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排序方式: 共有418条查询结果,搜索用时 31 毫秒
41.
Erosion is one of the major problems in many industrial processes, and in particular, in heat exchangers. The effects of flow velocity and sand particle size on the rate of erosion in a typical shell‐and‐tube heat exchanger were investigated numerically using the Lagrangian particle‐tracking method. Erosion and penetration rates were obtained for sand particles of diameters ranging from 10 to 500 µm and for inlet flow velocities ranging from 0.197 to 2.95 m/s. A flow visualization experiment was conducted with the objective of verifying the accuracy of the continuous phase calculation procedure. Comparison with available experimental data of penetration rates was also conducted. These comparisons resulted in a good agreement. The results show that the location and number of eroded tubes depend mainly on the particle size and velocity magnitude at the header inlet. The rate of erosion depends exponentially on the velocity. The particle size shows negligible effect on the erosion rate at high velocity values and the large‐size particles show less erosion rates compared to the small‐size particles at low values of inlet flow velocities. The results indicated that the erosion and penetration rates are insignificant at the lower end of the velocity range. However, these rates were found to increase continuously with the increase of the inlet flow velocity for all particle sizes. The particle size creating the highest erosion rate was found to depend on the flow velocity range. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
42.
Ruhul A. Sarker
Eldon A. Gunn
《Applied Mathematical Modelling》1994,18(12):672-678Coals are extracted from mines and upgraded on the surface for customers. The upgraded coals must be aged at least four weeks in a bank before being supplied to customers. Different sizes of banks are required for different lengths of time at different points in time. Bigger banks increase the floor space capacity and reduce handling costs. The proper location of banks reduces the total space requirement and bank movement after building. In this paper, we address the bank size and location problem and solve it by using a mathematical programming approach. 相似文献
43.
44.
Kate N. Fanning 《Tetrahedron letters》2007,48(48):8479-8481
A simple and direct approach for the synthesis of (S)-gizzerosine, an amino acid responsible for the disease, black vomit, and a potent histamine H2-receptor, has been developed in 10 steps and in 31% overall yield from l-aspartic acid. The key steps involved a two-carbon homologation of an l-aspartic acid semi-aldehyde and direct alkylation of unprotected histamine with a 6-hydroxynorleucine derivative. 相似文献
45.
Experimental results are presented for electrode erosion on copper cathodes in magnetically rotated arcs in argon, dry air, nitrogen, ammonia, and carbon monoxide as well mixtures of the above with argon. Water-saturated argon was also used. Erosion rates were determined by weight loss after chemical cleaning, and the runs were sufficiently long (between 5 to 60 min) to represent steady-state operation. Arc currents of 100 A and gas pressures of 1.1 atm. were used. Pure argon gave the highest erosion rates and the lowest arc velocities. Small concentrations of any of the diatomic gases in argon greatly increased the arc velocity and decreased the erosion rates. The results suggest that erosion is primarily a thermal phenomenon but that the surface chemistry can greatly influence erosion rates by modifying arc behavior. 相似文献
46.
47.
Leonid M. Blumberg 《Journal of separation science》1993,16(1):31-38
In linear chromatography (i.e. chromatography performed in the absence of sample overloading), when the plate height of a column is roughly uniform along its length, variations in the velocities of solutes are the only possible causes of erosion of efficiency. The sources of these variations (variations in capacity ratio and in the density of the mobile phase, etc.) play no direct role in the erosion of efficiency except through their effect on solute velocities. In other words, what eventually causes the erosion of efficiency is merely variation in the time required for solutes to traverse equally small segments of a column. Significant erosion can only arise from abrupt and deep deceleration of solutes in one or several relatively small segments of a column. If erosion of efficiency caused by pressure gradients in linear SFC is to be large, the depth and the sharpness of the deceleration of a solute must go beyond that hitherto confirmed experimentally. Many relevant examples are analyzed graphically. 相似文献
48.
The effects of N2 and CO contaminants in atmospheric-pressure argon on an arc rotating between two concentric copper electrodes has been studied using optical spectroscopy of copper lines. The axial temperature of the magnetically driven arc in Ar + %N2 was determined to be around 10,000 K for arc currents of SO to 200 A. The diffusion process of the copper vapor from the cathode was also studied. A copper density maximum 1 mm from the cathode along the arc column was found in Ar + %N2. Removal of the contaminated cathode surface layers by the arc when contaminant injection in the plasma gas was stopped was found to be a slow process with a time scale depending on the type of the gas contaminant. The presence of gas contaminant in the electrode material controls the cathode erosion mechanism and the overall arc behavior in the transition between a contaminated to a pure argon arc. 相似文献
49.
稀土对38CrMoAl钢软氮化层抗冲蚀磨损性能的影响 总被引:4,自引:1,他引:4
研究了稀土元素对38CrMoAl钢软氮化层抗冲蚀磨损性能的影响. 结果表明: 与软氮化相比, 稀土软氮化提高了38CrMoAl钢的抗冲蚀磨损性能, 同时提高了软氮化层的硬度以及钢的冲击韧度. 由于软氮化时稀土的渗入, 改善了渗层组织, 从而提高了38CrMoAl钢的抗冲蚀磨损性能和机械性能. 扫描电子显微镜对冲蚀磨损试样表面形貌的观察发现, 普通软氮化层的磨损特征为塑性变形形成的犁沟剥落, 并伴随着萌生横向裂纹, 有大块磨屑剥落; 而稀土软氮化层则为塑性变形形成的犁沟剥落. 相似文献
50.
Degradation profiles and surface wettability are critical for optimal application of electrospun fibrous mats as drug carriers, tissue growth scaffolds and wound dressing materials. The effect of surface morphologies and chemical groups on surface wettability, and the resulting matrix degradation profiles were firstly assessed for electrospun poly(d,l-lactide) (PDLLA) and poly(d,l-lactide)-poly(ethylene glycol) (PELA) fibers. The air entrapment between the fiber interfaces clarified the effects of various surface morphologies on the surface wettability. Chemical groups with lower binding energy were enriched on the fiber surface due to the high voltage of the electrospinning process, and a surface erosion pattern was detected in the degradation of electrospun PDLLA fibers, which was quite different from the bulk degradation pattern for other forms of PDLLA. Contributed by the hydrophilic poly(ethylene glycol) segments, the degradation of electrospun PELA fibers with hydrophobic surface followed a pattern different from surface erosion and typical bulk degradation. 相似文献