internal explosion-venting in utility tunnels by developing a comprehensive utility tunnel explosion process simulation platform. The factors affecting the efficiency of internal explosion venting were explored by varying the positions of vents and installing porous materials with different porosities. The results show that after implementing internal venting measures, there was a notable reduction in both overpressure and flame propagation velocity. Positioning the vent closer to the ignitor proved advantageous for explosion-venting. After installing porous materials in the vents, it was observed that materials with small PPI experienced quenching failure, allowing flames to penetrate into the explosion-venting interlayer and potentially trigger a secondary explosion. Conversely, porous materials with large PPI demonstrated successful venting and quenching capabilities. The study provides a scientific theoretical foundation for developing gas explosion venting strategies in utility tunnels.

The sulfonated branched polybenzimidazole(sb-PBI)membranes with theoretical sulfonation degrees of 30％,40％,50％,and 60％are prepared by reacting between synthesized branched polybenzimidazole and 1,4-butane sultone for application in all-vanadium flow battery(VFB).Among them,the sb-PBI-50 membrane shows excellent vanadium ion resistance(9.34× 10-9 cm2/min),proton conductivity(2.05×10-2 S/cm),and selectivity(2.20×106 S·min/cm3).The coulomb efficiencies(96.26％-98.35％),voltage efficiencies(73.50％-90.19％),and energy efficiencies(71.72％-86.82％)of VFB with sb-PBI-50 membrane are higher than those of commercial Nafion 212 membrane under the current density of 80-280 mA/cm2.In addition,the VFB assembled with sb-PBI-50 membrane can stably carry out 1170 charge-discharge cycles at 140 mA/cm2.The chemical structure and micro-morphologies can remain stable after long-term cycles,indicating that the sb-PBI-50 membrane has good application potential in VFB.

The membrane always plays as a crucial component of vanadium flow battery (VFB), and its proton selectivity and stability determine battery efficiencies and life. Herein, a series of permselective cross-linked sulfonated polyimide (PFSPI-DNBC) membranes are constructed by using crown ether with proper cavity size as cross-linker to break the trade-off effect between proton conductance and vanadium ions blocking. In contrast to commerical Nafion 212 membrane, the as-optimized PFSPI-DNBC-15 membrane reveals outstanding comprehensive properties: same area resistance (0.21 Omega cm2), excellent vanadium ions blocking (0.44x10- 7 cm2 min- 1) and 15.91 times higher proton selectivity (5.41x105 S min cm- 3). Furthermore, the PFSPI-DNBC-15 membrane shows higher Coulomb efficiencies (CEs: 97.45%-98.35%) and energy efficiencies (EEs: 68.58%-87.76%) compared with Nafion 212 membrane (CEs: 92.74%-95.26%; EEs: 67.39%-81.28%) at 100-280 mA cm- 2. Exhilaratingly, the PFSPI-DNBC-15 membrane shows remarkable chemical structural and morphological stabilities over 2280 VFB cycles at 180 mA cm- 2. The internal reasons of improved stability of PFSPI-DNBC-15 membrane are described by simulation calculations. To sum up, the PFSPI-DNBC-15 membrane possesses a bright application prospect in VFB.

Urban growth has promoted the use of underground spaces, where explosion accidents can be catastrophic. In this study, we investigated the effect of placing flexible construction in front of rigid obstacles on methane explosion protection by using an experimental platform and adjusting the blockage rate and spacing of the obstacles. It aims to reduce the risk of gas explosions in urban underground spaces. The results of the study show that the flame propagation peak speed and peak overpressure are reduced with the decrease in the blocking rate of the flexible obstacle when the blocking rate of the flexible obstacle is less than or equal to the blocking rate of the rigid obstacle, with the decrease in the spacing, the better the protection effect of the methane explosion. When the blockage rate of the flexible obstacle is greater than the blockage rate of the rigid obstacle and spacing is less than the height of the flexible obstacle, rigid and flexible obstacles are connected as a whole, increasing the strength of the explosion. This study can provide a theoretical basis and scientific guidance for optimizing rigid and flexible object hybrid layouts and methane explosion protection technology in urban underground spaces.

Series of novel branched sulfonated polyimide/graphite oxide@zeolite imidazolate framework-67 (bSPI/ GO@ZIF67) composite membranes were prepared by a solution-casting method for vanadium redox flow battery (VFB) application. ATR-FTIR, EDS and XPS analyses confirm the successful fabrication of the bSPI/GO@ZIF67 composite membranes. The optimized bSPI/GO@ZIF67-1.5 % composite membrane shows outstanding performance, including a favorable area resistance (0.15 Omega cm2), reduced vanadium ion permeability (1.64 x 10- 7 cm2 min- 1), and exceptional proton selectivity (1.97 x 105 min cm- 3) compared with Nafion 212. Meanwhile, the bSPI/GO@ZIF67-1.5 % composite membrane shows superior coulomb and energy efficiencies (97.5 %-99.3 % and 88.1 %-73.7 %, respectively) at 100 mA cm- 2-300 mA cm- 2, along with an extended self-discharge duration of 50.4 h, outperforming Nafion 212. Furthermore, the membrane maintains stability over 800 charge/discharge cycles at 160 mA cm- 2. Theoretical calculations reveal strong hydrogen bonding interactions between the nitrogen in the imidazole group of ZIF67 and the hydrogen in the sulfonic group of bSPI, with a bond distance of 1.06 & Aring; and an interaction energy of -12.42 kcal mol- 1 individually. This interaction enhances the chemical stability of bSPI while effectively balancing proton conduction and vanadium ion blocking due to the incorporation of GO@ZIF67 fillers. Overall, the bSPI/GO@ZIF67-1.5 % composite membrane demonstrates significant potential for use in VFBs, offering enhanced efficiency, durability, and stability.

Flexible materials deform during flame propagation, altering their blockage ratio and the force exerted on the fluid due to various influencing factors. This affects gas explosion characteristics, changes the flame structure, and reduces explosion overpressure and flame speed. To determine the impact of flexible protective devices on the protection mechanism against gas explosions, this experiment used flexible obstacles (polyurethane sponge) as the protective apparatus. Employing a self-built explosion experiment platform, the research investigated methane explosion flame evolution, flame propagation speed, and explosion overpressure under various sizes of pre-positioned flexible obstacles. The study focused on observing the morphological evolution of methane explosion flames, the speed of flame spread, and the explosion overpressure in scenarios with pre-positioned obstacles of different sizes. The results showed that inserting flexible obstacles effectively reduced explosion overpressure and flame front propagation speed. Based on the working conditions set up in this experiment, the maximum rate of decrease in explosion overpressure exceeds 50% and the maximum rate of decrease in flame front velocity is around 20%. With pre-positioned flexible obstacles, as the blockage ratio of the flexible obstacle increased, the severity of deflagration also increased, with both explosion overpressure and flame front speed rising with the blockage ratio. Explosion overpressure and flame front speed also increased with the thickness of the flexible obstacle; simultaneously, the flame front position advanced with the thickness of the flexible obstacle. When constructing close-range protection devices, the height of the protection device should be lower than the protected object (H < h), and the thickness of the protection device should not be too thick.

The polybenzimidazole membrane has a low proton conductivity, and its trade-off effect between proton conductivity and vanadium ions blocking has not been addressed. Therefore, improving the proton conductivity and proton selectivity of polybenzimidazole membrane is crucial for its development in vanadium flow battery (VFB). In this work, two types of sulfonated polybenzimidazole (SPBI and HSPBI) membranes with flexible sulfoalkyl pendants are prepared by ring-opening and substitution reactions for application in VFBs. Compared with poly(4,4′-diphenylether-5,5′-bibenzimidazole) (OPBI) membrane, SPBI and HSPBI membranes exhibit remarkable proton conductivities. However, the vanadium ions blocking capabilities of SPBI and HSPBI membranes show a slight decline. Excitingly, the HSPBI membrane achieves the highest proton selectivity (1.54 × 106 S min cm−3) compared with OPBI (6.28 × 105 S min cm−3), SPBI (1.30 × 106 S min cm−3) and commercial Nafion 212 (0.43 × 105 S min cm−3) membranes. Lastly, all membranes are separately assembled into VFBs to verify their battery performances. The HSPBI membrane shows higher Coulomb efficiencies (94.74–99.41

To mitigate the consequences of hydrogen-blended natural gas explosion accidents, this study established a simulated explosion-venting interlayer platform to systematically investigating the effects of vents with different sizes combined with porous materials on flame propagation and pressure suppression during hydrogen-blended natural gas explosions. The results demonstrate that porous materials effectively quenched flames at vents, achieving flameless venting. Vent sizes significantly influenced suppression efficiency. For a 36 cm2 vent, compared to scenarios without an explosion-venting interlayer, the maximum flame propagation velocity attenuation rates under varying hydrogen blending ratios reached 67.53%, 74.12%, 71.40%, and 55.75%, while the maximum explosion pressure in Gas Compartment 1 decreased by 71.4%, 64.52%, 47.20%, and 39.43%, respectively. When the vent size increased to 64 cm2, both flame propagation velocity and spatial range were further suppressed. The corresponding maximum flame velocity attenuation rates improved to 86.29%, 79.86%, 75.32%, and 72.71%, with maximum explosion pressure reductions of 69.85%, 69.39%, 64.98%, and 64.18% in Gas Compartment 1. Compared to the 36 cm2 configuration, the 64 cm2 vent exhibited enhanced stability in explosion suppression and significantly reduced downstream compartment impact. This research provides critical technical insights for designing explosion mitigation strategies forhydrogen-blended natural gas in utility tunnels.

This study introduces an explosion-venting interlayer strategy aimed at enhancing the explosion resistance of utility tunnels. Employing a specially designed experimental platform, the research investigates the influence of vent location and size on the efficacy of the explosion-venting interlayer within these tunnels. The findings demonstrate that porous materials with a porosity of 20 PPI (pores per inch) effectively extinguish flames and inhibit their penetration into the explosion-venting interlayer. During the initial stage of flame development, the explosion venting interlayer effectively controls flame propagation and overpressure. However, its suppressive effect diminishes during the rapid development phase of the flame. Furthermore, enlarging the vent size substantially enhances the performance of the explosion-venting interlayer, thereby safeguarding downstream compartments and preserving the structural integrity of the explosion-venting interlayer. When using 10 PPI porous materials, the vent effectively suppresses flames during the initial development stage. However, during the rapid flame development phase, it is less effective compared to 20 PPI materials. Reduced porosity decreases overpressure in the main compartment; however, the impact of reduced porosity on overpressure diminishes with larger vents. This study offers significant insights into the safe operation of hydrogen-blended natural gas within utility tunnels.

A novel tricarboxylic acid monomer (4,4 ',4 ''-(benzene-1,3,5-trioxy) tribenzoic acid) has here been innovatively synthesized, and branched polybenzimidazole (b-PBI) membranes with different theoretical branching degrees have been constructed for applications in vanadium redox flow battery (VRFB). Compared with the traditional linear polybenzimidazole (OPBI) membrane, the b-PBI membranes demonstrated higher proton conductivities and selectivities. Among these membranes, the b-PBI-15 membrane was found to have an outstanding proton conductivity (1.09 x 10(-2) S/cm), which was 2.50 times that of the OPBI membrane (4.36 x 10(-3) S/cm). Moreover, the proton selectivity of b-PBI-15 membrane achieved a value of 2.15 x 10(6) Smin/cm(3), which was 1.52 and 51.19 times as many as those of the OPBI (1.41 x 10(6) Smin/cm(3)) and commercial Nafion 212 (0.42 x 10(5) Smin/cm(3)) membranes, respectively. Also, the b-PBI-15 membrane showed higher coulomb efficiencies (96.45 % similar to 98.30 %) and energy efficiencies (69.78 % similar to 86.46 %), as well as similar voltage efficiencies (70.99 % similar to 89.64 %), as compared with the Nafion 212 membranes at 80 mA/cm(2) similar to 280 mA/cm(2). Remarkably, the 1000 VRFB charge-discharge cycles were stable for the b-PBI-15 membrane at 140 mA/cm(2), which showed excellent structural and micro-morphic stability. Simulation calculations were also performed to clarify the internal reasons for the changes of proton conductivity and stability of b-PBI membrane. In summary, the b-PBI-15 membrane showed a promising potential for application in the VRFB.

In this work, a new branched trianhydride monomer 1,3,5-tris(4-naphthyloxy-1,8-diacid) phthalic anhydride is established for improving the chemical/dimensional stability and proton conduction of the branched sulfonated polyimide (BSPI) membrane for application in vanadium flow battery (VFB). Compared with linear SPI-60 membrane containing conventional dianhydride monomer 1,4,5,8-naphthalenetetra-carboxylic dianhydride, BSPI-60 membrane exhibits remarkable resistance to vanadium ions, proton conduction and structural stability. Besides, the challenge of simultaneously improving vanadium ions resistance and proton conductance is tackled. The proton selectivity of BSPI-60 membrane achieves 1.11 x 105 S center dot min/cm3, which is 2.8 and 2.5 times higher than both SPI-60 (0.39 x 105 S center dot min/cm3) and commercial Nafion 212 (0.44 x 105 S center dot min/cm3) membranes, respectively. At the same time, BSPI-60 membrane exhibits higher coulomb efficiencies (97.2 %-99.3 %) and energy efficiencies (85.6 %-69.5 %) compared those of SPI-60 and Nafion 212 membranes at 100-300 mA/cm2. Remarkably, the 500 cycles of BSPI-60 membrane at 140 mA/cm2 are also stably executed. The internal reasons for enhanced chemical/dimensional stabilities and proton conduction of BSPI-60 membrane are clarified from theoretical calculations with mean square displacement value, fractional free volume and natural bond orbital charge via density functional theory and molecular dynamics simulation. Our study encompasses not only the synthesis of a novel branched trianhydride monomer but also the development of a BSPI membrane with a unique molecular structure specifically designed for VFB applications.

The factor of combustion and explosion remains one of the main constraints on coal mining and management. To clarify the impact of structural properties on the consequences of gas explosion disasters during coal mining, this article conducts a study on the impact of the elastic modulus of structures on gas explosion disasters. The research results indicate that in the case where structures with high elastic modulus must exist, the elastic modulus of the structure has minimal impact on the structure during the early stage of flame development. The area of flame front and the degree of deflagration also decrease with the increase of elastic modulus, but the disturbance degree of airflow and flame in the pipe increases with the increase of elastic modulus. The peak flame velocity at elastic modulus of 0.7 GPa and 2.8 GPa increased by 3.56% and 7.47% compared to elastic modulus of 0.18 GPa, respectively; The upstream overpressure peak increased by 24.63% and 42.52%; The downstream overpressure peak increased by 11.19% and 20.62%. The peak values of flame velocity and overpressure increase with the increase of elastic modulus, while the explosion intensity and pressure rise rate increase with the increase of elastic modulus. The explosion intensity index at elasticmodulus 2.8 GPa is approximately 1.45 times that at elastic modulus 0.18 GPa. Therefore, it is necessary to choose structures with smaller elastic modulus as much as possible to achieve the best fire and explosion suppression effect.

A set of colorless polyimide (CPI) films with norbornene-aliphatic ring structures has here been prepared through polycondensation reactions by using cyclopentanone bis-spironorbornane tetracarboxylic dianhydride (CpODA), 4,4 '-(hexafluoroisopropyl)diphthalic anhydride (6FDA) and 4,4 '-diaminodiphenyl ether (ODA) monomers as raw materials. The transmissivities, dielectric properties and thermal stabilities of CPI films are optimized by adjusting the CpODA-to-6FDA molar ratios. Compared with the aromatic and aliphatic PI films, the thermal stabilities and transmissivities of CPI films are well balanced. Moreover, the CPI films possessed low dielectric constants and low dielectric losses. The thermal expansion coefficients, temperatures at a 5% weight loss and glass-transition temperatures are maintained at 31-41 ppm K-1, 461-484 degrees C and 348-362 degrees C, respectively. In addition, the transmittances (86-89%), dielectric constants (2.15-2.47) and dielectric losses (<0.023) are all prominent. In short, the CPI films have been shown to have a high potential for use in the display technology.

With the rapid expansion of the national economy and strategic adjustments to the energy structure, natural gas, a crucial clean energy source, encounters significant safety challenges during transportation in utility tunnels, owing to its flammable and explosive nature. To effectively address the current issues in response technologies for gas explosions in utility tunnels, such as inadequate control over the flame propagation range, limited attenuation of overpressure, and the mechanical impact damage effects on the internal structures of the utility tunnels and surrounding buildings, a small-scale experimental platform was constructed independently. This platform is designed to explore how the area and position of vents affect the characteristics of methane explosions within tunnels, utilizing the explosion venting mechanism. The results indicate that, for the same venting position, the maximum flame propagation distance, speed, and peak overpressure all decrease as the venting area increases. When the vent is located at position 1 in each compartment, the reduction in maximum flame propagation distance and speed is the most significant. The maximum decrease in peak overpressure occurs at venting position 2. When the venting position is closer to the ignition source, the rate of explosion overpressure rise and the explosion index both decrease with an increase in venting area, with the most significant reduction occurring at venting position 1. Conversely, when the venting position is farther from the ignition source, the rate of explosion overpressure rise and the explosion index actually increase, with the most significant increase occurring at venting position 4. The research findings offer a theoretical foundation and scientific guidance for developing new technologies aimed at mitigating gas explosion disasters in utility tunnels through internal venting.

In this paper, a new functional diamine monomer 2-methyl-1,4-bis(4-amino-2-trifluoromethyl) benzene (FAPOB) is designed and synthesized for further improving the performance of branched sulfonated polyimide (SPI-B) membrane for implementation in vanadium redox flow battery (VRB). At the same time, the sulfonation levels of SPI-B membranes are accurately regulated by modifying the proportion of FAPOB and 4,4 '-diaminobiphenyl-2,2 ' disulphonic acid. Among them, the SPI-B-50 membrane with 50 % sulfonation degree exhibits a remarkable proton selectivity of 2.31 x 105 S min/cm3, which is 5.5 times higher than the Nafion 212 (NR212) membrane. Moreover, the SPI-B membrane's stability is significantly improved due to its branched structure and the presence of numerous trifluoromethyl groups. Compared to NR212 membrane, SPI-B-50 membrane demonstrates superior coulomb and energy efficiencies at the same current density. Furthermore, the SPI-B-50 membrane exhibits a higher voltage holding capacity compared to the NR212 membrane. Remarkably, the SPI-B-50 membrane maintains stable efficiencies even after undergoing more than 500 charge-discharge cycles. This research not only involves the innovative synthesis of a novel diamine monomer but also the construction of various SPI-B membranes with a unique molecular structure specifically designed for VRB applications.

Low-velocity laminar flames gradually accelerates under the joint action of various mechanisms, and develops from deflagration to detonation, and the mechanism in this process is the focus of explosion dynamics research. This article presents experimental results of the propagation of premixed hydrogen/methane flames in square-section channels with flexible and rigid obstacles at a blockage ratio (BR) of 0.3. Theory and experiment show that the acceleration effect of flexible obstacles on flame is weaker than that of rigid obstacles. The results show that there are many differences in the physical mechanism of flame acceleration. It is mainly reflected in the difference between the two obstacles on turbulence guidance, and the difference in the peak pressure of flame propagation. The flexible obstacles create smaller turbulence and absorbs the transverse waves within the pipe that continuously accelerate the flame. At the same time, compared with rigid obstacles, flexible obstacles can effectively reduce the peak flame tip speed Vmax, and the peak flame tip speed reduction rate is the highest by 22.86%. In addition, unburned pockets formed by obstacles play a key role in the acceleration of the flames. The expansion of gas in the flexible obstacle pocket expands the obstacle spacing, accelerates the fuel combustion in the pocket, and avoids the concentrated release of fuel energy. The intensity of the turbulence and the velocity of the flame are lower after passing through the obstacle area, showing a lower explosion risk than rigid obstacles.

Membrane with remarkable proton conductance and selectivity plays a key role in obtaining high vanadium flow battery (VFB) performance. In this work, the trade-off effect between proton conductance and vanadium ion blocking was overcome by the introduction of a cross-linking structure to prepare covalent cross-linked fluorine-containing sulfonated polyimide (CFSPI-PVA) membranes. Herein, the CFSPI-PVA-15 membrane possesses excellent comprehensive properties, including acceptable area resistance (0.21 Omega cm(2)), lower vanadium ion permeability (0.76 x 10(-7) cm(2) min(-1)), and remarkable proton selectivity (3.11 x 10(5) min cm(-3)) compared with the commercial Nafion 212 membrane. At the same time, the CFSPI-PVA-15 membrane exhibits higher coulomb efficiencies (97.26%-99.34%) and energy efficiencies (68.65%-88.11%) and a longer self-discharge duration (29.2 h) in contrast with the Nafion 212 membrane. Moreover, 500 cycles of the CFSPI-PVA-15 membrane at 160 mA cm(-2) are also stably executed. The internal reasons for the improved chemical stability of the CFSPI-PVA-15 membrane are clarified from theoretical calculations with the mean square displacement value and fractional free volume. Therefore, the CFSPI-PVA-15 membrane exhibits great potential for application in VFB.

A large number of gas explosion accidents have shown that secondary explosions are more dangerous and destructive than the primary. Based on the self-designed sliding experiment platform, the influence of sliding device on the evolution behavior of fuel enriched and lean flame fronts be compared. The study shown that adjusting the initial sliding position of porous media to 40 cm and using an appropriate spring coefficient can effectively extinguish methane flame in both fuel enriched and fuel lean combustion states. This method can reduce the range of flame diffusion, burning time and intensity compared with using fixed porous media, and also the maximum explosion overpressure. When using a sliding device in methane lean combustion, it can achieve significant reductions in the duration of the reverse diffusion flame (up to 64.02%), the quenching time of the flame (up to 44.21%), and the explosion overpressure inside the tube (up to 24.2%). During rich methane combustion, using sliding device can result in a reduction of up to 62.26% in the duration of the reverse diffusion flame, up to 46.81% in the quenching time of the flame, and up to 44.12% in the explosion overpressure inside the tube. Additionally, the inhibitory effect of the sliding device and the increase in elastic coefficient follow a pattern of initially increasing and then decreasing. In general, the sliding device is more effective in suppressing methane flames and overpressure during both enriched and lean fuel combustion than fixed device. The results can provide valuable insights for the development of secondary explosion prevention technology, which is crucial for preventing and managing methane explosion accidents.

As a key component of vanadium redox flow battery (VRFB), the ideal membrane with high proton conductance together with high vanadium ions resistance is urgently required. In this work, a permselective monomer di (aminobenzo)-18-crown-6 with proper aperture of 0.26-0.32 nm is synthesized to prepare branched sulfo-nated polyimide containing crown ether (ce-bSPI-x) membranes. In virtue of the excellent balance between vanadium ions resistance and proton conductance, the ce-bSPI-60 membrane possesses the optimum physico-chemical properties among all ce-bSPI-x membranes. Subsequently, in comparison with commercial Nafion 212 membrane, the ce-bSPI-60 membrane demonstrates higher coulomb efficiencies (CEs) (96.50%-99.39%) and energy efficiencies (EEs) (69.36%-85.45%). Furthermore, the ce-bSPI-60 membrane can achieve 80% of EE at 140 mA cm-2, which is in a superior position compared with other SPI-based membranes reported in recent years. 1000-time cycles at 140 mA cm-2 without obvious structural and morphological changes proves the excellent durability of ce-bSPI-60 membrane. To sum up, the as-prepared ce-bSPI-60 membrane exhibits a great potential to match the demand of application in VRFB.

To improve the safety of the methane/hydrogen mixture pipeline network, The experimental deflagration quenching behavior of porous materials on hydrogen mixed methane in barrier tubes was studied, the influence of the hydrogen mixing ratio on the quenching results of porous materials and the transient change of overpressure was discussed, the critical quenching hydrogen mixing ratio of porous materials was explored. Results show that the hydrogen mixing ratio has a significant effect on the quenching results of porous materials. According to the different quenching results of porous materials under different hydrogen mixing ratios, the successful quenching zone (4<19%) and the quenching failure zone (4 > 19%) can be divided. It can be determined that the critical quenching hydrogen mixing ratio is 4 = 19%. The critical quenching speed is 33.0 m/s. When the porous material is coupled with hydrogen mixing, the pressure curve appears as a "multi-peak" phenomenon, and the maximum pressure peak is generated by the "multi-peak" game. If the hydrogen mixing ratio is greater than the critical quenching hydrogen mixing ratio, it may bring about the uncertainty of the maximum pressure peak and increase the unpredictability of the explosion hazard to the gas pipeline network. Therefore, reasonable hydrogen mixing is conducive to improving the safety of methane/hydrogen mixture pipeline