内压圆筒组合应力校核问题的探讨

国标GB150-89《钢制压力容器》中规定,当考虑温差应力时,组合应力应满足σ_B≤2·[σ]~t·φ。本文论证在满足σ_B≤2·[σ]~t·φ的条件下,(1)内壁温度高于外壁温度的单层内压圆筒,内外壁温差Δt≤2.3p,℃;(2)外壁温度高于内壁温度单层内压圆筒,外内壁温差Δt≤0.9p,℃时,均可不做组合应力校核。(3)在GB150-89标准规定的适用范围内,单层圆筒热应力可用σit=2·Δt,MPa;σot=1.6Δt,MPa 来估算。     

基于ANSYS的立式厚壁压力容器应力分析

应用ANSYS软件分析了立式厚壁压力容器工作时筒体与封头的应力分布。结果表明:最大等效应力处于在筒体的内壁区域;等效应力从筒体或封头内壁到筒体或封头外壁呈近乎线性下降。筒体与封头的连接处附近外壁和内壁的等效应力变化最大。     

基于ANSYS的立式储罐应力分析

应用ANSYS软件分析了立式储罐工作时罐体与封头的应力分布.结果表明：储罐罐体受载荷作用时等效应力较大,最大等效应力处于罐体的内壁区域;罐体与封头连接区内壁处的等效应力值最大,随着由内壁向外壁的推移,等效应力呈近乎线性下降;人孔内壁处附近的等效应力值最高.     

自增强高压圆筒的最小壁厚

承受内压的高压圆筒的壁厚,各国的规范有不同的计算方法,当用第三强度理论计算时(如美国ASME核容器规范),一般总是以内壁应力为应力判据,因为圆筒的内壁存在着最大的应力。但是,如果圆筒经过自增强处理,则     

自增强圆筒的最佳弹塑性半径

<正> 一、前言经过自增强处理的厚壁圆筒,内壁处于塑性状态,外壁处于弹性状态;具有应力分布均匀,平均应力低,承载能力大,弹性操作范围广,疲劳寿命高等优点,现已在石化工业上得到广泛应用。近年来,不少的科学工作者对厚壁圆筒的弹塑性半径进行了理论和实验的研究,由     

压力载荷作用下非圆截面管件的应力分析

采用有限元方法,分析了含椭圆度的直管、弯头在内压或内压与轴向载荷共同作用下的应力分布.考察不同载荷方式与椭圆度条件下,直管、弯头的应力分布和大小.结果表明:在两种加载方式下,含椭圆度直管的应力集中区域在长轴端部的内壁侧与短轴端部的外壁侧;仅内压作用下,弯头应力最集中的区域为弯头与直管交界处的内壁侧;当内压与轴向载荷共同...     

ANSYS辅助弹塑性状态下的内压厚壁圆筒应力分析

采用ANSYS有限元软件对弹塑性状态下的内压厚壁圆筒的三向应力进行应力分析,直观展示厚壁圆筒的径向应力σ_r、环向应力σ_β和轴向应力σ_z的分布规律。ANSYS计算结果与解析解吻合较好:弹塑性状态下厚壁圆筒的径向应力为压应力,随半径而减小;环向应力为拉应力,其值在塑性区随半径增大而增大,在弹性区随半径增大而减小,在临界面处取得最大值;轴向应力在塑性区随半径增大而增大,在弹性区为一恒定值。ANSYS为厚壁圆筒的应力分析提供了可靠且高效的手段。     

竖直套管内带热源的多孔介质中的自然对流

为研究内热源存在时多孔介质中流动和传热的特性,采用数值方法对上下底绝热、内外壁存在温差时,竖直套管中带均匀容积热源的多孔介质内的自然对流进行了分析。考查了内、外Rayleigh数之比Rai／Ra、高宽比A及半径比k对流场、温度场以及局部和平均Nusselt数的影响。研究结果表明,Rai／Ra和A较大时,内、外壁面附近分别形成两个逆向环流,温度场出现θ>1的高温区和θ<1的低温区,高温区的范围随Rai／Ra和A的增大而扩大。内壁面局部Nusselt数沿管长先增大后下降,分界点位置随k的减小和A的增大下移;外壁面局部Nusselt数在管上部区域迅速增大。内壁面平均Nusselt数Nui与Rai／Ra的增加呈现负的线性关系。     

干湿时间比对海工混凝土结构氯盐扩散的影响研究

为了探究海洋环境干湿交替区混凝土结构中氯离子扩散规律,将干湿时间比量化,对应连云港港口泊位现场环境与结构状况设计进行干湿交替区的混凝土构件在不同干湿时间比和不同压应力水平下的室内氯盐加速侵蚀试验,以混凝土内部扩散区的氯离子扩散系数和表面氯离子浓度作为侵蚀指标,将室内加速试验与现场试验的结果对比,分析干湿时间比和应力水平对氯离子扩散的影响.结果证明室内试验取得良好的加速侵蚀效果,试验结果表明对于干湿交替区的混凝土结构,干湿时间比对氯离子扩散的影响十分显著,不同的干湿时间比甚至将氯离子扩散系数提高2倍,其影响力远高于压应力水平.     

电流密度和抛光时间对镍钛合金管电解抛光的影响

采用高氯酸?冰醋酸体系对镍钛合金管电解抛光.在温度25°C及抛光间隙15 mm的条件下研究了抛光时间(60～120 s)和电流密度(0.75～1.75 A/cm2)对抛光效果的影响.结果表明,随着抛光时间延长或电流密度增大,钛合金管的表面粗糙度先减小后增大,残余压应力先增大后减小,较佳的电流密度和抛光时间分别为1.15 A/cm2和90 s.在该条件下电解抛光后,镍钛合金管表面平整光亮,凹坑最少,表面粗糙度最小(为53.8 nm),表面残余压应力最大(为175.8 MPa).     

The effect of the embedded interface dynamics on mass transport in immiscible polymer blends

Mass transport of solvents into immiscible blends may exhibit a non-Fickian behavior due to the deformation of the embedded interface that couples with diffusion. We introduce an interface area covariant tensor N as a structural state variable and derive a set of thermodynamically-consistent PDEs and ODEs transport equations for the bulk and time-dependent boundaries. The proposed model, which is a reformulation of that derived by El Afif (2008) and El Afif et al. (2003), improves both mathematically and numerically the investigation of the diffusion-interface coupling and provides reasonable predictions of the sorption-permeation one dimensional treatment affording good agreement with experimental data. The tensor N englobes, into a single morphological quantity, all information regarding diffusion-induced changes in the size and shape anisotropy of the interface area. Predicted results include concentration, components of N , residual stresses, mass-uptake, and swelling. Scaling leads to three relevant dimensionless parameters: a mixing-interface coupling constant and bulk and boundary diffusion Deborah numbers.     

Stability of ancient masonry towers: Moisture diffusion, carbonation and size effect

Moisture diffusion and carbonation influence the behavior of multiple-leaf ancient masonry walls, producing during centuries a redistribution of stresses from the core of lime mortar concrete to the external cladding of stiff masonry. This is likely one of the causes of long-time damage of some ancient masonry towers. With these motivations, coupled processes of moisture diffusion, carbon dioxide diffusion and carbonation reaction are analyzed numerically. Due to the absence of models and data for lime mortar, one of the simplest models proposed for Portland cement concrete is adapted for this purpose. The results reveal the time scales of the processes involved and their dependence on wall thickness (size). It is found that the temporal scale is set mainly by diffusion of moisture trough the massive concrete wall and is only slightly modified by carbonation. Moisture evolution in time is needed for stress analysis that is relegated to a subsequent paper.     

Variation of intraparticle diffusion parameter during adsorption of p‐chlorophenol onto activated carbon made from apricot stones

The adsorption of para‐chlorophenol onto an active carbon made from waste apricot stones has been studied. The batch kinetic adsorption processes have been measured for a range of system variables including agitation rate, initial concentration of para‐chlorophenol, mass of carbon and particle size of carbon. The extent of adsorption is reported as plots of solid phase concentration against the square root of time. An intraparticle diffusion parameter is used to describe the mass transfer within the adsorbent. This parameter varies with the square root of time and can be related to the type of structure which occurs within an activated carbon. A correlation is proposed relating the process variable with the intraparticle diffusion parameter in each of the three mass transfer regions. Copyright © 2003 Society of Chemical Industry     

Solid Fission Product Diffusion in Irradiated Coated Particles

Solid-fission-product diffusion was studied in pyrolytic carbon (PyC) coated particles. A method for determining diffusion coefficients is described. Changes in fission-product concentration profiles in the PyC are measured as a function of post-irradiation annealing time and temperature. The influence of irradiation history and type of PyC on the diffusion behavior of Cs isotopes is demonstrated.     

响应曲面法优化木薯酒精污泥基活性炭制备及对没食子酸的吸附性能

以木薯酒精厂生产过程中产生的脱水污泥为原料,采用响应曲面法 Box-Behnken模型优化了木薯酒精污泥基活性炭的制备工艺,同时对最优成品进行一系列表征分析,并将其应用于没食子酸废水的处理研究。活性炭的最优制备条件为活化温度489℃,浸渍时间14 h,活化时间51 min,氯化锌浓度21.53%,该条件下样品的碘吸附值达521.64 mg/g。表征分析显示其表面布有众多孔壁较薄、大小不一的孔洞,金属含量较小,BET比表面积达441.86 m²/g,平均孔径为2.50 nm,拥有丰富的微孔结构,表面富有较多的含氧官能团。考察了活性炭投加量、pH、接触时间、溶液温度对样品去除水中没食子酸的影响。结果表明,样品能够高效去除没食子酸,且随着投加量的增加和pH值降低,没食子酸的去除率呈增长趋势。木薯酒精污泥基活性炭对没食子酸的吸附符合pseudo second-order动力学模型和Freundlich等温模型,最大吸附量为126.72 mg/g。扩散机理显示除颗粒内扩散外也包含液膜扩散过程。热力学分析表明该吸附反应是自发进行的吸热且熵增的过程。本研究将为制备高性能污泥活性炭并应用于高浓度天然有机物废水处理提供理论基础。     

间歇吸附器内活性炭吸附水中微量三氯甲烷——孔扩散模型和表面扩散模型

<正> 近10多年来,各国对饮水氯化处理中的副作用研究甚多．现已发现氯化饮水中含有不同 性质的有机物约300种“’,其中三卤甲烷含量突出,而活性炭吸附是脱除其中不同性质有机物 的有效方法’‘－‘’．一般情况下,溶质在吸附剂内的扩散过程是整个吸附过程的控制步骤．但目 前文献仅限干研究活性炭吸附三卤甲烷的能力,很少涉及与吸附速率有关的有效扩散系数．     

Mass diffusion coefficients of polymer films using real-time holographic interferometry

The mass diffusion coefficient is obtained using real-time holographic interferometry. The stresses induced during desorption and absorption of moisture are monitored as a function of time at various relative humidities. A mathematical relationship is applied to relate these stresses to the moisture diffusion through the thickness of the films. The advantage of the holographic interferometry technique is that both the swelling stress as a function of time and the mass diffusion coefficient can be quantified simultaneously during the same experiment. Several films and coatings were investigated: polyimides (PMDA–ODA and BPDA–PAA), photographic gelatin, and cellulose acetate. Each exhibited characteristic Fickian diffusion behavior. A gravimetric technique was employed to validate the holographic interferometry results. The moisture diffusion coefficients determined by holographic interferometry agreed well with reported literature values. © 1996 John Wiley & Sons, Inc.     

Carbon tetrachloride absorption in low-density polyethylene pellets: Concentration profiles by electron microprobe analysis

The concentration profiles of carbon tetrachloride in low-density polyethylene pellets after various periods of absorption (1–6 h) at 40°C have been measured in a new application of electron probe microanalysis using energy dispersive x-ray spectroscopy (EDAX). The concentration profiles were determined from an EDAX scan of chlorine content along the diameter of a cylindrical pellet (4-mm diameter) mounted in a scanning electron microscope. The maximum chlorine content seen in the EDAX scan was presumed to reflect the equilibrium surface concentration, eliminating the need to calibrate the system and enabling direct interpretation of the EDAX scan as a concentration profile. The concentration profiles revealed that absorption of CCl₄ in LDPE pellets took place with a sharp moving boundary, with the depth of penetration proportional to (time)^½ rather than to time as in case II diffusion. This behavior was attributed to a discontinuous relationship between diffusivity and concentration, resulting in a sharper than expected fickian diffusion profile. The EDAX technique, although requiring further refinement, appears to be a valuable method for assessing slow diffusion in thick polymer samples for those penetrants detectable by EDAX.     

A Model for Silicon Self-Diffusion in Silicon Carbide: Anti-Site Defect Motion

A simple defect interaction model was developed that explains the identical activation energies observed for carbon and silicon diffusion in single-crystal silicon carbide. In accord with experimental measurement of nonstoichiometry, the model requires a substantial concentration of silicon anti-site defects. The diffusion of silicon is limited by the motion of these defects; this is suggested to occur by their interaction with carbon vacancies. The model predicts that boron doping will increase both carbon and silicon diffusion coefficients.     

活性炭对苯酚的吸附研究

进行了活性炭处理含苯酚废水的应用研究,考察了影响苯酚吸附效果的因素。确定了处理水中苯酚的最佳条件:吸附平衡时间为30 min;最佳pH值为6左右;苯酚初始浓度为10 mg/L;投炭量为20～25 mg/L;苯酚的吸附率高达97.4%;温度对苯酚吸附率的影响不明显。研究了活性炭对苯酚的吸附动力学特性,分别用伪一级动力学方程、伪二级动力学方程、修正伪一级动力学方程和颗粒内扩散模型进行拟合,对于不同浓度的苯酚废水都只有伪二级动力学方程拟合程度比较高,伪二级动力学方程更为真实地反映苯酚在活性炭上的吸附机理。