Ultrasonic vibration mill-grinding of single-crystal silicon carbide for pressure sensor diaphragms

Single-crystal silicon carbide (SiC) has gained tremendous attention for harsh-environment sensor applications due to its high-temperature tolerance and chemical resistance. However, there are many technological challenges in the fabrication of single-crystal SiC sensing microstructures such as thin SiC diaphragms for pressure sensors. This paper presents an ultrasonic vibration mill-grinding (UVMG) technique for the fabrication of 6H-SiC sensor diaphragms. The fundamental machining characteristics of UVMG are investigated experimentally compared with conventional mill-grinding (CMG). The experimental results show that the axial grinding force in UVMG is reduced by 60–70% compared to that in CMG. In addition, the wheel loading is severe in CMG, while the issue of wheel loading is significantly alleviated in UVMG due to the discontinuous cutting characteristic achieved in this method. As a result, sharp increase of the axial grinding force, which is accompanied by the crack of SiC workpiece, happens frequently in CMG after a total grinding depth of 200 µm. By contrast, the axial grinding force is stable in UVMG during the total grinding depth of at least 900 µm. The ultrasonic vibration in UVMG results in rough surface finish due to the material-removal mechanism of brittle fracture. However, by taking the advantages of better machining stability in UVMG and better surface roughness in CMG, extremely thin SiC sensor diaphragms with satisfactory surface quality can be achieved. Finally, we demonstrate the successful fabrication of a thin SiC diaphragm with a thickness of 20.3 µm.     

一种数字式高温燃油控制阀的特性研究

该文提出了一种数字式高温燃油控制阀,可以实现对高温燃油的连续精确控制。首先,针对高温的恶劣工况,进行了方案设计,包括前置级伺服阀的选用、主阀阀口的设计、整阀的冷却设计,介绍了其结构组成及工作原理;之后分别对高温阀的热特性和控制特性进行了仿真分析,结果表明该方案的高温阀能够满足设计要求。     

Geometry optimization and pressure analysis of a proton exchange membrane fuel cell stack

For proton exchange membrane fuel cells (PEMFCs), the distribution of reactant streams in the reactor is critical to their efficiency. This study aims to investigate the optimal design of the inlet/outlet flow channel in the fuel cell stack with different geometric dimensions of the tube and intermediate zones (IZ). The tube-to-IZ length ratio, the IZ width, and the tube diameter are adjusted to optimize the geometric dimensions for the highest pressure uniformity. Four different methods, including the Taguchi method, analysis of variance (ANOVA), neural network (NN), and multiple adaptive regression splines (MARS), are used in the analyses. The results indicate the tube diameter is the most impactive one among the three factors to improve the pressure uniformity. The analysis suggests that the optimal geometric design is the tube-to-IZ length ratio of 9, the IZ width of 14 mm, and the tube diameter of 9 mm with the pressure uniformity of 0.529. The relative errors of the predicted pressure uniformity values by NN and MARS under the optimal design are 1.62% and 3.89%, respectively. This reveals that NN and MARS can accurately predict the pressure uniformity, and are promising tools for the design of PEMFCs.     

An experimental study on the oscillation of the propagating syngas-air flame in a duct

In this paper, premixed syngas-air flame propagating from the open end to the closed end were experimentally investigated. The effects of equivalence ratios, 0.8 ≤ Ф ≤ 1.2, and hydrogen volume fractions, 10% ≤ α(H₂) ≤ 90%, on flame deformation and oscillation had been discussed in detail. The tulip-like flame was observed because of the large pressure gradient. Results indicate that the pressure wave plays an important role in the flame deformation and oscillation. The flame oscillates as hydrogen volume fraction varies. There are two oscillation modes. When the flame oscillates as mode Ⅰ, the flame first oscillates smoothly, then the oscillation is gradually enhanced, and finally the oscillation decays. The interaction of flame and pressure waves continuously stimulates the flame deformation and oscillation, finally the violent flame folding emerges in the later stage. When the flame oscillates as mode Ⅱ, the flame just oscillates violently in the early stage.     

WSGG models for radiative heat transfer calculations in hydrogen and hydrogen-mixture flames at various pressures

Radiative heat transfer strongly influences pollutant emission prediction in combustion systems. In this work, the weighted sum of gray gas (WSGG) models have been developed for calculating radiative heat transfer in hydrogen and hydrogen-mixture flames. The total pressure effect on cut-off width of the Lorentz line profile is analyzed and properly considered in the line by line (LBL) calculations. Based on the LBL benchmark results, two sets of WSGG model correlations have been proposed for H₂O and its mixture with CO₂ at a molar ratio (Mr) of 3, representing the typical combustion products of the hydrogen and a hydrogen-rich mixture (e.g., 50% hydrogen and 50% methane). The WSGG models are applicable and accurate with a total pressure ranging from 1 to 60 atm. Partial pressure is explicitly applied as an independent variable in the model coefficients to account for its nonlinear effect on gas emissivity, which is particularly important for a participating gas medium with a large amount of H₂O at a total pressure below 5 atm. Detailed studies are carried out to solve radiative heat transfer in non-isothermal and non-homogeneous gas media at different conditions. Results show improvement over the existing WSGG models at the atmospheric pressure and have good agreement with LBL solutions under various conditions.     

Experimental investigation of the effects of contraction on tsunami-induced forces and pressures on a box section bridge

Many bridges that lie within possible tsunami inundation zones are critical links in transport networks. Some efforts have been made to determine the effects of tsunamis on bridges, but only a limited range of published design guidelines are available. Therefore, it is necessary to further investigate the effects of tsunamis on bridges. In the current study, physical modeling experiments were carried out to measure bore impact forces and pressures for various tsunami bore strengths on a bridge deck with different abutment types (wing wall and spill-through) and different opening and submergence ratios. The experiments were conducted in a wave flume with dimensions of 14 × 1.2 × 0.8 m (length × width × height), equipped with an automatic gate designed to generate a tsunami bore. The horizontal and vertical forces showed an increasing trend with increasing submergence ratio for both types of abutment. However, the horizontal force showed a decreasing trend as the opening ratio decreased, while the vertical force initially increased as the opening ratio decreased, until it reached a peak value, and then it started to decrease. The overall shapes of the results for both types of abutment are similar, with higher values for spill-through abutments due to their lower energy dissipation rates. Based on the experimental data, empirical equations are proposed for estimation of tsunami loads as a function of opening and submergence ratios.     

对采煤机摇臂调高抖动问题的研究

分析了采煤机调高系统产生抖动的原因,并提出了可靠的解决方法,实用效果良好。     

跳汰机风阀的改造

用数控气动风阀替换卧式手动风阀 ,解决了手动风阀在使用中存在的问题 ,减少了事故 ,提高了洗选效率。     

液压凿岩机配油阀运动行程的设计计算

分析了液压凿岩机配油阀的主要能量损失 ,给出了其计算表达式。以配油阀的能量损失最小和定位稳定可靠为目标 ,导出了一组计算配油阀运动行程的方程式 ,指出了确定运动行程的方法并通过实例进行了计算