Title : Hybrid enthalpy method for Finite Element Thermal Analysis of multi-materials involving multi-orientations of the thermal conductivity tensor.
The anisotropic problem of thermal conduction in a incompressible solid is generally treated in a reference coordinate system, which adequately describes its thermal conductivity tensor (Cartesian, cylindrical or spherical). For this problem, numerical treatment is delicate, especially if the thermophysical properties are non-linear or if the anisotropic medium undergoes a phase change. In this presentation, we propose an approach using only one reference system (for example the Cartesian) to treat the anisotropic thermal conduction of problems for which the multi-material solid is characterized by a set of tensors of thermal conductivity of different natures (Cartesian and/or cylindrical and/or spherical), with or without phase change. The nonlinear heat conduction problem involving phase changes is solved using hybrid three-dimensional volumetric specific enthalpy based on finite-element analysis. The proposed approach is validated with analytical testing for two anisotropic media (cylinder and spherical with convective transfer with variable circumference) and with two experimental tests related to the heating of frozen woods. An example on the characterization of the phytosanitary treatment time of wood by microwaves, in accordance with FAO International Standard No.15, will be presented.
• The proposed approach can be deployed or integrated into several areas of the engineering sciences. By way of example, in thermal science, it makes it possible to analyze the heat absorbed in multi-material anisotropic media, with or without phase change, involving thermal conductivities of different nature (cylindrical, Cartesian, etc.). Here are some examples :
o Thawing or Drying of multi-material products (wooden products for example);
o Phytosanitary treatment of multi-material products
o Electromagnetic radiation absorbed by surrounding areas of target tissues (human or animal)
o Cooling of Li-ion batteries characterized by strong anisotropy of thermal conduction in Li-ion cells, etc.