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A-C magneto hydrodynamic instability

IP.com Disclosure Number: IPCOM000128024D
Original Publication Date: 1977-Dec-31
Included in the Prior Art Database: 2005-Sep-14
Document File: 5 page(s) / 18K

Publishing Venue

Software Patent Institute

Related People

McHale, Edward Joseph: AUTHOR [+3]

Related Documents

http://theses.mit.edu:80/Dienst/UI/2.0/Describe/0018.mit.theses/1977-63: URL

Abstract

A theory describing a purely hydromagnetic instability of a dense, viscous, electrically conducting fluid under the action of an alternating magnetic field is presented. Experiments on the onset and growth of instability in a planar layer of fluid are also reported.

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A-C MAGNETO HYDRODYNAMIC INSTABILITY

by

EDWARD JOSEPH McHALE
B.S., Massachusetts Institute of Technology (1974)

M.S., Massachusetts Institute of Technology (1974)

Submitted in partial fulfillment of the requirements for the degree of (DOCTOR OF SCIENCE) at the Massachusetts Institute of Technology

1977

SIGNATURE OF author: [[signature omitted]]

Department of Electrical Engineering

February 7, 1977

CERTIFIED BY: [[SIGNATURE OMITTED]]

James R. Melcher

Professor of Electrical Engineering Thesis Supervisor ACCEPTED BY: [[SIGNATURE OMITTED]]

Chairman, Departmental Committee on Graduate Students ARCHIVES MASSACHUSETTS INSTITUTE OF TECHNOLOGY LIBRARIES JUN 29 1977

Massachusetts Institute of Technology Page 1 Dec 31, 1977

Page 2 of 5

A-C magneto hydrodynamic instability

-2-

A-C MAGNETO HYDRODYNAMIC INSTABILITY

by

EDWARD JOSEPH McHALE

Submitted to the Department of Electrical Engineering, February 7, 1977, in partial fulfillment of the requirements for the Degree of Doctor of Science.

ABSTRACT

A theory describing a purely hydromagnetic instability of a dense, viscous, electrically conducting fluid under the action of an alternating magnetic field is presented. Experiments on the onset and growth of instability in a planar layer of fluid are also reported.

In the theory, the effects of fluid motion and magnetic field on one another are found self- consistently, to linear terms. In determining the fluid response to the magnetic force, a " time average " model is used. Predictions of critical field strength and growth rates for the instability, are computed for a variety of boundary conditions. A rotor model which illustrates the physical mechanism of the instability is also developed.

The distinctive visual appearance of the magnetically caused motion is contrasted experimentally with the observed appearance of motion caused by thermal gradients and driven hydrodynamic turbulence. The critical

field strength required for the onset of fluid motion is measured as a function of frequency of the applied field. These measurements agree with theoretical predictions over more than an order of magnitude variation in frequency. This frequency range includes low frequencies for which the finite depth of the fluid layer is very important, and higher frequencies for which it is relatively unimportant.

The critical field strengths determined here experimentally and theoretically set an upper limit on the extent to which a fluid layer can be levitated, depressed, or transported magnetically at a given frequency. This sets a practical limit on many forming and metalurgical processes.

The growth times observed experimentally differ greatly from those predicted theoretically. The former are typically be...