Experimental study of spontaneous ignition induced by sudden hydrogen release through tubes with different shaped cross-sections

The shock wave dynamics, spontaneous ignition and flame variation during high-pressure hydrogen release through tubes with different cross-section shapes are experimentally studied. Tubes with square, pentagon and circular cross-section shapes are considered in the experiments. The experimental results show that the cross-section shape of the tube has no great difference on the minimum burst pressure for spontaneous ignition in our tests. In the three tubes with length of 300 mm, spontaneous ignition may occur when overpressure of shock wave is 0.9 MPa. When the spontaneous ignition is induced in a non-circular cross-section tube, the possible turbulent flow in the corner of the tube increases can promote the mixing of hydrogen and air, thus producing more amount of the hydrogen/air mixture. As a result, both the peak light signal and flame duration detected in the non-circular cross-section tubes are more intense than those in the circular tube. The smaller angle of the corner leads to a more intensity flame inside tube. When the hydrogen flame propagates to the tube exit from the circular tube, the ball-like flame developed near tube exit is relatively weak. In addition, second flame separation outside the tube is observed for the cases of non-circular cross-section tubes.     

塑料异型材挤出机头变截面流道的计算机分析

根据塑料馆体流变学理论，推导了狭缝流道压力降计算公式；在此基础上，又采用横截面／假想区域法推得变截面流道的压力降计算公式，并通过计算机编程实现了塑料异型材挤出机头成型段、压缩段的流动分析；最后用实例验证了其可行性。     

EAST托卡马克上截面效应对电荷交换复合光谱测量结果的影响

离子温度和旋转速度是聚变等离子体中的重要物理参数,在先进实验超导托卡马克EAST(Experimental Advanced Superconducting Tokamak)上电荷交换复合光谱(Charge e Xchange Recombination Spectroscopy,CXRS)诊断是测量这些物理参数的标配诊断之一。由于截面效应的存在,CXRS诊断测量的谱线线型会受到影响,导致得到的离子温度和旋转速度偏离实际值,为了得到真实值,需要对离子温度和旋转速度进行修正。在EAST上,分别采用常用的动力学理论和数值计算方法对测量到的实验数据进行修正,同时对比两种方法对截面效应的修正结果,可以看出两种方法得到的结果趋势基本一致。对2015年EAST上电荷交换复合光谱测量到的典型的实验数据进行修正,结果表明在目前的放电条件下截面效应对离子温度的影响比较小,而对旋转速度的影响低于10%。     

双螺杆真空泵的新型椭圆弧型螺杆转子研究

针对现有螺杆转子存在尖点的问题,提出了一种新型椭圆弧型转子。建立了椭圆的啮合模型,基于该模型采用椭圆弧及其包络线构建了转子截面型线,并验证其啮合性能。讨论了圆心角参数大小对椭圆弧型线构成方式的影响。计算对比圆弧修正转子和所提出的新型转子的性能,结果表明:新型螺杆转子具有更大的面积利用率,更短的空间接触线和面积更小的泄漏三角形,抽气量和密封性都得到提高。     

Human capital and energy consumption: Evidence from OECD countries

We examine the effect of human capital on energy consumption for a panel of OECD economies over the period 1965–2014. Our preferred results, which account for cross-sectional dependence and structural breaks, suggest that a one standard deviation increase in human capital reduces aggregate energy consumption by 15.36%. When we distinguish between clean and dirty energy consumption, we find that human capital generates significant positive externalities for the environment. Specifically, we find that a one standard deviation increase in human capital is associated with a 17.33% decrease in dirty energy consumption and an 85.54% increase in clean energy consumption. Our findings reinforce the social benefits of investing in human capital and suggest a promising avenue for energy conservation without impeding economic growth.     

Study on production of Pd and characterisation of possible contaminants in the proton irradiation of Rh up to 28 Mev

Excitation functions for the proton-induced reactions on ¹⁰³Rh of importance in the production of the medically used ¹⁰³Pd were studied by the stacked foil technique. Several experiments at incident energies between 14.7 and 29.4 MeV allowed reliable determination of the cross-sections for ¹⁰¹Pd, ¹⁰³Pd, ^101m,101gRh and ^102m,102gRh. Measurements for ¹⁰³Pd were done in the X-line region as well as for γ-lines and show 25% difference. The new experimental values are compared to the available literature values and show mostly higher values. Thick target yields were calculated that are in good agreement with earlier published values. Practical upper limit of incident energy to be used in production runs is derived.     

Design of wearable and wireless electrical impedance tomography system

Electrical impedance tomography (EIT) is a non-invasive approach to reconstruct the cross-section impedance image of the body. Many EIT systems and impedance image reconstruction algorithms have been proposed in previous studies. However, most of these EIT systems are bulky to cause the limitation of applications. In this study, a wearable and wireless EIT system is proposed to reconstruct impedance images non-invasively and wirelessly. By microminiaturizing the conventional EIT system, the proposed system can provide the advantages of small volume and wireless transmission to reduce the application limitation of conventional EIT systems. Finally, the phantom experiment is tested to validate the performance of the proposed EIT system. The experimental results show the average BR value of the reconstructed image obtained by the proposed system being 1.3 ± 0.2 and the averaged location error ratio being about 6.27 ± 3.14%. Therefore, the proposed wearable and wireless EIT system can be viewed as a good system prototype and may be applied to more clinical applications in the future.     

Non-deposition self-cleansing design criteria for drainage systems

Self-cleansing is a substantial aspect of the drainage systems in which it is desired to minimize the sediment deposition that can cause channel blockage and surcharge early overflows. In the conventional self-cleansing design criteria of drainage systems, a single value of velocity or shear stress is used based on experience. In the recent decades rather than using a single value, non-deposition design concept has been further modified to develop self-cleansing models based on higher number of parameters considering flow, fluid, sediment and channel characteristics. However, non-deposition self-cleansing models have been mostly developed for circular channels, and none of the models considers yet the effect of channel cross-section although some models take into account the pipe diameter, hydraulic radius and cross-section area as independent variables. In this study, a self-cleansing model considering the effect of cross-section by a shape factor available in the literature is developed to determine the non-deposition particle Froude number for bed load sediment transport. The model is developed using experimental data of circular, rectangular and U-shape channel cross-sections from the literature; and data of trapezoidal channel cross-section from experiments carried out in this study. For validation of the model, data collected in this study is used together with four different sources of data taken from the literature. Validation of the model for each cross-section data shows its wide range applicability in terms of different channel cross-sections.     

基于ABAQUS数值模拟的采区巷道断面形状优化研究

 选取矩形、梯形、直墙半圆拱形、圆弧拱形、三心拱形、直墙半圆加反拱形6种常用采区巷道断面形状进行数值模拟分析,研究不同巷道断面形状开挖后位移分布,分析表明直墙半圆拱形巷道变形量最小,且加设反拱后对于减少底臌量效果明显。选取矩形和直墙半圆拱形断面作为代表断面,分析不同埋深H及侧压力系数λ对采区巷道变形特征、围岩应力影响。在此类围岩条件下,当采区巷道埋深小于400 m、侧压力系数小于1.6时,矩形巷道和直墙半圆拱形巷道围岩变形量差距较小,此时可以选择矩形巷道断面以满足经济性要求。     

Analytical model to study the curling phenomena in wide flange trapezoidal panels

In this paper, an original analytical model to study the nonlinear flange curling in wide double-flange panels is presented. Flange curling phenomenon is the tendency of wide thin flanges (in compression or tension) to move towards the neutral axis of thin-walled members under bending. Since the earlier work of Winter, there has been scarce investigation on the flange curling phenomena. Despite the simplicity of the formula developed by Winter to account for flange curling effect, which is used in current steel codes (e.g., EC3), recent works showed that this expression is rather restrictive and does not apply to all cases. The analytical formulae developed here is rather general since they (i) consider the restraining effect provided by the web, (ii) account for the shift of the neutral axis due to curling, (iii) incorporate the decrement of the second moment of area due to curling, and (iv) are fully analytical, thus avoiding iterative techniques. The analytical model is applied to study the curling behaviour of trapezoidal (double-flange) panels and is validated by means of comparisons with experimental results available in the literature. Since EC3 rules state that the tensioned wide flange in liner trays should be reduced if the curling displacement is higher than 5% of the web height, approximate expressions to evaluate the reduced width of wide flanges are presented.