Characteristics of a finite-length MHD traveling-wave cylindrical accelerator or generator.

Abstract

Previous work in MHD a.c. electrodeless generators has shown that a major portion of the losses are due to fringing effects related to the small number of wavelengths of the device. This theoretical study determines quantitatively the electrical efficiency of a cylindrical accelerator or generator of length comprising any integral or fractional number of wavelengths of the primary coil windings. The analysis employs the classical MHD equations and takes advantage of the usual simplifying assumptions. In the second part of the paper, a solution is presented which determines the correction coils necessary to eliminate first-order fringing losses. It has been found that, if the phase velocity of the magnetic field is greater than the fluid velocity, i.e., an accelerator, fringing may cause the device to act as a Joule heater rather than an accelerator. Indeed, for very small slips, most of the energy goes into Joule heating. For negative slip the device is a true generator, except for a region where the slip is small. Performance maps are presented which show, for a given radius and length, the electrical efficiency of the device as a function of the slip, whether it behaves as an accelerator, a Joule heater, or a generator. Numerical results also are shown for the aforementioned maps when correction coils are employed to elimiate first-order fringing losses in the device.