1.2: Applications

Transducers and rotating machines that are described by the lumped parameter models of Chapter 4 are so pervasive a part of modern day technology that their development might be regarded as complete But, with new technologies outside the domain of electromechanics, there come new needs for electromechanical devices. The transducers used to drive high-speed computer print-outs are an example. Ne devices in other areas also result in electromechanical innovations. For example, high power solidstate electronics is revolutionizing the design and utilization of rotating machines.

As energy needs press the capabilities of electric power systems, rotating machines continue to be the mainstay of energy conversion to electrical form. Synchronous generators are subject to increasingly stringent demands. To improve capabilities, superconducting windings are being incorporated into a new class of generators. In these synchronous alternators, magnetic materials no longer play the essential role that they do in conventional machines, and new design solutions are required.

The Van de Graaff machine also considered in Chapter 4 should not be regarded as a serious approach to bulk power generation, but nevertheless represents an important approach to the generation of extremely high potentials. It is also the grandfather of proposed energy conversion approaches. An example is the electrogasdynamic "thermal-to-electric" energy converter of Chapter 9, Sec. 9.

Chapters 5 and 6 begin to hint at the diversity of applications outside the domain of lumped parameter electromechanics. The behavior of charged particles in moving fluids is important for understanding liquid insulation in transformers and cables. Again, in the area of power generation and distribution, ions and charged macroscopic particles contribute to the contamination of high-voltage insulators. Also related to the overhead line transmission of electric power is the generation of audible noise. In this case, the charged particles considered in Chapter 5 contribute to the transduction of electrical energy into acoustic form, the result being a sufficient nuisance that it figures in the determination of rights of way.

Some examples in Chapter 5 are intended to give basic background relevant to the control of particulate air pollution. The electrostatic precipitator is widely used for air pollution control. Gases cleaned range from the recirculating air within a single room to the exhaust of a utility. With industries of all sorts committed to the use of increasingly dirtier fuels, new devices that also exploit electrical forces are under development. These include not only air pollution control equipment but devices for painting, agricultural spraying, powder deposition and the like.

Image processing is an application of charged particle dynamics, as are other matters taken up in later chapters. Charged droplet printing is under development as a means of marrying the computer to the printed page. Xerographic and aerosol printing of considerable variety exploit electrical forces on particles.

A visit to a printing plant, to a paper mill or to a textile factory makes the importance of charges and associated electrical forces on moving materials obvious. The charge relaxation processes considered in Chapter 5 are fundamental to understanding such phenomena.

The induction machines considered in Chapter 6 are the most common type of rotating motor. But related interactions between moving conductors and magnetic fields also figure in a host of other applications. The development of high-speed ground transportation has brought into play the linear induction machine as a means of propulsion, and induced magnetic forces as a means of producing magnetic lift. Even if these developments do not reach maturity, the induction type of interaction would remain important because of its application to material transport in manufacturing processes, and to melting, levitation and pumping in metallurgical operations. The application of induced magnetic forces to the sorting of refuse is an example of how such processes can figure in seemingly unrelated areas.

Chapter 7 plays a role relative to fluid mechanics that Chapter 2 does with respect to electromagnetics. Without a discourse on the applications of this material in its own right, consider the relevance of topics that are taken up in the subsequent chapters.

Fields can be used to position, levitate and shape fluids. In many cases, a static equilibrium is desired. Examples treated in Chapter 8 include the levitation of liquid metals for metallurgical purposes, shaping of interfaces in the processing of plastics and glass, and orientation of ferrofluid seals and of cryogenic liquids in zero gravity environments.

The electromechanics of systems having a static equilibrium is often dominated by instabilities The insights gained in Chapter 8 are a starting point in understanding atomization processes induced by means of electric fields. Here, droplets formed by means of electric fields figure in electrostatic paint spraying and corona generation from conductors under foul weather conditions. Internal instabilities also taken up in Chapter 8 are basic to mixing of liquids by electrical means and for electrical control of liquid crystal displays. Both two-phase (boiling and condensation) and convective heat transfer can be augmented by electromechanical coupling, usually through the mechanism of instability. Perhaps not strictly in the engineering domain is thunderstorm electrification. The stability of charged drops and the electrohydrodynamics of air entrained collections of charged drops are topics touched upon in Chapter 8 that have this meteorological application.

The statics and dynamics of hydromagnetic equilibria is now a subject in its own right. Largely because of its relevance to fusion machines, the discussion of hydromagnetic waves and surface instabilities serves as an introduction to an area of active research that, like other applications, has important implications for the energy posture. Internal modes taken up in Chapter 8 also have counterparts in hydromagnetics.

Magnetic pumping of liquid metals, taken up in Chapter 9, has found application in nuclear reactors and in metallurgical operations. Electrically induced pumping of semi-insulating and insulating liquids, also discussed in Chapter 9, has seen application, but in a range of modes. A far wider range of fluids have properties consistent with electric approaches to pumping and hence there is the promise of innovation in manufacturing and processing.

Magnetohydrodynamic power generation is being actively developed as an approach to converting thermal energy (from burning coal) to electrical form. The discussion of this approach in Chapter 9 is not only intended as an introduction to MHD energy conversion, but to the general issues confronted in any approach to thermal-to-electrical energy conversion, including turbine-generator systems. The electrohydrodynamic converter also discussed there is an alternative to the MHD approach that sees periodic interest. For that reason, its applicability is a matter that needs to be understood.

Inductive and dielectric heating, even of materials at rest and with no electromechanical considerations, are the basis for important technologies. These topics, as well as the generation and transport of heat in electromechanical systems where thermal effects often pose primary design limitations, are part of the point of the first half of Chapter 10. But, thermal effects can also be central to the electromechanical coupling itself. Examples where thermally induced property inhomogeneities result in such coupling include electrothermally induced convection of liquid insulation.

Electromechanical coupling seated in double layers, also taken up in Chapter 10, relates to processes (such as electrophoretic particle motions) that see applications ranging from the painting of automobiles to the chemical analysis of large molecules. One of the reasons for including electrokinetic and electrocapillary interactions is the suggestion it gives of mechanisms that can come into play in biological systems, a subject that draws heavily on physicochemical considerations. The purely electromechanical models considered here serve to identify this developing area.

The electromechanics of streaming fluids and fluid-like systems, taken up in Chapter 11, has perhaps its best known applications in the domain of electron beam engineering. Klystrons, traveling-wave tubes, resistive-wall amplifiers and the like are examples of interactions between streams of charged particles (electrons) and various types of structures. The space-time issues of Chapter 11 have general application to problems ranging from the stimulation of liquid jets used to form drops, to electromechanical processes for making synthetic fibers, to understanding liquid flow through "wall-less" pipes (in which electric or magnetic fields play the role of a duct wall), to beam-plasma interaction that result in instabilities that are used as a mechanism for heating plasmas.