MELTING OF ICE AROUND A HORIZONTAL ISOTHERMAL CYLINDRICAL HEAT SOURCE

Processes during melting from a horizontal cylindrical heat source of uniform surface temperature embedded in ice have been studied experimentally. The volume of the melt and its shape were photographed at different times for various constant temperatures of the heat source. At early times and under all conditions, the melt occupied a cylindrical annulus. At later times free convective motion caused pear-shaped melt contours which pointed downward when the temperatures of the heat source were below 7°C and upward when the temperatures were above 8°C. Instabilities in cellular natural convection motion resulted in waviness of the interface. The location and magnitude of these ripples were found to depend on the temperature of the heat source and the melt layer thickness. Shadowgraph techniques were used to determine local heat transfer coefficients at the heat source surface.     

R108A型柴油机的开发研制

本文就由R105系列柴油机经扩缸、加长行程为R108A系列柴油机的研制开发过程作了介绍,较为详细的说明了零部件的结构设计及整机的性能和可靠性。     

Effect of a Magnetic Field on a Micropolar Fluid Flow in the Vicinity of an Axisymmetric Stagnation Point on a Circular Cylinder

The effect of a magnetic field on a micropolar fluid flow in the vicinity of an axisymmetric stagnation point on a circular cylinder is studied numerically. The governing conservation equations of continuity, momentum and angular momentum are partial differential equations which are transformed into a system of ordinary differential equations by using the usual similarity transformations. The resulting system of coupled non‐linear ordinary differential equations is solved numerically by using the shooting method. The numerical results indicate the velocity, angular velocity and pressure distributions for different parameters of the problem including Reynolds number, magnetic parameter and dimensionless material properties, etc. In addition, the effect of the pertinent parameters on the local skin friction coefficient and the couple stress are discussed numerically and illustrated graphically.     

圆柱线接触副（非修形）表面润滑效应分析

滚动轴承中圆柱滚子的线接触长度为有限值，在充分供油情况下，它有其独特的润滑现象一油膜压力分布规律和油膜厚度分布规律，这些是经典线接触ＥＨＤ所不能揭示的。本文旨地阐明这一点。     

空压机气阀故障及其预防

气阀是空压机中最重要和最易损坏的部件之一。对5L-40／8型空压机气阀主要是正确进行定期保养、检修、安装、及时排除故障。     

油缸下降超速与平衡阀的选择

对挖掘机出厂试验中出现动臂油缸下降超速的问题进行了分析，叙述了平衡阀的工作原理、特点及选择方法，提出了改进措施，并进行了试验验证。     

单纤维平均梳理力的研究

建立了单纤维平均梳理力的计算公式,通过工艺实验揭示了不同梳理工艺条件下,单纤维平均梳理力对生条中棉结和短绒的影响,并根据单纤维平均梳理力推算了锡林齿条前角其余角的最小值.     

缸盖渗漏缺陷的主要类型与成因分析

由于影响缸盖渗漏缺陷的因素众多,仅仅依靠几个铸件判定缺陷的类型非常困难.本文通过对23个缺陷缸盖的解剖,确定了缺陷的主要类型,采用扫描电镜等手段分析了缺陷形成原因,提出了工艺改进措施.     

偏斜交圆柱圆锥表面展开图计算机绘制数模原理

分析了轴线偏斜交的圆柱与圆锥相对位置关系,建立了偏斜交圆柱、圆锥表面展开图及相贯曲线绘制的数学模型,并编制了通用计算机绘图程序,给出计算机绘制的展开图样例。     

Roughness variability in the honing process of steel cylinders with CBN metal bonded tools

Herein are presented roughness results of honing of steel cylinders with cubic boron nitride (CBN) abrasive tools. Different honing parameters such as honing stone pressure against the workpiece, tangential speed of the honing head as well as grain size of the abrasive stone were varied in order to determine their influence on the surface roughness of cylinders. Four different strategies were implemented to measure and characterise roughness of inner surfaces of honed steel cylinders. The variability in results obtained with each strategy is compared. The first three strategies consist in measuring roughness at one, three or nine points, respectively, which are uniformly distributed over a circumference located at one of the cylinder ends. The fourth strategy is based on the third one: it entails measuring roughness at nine points, and then subsequently filtering results to eliminate any extreme roughness value lying outside the boundaries set by Chauvenet's criterion. At each point of measurement, roughness is measured in the direction of the cylinder generatrix. It was verified that the larger the number of measurement points, the lower the variability in roughness values obtained. Therefore, it is recommended to make at least nine measurements per cylinder and to filter values to avoid any non-representative, outlier value. The variability in these values was quantified firstly according to relative differences. Secondly, variability was quantified by means of the coefficient of variation which provides smaller values than the relative difference, although less intuitive and less direct.