Influence of lubricant on the motion of a body in an electromagnetic railgun accelerator.: III.: Temperature distribution in the armature, rail, and liquid film

The effect of a conducting liquid lubricant on the heating of a rail and projectile (armature) is studied theoretically and experimentally. It is shown that both the Joule and friction heating of the accelerated body can be reduced significantly by using resistive liquid films. When the contact resistance of the film is high, its temperature is determined by two competing processes: Joule heating and heat removal by the moving film. As a result, the dependence of the film temperature on the magnetic Reynolds number, its thickness, and its resistance is nonmonotonic. In the limiting case where the velocity skin effect is completely suppressed and the magnetic Reynolds number is sufficiently high, the film temperature is extremely low. In intermediate cases, however, the film temperature can turn out to be rather high and exceed the melting point of the armature. Viscous dissipation in the liquid film has no significant effect on the temperature of the rail-armature interface until the melting of the armature is determined by Joule heating within it. In the case where the velocity skin effect is strongly suppressed, viscous dissipation along with Joule heating in the resistive film can become one of the major factors controlling the attainable velocity of bodies in railguns. (C) 1999 American Institute of Physics.