The importance of fluid flow and heat transfer with a change in phase arises from the fact that many industrial processes rely on these phenomena for materials processing or for energy transfer; e.g. petroleum processing, paper-pulping, power plants. Classical thermodynamics tells us that a phase is a macroscopic state of matter which is homogeneous in chemical composition and physical structure; e.g., a gas, liquid or solid of a pure component. Two-phase flow is the simplest case of multiphase flow in which two phases are present for a pure component. Sometimes the term "multi-component" is used to describe flows in which the phases consist of materials of different chemical substances. For example, a flow of steam and water is a two-phase flow with a single component, while an air-water flow is a two-phase/two component flow. In blood flow the plasma/platelet-corpulses are a two-phase/multi-component flow (liquid/solid). In some applications one can have a single phase of two immiscible liquids (oil-water) flowing and treat this as multi-component flow. There are many common examples of multiphase flow in everyday life, such as rain or snow, a boiling teapot or coffee percolator, steam condensation on walls or a cold glass of beer.
The major objective of this 'primer' is to provide the student or practicing engineer with a working knowledge of multi-phase flow and heat transfer fundamentals that can be used in system design and analyses. Specifically, we intend to provide a summary of the current state of knowledge, referenced sources of data and correlations, first principles analysis techniques, and some examples of various industrial applications. This book has been patterned after information in graduate courses that have been offered at the University of Wisconsin and industrial short courses and workshops for over 15 years. Topics include flow patterns, pressure drop and void fraction, critical flow, pool boiling and forced convection heat transfer and condensation. Additional special topics are to be added later.
In this introduction we provide an overview into phase change processes by considering every day examples of pool boiling, multi-phase flow boiling and condensation. Also as part of this introduction we introduce some basic definitions.