Additional Conditions in Boundary Value Problems of Heat Conduction (Review)

A review of studies related to the use of additional boundary conditions (ADBs) and additional sought functions (ADFs) in obtaining analytical solutions to heat conduction problems is presented. ADВs allow the equation to be executed at the boundaries, which leads to its execution inside the domain, excluding direct integration over the spatial coordinate. ADF allows one to reduce a partial differential equation to an ordinary differential equation, from the solution of which the eigenvalues of the boundary value problem are found. Eigenvalues in classical methods are found from the solution of the Sturm–Liouville boundary value problem formulated in the domain of a spatial variable. Consequently, the method used in this work leads to another algorithm for their determination, based on the solution of a temporary differential equation, the order of which is determined by the number of approximations of the resulting solution. In a problem based on determining the front of a temperature disturbance, the equivalence of solutions to the parabolic and hyperbolic heat equations was found. And, in particular, a number of approximations have been found that limit the speed of propagation of a thermal wave in the solution of a parabolic equation to a value equal to its real value for a specific material, at which it coincides with the solution of the hyperbolic equation.