Theoretical analysis of heat transfer in laminar pulsating flow

Pulsation effect on heat transfer in laminar incompressible flow, which led to contradictory results in previous studies, is theoretically investigated in this work starting from basic principles in an attempt to eliminate existing confusion at various levels. First, the analytical solution of the fully developed thermal and hydraulic profiles under constant wall heat flux is obtained. It eliminates the confusion resulting from a previously published erroneous solution. The physical implications of the solution are discussed. Also, a new time average heat transfer coefficient for pulsating flow is carefully defined such as to produce results that are both useful from the engineering point of view, and compliant with the energy balance. This rationally derived average is compared with intuitive averages used in the literature. New results are numerically obtained for the thermally developing region with a fully developed velocity profile. Different types of thermal boundary conditions are considered, including the effect of wall thermal inertia. The effects of Reynold and Prandtl numbers, as well as pulsation amplitude and frequency on heat transfer are investigated. The mechanism by which pulsation affects the developing region, by creating damped oscillations along the tube length of the time average Nusselt number, is explained.     

Texture Changes During the Ripening of Port Salut Argentino Cheese in 2 Sampling Zones

ABSTRACT: Texture changes during ripening of Port Salut Argentino cheese for different sampling zones were studied. Compression relaxation tests were performed and results were analyzed using both Maxwellian and Peleg's models. Elastic equilibrium modulus obtained from the Maxwellian model decreased from 1.22 to 0.11 10⁴Pa during ripening. The constants derived from Peleg's model, k₁ and k₂, diminished with ripening time from 1.18 to 0.71 min and from 1.27 to 1.12, respectively. Asymptotic equilibrium modulus from Peleg's model decreased from 0.95 to 0.07 10⁴Pa during ripening. Rate parameters derived from a 1st order kinetics applied to both equilibrium moduli showed that the decrease was faster in the external zone (0.0846 d⁻¹) than in the central zone (0.0368 d⁻¹). The correlation between equilibrium moduli, salt concentration, moisture content, and maturation indexes was obtained with a determination coefficient of 0.76.     

栲胶法变换气脱硫工艺

介绍了栲胶法脱硫的原理，工艺流程及规整填料在脱硫塔中的应用。     

合成氨中置锅炉的修复

本文在分析中置锅炉失效原因的基础上，提出了详细的修复措施，为类似情况的设备修复提供了借鉴。     

人力资源投资评价应解决的两个重要问题

阐述了企业人力资源投资财务评价应解决的两个重要问题：评价对象的分类和项目的财务现金流量的内容。     

流量自动控制的设计与实现

文章通过分析多相流模拟井的实际工作要求 ,提出了简单实用的流量自动控制模型。应用成型的计算机数据采集和控制模块及稳定可靠的流量控制部件 ,实现了各相流量的自动控制过程。该流量自动控制系统调节精度高、速度快、整体造价低 ,在实际应用中取得了良好的效果。     

长距离油、气、水混输管道内壁流动腐蚀的研究进展

就近几十年来，多相流管线的流动腐蚀（CO2腐蚀，H2S腐蚀，腐蚀/冲蚀协同作用），腐蚀/冲蚀数学模型和设计准则，腐蚀检测，腐蚀防护与控制技术等方面的研究进展进行了综述。指出了当前研究中所存在的一些问题，就多相流的研究方向提出了相应的建议。     

高温预析出对Al-Zn-Mg系铝合金时效硬化和应力腐蚀的影响

研究了高温固溶后降温处理工艺对中强可使预析出LC52和7039铝合金的组织、时效硬化和应力腐蚀的影响。金相观察发现,高温预析出可优先在晶界处产生,并提高随后时效状态下晶界析出相的不连续分布程度,温度降低到一定程度晶内和晶界产生大量析出。合金拉伸性能和应力腐蚀结果表明,预析出在保持强度和塑性的同时,可提高抗应力腐蚀性能。而预析出温度降低,合金强度呈下降趋势。     

Simulation of Strength Distribution in Ground Ceramics by Incorporating Residual Stress Effect

Strength of ground ceramics may be affected by residual stress as well as surface flaws induced by grinding. Strength prediction for ground ceramics is convenient for mechanical design of ceramic components. In this article, a numerical procedure based on fracture mechanics was proposed to estimate strength distribution of ground ceramics by considering grinding-induced residual stress. Bending strength and residual stress of ground ceramics were measured for three grinding-conditions. By comparison of simulated results with experimental ones, it was revealed that strength characteristics in experiments were well simulated by using the proposed procedure.     

Motion and structure interpretation of an optical switch

This paper focuses on tracking, reconstruction and motion estimation of a well-defined MEMS optical switch from a microscopic view. For out-of-view reconstruction, a homography capable of transforming feature points and feature lines between a microscopic image and a CAD model of the switch is implemented. The homography between two sequential microscopic images is decomposed and factorized for motion estimation. Optical flow has also been explored to provide rough estimations of rotation centre and angle. The paper also illustrates motion parameter optimization principles to deal with uncertainty inherent in micro world. After non-linear optimization, estimation accuracy for rotation angle and rotation centre can reach 0.06° and pixel level, respectively.