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51.
52.
弥散燃料与弥散可燃毒物由于具有双重非均匀性,采用传统体积均匀化方法(VHM)会带来较大的计算偏差。反应性等效物理转换(RPT)方法被应用于含弥散燃料的双重非均匀系统,具有方法简单且计算精度较高的特点。本文首先对传统RPT方法和改进RPT(IRPT)方法进行了分析和验证,结果表明,这2种方法对于含有弥散可燃毒物的双重非均匀系统燃耗过程中依然存在相对较大的计算偏差;然后提出环形RPT(RRPT)方法和2步环形RPT(TRRPT)方法分别用于处理含单一颗粒类型和含2种颗粒类型的双重非均匀系统,通过含不同类型可燃毒物的算例验证并与蒙卡颗粒模型基准解对比可知,本文提出的RRPT方法和TRRPT方法可用于处理含弥散燃料和弥散可燃毒物的双重非均匀系统,相比传统方法具有更高计算精度和更广适用范围。 相似文献
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54.
ASME B31G-2012标准在含体积型缺陷管道剩余强度评价中的应用研究 总被引:1,自引:0,他引:1
为了确定石油天然气输送管道能否在规定的管道压力下正常运行,避免油气管道发生安全事故,必须对含体积型缺陷的管道进行剩余强度评价。以断裂力学和工程实践经验相结合的半经验公式作为含体积型缺陷管道进行剩余强度评价的标准已经被国内外所广泛采用。为此分析研究了ASME B31G-2012标准的3种流变应力计算方法,得出各管线钢在选用不同方式计算流变应力时,管道剩余强度值之间所存在的差异,剩余强度评价结果也会存在着不同的保守性。进而计算了不同条件下安全系数的选取范围,讨论了地区等级变化对安全系数的影响程度;并针对ASME B31G-2012标准比较了原剩余强度计算公式和改进后的剩余强度计算公式,认为改进后公式通过改变鼓胀系数和缺陷投影面积降低了剩余强度评价结果的保守性;最后通过实际工程运用明确了流变应力、安全系数、剩余强度计算公式的选取原则。结论认为:在实际应用中需要综合考虑管道使用年限、管材性质、缺陷特征、所处地区等级、检测技术及业主要求等多方面的因素来确定如何选取评价管道剩余强度的相关参数。 相似文献
55.
A needle penetrometry was performed loading steady force in a range from 1×10−3 to 2 N to pelletized coal upon heating via a cylindrical needle. From the observed effects of shear rate on apparent viscosity of softening coal pellet, defined as the shear-rate to shear-stress ratio, it was found that the pellet behaved as a Newtonian fluid for shear rates lower than a critical one while as a pseudo-plastic fluid for higher shear rates. The penetrometry was also carried out varying the force with time. The variable force loading enabled to maintain the shear rate well below the critical one, and thereby to measure the apparent viscosity of coal pellets as Newtonian fluids over a temperature range from 600 to 800 K. Upon heating at 10 K min−1, the apparent viscosity of Goonyella coal pellet decreased from about 1010 Pa s at 640 K down to a minimum of about 104 Pa s at 755 K, and increased up to 109 Pa s at 800 K. In a course of heating as above, the viscosity of Blind Canyon coal pellet decreased above 600 K, underwent a minimum of about 106 Pa s at 715 K, and increased up to 1010 Pa s at 770 K. Decreasing the heating rate from 10 to 3 K min−1 caused the minimum viscosities of the pellets to increase by 1-2 orders of magnitude. 相似文献
56.
The aim of this paper is the detailed analysis of different well-known thermodynamic efficiencies usually used to characterize hermetic compressors. Attention is focussed on the volumetric efficiency, the isentropic efficiency, and the combined mechanical–electrical efficiency. A procedure is presented to detach these efficiencies into their main components (physical sub-processes) to get deeper insight on the overall behavior.The volumetric efficiency is split into partial efficiencies related to pressure drop and heat transfer effects, supercharging effects, superdischarging effects, leakages, etc. The isentropic efficiency is detached using two different points of view: the work associated to the individual sub-processes (compression, discharge, expansion, suction), and the work associated to the underpressures, overpressures, and between the inlet and outlet mean compressor pressures. Finally, the combined mechanical–electrical efficiency is related to the heat transfer losses/gains, and to the exergy transfers and exergy destroyed.Even though some of the concepts introduced in the paper can be applied to different kinds of compressors, the discussion is specially focussed on hermetic reciprocating compressors. An advanced simulation model developed by the authors has been used to generate data to illustrate the possibilities of the detailed thermodynamic characterization proposed. The criteria developed are useful tools for comparison purposes, to characterize compressors, and to assist designers during the optimization process. 相似文献
57.
A theoretical framework to describe the behavior of natural clay is proposed in a new four-dimensional space, consisting of the current stress state, stress history, the current voids ratio, and a measure of the current soil structure. A key assumption of the proposed framework is that both the hardening and the destructuring of natural clay are dependent on plastic volumetric deformation. Two different assumptions about how this destructuring occurs are proposed, based on which two versions of a complete constitutive model have been formulated. The behavior of reconstituted soil can also be simulated by the proposed model as a special case where the structure of soil has no effect on soil deformation. Characteristics of the proposed model are demonstrated through systematic simulations of the influence of soil structure on clay behavior. The simulated behavior of natural clay is compared qualitatively with widely available experimental data. It is seen that the proposed model successfully represents the main features of natural clays with various soil structures. 相似文献
58.
A novel computational fluid dynamic (CFD) modeling procedure was developed in order to simulate ultraviolet (UV) photoreactors in the Eulerian framework. In this procedure, the governing equations of radiation distribution, mass conservation, momentum conservation, and species mass conservation are solved together in order to determine the radiant energy field, velocity field, and the concentration profile of microorganisms at steady state conditions. The general method presented can be employed to derive the volumetric inactivation rate and the theoretical efficiency of a UV photoreactor. The integrated CFD model of UV photoreactor performance was successfully evaluated with experimental biodosimetry results. The verified procedure can be applied to the simulation and design optimization of UV photoreactors with different geometries and operating conditions. 相似文献
59.
S.H. Masood W. Rattanawong 《The International Journal of Advanced Manufacturing Technology》2002,19(3):209-216
The paper presents the development of a generic part orientation system for rapid prototyping by considering the issue of
volumetric error encountered in parts during the layer by layer building process in a rapid prototyping (RP) system. An algorithm
is developed that slices the part with horizontal planes and computes the volumetric error in the part at different orientations
by rotation about user-specified axes. The system recommends the best orientation based on the least amount of volumetric
error in the part. The system has been tested using several examples of simple and complex parts. The generic part orientation
system is believed to be first of its kind based on a volumetric error approach and will be useful for RP users in creating
RP parts with a higher level of accuracy and surface finish, and also for intelligent process planning in rapid prototyping.
RID="
ID=" <E5>Correspondence and offprint requests to</E5>: Assoc. Prof. S. H. Masood, CAD/CAM/CAE Group, Industrial Research
Institute Swinburne, Swinburne University of Technology, Hawthorn, Melbourne, 3122 Australia. E-mail: smasood@swin.edu.au 相似文献
60.
Storing as much energy as possible in as compact a space as possible is an ever-increasing concern to deal with the emerging “space anxiety” in electrochemical energy storage (EES) devices like batteries, which is known as “compact energy storage”. Carbons built from graphene units can be used as active electrodes or inactive key materials acting as porous micro- or even nano-reactors that facilitate battery reactions and play a vital role in optimizing the volumetric performance of the electrode and the battery. In this review, we discuss and clarify the key issues and specific strategies for compact energy storage, especially in batteries. The use of shrinkable carbon networks to produce small yet sufficient reaction space together with smooth charge delivery is highlighted as the simplest structure–function-performance relationship when used in supercapacitors and is then extended to overcome problems in compact rechargeable lithium/sodium/potassium batteries. Special concerns about cycling stability, fast charging and safety in compact batteries are discussed in detail. Strategies for compact energy storage ranging from materials to electrodes to batteries are reviewed here to provide guidance for how to produce a compact high energy battery by densifying the electrodes using customized carbon structures. 相似文献