傳遞現(xiàn)象英文原版 transport phenomena 傳遞現(xiàn)象英文原版 ,適合復(fù)制

1、Chapter 0The Subject of Transport PhenomenaTransport phenomena is essential for understanding many processes in engineering, agriculture, meteorology, physiology, biology, analytical chemistry, material, science, and oth

2、er areas.§0.1 What are the transport phenomena?The subject of transport phenomena includes three closely related topics: fluid dynamics, heat transfer, and mass transfer.Fluid dynamics: transport of momentumHeat tra

3、nsfer: transport of energyMass transfer: transport of mass of various chemical species.These three transports should be studied together for the following reasons:? They frequently occur simultaneously.? The basic equati

4、ons that describe the three transport are closely related.? The mathematical tools needed for describing these phenomena are very similar.? The molecular mechanisms underlying the various transport phenomena are very clo

5、sely related.The main aim of this book is to give a balanced overview of the field of transport phenomena, present the fundamental equations of the subject, and illustrate how to use them to solve problems.§0.2 Thre

6、e levels at which transport phenomena can be studied? Macroscopic level: length scales centimeter or meters? Microscopic level: length scales micron to centimeter? Molecular level: length scales 1 to 1000 nanometers§

7、;0.3 The conservation laws: an example(a) Law of conservation of mass, the total mass of the molecules entering and leaving the collision must be equal.(b) The law of conservation of momentum the sum of the momentum of a

8、ll the atoms before the collision must equal that after the collision.(c) According to the law of conservation of energy, the energy of the colliding pair of molecules must be the same before and after the collision. (d)

9、 Finally, the law of conservation of angular momentum can be applied to a collision §0.4 Concluding commentsTo use the macroscopic balances intelligently, it is necessary to use information about inter-phase transpo

10、rt that comes from the equations of change. To use the equations of change, we need the transport properties, which are described by various molecular theories. Therefore, from a teaching point of view, it seems best to

11、start at the molecular level and work upward toward the larger systems.All the discussions of theory are accompanied by examples to illustrate how the theory is applied to problem solving. Then at the end of each chapter

12、 there are problems to provide extra experience in using the ideas given in the chapter. The problems are grouped into four classes:Class A: Numerical problems, which are designed to highlight important equations in the

13、text and to give a feeling for the orders of magnitude.Class B: Analytical problems that require doing elementary derivations using ideas mainly from the chapter.In Fig. 1.1-1 we show a pair of large parallel plates, eac

14、h one with area A, separated by a distance Y. In the space between them is a fluid either a gas or a liquid. This system is initially at rest, but at time t = 0 the lower plate is set in motion in the positive x directio

15、n at a constant velocity V. As time proceeds, the fluid gains momentum, and ultimately the linear steady-state velocity profile shown in the figure is established. We require that the flow be laminar (“l(fā)aminar“ flow is t

16、he orderly type of flow that one usually observes when syrup is poured, in contrast to “turbulent“ flow, which is the irregular, chaotic flow one sees in a high-speed mixer). When the final state of steady motion has bee

17、n attained,a constant force F is required to maintain the motion of the lower plate. Common sense suggests that this force may be expressed as follows:That is, the force should be proportional to the area and to the velo

18、city, and inversely proportional to the distance between the plates. The constant of proportionality μ is a property of the fluid, defined to be the viscosity. We now switch to the notation that will be used throughout t

19、he book. First we replace F/A by the symbol τyx, which is the force in the x direction on a unit area perpendicular to the y direction. It is understood that this is the force exerted by the fluid of lesser y on the flui

20、d of greater y. Furthermore, we replace V/Y by --dv/dy. Then, in terms of these symbols, Eq. 1.1-1 becomesThis equation, which states- that the shearing force per unit area is proportional to the negative of the velocity