Fluid Mechanics - Introduction
Fluid Mechanicsis that section of applied mechanics, concerned with the statics and dynamics of liquids and gases.
A knowledge of fluid mechanics is essential for the chemical engineer, because the majority of chemical processing operations are conducted either partially or totally in the fluid phase.
The handling of liquids is much simpler, much cheaper, and much less troublesome than handling solids.
Even in many operations a solid is handled in a finely divided state so that it stays in suspension in a fluid.
Fluid Statics: Which treats fluids in the equilibrium state of no shear stress
Fluid Mechanics: Which treats when portions of fluid are in motion relative to other parts.
Fluids and their Properties
Fluids
In everyday life, we recognize three states of matter:solid,liquid and gas. Although different in many respects, liquids and gases have a common characteristic in which they differ from solids: they are fluids, lacking the ability of solids to offer a permanent resistance to a deforming force.
A fluid is a substance which deforms continuously under the action of shearing forces, however small they may be.Conversely, it follows that:
If a fluid is at rest, there can be no shearing forces acting and, therefore, all forces in the fluid must be perpendicular to the planes upon which they act.
Shear stress in a moving fluid
Although there can be no shear stress in a fluid at rest, shear stresses are developed when the fluid is in motion, if the particles of the fluid move relative to each other so that they have different velocities, causing the original shape of the fluid to become distorted. If, on the other hand, the velocity of the fluid is same at every point, no shear stresses will be produced, since the fluid particles are at rest relative to each other.
Differences between solids and fluids:
The differences between the behaviours of solids and fluids under an applied force are as follows:
For a solid, the strain is a function of the applied stress, providing that the elastic limit is not exceeded. For a fluid, the rate of strain is proportional to the applied stress.
The strain in a solid is independent of the time over which the force is applied and, if the elastic limit is not exceeded, the deformation disappears when the force is removed. A fluid continues to flow as long as the force is applied and will not recover its original form when the force is removed.
Differences between liquids and gases:
Although liquids and gases both share the common characteristics of fluids, they have many distinctive characteristics of their own. A liquid is difficult to compress and, for many purposes, may be regarded as incompressible. A given mass of liquid occupies a fixed volume, irrespective of the size or shape of its container, and a free surface is formed if the volume of the container is greater than that of the liquid.
參考答案:流动力学-介绍
区分应用的技工，与液体和气体statics和动力学有关的流动性Mechanicsis。
因为多数化工处理作业在可变的阶段，部份地或完全进行流动力学知识为化学工程师是根本的。
处理液体比处理固体简单，便宜和较不麻烦的。
在许多操作固体在一个精巧分开的状态被处理，以便它在悬浮在流体停留。
流动性Statics ： 哪些在均衡状态对待流体没有抗剪应力
流动力学： 哪些对待，当流体的部分在行动相对其他零件。
流体和他们的物产
流体
在日常生活中，我们认可问题三个状态：固体、液体和气体。 虽然不同在众多方面，液体和气体有他们与固体不同的一个共同的特征： 他们是流体，缺乏固体的能力提供对扭屈的力量的永久抵抗。
流体是连续扭屈在剪切力的行动之下的物质，然而小他们也许是。相反地，它跟随那：
如果流体是休息，不可以有剪切力行动，并且，因此，所有力量在流体一定是垂直的到他们行动的飞机。
抗剪应力在移动的流体
虽然在流体不可以有抗剪应力休息，抗剪应力被开发，当流体在行动时，如果可变的移动的微粒相对，以便他们有不同的速度，造成流体的原始的形状成为变形了。 如果，另一方面，流体的速度是同样在每点，抗剪应力不会导致，因为可变的微粒休息相对。
在固体和流体之间的区别：
在固体行为和流体之间的区别在应用的力量之下是如下：
为固体，张力是应用的重音的作用，提供弹性极限没有超出。 为流体，张力的率与应用的重音是比例。
张力在固体是力量是应用时间的独立，如果弹性极限没有超出，变形消失，当取消时力量。 流体继续流动，只要力量是应用的，并且不会恢复它原始的形式，当取消时力量。
在液体和气体之间的区别：
虽然液体和气体两份额流体的共同的特征，他们有他们自己的许多特别特征。 液体是难为许多目的压缩，并且，也许认为不可压缩。 液体特定大量占领固定的容量，不问它的容器大小或形状，并且自由表面被形成，如果容器的容量是大于液体。
