The hyperbolic heat conduction equation in an anisotropic material

In this work, the phase-lag concept in the wave theory of heat conduction i s extended to describe the thermal behavior of anisotropic material. This i s achieved by assuming that there are phase-lags of different magnitudes be tween each component of the heat flux vector and the summation of temperatu re gradients in all directions of the orthogonal coordinate system. Also, e xpressions are provided to specify the locations of the principal coordinat e axes, the principal thermal conductivities and the principal thermal rela xation times.