We propose a technique for solving nonstationary heat-conduction problems for thermosensitive bodies with simple nonlinearity (the coefficients of thermal conductivity and the heat capacity per unit volume depend on temperature, but the coefficient of thermal diffusivity is constanO heated by convective heat exchange from the surrounding medium.Nonlinear heat-conduction problems for thermosensitive structural elements made of materials whose coefficient of thermal conductivity ~,, and heat capacity per unit volume c, depend on temperature in such a way that their ratio, the coefficient of thermal diffusivity a, is constant, can be completely linearized using the Kirchhoffvariable [lO] in the case when the temperature or heat flux is prescribed on the surface. We consider a method of solving nonstationary problems when convective heat exchange occurs across the entire surface or part of it and the Kirchhoff variable linearizes the heat-conduction problem only partially.Suppose a thermosensitive body is heated by sources arbitrarily distributed over its volume with density W(x, y, z, "0, and by the surrounding medium, from which heat exchange across the boundary S of the body occurs according to Newton's law. Then the temperature of the body is determined from the heat equation Here t,. is the temperature of the medium surrounding the surface S, or, is the coefficient of thermal emission from this surface, t i is the initial temperature of the body, and n is the exterior normal to the surface.We introduce the notation T = t/t o , and we write the coefficient of thermal conductivity and the heat capacity per unit volume of the material of the body in the form L, (t) = ~o L; (T), c,(t) o .
= c, c, (T). Here t o isthe base temperature, Z~ and c o are quantities having dimensions, and the superscript 9 denotes the corresponding dimensionless quantities F
= ~,;(T)dT.(3) ri We reduce the problem (1), (2) to the forms.where T(0) is the temperature expressed in terms of the Kirchhoff variable (3). Hence, the original problem has been partially linearized: the heat-exchange condition (5) contains the nonlinear expression for the temperature T(0) on the surface S. Let us assume that the value of the temperature