Principles of Momentum Transfer and Overall Balances

The flow and behavior of fluids is important in many of the unit operations in process engineering. A fluid may be defined as a substance that does not permanently resist distortion and, hence, will change its shape. In this text gases, liquids, and vapors are considered to have the characteristics of fluids and to obey many of the same laws. 

In the process industries, many of the materials are in fluid form and must be stored, handled, pumped, and processed, so it is necessary that we become familiar with the principles that govern the flow of fluids and also with the equipment used. Typical fluids encountered include water, air, CO2, oil, slurries, and thick syrups. 

If a fluid is inappreciably affected by changes in pressure, it is said to be incompressible. Most liquids are incompressible. Gases are considered to be compressible fluids. However, if gases are subjected to small percentage changes in pressure and temperature, their density changes will be small and they can be considered to be incompressible. 

Like all physical matter, a fluid is composed of an extremely large number of molecules per unit volume. A theory such as the kinetic theory of gases or statistical mechanics treats the motions of molecules in terms of statistical groups and not in terms of individual molecules. In engineering we are mainly concerned with the bulk or macroscopic behavior of a fluid rather than with the individual molecular or microscopic behavior. 

In momentum transfer we treat the fluid as a continuous distribution of matter or as a continuum . This treatment as a continuum is valid when the smallest volume of fluid contains a large enough number of molecules so that a statistical average is meaningful and the macroscopic properties of the fluid such as density, pressure, and so on, vary smoothly or continuously from point to point. 

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Chap. 2 Principles of Momentum Transfer and Overall Balances... 

This part, dealing with fundamental principles, includes the following chapters 1. Int. -oduction to Engineering Principles and Units 2. Principles of Momentum Transfer and Overall Balances 3. Principles of Momentum Transfer and Applications 4. Principles of Steady-State Heat Transfer 5. Principles of Unsteady-State Heat Transfer 6. 

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