Search

Copyright of Journal of Dalian University of Technology / Dalian Ligong Daxue Xuebao is the property of Journal of Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Improving rotor stability and reducing leakage at various working parts of gas turbines is an important topic that experts and scholars have always pursued. In this article, a new type of hole-diaphragm-labyrinth seal (HDLS) structure is obtained by introducing an additional damping source. The HDLS structure is built by the traditional diaphragm labyrinth seal (DLS) with a single hole added to the diaphragm. The simulation under different working conditions of three different seal structures is carried out by ANSYS Fluent. Subsequently, the tangential force under different whirl frequencies was obtained. Meanwhile, the empirical parameters in Childs' model of the dynamic performance of rotor-seal structures were obtained. The results show that the HDLS achieved a 71.4% improvement in the direct stiffness coefficient and a 71.8% improvement in the direct damping coefficient of the traditional labyrinth seal. The leakages of HDLS at different rotation speeds were lower than those of DLS by 1.53% and LS by 3.64%. The HDLS can be comprehensively considered the most promising seals among LS, DLS, and HDLS not only by stability but also by mass flow leakage in the rotor system. [ABSTRACT FROM AUTHOR]

A new gas-atomization method was developed to produce metallic powders at ultralow atomizing pressures. The working gas speeds up into a venturi nozzle and aspirates the molten metal resulting in a dynamic mix and breakup of the melt into fine metallic powder. Aluminium was atomized through the flow of carbon dioxide at various pressures and the produced powders were characterized in terms of surface and volume properties to assess their purity and industrial applicability. The current nozzle configuration allowed the production of Aluminium powder with average diameter of d 50 =139 μm at an atomizing pressure as low as 0.5 bar. Aluminium powder production, Powder characterization, Venturi nozzle [ABSTRACT FROM AUTHOR]

The economic threat of climate change: A multilevel analysis of the relationship between working in a greenhouse gas intensive sector, economic insecurity and climate policy scepticism among the lower educated in Europe This research set out to determine to what extent the relationship between working in a greenhouse gas intensive sector and climate policy scepticism can be explained by economic insecurity, while also examining the contextual influence of national commitment to climate change mitigation. Focusing on the lower educated of 21 European countries (N = 10.060) and conducting two multilevel analyses, this research found that working in a greenhouse gas intensive sector leads to more climate policy scepticism. This substantiates the idea that values of climate change scepticism are more present in the social environment of more greenhouse gas intensive sectors. This relationship is, however, not substantially explained by economic insecurity. Finally, this research found that working in a greenhouse gas intensive sector does not lead to more economic insecurity and that this relationship is only partially and minimally influenced by an extensive national climate policy agenda. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Dalian University of Technology / Dalian Ligong Daxue Xuebao is the property of Journal of Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Gas sensing properties of pure ZnO and CuO layered ZnO nanostructures prepared on Micro Electro Mechanical system (MEMS) devices has been investigated. ZnO nanostructure is prepared using hydrothermal process and the structure deposited has rough surface with number of pores. CuO films (25 nm and 50 nm) are deposited on the ZnO nanostructure using RF sputtering process and the total thickness of 25 nm CuO layered ZnO is recorded about 3.30 µm. For the sake of gas sensing working conditions, MEMS microheater thermal properties are also studied. CuO coated ZnO MEMS device is tested for H2S gas at 200 °C temperature. Gas sensing properties of 25 nm thickness CuO on ZnO MEMS device sensor shown 42.5% of enhanced sensing response at 1 ppm when compared to pure ZnO sensor which only showed 23.2% response. The enhanced sensing response is due to the formation of CuO and ZnO heterojunctions. The sensor exhibited good sensitivity towards H2S gas than other gases (SO2, CO, NH3 and ethanol) at the operating temperature of 200 °C. A random repeatability test at 800 ppb H2S gas concentration is done with 25 nm CuO layered ZnO which showed good repeating sensing results. [ABSTRACT FROM AUTHOR]

This article proposed a new solution to do the plasma cleaning under low pressure based on a domestic microwave oven. A conical bottle was placed in the oven according to the electric field distribution calculated by finite element method and Helmholtz equation. A vacuum pump was employed to make a low pressure environment in the bottle to generate plasma. Experiments demonstrated that discharges in the domestic microwave oven under low pressures from 100 Pa to 300 Pa can be easily triggered and maintained when the working gases were argon and air. The lower the pressure was, the easier to trigger and generate plasma, and the more uniform the plasma inside the conical bottle was. Experiments also found that this low-pressure Ar plasma generated in the domestic microwave oven can efficiently clean up the oils on the metallic sheets or glass substrates without damaging them. [ABSTRACT FROM AUTHOR]

Heterogenous photocatalysis is a suitable technology for the removal of contaminants of emerging concern (CEC), such as parabens, from wastewaters. However, typically the photocatalyst is applied as a powder, which requires time-consuming and expensive supplementary separation processes, for its separation and recovery. Therefore, supported-photocatalysis has gained interest in the scientific community. To develop a suitable supported photocatalyst, commercial TiO 2 (P25) powder was immobilized in polydimethylsiloxane (PDMS) membranes, to promote the degradation of three parabens (methylparaben -MP, ethylparaben -EP, and propylparaben -PP), under UV irradiation. To enhance the photocatalytic activity of the membranes, a plasma process was applied during their preparation. The plasma process operating conditions were optimized, regarding the working gas, the power applied, the pressure used and the processing time selected. Thus, the best conditions, among those analyzed, were the use of argon as the working gas, a power of 100 W, a pressure of 0.6 mbar and an operating time of 4 min. To assess the photocatalytic activity, two protocols, which varied in the P25 immobilization methodology (surface or matrix), were developed. It was concluded that PDMS membranes with P25 on the surface achieved higher removals of parabens during the photocatalytic oxidation and, when the preparation parameters were optimized, these membranes achieved removals of 53 ± 2%, 53 ± 0%, 58 ± 2% for EP, MP and PP, respectively. As such, in this study, it was possible to develop a protocol to produce hydrophilic and photocatalytic P25/PDMS membranes efficient in the abatement of parabens under UV irradiation. [Display omitted] [ABSTRACT FROM AUTHOR]

Indium oxide (In 2 O 3) gas sensors are regarded as one of the potential materials for detecting and quantifying hazardous gases for monitoring systems and public safety assurance to address the severe environmental problems plaguing our civilization. In this work, In 2 O 3 /PANI composites were synthesized using the hydrothermal technique to explore nitrogen dioxide (NO 2) sensing capabilities. The scanning electron micrographs (SEM), crystal structures (XRD), energy dispersive X-ray analysis (EDS), and the gas sensing properties were investigated to ascertain the morphology, purity, response/recovery time, optimal temperature, and recyclability. The samples displayed a gas-accessible structure with stacks of several porous nanosheets. The as-synthesized In 2 O 3 /PANI-1 sensors have extremely high responses (341.5 @ 30 ppm, 12.8 @ 3 ppm) to NO 2 gas at a working temperature (250 °C), quick response times (24 s @ 30 ppm, 47 s @ 3 ppm) and recovery times (53 s @ 30 ppm, 74 s @ 3 ppm), and a low detection limit (300 ppb). Following a series of testing, high repeatability and selectivity were obtained. Furthermore, the In 2 O 3 /PANI sensor's fundamental detecting mechanism for NO 2 gas was completely discussed. In addition, a developed mechanism defining the performance of the nanosheet-based sensors in NO 2 gas is shown, which is backed by density functional theory (DFT) calculations to investigate the electrical characteristics of In 2 O 3 /PANI composites. This work offers an intriguing perspective as well as a useful strategy for fabricating long-lifetime In 2 O 3 -based nanosheets using the hydrothermal process. [Display omitted] • Synthesis of unique hollow In 2 O 3 /PANI Nanosheets Clusters by a simple method. • High specific surface area, porosity and synergistic benefit sustained with clustered nanostructures. • Detailed DFT calculations for gas sensing mechanism in adsorptions. • The fabricated sensor exhibits high selectivity and response towards NO 2 gas. [ABSTRACT FROM AUTHOR]

Carbon dioxide gas as a working gas produces a stable plasma-torch by making use of 2.45 GHz microwaves. The temperature of the torch flame is measured by making use of optical spectroscopy and a thermocouple device. Two distinctive regions are exhibited, a bright, whitish region of a high-temperature zone and a bluish, dimmer region of a relatively low-temperature zone. The bright, whitish region is a typical torch based on plasma species where an analytical investigation indicates dissociation of a substantial fraction of carbon dioxide molecules, forming carbon monoxides and oxygen atoms. The emission profiles of the oxygen atoms and the carbon monoxide molecules confirm the theoretical predictions of carbon dioxide disintegration in the torch. Various hydrocarbon materials may be introduced into the carbon dioxide torch, regenerating new resources and reducing carbon dioxide concentration in the torch. As an example, coal powders in the carbon dioxide torch are converted into carbon monoxide according to the reaction of CO 2 + C → 2CO, reducing a substantial amount of carbon dioxide concentration in the torch. In this regards, the microwave plasma torch may be one of the best ways of converting the carbon dioxides into useful new materials. [ABSTRACT FROM AUTHOR]

In this study, well-designed layer-like WO 3 was synthesized by a facile hydrothermal route. Different characterization techniques have been conducted to comprehensively investigate the properties of morphology and structure of WO 3 -based sensing materials. The resultant consequences demonstrated that the layer-like WO 3 with abundant mesoporous structure displayed higher specific surface area with respect to the pristine WO 3 nanoplates. For the first time, the excellent gas sensing device based on layer-like WO 3 was constructed successfully, which achieved an admirable gas-sensing response of 106 towards 5 ppm nitrogen dioxide gas at the working temperature of 160 ℃, with a favorable selectivity, and the lowest detection limit was reached to 0.243 ppb. Moreover, the layer-like WO 3 sensor possessed considerable reproducibility and stability even in aging tests for 30 days. Those results can be ascribed to this promising structure optimization, which not only provides more reaction active sites but also promoted the gas sensing reaction procedure. Undoubtedly, this work is believed to be useful to offer a feasible strategy to enhance NO 2 gas response in practical application. [Display omitted] • Lasagna-like WO 3 was first prepared by a facile hydrothermal reaction. • The gas sensor based on lamellar structure WO 3 showed excellent sensitivity towards NO 2 gas. • The lasagna-like WO 3 sensor can be utilized to detect ppb-level NO 2. [ABSTRACT FROM AUTHOR]

In the present article, the effects of three important flow control techniques, i.e. control by strakes, jets, and flares, on the aerodynamic characteristics and performance of a number of body configurations at high speeds are reviewed. The results are based on previous studies conducted by the author in a hypersonic gun tunnel at a Mach number of 8.2 and a Re∞/m=9 200 000. Air was used as the working gas. The tests employed schlieren photography to study the overall flow field. Quantitative studies have been made by pressure measurements. The forces were measured with a three-component balance equipped with semiconductor strain gauges. The surface flow was studied using the oil-dot technique. [ABSTRACT FROM AUTHOR]

Gas emission in underground coal mines is of crucial importance. It is the potential cause of several health and safety issues such as gas explosion and gas poisoning. The emission of toxic and explosive gases in underground workings creates an unsafe environment, complicates the design of ventilation system, and increases the operating cost. The prediction of gas emission has long been associated with levels of uncertainty arising from parameters such as gas content and composition. This paper aims to identify the parameters affecting the uncertainty associated with the gas emission and determine the gas emission using the Monte Carlo simulation (MCS). A three-dimensional Computational Fluid Dynamics (CFD) model is developed to estimate the gas distribution and required airflow rate for ventilating the mine workings considering the gas content uncertainty. The CFD simulation is also carried out using the Monte Carlo modeling results to determine the effect of the uncertainty associated with the gas emission on the distribution of the required airflow rate. Several ventilation scenarios are investigated to determine the optimum ventilation air characteristics. It is found that for any specific design scenario, the ventilation system can be designed such that the mining operation can be carried out safely and with minimum cost. • Impact of gas emission uncertainty on performance of an auxiliary ventilation system is studied. • Monte Carlo and CFD are used for uncertainty analysis and fluid flow simulation, respectively. • Gas concentration increases with an increase of gas emission rate and a decrease of exhaust flow. • Gas emission uncertainty affects required ventilation design requirements and associated cost. • Critical gas emission needs be determined for selecting the most appropriate ventilation system. [ABSTRACT FROM AUTHOR]