NIR驱动MWCNT修饰的超滑PI光热响应膜表面液滴定向输运

目的 制备多壁碳纳米管(MWCNT)修饰的超滑聚酰亚胺(PI)光热响应膜表面,实现近红外光(NIR)驱动液滴定向输运.方法 基于静电纺丝结合喷涂法制备MWCNT修饰的超滑PI光热响应膜表面,分别通过扫描电子显微镜、接触角测量仪、红外热成像仪表征样品的微观形貌、润湿特性及光热特性,分析液滴大小与润滑油黏度对液滴定向输运的影响规律,研究NIR驱动液滴在MWCNT修饰的超滑PI光热响应膜表面定向输运的作用机理.结果 MWCNT修饰PI膜表面的疏水性提高,液滴静态接触角从115°增大至160°.NIR连续照射MWCNT修饰的超滑PI光热响应膜表面90 s,表面温度的最大上升速率为42.6℃/s,表面最大温度达到123.6℃.通过NIR照射超滑PI纳米纤维膜表面,表面局部温度上升,产生润湿梯度力,驱动液滴在表面定向输运.液滴定向输运与润湿梯度力及粘滞阻力有关.超滑PI光热响应膜表面的润滑油黏度相同时,液滴体积越小,粘滞阻力越小,液滴定向输运的速度越快.5μL液滴在润滑油黏度为0.65 mm2/s的超滑PI光热响应膜表面的运动速度最大,运动速度为1.64 mm/s.液滴体积相同时,超滑PI光热响应膜表面的润滑油黏度越大,液滴受到的润湿梯度力越小.5μL液滴在润滑油黏度为100 mm2/s的超滑PI光热响应膜表面的润湿梯度力Fwet-grad最小,润湿梯度力为6.39×10?6 N.结论 MWCNT修饰的超滑PI光热响应膜表面具有良好的光热效应,NIR可精准驱动单液滴及多液滴在表面的定向输运.     

Upgrading the Arlberg tunnel to current safety standards

Austrian road tunnels within the Trans-European Road Network (TERN) must fulfil the requirements of the Directive 2004/54/EC (European Commission, 2004) not later than April 2019. This regulation has to be applied to all tunnels in the TERN with a length of more than 500 m, whether they are in operation, under construction or at design stage, and aims at ensuring a minimum level of safety for road users. One of the main features of this directive is the requirement for providing an egress possibility to a safe environment every 500 m throughout the whole tunnel.The Arlberg road tunnel has a length of some 15.5 km and is in operation for more than 35 years. It is a single tube tunnel operated with bi-directional traffic, but carries a quite low traffic volume. Hence, the construction of a second tube is not really cost effective. Currently the tunnel is equipped with a transversal ventilation system with remotely controlled smoke extraction dampers providing smoke extraction every 100 m. The maximum distance between egress possibilities to a save environment is some 1500 m. Due to the high costs of a construction of a second tube or a parallel running escape gallery, a novel solution was found. The existing fresh air duct will be used as safe escape way between the existing egress possibilities. This solution has big impacts on the ventilation system and on the requirements for thermal structure protection of the new egress ways, i.e. the fresh air duct. In order to overcome this problem, massive changes in the ventilation design have to be performed, accompanied by the installation of a high-pressure water-mist system for structure protection.     

Experimental investigation of low-pressure refrigerant mixtures for micro cryogenic coolers

Micro Cryogenic Coolers (MCCs) can achieve very small sizes and high efficiencies when operating with a refrigerant mixture, but micro-scale compressors have a limited pressure output. Four refrigerant mixtures were designed to operate between 0.4 MPa and 0.1 MPa, and tested in a MCC system both with and without pre-cooling. For comparison, two pure refrigerants were tested as well. Without pre-cooling, each mixture exhibited considerably lower cooling power than the design value. With pre-cooling, the mixtures exhibited unsteady cooling temperatures accompanied by flow pulsations after a period of time. The low cooling power, unsteady temperatures, and time required for the pulsations to occur are analyzed in terms of composition change due to liquid hold-up in the annular and intermittent flow regimes.     

Comparison of ignition,injection and micro - Explosion characteristics of RP-3/ ethanol and biodiesel / ethanol mixed drops

The ignition, injection, and micro-explosion characteristics of aviation fuel (RP-3)/ethanol mixed droplets and biodiesel/ethanol mixed droplets at different proportions under high temperature conditions (420 °C) were compared using an experimental setup. A device for measuring small droplet volumes was designed using an infusion set and different types of needles, and a corresponding equation was established. Mixed droplets suspended on high-temperature resistance nichrome wire with a diameter of 0.2 mm were heated by sending them to a position approximately 2 mm from the forklift preheating plug using a moving rail. SLR and high-speed cameras were used to observe the flame structure as well as the injection and micro-explosion of the mixed droplets during combustion, respectively. Expansion, injection, and micro-explosion were observed in the biodiesel/ethanol mixed droplet experiments when the biodiesel content was 60%. Although the micro-explosion of mixed droplets of aviation fuel/ethanol was not observed, expansion and ejection of the droplets were observed. Image Pro-plus software was used to calculate the diameters at different times in the combustion cycle of the droplets. Through this analysis, the occurrence of micro-explosion was described, and a model for the calculation of micro-explosion strength was established.     

Thermodynamic and economic analyses of a coal and biomass indirect coupling power generation system

The coal and biomass coupling power generation technology is considered as a promising technology for energy conservation and emission reduction. In this paper, a novel coal and biomass indirect coupling system is proposed based on the technology of biomass gasification and co-combustion of coal and gasification gas. For the sake of comparison, a coal and biomass direct coupling system is also introduced based on the technology of co-combustion of coal and biomass. The process of the direct and the indirect coupling system is simulated. The thermodynamic and economic performances of two systems are analyzed and compared. The simulation indicates that the thermodynamic performance of the indirect coupling system is slightly worse, but the economic performance is better than that of the direct coupling system. When the blending ratio of biomass is 20%, the energy and exergy efficiencies of the indirect coupling system are 42.70% and 41.14%, the internal rate of return (IRR) and discounted payback period (DPP) of the system are 25.68% and 8.56 years. The price fluctuation of fuels and products has a great influence on the economic performance of the indirect coupling system. The environmental impact analysis indicates that the indirect coupling system can inhibit the propagation of NO_x and reduce the environmental cost.     

A skeletal n-butane mechanism with integrated simplification method

A new skeletal mechanism of n-butane is developed for describing its ignition and combustion characteristics applicable over a wide range of conditions: initial temperature 690–1430 K, pressure 1–30 atm, and equivalence ratio 0.5–2.0. Starting with a detailed chemical reaction kinetic model of 230 species and 1328 reactions (Healy et al., Combust. Flame, 2010), the directed relation graph method is applied as the first step to derive a semi-detailed mechanism with 134 species. Then, the reaction path analysis in conjunction with temperature sensitivity analysis is used to remove the redundant species and reaction paths simultaneously under the condition of low-temperature and moderate-to-high temperatures, respectively. Finally, a skeletal n-butane mechanism consisting of 86 species and 373 reactions can be obtained. Mechanism validation indicates that the new developed skeletal mechanism is in good agreement with the detailed mechanism in predicting the global ignition and combustion characteristics. The new skeletal mechanism is further validated using extensive available literature data including rapid pressure machine ignition delay time, shock-tube ignition delay time, laminar flame speed, and jet-stirred reaction oxidation, covering a large range of temperatures, pressures, and equivalence ratios. The comparison results demonstrate that a satisfactory agreement between predictions and experimental measurements is achieved.     

Detailed chemical effects of ammonia as fuel additive in ethylene counterflow diffusion flames

Ammonia is considered one of the most competitive fuels due to its carbon neutrality. The chemical effects of NH₃ are distinguished by kinetic analysis via adding NH₃ as reactive NH₃ and fictitious inert NH₃. The flame temperature and the mole fraction profiles affected by the chemical effects of NH₃ addition for important species and soot are analyzed, with special emphasis on soot and its important precursor polycyclic aromatic hydrocarbons (PAHs). The results illustrate that NH₃ addition inhibits the production of A1-A4. The chemical effects of ammonia decrease the hydrogen abstraction–C₂H₂–addition (HACA) surface growth rate and PAH condensation rate, which further reduces soot volume fraction and average particle diameter D₆₃. The ammonia decomposition pathways interact with ethylene decomposition pathways via the four reactions: NH₃ + C₂H₅ = C₂H₆ + NH₂, HCN + C₂H₅ = C₂H₆ + CN, NH₂ + C₂H₄ = C₂H₃ + NH₃, and CH₂CH₂NH₂ = C₂H₄ + NH₂. The dilution and thermal effects of NH₃ are dominant effects on soot reduction, while the chemical effects further inhibit soot formation.     

Nanostructure and reactivity of soot from biofuel 2,5-dimethylfuran pyrolysis with CO2 additions

This paper investigated the nanostructure and oxidation reactivity of soot generated from biofuel 2,5-dimethylfuran pyrolysis with different CO₂ additions and different temperatures in a quartz tube flow reactor. The morphology and nanostructure of soot samples were characterized by a low and a high resolution transmission electron spectroscopy (TEM and HRTEM) and an X-ray diffraction (XRD). The oxidation reactivity of these samples was explored by a thermogravimetric analyzer (TGA). Different soot samples were collected in the tail of the tube. With the increase of temperature, the soot showed a smaller mean particle diameter, a longer fringe length, and a lower fringe tortuosity, as well as a higher degree of graphization. However, the variation of soot nanostructures resulting from different CO₂ additions was not linear. Compared with 0%, 50%, and 100% CO₂ additions at one fixed temperature, the soot collected from the 10% CO₂ addition has the highest degree of graphization and crystallization. At three temperatures of 1173 K, 1223 K, and 1273 K, the mean values of fringe length distribution displayed a ranking of 10% CO₂>100% CO₂>50% CO₂ while the mean particle diameters showed the same order. Furthermore, the oxidation reactivity of different soot samples decreased in the ranking of 50% CO₂ addition>100% CO₂ addition>10% CO₂ addition, which was equal to the ranking of mean values of fringe tortuosity distribution. The result further confirmed the close relationship between soot nanostructure and oxidation reactivity.