Dear Friends, Solving a problem of a transient conduction in non-homogeneous material composed of glass, ceramic immersed in a stagnant fluid, I should determine the interfaces thermal conductivities between materials od different nature. This was done through the heat balance in every interface node (see Patankar for eg.). My question is : The derivation of the interface conductivity suppose that the 02 adjacent nodes in every interface are composed of the same material inorder to be able to apply the equation of Fourier between them. If this is true shall we also determine the interface thermal capacity even if the control volume of the node in the interfaces are just in contact (every control volume is composed of an homogeneous material).? thank you in advance for your contribution

1) For the conductivity, you should use an harmonic mean when you evalute the flux between the control volumes (this is well explained in patankar)(I assume you use finite volumes) 2) For the capacity, this quantity should be constant on each elements (if you use a Galerkin volume type scheme) or constant over a control volume (classical finite volumes). This quantity is volumetric and has nothing to do with the interfaces.