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11.3  MODIFICATION OF PERMEABILITY                                   197


            Suppose  that  the  relationships {11.40)  and  {11.47)  hold,  i.e.,  we  neglect  the
         outlined variations of Hand Z.  In this case, according to {11.34), e(o)  ~  2.5, and
         the condition {11.42) holds for a/ao > 1.5.  It follows  accordingly that

                                        HB*
                                                     2
                                     3
                                   w*  ~  -A  ~  1.8 · 10  t               {11.56)
                                          Xo
         This implies that a/ao "' 10 when  t"' 10 seconds.
            If, however, we suppose that the capillary is shut off for a"' r = 8 ·10 5 m, then
         t ~  0.8 hours.
            {11.56) implies that


            Therefore


         and the left  side of (  11.36) is of the order of

                                         2
                                                    11
                                                            8
                            w*w~  +  3/2(w:) ~  -{4 · 10 + 2 · 10 )
            The term in the right side of the equation is of the order of



         It follows  that for  the given  characteristic parameters, the dynamic terms in  the
         Rayleigh-Lamb equation  may  indeed  be  neglected.  Thus this equation  assumes
         the form  {11.40), and the dynamics of the bubble growth is taken into account in
         the equation {11.35).
            Thus the following stages of the reversible change of the permeability for a mi-
         cro heterogeneous medium as the electric current passes through it can be outlined,
         based on the theoretical analysis and the obtained experimental data.

            1.  Increase  of the  electric  conductivity  and  the  permeability  of the  medium
              caused by the destruction of the bounded fluid  on  the surface of capillaries
              and  by  the decrease of its  viscosity.  At  the same  stage,  the  migration  of
              bubbles of fluid  towards the thin capillaries of the medium, which  are heat
              sources, takes place.

           2.  Termination of the growth of the electric conductivity and the permeability
              and  the formation  of a  "platform"  in  I<(t)  and  E{t)  coordinates.  At  this
              stage, the growth of bubbles of vapor takes place at a temperature less than
              the boiling point.  These bubbles shut off the capillaries and make up for the
              increase of the electric conductivity and the permeability of the fluid caused
              by the increase of the capillary cross-sections.
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