第五章+液体在管道中流动的基础知识概述.ppt

* * 第五章 液体在管道中流动的基础知识（Basics of Hydraulic Flow in Pipes） 5.1概述（INTRODUCTION） 迄今为止我们还没有研究液体在管道中流动时由于摩擦而产生的能量损失的机理。液体是直观的，像水和汽油，它们比像油液这样高粘度的液体容易流动。流动的这个阻尼实质上是液体粘度的度量标准。粘度越大的流体越不容易流动也就是流动所需的能量越大。这些能量的减少是因为它散失成了热及代表了损耗的能量（Up to now we have not investigated the mechanism of energy losses duo to friction associated with the flow of a fluid inside a pipe. It is intuitive that liquid, such as water or gasoline, flow much more readily than do heavier liquids such as oil. The resistance to flow is essentially a measure of the viscosity of the fluid. The greater the viscosity of a fluid, the less readily it flows and the more energy is required to move it. This energy is loss because it is dissipated into heat and thus represents wasted energy）。 能量损失总是出现在被称为管接头的管道收缩部位，管接头是一个输送和控制液体的元件（与直管不同）。例如阀、三通管接头、弯头和节流口。通过管接头流动的路径性质确定了能量损失的多少。一般来说，路径越弯曲，损失越大。在许多液体传动的使用中，管接头造成的能量损失超过了管道中因粘性流动的损失（Energy losses also occur in pipeline restrictions called fittings. A fitting is a component（other than a straight pipe）that is use to carry or control the fluid. Examples are valves, tees, elbows, and orifices. The nature of the flow path through a fitting determines the amount of energy losses. Generally speaking, the more torturous the path, the greater the losses. In many fluid power applications, energy losses due to fittings exceed those due to viscous flow in pipes）。 在液压传动系统中所有的能量损失保持在最小的容许范围是非常重要的。这要求适当选择组成系统的油管和管接头的尺寸。通常，油管直径或管接头尺寸越小，损失越大。然而，使用大直径管道和管接头会增大成本以及对空间利用不利。因此，元件尺寸的选择就代表在能量损失、元件成本和空间占用三者之间的平衡（It is very important to keep all energy losses in a fluid power system to a minimum acceptable level. This requires the proper selection of the sizes of the pipes and fittings which make up the system. In general, the smaller the pipe diameter or fitting size, the greater the losses. However, using large-diameter pipes and fittings results in greater cost and poor space utilization. Thus, the selection of component sizes represen