Homogenization of a degenerate parabolic problem in a highly heterogeneous medium with highly anisotropic fibers

We consider the homogenization of a heat transfer problem in a periodic medium, consisting of a set of highly anisotropic fibers surrounded by insulating layers, the whole being embedded in a third material having a conductivity of order 1. The conductivity along the fibers is of order 1, but the conductivities in the transverse direction and in the insulating layers are very small, and related to the scales mu and lambda respectively. We assume that mu (resp. lambda) tends to zero with a rate mu=mu(epsilon) (resp. lambda=lambda(epsilon)), where epsilon is the size of the basic periodicity cell. The heat capacities c(i) of the i-th component are positive, but may vanish at some subsets, such that the problem can be degenerate (parabolic-elliptic). We show that the critical values of the problem are gamma=lim(epsilon -> 0)epsilon(2)/mu and delta=lim(epsilon -> 0)epsilon(2)/lambda, and we identify the homogenized limit depending on whether gamma and delta are zero, strictly positive, finite or infinite. (C) 2008 Elsevier Ltd. All rights reserved.