Study on Numerical Simulation for Control of Winding Process of Thin Wall Spiral Tube

Being aimed at the inside wall wrinkling and sinking phenomenon of palladium-yttrium alloy thin wall spiral tube used for preparation of high purity hydrogen, extraction of hydrogen isotope, and purification and separation of hydrogen in the winding process, this article analyzed the reasons for above phenomena, established a numerical simulation model of winding process of above tube, using elastic-plastic Finite Element method analyzed the max. tensile stress and max. compression stress and their locations, thereby provides a theory base for the control of working forming course of thin wall spiral tube.

厚壁岔管的应力分析

文中用有限单元法的三维等参元对岔管进行了应力分析,给出了岔管交接区的影响范围L=2.7(Rt)^(1/2)。对已有实验结果的岔管进行了计算,计算表明:用三维等参元分析厚壁岔管是有效的方法。文中的程序可用于分析各种回转体岔管,例如锥形岔管。

Increased photo-catalytic removal of sulfur using titania/MWCNT composite

Titania coating of multi wall carbon nano tube(MWCNT) was carried out by sol-gel method in order to improve its photo catalytic properties.The effect of MWCNT/TiO_2 mass to volume ratio on adsorption ability,reaction rate and photo-catalytic removal efficiency of dibenzothiophene(DBT) from n-hexane solution was investigated using a 9 W UV lamp.The results show that the addition of nanotubes improves the photo-catalytic properties of TiO_2 by two factors;however,the DBT removal rate versus MWCNT content is found to follow a bimodal pattern.Two factors are observed to affect the removal rate of DBT and produce two optimum values for MWCNT content.First,large quantities of MWCNTs prevent light absorption by the solution and decrease removal efficiency.By contrast,a low dosage of MWCNT causes recombination of the electron holes,which also decreases the DBT removal rate.The optimum MWCNT contents in the composite are found to be 0.25 g and 0.75 g MWCNT per 80 m L of sol.

NiO_(x) Nanoparticle Synthesis by Chemical Vapor Deposition from Nickel Acetylacetonate

Ni/NiO nanoparticles were synthesized by metal organics chemical vapor deposition of nickel acetylacetonate in an externally heated tube flow reactor at moderate temperatures, up to 500°C. Particle production and characteristics were studied by evaluating the effects of reactor temperature, precursor concentration, and flow rate through the reactor. In addition, two precursor decomposition methods were examined: thermal decomposition and reduction by hydrogen. Particle production was monitored with a scanning mobility particle sizer, and particle characteristics were studied using transmission electron microscopy, high resolution transmission electron microscopy, selected area electron diffraction, and energy dispersive spectroscopy. The presence of hydrogen in the reaction mixture influenced significantly both particle production and their characteristics.

Reliability improvement of gas discharge tube by suppressing the formation of short-circuit pathways

After cumulative discharge of gas discharge tube(GDT),it is easy to form a short circuit pathway between the two electrodes,which increases the failure risk and causes severe influences on the protected object.To reduce the failure risk of GDT and improve cumulative discharge times before failure,this work aims to suppress the formation of two short-circuit pathways by optimizing the tube wall structure,the electrode materials and the electrode structure.A total of five improved GDT samples are designed by focusing on the insulation resistance change that occurs after the improvement;then,by combining these designs with the microscopic morphology changes inside the cavity and the differences in deposition composition,the reasons for the differences in the GDT failure risk are also analyzed.The experimental results show that compared with GDT of traditional structure and material,the method of adding grooves at both ends of the tube wall can effectively block the deposition pathway of the tube wall,and the cumulative discharge time before device failure is increased by 149%.On this basis,when the iron-nickel electrode is replaced with a tungsten-copper electrode,the difference in the electrode’s surface splash characteristics further extends the discharge time before failure by 183%.In addition,when compared with the traditional electrode structure,the method of adding an annular structure at the electrode edge to block the splashing pathway for the particles on the electrode surface shows no positive effect,and the cumulative discharge time before the failure of the two structures is reduced by 22.8%and 49.7%,respectively.Among these improved structures,the samples with grooves at both ends of the tube wall and tungsten-copper as their electrode material have the lowest failure risk.

On-Line Life Monitoring Technique for Tube Bundles of Boiler High-Temperature Heating Surface

High-temperature heating surface such as superheater and reheater of large-sized utility boiler all experiences a relatively severe working conditions. The failure of boiler tubes will directly impact the safe and economic operation of boiler. An on-line life monitoring model of high-temperature heating surface was set up according to the well-known L-M formula of the creep damages. The tube wall metal temperature and working stress was measured by on-line monitoring, and with this model, the real-time calculation of the life expenditure of the heating surface tube bundles were realized. Based on the technique the on-line life monitoring and management system of high-temperature heating surface was developed for a 300 MW utility boiler. An effective device was thus suggested for the implementation of the safe operation and the condition-based maintenance of utility boilers.

A New Structure of Cooling Wall Tube for Supercritical CO_(2)Coal-Fired Power Plants

In terms of developing supercritical CO_(2)(sCO_(2))coal-fired power plants,enhancing cooling wall performance is one of significant factors to improve system performance.In this paper,a new cooling wall tube structure is proposed to match the non-uniform heat flux(NUH)with the thermal resistance by changing the cooling wall tube eccentricity.A three-dimensional multi-physical coupling model of cooling wall is constructed to compare the novel structure to the conventional structures.The properties of fluid dynamics,thermal stress,coupled heat transfer and cooling wall deformation are analyzed.In contrast to the traditional structure,the maximum temperature and circumferential temperature difference(CTD)of the proposed structure can be reduced by 2%and 27.4%,respectively.The essential working parameters related to the performances of the cooling wall tube are discussed.The maximum temperature of the new structure is reduced by 8-13 K and the maximum thermal stress is reduced by about 10%-15%under all the simulated working conditions when the eccentricity changes from 0 to 0.2.The proposed structure can effectively reduce the maximum temperature and circumferential temperature gradient under NUH.Consequently,a novel insight is put out for the design and optimization of the cooling wall tube in coal-fired power plants.

Structure of Graphene, and Mechanical and Bonding Characteristics of Single Wall Carbon Nanotube by Linear Scaling Quantum Mechanical Method

Using a linear scaling self-consistent-charge density functional tight binding （SCC-DFTB） and an ab initio Omol method, the bonding characteristics and Young＇s modulus of （10, 0） and （10,10） single-walled carbon nanotubes are calculated. The structure of a graphene is also calculated. It is found that the C-C and C-H bond length, their distribution characteristics on the tube, and Young^s modulus of the tube by linear scaling SCC-DFTB are identical to those by ab initio, while the computing cost by the linear scaling SCC-DFTB is reduced by more than 30 times as compared with that by the Dmol for the （10,0） and （10,10） tubes. By computing the structure of a graphene it is also found that the linear scaling SCCDFTB is reliable and time-saving.

THE ENVELOPE SOLITON OF STRESS WAVE ON THE WALL OF A FLUID-FILLED CIRCULAR TUBE

The reductive perturbation method of multiple-scales is used to investigate the weak nonlinear modulation of the stress wave on the wall of a fluid-filled elastic circular tube. In the case of a single mode, the nonlinear Schrodinger equation which the wave amplitude satisfies and its envelope soliton solution of stress wave are obtained.

Exceptionally Preserved Caddisfly Larval Cases(Insecta) from the Lower Cretaceous of the Liupanshan Basin, Western China

Abundant well-preserved tubular fossils of caddisfly （Insecta： Trichoptera） larval cases are reported from the Early Cretaceous Madongshan and Naijiahe formations of the Liupanshan Basin, Ningxia Province, western China. Most cases were mainly preserved in life position and densely packed in various layers. Individual cases in each layer tended to be same in size and were erect and parallel to one another and open at both ends. In a transverse section cut perpendicular to the long axis of the cases, individual case appears to form a rounded ring. Small cases are elliptic in a cross-section oblique to the long axis of the cases. Tube walls are nearly subparallel to one another in longitudinal section with both ends being open. The caudal end of the case slightly tapers and usually points downward. The cases were closely packed, almost touching with one another and lacking bifurcate or connecting struc- ture. The overwhelming majority of cases were partially or fully filled with calcite. The case wall em- braces a medium particle layer flanked by inner and outer organic layers. Individual particles are ovate in outline and comprise cryptocrystalline or ganic pellets. SEM imaging shows that those pellets are sub-cylindrical in outline and elliptic in cross section, and are made primarily of calcium carbonate. All features observed justify the assignment of the Liupanshan caddisfly cases to ichnogenus Coprindusia. The extinct insect Ningxiapsyche fangi was found in association with the Liupanshan caddisfly larval cases, and thus could be the candidate of the potential trace-maker.