英语翻译流体性能

Properties of Fluid(流体性能)In this chapter we discuss a number of fundamental properties of fluids. An understanding of these properties is essential for us to apply basic principles of fluid mechanics to the solution practical problem.这篇我们讨论一些流体的基本性能。

了解这些基本性能对于我们用流体力学基本原理解决实际问题是非常有用的。

1 DISTINCTION BETWEEN A SOLID AND A FLUID液体和固体的区别The molecules of a solid are usually closer together than those of a fluid. The attractive forces between the molecules of a solid are so larger that a solid tends to retain its shape.This is not the case for a fluid，where the attractive forces between the molecules are smaller.An ideal elastic solid will deform under load and，once the load is removed，will return to its original state．Some solids are plastic. These deform under the action of a sufficient load and deformation continues as long as load is applied，providing the material does not rupture. Deformation ceases when the load is removed，but the plastic solid does not return to its original state．固体中的化学分子往往比液体中的分子排列紧密。

固体分子之间的吸引力很大以至于固体能保持其外形。

但是液体分子之间的吸引力就小的多了。

理想的弹性固体在压力作用下会变形撤去压力就会恢复原形。

还有一些塑性固体在保证材料不被破坏的情况下给其不断施加压力变形就会不断持续，当撤去外力变形停止，但是塑性固体不会恢复其原有的形状。

The intermolecular cohesive forces in a fluid are not great enough to hold the various elements of the fluid together. Hence a fluid will under the action of the slightest stress and flow will continue as long as the stress is present.液体分子之间的凝聚力不足以使各种分子集中在一起，所以当液体受到很小的压力就会持续流动只要有力地存在。

2 DISTINCTIONS BETWEEN A GAS AND A LIQUID气体和液体之间的区别A fluid may be either a gas or a liquid ．The molecules of a gas are much farther apart than those of a liquid．Hence a gas is very compressible，and when all external pressure is removed，it tends to expand indefinitely．A gas is therefore in equilibrium only when it is completely enclosed. A liquid is relatively incompressible，and if all pressure，except that of its .own vapor pressure，is removed，the cohesion between molecules holds them together，so that the liquid does not expand indefinitely. Therefore a liquid may have a free surface，i. e.，a surface from which all pressure is removed，except that of its own vapor.流体可能是气体或者液体。

气体分子之间的距离远比液体分子之间的距离远得多，所以气体是非常容易压缩的，当所有的外部压力全部消失，气体就可能会不限制的膨胀下去。

因此只有当气体完全封闭时才会处于平衡状态。

而液体似乎是不可压缩的，当除了自身的压力之外的力全部消失则分子之间的作用力就会相互作用在一起，所以液体不会无限制的膨胀的。

因此液体会有一个自由面在这个面上除了自身的吸引力之外合外力为零。

A vapor is a gas whose temperature and pressure are such that it is very near the liquid phase. Thus steam is considered a vapor because its state is normally not far from that of water. A gas may a highly super-heated vapor，that is，its state is far removed from the liquid phase. Thus air is considered a gas because its state is normally very far from that of liquid air.水蒸气是当气体的温度和压力都足以使其液化时候的一种液相。

所以蒸汽通常被认为是水蒸气由于他们的状态基本差不多。

气体可能是高温加热时候的蒸汽也就是说气体的状态远不同于液相，所以空气被认为是一种状态远不同于液态空气的气态。

The volume of a gas or vapor is greatly affected by changes in pressure or temperature or both. It is usually necessary，therefore，to take account of changes in volume and temperature in dealing with gases or vapors. Wherever significant temperature or phase changes are involved in dealing with vapors and gases，the subject is largely dependent on heat phenomena.④Thus fluid mechanics and thermodynamics are interrelated.气体或水蒸气的体积很大程度受到压力或者温度或者二者同时影响。

因此考虑气体和水蒸气的体积和温度变化是有必要的。

无论在什么情况下温度或者物相的变化都与水蒸汽和气体紧密相关，这种现象在很大程度上取决于热现象，所以流体力学和热力学是相通的。

3 DENSITY，SPECIFIC WEIGHT，SPECIFIC VOLUME，AND SPECIFIC GRA VITY密度，比重，比体积和比重The densityρ，or more strictly，mass density，of a fluid is its mass per unit volume，while the specific weight γis its weight per unit volume．In the British Gravitational system density ρwill be in slugs per cubic foot，which can also be expressed as units of 1 b·sec2／ft4．密度ρ或者更严格的说是质量密度，对于流体而言是单位体积的质量当比重γ是单位体积的重量。

在英国重力学体系中密度ρ是每英尺的目数或者说是1 b ·sec 2／ft 4。

Specific weight γ represents the force exerted by gravity on a unit volume of fluid ，and therefore must have the units of force per unit volume ，such as pounds per cubic foot.Density and specific weight of a fluid are relate as ：g γρ= or g ργ=比重γ 代表地球引力对单位体积流体的力，所以单位体积必须有力的作用，比如每英尺所能放的英镑数，流体的密度和比重被定义为g γρ= or g ργ=。

Note that density p is absolute ，since it depends on mass ，which is independent of location. Specific weight γ ，on the other hand ，is not absolute ，since it depends on the value of the gravitational acceleration g which various with location ，primarily latitude and elevation ．Above mean sea level.注意到密度是绝对的因为它决定于质量而与位置无关，然而比重是相对的，因为它决定于随位置，维度，海拔不同而不同的重力加速度，Densities and specific weight of fluids vary with temperature ．Appendix provides commonly needed temperature variations of these quantities for water and air. It also contains densities and specific weights of common gases at standard atmospheric pressure and temperature.流体的密度和比重随温度变化。