Effects of Working Fluid,Tubeside Enhancement and Bundle Depth on the Optimized Fin Geometry of a Horizontal Condenser Tube

A theoretical study has been made to optimize the fin geometry of a horizontal finned tube which is to be usedfor condensers that handle the vapor load of a liquid phase change cooling module.Systematic numerical calcu-lations of the vapor to coolant heat transfer have been performed for parametric values of fin height,fin spacing,vertical bundle depth and tubeside heat transfer coefficient.Three dielectric fluids (R-113,FC-72,and FC-87)at atmospheric pressure were selected as the working fluids.For a single tube with optimized fin geometry,theaverage heat flux increased in the order of FC-87,R-113 and FC-72.Both the optimum fin height and optimumfin spacing increased with increasing vertical bundle depth.     

A Model for Flooding Prediction in Circular Tubes

Flooding phenomenon limits the stability and the flow of a liquid film falling along the walls of a channel in which a gas is flowing upwards.As known, the entrainment effect can completely prevent the liquid to fall from its natural flow. The present work proposes a new mechanistic model for the prediction of the onset of flooding in vertical and inclined pipes in the presence of obstructions, as well as taking into account the viscosity effect. The good performance of the model in the different geometrical conditions and for variable viscosities of the liquid component assesses the validity of the hypothesis that the instability of a wavelike disturbance limits the countercurrent flow in a channel.     

澳大利亚水库淤积问题

水库淤积已经成为澳大利亚的一个严重问题,介绍了澳大利亚的水库快速淤积和极端淤积的几个实例,分析了水库完全淤死的原因。大坝和水库应该以冲沙的形式进行系统的管理,在干旱期必须加强流域的水土保持措施。     

超临界流体中的传热：传热机理分类

因为较小的温度变化就能引起物理性质的明显改变，没有现存的工程关系式和模型能精确地预测超临界流体中的传热。本文力求将现存关系式适用的工况进行分类并更好地理解这些局部传热机理。第一个目标是本文关注的焦点。FLUENT被用来计算各种热流密度和质量流速工况下的壁面温度，其结果用来与实验数据相比较。因为模型是为宽范围流动工况而设计的，所以，应进行某些假设。模拟表明，在高质量流速工况下吻合较好，这时浮力效应可以被忽略。但是，FLUENT在预测高热流密度和低质量流速混合工况中见到的局部低传热速率时遇到困难。一个新的依赖于热流密度和质量流速通用参数被发展来区分在何种工况下这个FLUENT标准模型是适用的，这个全局Fmude数能被用作预测在何种工况下浮力效应占主导地位和更低的传热速率会发生的参数。     

A Newly Developed Non, Destructive Tritium Measurement Technique and Its Application to V-4Cr-4Ti Alloy

A non-destructive and in-situ technique for the measurement of tritium in materials, namely β-ray-induced X-ray spectrometry （BIXS）, has been developed recently. In the present study a V-4Cr-4Ti alloy was pre-heated at 1000℃ for 2 h to form a recrystallization structure before the tritium absorption experiments were conducted. Firstly the hydrogen isotope gas was charazterized by means of a quadrupole mass spectrometer （QMS） and a small-sized ionization chamber. Then hydrogen isotope absorption tests of V-4Cr-4Ti alloy were performed at 400 ℃ and the atomic concentration of hydrogen isotope in V-4Cr-4Ti alloy was estimated as 0.17% with a tritium content of approximately 2.5 ppm. Experimental results indicate that BIXS is a quite useful tool for quantitatively measuring the tritium content and tritium distribution in the surface layers of vanadium alloys and no strong trapping effects of tritium exist in the pre-heated V-4Cr-4Ti alloy.     

采用特殊的钻头和底部钻具组合对井眼的保径至关重要

本文叙述了采用特殊的钻头和底部钻具组合对井眼的保径的重要性。指出如果采用特殊的钻头和扩孔器钻井,尽管投资较大,但所增加的投资可由增大钻速、减小扭矩和加大进尺等补偿回来。并通过钻头类型的选择;适用钻头的选择;特殊钻头的加工;底部钻具组合的说明进一步阐述各种保径齿钻头的特性及其效能。