Micro-wrinkled palladium surface for hydrogen sensing and switched detection of lower flammability limit

We report the development and testing of a novel hydrogen sensor that shows a very peculiar response to hydrogen exposure, due to its micro-structured palladium surface. The fabrication of the wrinkled Pd surface is obtained using an innovative, fast and cheap technique based on the deposition of a thin Pd film on to a thermo-retractable polystyrene sheet that shrinks to 40% of its original size when heated. The buckling of the Pd surface induced by shrinking of the substrate produces nano and micro-wrinkles on the sensor surface. The micro-structured sensor surface is very stable even after repeated hydrogen sorption/desorption cycles. The hydrogen sensing mechanism is based on the transitory absorption of hydrogen atoms into the Pd layer, leading to the reversible change of its electrical resistance. Interestingly, depending on hydrogen concentration the proposed sensor shows the concurrent effect of both the usually described behaviors of increase or decrease of resistance, related to different phenomena occurring upon hydrogen exposure and formation of palladium hydride. The study reports and discusses evidences for an activation threshold of hydrogen concentration in air switching the behavior of sensor performances from, e.g., poor negative to large positive sensitivity and from slow to fast detection.     

低热值C2H4-AIR-N2预混气体在多孔介质内的燃烧特性研究

利用自行设计的多孔介质实验台,对C2 H4-AIR-N2预混气体在多孔介质燃烧器内的燃烧特性进行了实验研究,分析燃料当量比、预混气体流速以及N2稀释比对预混气体的可燃极限、火焰传播方向、火焰温度分布以及污染物排放的影响.研究表明:随着稀释比的上升,预混气体的可燃极限范围缩小,火焰向上游传播的工况逐渐减少;燃烧器内最高火...     

Lean flammability limits for stable performance with a porous burner

Applications of porous burners are of high interest due to many advantages such as extended lean flammability limit in comparison with free flame structures. In this work, laminar premixed flame propagation of methane/air mixture in a porous medium is numerically investigated. An unsteady one-dimensional physical model of a porous burner is considered, in which the flame location is not predetermined. The computational domain is extended beyond either side of the porous medium to accurately model reactions close to the edges of the solid matrix. After validation of the model and performing a baseline simulation, a parametric study is carried out to investigate the lean flammability limits of the burner and the unstable flash-back/blow-out phenomena. Stable performance diagrams are given for two controlling parameters of turn–down ratio and porous medium porosity. The simulation results indicate that the stable performance range of the burner is extended when the equivalence ratio increases; however, the blow-out region expands with an increase in the firing rate. For constant values of porosity and firing rate, increasing the equivalence ratio can change the operating regime of the burner from blow-out to a stable condition. It is observed that by the variation of porosity in the range of 0.6–0.9, and for the equivalence ratios of more than 0.6, the flame flash-back cannot occur. An equivalence ratio of 0.43 is found to be the lower limit at which the flame stabilizes in the matrix.     

二元可燃混合气体爆炸上限的理论预测

确定了影响可燃气体爆炸上限的特征理化因素,如化学计量浓度、临界压力和燃烧热等,构建了混合物理化参数来表征混合气体的理化特征.将这些参数作为输入变量,分别应用多元线性回归和多元非线性回归方法对二元可燃混合气体爆炸上限与上述混合物理化参数之间的内在相关性进行研究,建立了根据混合物理化参数预测二元可燃混合气体爆炸上限的数学模型.两种方法对训练集的预测平均绝对误差分别为2.39％和1.272％;对测试集的预测平均绝对误差分别为2.185％和1.888％.结果表明,两种模型爆炸上限的预测值与文献值均符合较好,在可接受误差范围之内.该方法的提出为工程上提供了一种预测二元可燃混合气体爆炸上限的新方法.     

超高能放电对扩大均质混合气稀燃极限的研究

建立了一套超高能放电装置,其放电能量可以达到10J以上．根据在大气压力和环境温度下的点火实验,分析了着火界限扩展的影响因素．实验结果表明,采用宽间隙火花塞,改进电极形状,可以在一定范围内扩大着火稀限,而辛烷值对着火稀限的影响不明显．首次提出并实现了超高能放电的装置,实验结果显示该装置可大幅度扩展着火稀限．     

微通道壁面加热对甲烷空气预混火焰传播特性的影响

对于甲烷和空气预混合气在矩形微燃烧室内的燃烧过程,采用加热片加热,对比分析了在外部加热时,有无隔板对燃烧稳定性的影响,并分析了不同加热温度下隔板式燃烧室内火焰传播特性。实验结果表示,随着加热温度的提升,隔板型燃烧室稳定燃烧区域不断增大;加热温度高于600K,隔板型燃烧室的火焰吹熄极限有明显改善;高温加热利于提高隔板型燃烧室在较大流量情况下燃烧的稳定性。相较于单通道燃烧室,外部加热对隔板型燃烧室燃烧稳定性的改善更加明显。     

内燃机排气余热ORC中异丁烷-CO2混合工质的可燃性分析

针对内燃机高温排气与ORC工质的匹配问题,提出了一组安全且环保的烷烃/CO_2混合工质。为了解决混合工质泄漏后可燃的问题,按照美国ASTME681-2009标准提出测量异丁烷-二氧化碳混合工质可燃区域的实验手段。实验结果表明,异丁烷的可燃下限随阻燃剂二氧化碳的加入基本不变,可燃上限随着阻燃剂的加入迅速减小。并基于临界火焰温度理论建立了预测异丁烷-二氧化碳混合工质可燃极限的模型,与试验值相比较表明,预测模型可以较好地预测异丁烷的可燃下限,上限预测误差较大。     

Modelling the effect of water fog on the upper flammability limit of hydrogen–oxygen–nitrogen mixtures

Nitrogen dilution and very fine water mist fogs have both been suggested as possible methods of controlling flammable hydrogen–air mixtures by modifying the flammability limits to prevent ignition. A simplified theoretical model, based upon the inhibition parameter concept, is developed allowing the effect of nitrogen dilution and very fine water fog upon the upper flammability limit (UFL) of hydrogen–oxygen–nitrogen mixtures to be predicted and compared with corresponding experimental test data. The model predicts similar general trends in behaviour with regard to the effect of water fog upon the UFL to those observed in the experimental tests. The results suggest that the combination of nitrogen dilution and high density water fog can produce a significant reduction in the range of the UFL and total extent of the flammable region.     

Theoretical models and experimental results on the temperature dependence of polyfluorene solar cells

The temperature dependence of device parameters of polymer solar cells based on alternating copolyfluorene incorporating dioctyl-fluorene and di-thienyl-benzothiadiazole (APFO-3) mixed with [6,6]-phenyl-C61-butyric acid methylester (PCBM) was modeled theoretically by simulation and investigated experimentally under illumination of AM1.5 (100 mW/cm²). Both simulation and experimental results show photocurrent, fill factor and power conversion efficiency all increase, and the open-circuit voltages monotonically decrease with temperature increase from room temperature (RT) to 120 °C. These results can be explained by taking into account the temperature dependence of the mobility, and the thermal activation of the injection current from the electrodes. The increase of PCE with temperature is a distinguishing feature of polymer solar cells.     

Status of coal gasification processes

The current status of a number of processes which have been or are being developed to produce high-Btu, medium-Btu, and low-Btu gas from coal is given.     

Production of synthesis gas by co-gasifying coke and natural gas in a fixed bed reactor

The production of synthesis gas has gained increasing importance because of its use as raw material for various industrial syntheses. In this paper synthesis gas generation during the reaction of a coal/methane with steam and oxygen, which is called the co-gasification of coal and natural gas, was investigated using a laboratory scale fixed bed reactor. It is found that about 95% methane conversion and 80% steam decomposition have been achieved when the space velocity of input gas (oxygen and methane) is less than 200 h⁻¹ and reaction temperature about 1000 °C. The product gas contains about 95% carbon monoxide and hydrogen. The reaction system is near the equilibrium when leaving the reactor.     

Role of CeO2/ZrO2 mole ratio and nickel loading for steam reforming of n-butanol using Ni–CeO2–ZrO2–SiO2 composite catalysts: A reaction mechanism

This study presents steam reforming of n-butanol to synthesis gas using high surface area mesoporous Ni–CeO₂–ZrO₂–SiO₂ composite catalysts. The reaction proceeds through a combination of dehydrogenation, dehydration, and cracking reactions with propanal, butanal, and C₂–C₄ hydrocarbons as intermediate compounds. The ceria forms a solid solution with zirconia, promotes dispersion of nickel, and enhances oxygen storage/release capacity. The carbon conversion to synthesis gas (CCSG) and hydrogen yield are thus enhanced with increasing CeO₂/ZrO₂ mole ratio up to 1:2 and decreased slightly for higher mole ratios. The CCSG and hydrogen yield are also boosted by increasing the amount of nickel in the catalyst up to 20 wt%. 1:2 CeO₂/ZrO₂ mole ratio and 20 wt% nickel content are thus deliberated as optimum. The optimum catalyst exhibits stable catalytic performance for about 30 h time-on-stream. The study further presents the effect of temperature and steam/carbon mole ratio on n-butanol steam reforming.     

Autothermal reforming of methane to synthesis gas: Modeling and simulation

Autothermal reforming (ATR), that is the combination of non-catalytic partial oxidation and adiabatic steam reforming, is an important process to produce synthesis gas (syngas) from natural gas. The main scope of this work is proposing a mathematical model considering an autothermal reformer consisting of two distinct sections; a combustion section and a catalytic bed section. In the combustion section, temperature and composition were predicted using 108 simultaneous elementary reactions considering 28 species. The results were considered as initial conditions for the catalytic bed section. A one-dimensional heterogeneous reactor model was used for kinetic simulation of the second section. Results of the model were compared by ATR process published data.     

High gas dependence for power generation in Thailand: The vulnerability analysis

Thailand uses 74% of its natural gas supply for power generation and 70% of its power comes from gas-based technology. High dependence on natural gas in power generation raises concerns about security of electricity supply that could affect competitiveness of Thai manufacturing and other industries at the global level. The effect of fuel dependence on security of electricity supply has received less emphasis in the literature. Given this gap, this research examines the economic impact of high dependence on natural gas for power generation in Thailand by analyzing the effect of changes in fuel prices (including fuel oil and natural gas) on electricity tariff in Thailand. At the same time, the research quantifies the vulnerability of the Thai economy due to high gas dependence in power generation. Our research shows that for every 10% change in natural gas price, electricity tariff in Thailand would change by 3.5%. In addition, we found that the gas bill for power generation consumed between 1.94% and 3.05% of gross domestic product (GDP) between 2000 and 2004 and in terms of GDP share per unit of energy, gas dependence in power generation is almost similar to that of crude oil import dependence. We also found that the basic metal industry, being an electricity intensive industry, is the most affected industry. Additionally, we find that volatility of gas price is the main factor behind the vulnerability concern. The research accordingly simulates two mitigation options of the problem, namely reducing gas dependence and increasing efficiency of gas-fired power plants, where the results show that these methods can reduce the vulnerability of the country from high gas dependence in power generation.     

Temperature dependence of kinetic behaviour of sol–gel deposited electrochromics

The kinetic behaviour of sol-gel deposited electrochromic films is affected by temperature in a complex manner and may be modelled by considering the reaction mechanism, and in particular, the rate-limiting steps. If assumptions are made about the rate-limiting steps in a reaction, a model may be formed which can be used to provide information about the kinetic parameters such as diffusion coefficient and charge transfer resistance. Changes in the free energy of a reaction are observed as changes in the electrical potential associated with the cells and electrodes. We have measured changes in the switching characteristics of a sol–gel deposited electrochromic film and modelled these results in order to extract information about the change in lithium chemical diffusion coefficient (D) with temperature. Values of D estimated using the model described in this paper are in close agreement with those determined by other means, however there are some anomalies at high temperatures.     

The effect of temperature on the performance of dye-sensitized solar cells based on a propyl-methyl-imidazolium iodide electrolyte

The performance of dye-sensitized solar cells (DSSC), based on an ionic liquid (propyl-methyl-imidazolium iodide) electrolyte, has been evaluated at varying iodine concentrations and cell temperatures (5–50 °C) for two irradiancies (0.1 and 1 sun). At 1 sun and at lower temperatures, the short-circuit current (J_SC) is limited by the diffusion of tri-iodide, while at higher temperatures, the J_SC decreases due to more pronounced recombinations. Also, the conversion efficiency of a DSSC resembles the J_SC behaviour. At 0.1 sun irradiance, the efficiency monotonically decreases with increasing temperature, while at 1 sun, a five-fold increase in efficiency is observed.     

Electricity capacity expansion in Thailand: An analysis of gas dependence and fuel import reliance

Electricity generation in Thailand is highly dependant on natural gas. Recent research has revealed that the Thai economy would become more vulnerable from high gas dependence in the power sector. This paper aims to assess the economic impact of gas dependence in power generation in the coming decades. To fulfil this objective, two scenarios of electricity capacity planning were developed and the results were analysed to understand the changes in gas dependence and the effects on import reliance. It is found that from 2011 to 2025, the average cost of natural gas for power generation will account for 2.41% of gross domestic product (GDP) while high oil price in international energy markets would push this cost to 2.97% of GDP. In addition, reliance on fuel imports for power generation, particularly natural gas and coal, is going to be another crucial concern to the security of energy supply as the costs of these imports during the planning horizon will increase significantly at an average rate of 6.78% per year.