High reliahility resulting from the absence of moving parts makes the electromagnetic pump an attractive choice for handling conductive liquids. Knowledge of the basic mathematical relationships, performance-limiting factors, and operating principles of electromagnetic pumps is essential if further fruitful applications are to be realized It is well known that a current-carrying conductor experiences a force when it is placed, in the proper direction, in a magnetic field. Innumerable electro mechanical devices are based upon this principle. Although the current-carrying conductor ordinarily is a solid, there are two groups of devices in which the solid conductor is replaced by a different medium.In the first of these groups the current is carried in a conducting gas, taking the place of the solid con ductor in a magnetic field. Two significant representa tives of this group of devices are MHD (magnetohydrodynamic) generators and ion engines for spacevehicle propulsion. The second group employs a conducting liquid in place of the solid conductor. Electromagnetic pumps and flowmeters are the most important devices in this category.This article deals with the latter group of electro mechanical devices, with emphasis on electromagnetic pumps. A number of papers and articles have been written on the subject of electromagnetic pumping of Hquid metals; most of these, however, have been concerned with the development and operation of large pumps used in atomic power plants for circu lating liquid metal coolants. Through presentation here of a survey of all kinds and types of electro magnetic pumps-including even some types that at the moment enjoy merely academic recognitionit is hoped to create more interest in these devices and stimulate further investigations that will result in new and not yet thought of applications of these pumps. BASIC PRINCIPLESBefore we turn to a discussion of the various types of pumps, let us develop some basic mathematical relationships. Starting with the vector equation for the force exerted on a current-carrying conductor: F = (71) X Β (1) in which R. Panholzer. Member IEEE, is with the Department of Elec trical Engineering, Stanford University, Stanford, Calif. F = force vector, newtons / = total current, amperes 1 = length of the conductor inside the magnetic field, meters Β = magnetic flux density, webers/meter^we will first modify this equation to fit the situation for a small particle of conducting Hquid dx dy dz as represented in Fig. 1. If we consider the force ac cording to equation 1 on this liquid particle in the X direction, we obtain dFx = JyB^ dx dy dz(2)The subscripts in this equation indicate the compo nent of the vector quantities in the x, y, or ζ direction. Γ dz I -*-y

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