HEAT AND MOISTURE DIFFUSION IN MAGNETIC-TAPE PACKS

The purpose of this paper is to present theory and experiments on heat and moisture diffusion in magnetic tape packs. The theory includes an isotropy effects. The same fundamental mathematical theory is applied to heat and moisture diffusion. The tape packs have been submitted to a variety of thermal and hygroscopic conditions. By fitting experiment al curves, a heat diffusivity coefficient of 1.8 . 10(-7) m2/s was obt ained for the radial direction. Separate experiments showed that the h eat diffusivity in the axial direction is about twice the value in the radial direction. For the radial moisture diffusivity coefficient, a literature value of 4 . 10(-13) m2/s is used. Fitting experimental cur ves then shows that the axial diffusion is about 300 to 500 times fast er than the radial diffusion, which indicates that most of the moistur e enters through the faces of the pack. Finally, it is shown that the experimental pack boundaries are not at a fixed temperature. Heat diff usion experiments in a stirred water bath best approximate the constan t temperature requirement, and theoretical fits to those experimental curves have been most satisfactory.