On one method for analytical solution of Graetz–Nusselt problem

An approximate analytic solution of heat transfer problem for fluid flow in a circular tube is found using the method of separation of variables, based on the introduction of additional boundary conditions. It is shown that already in the fourth approximation over the range of dimensionless axial coordinate $0{,}0025 \le x<\infty $, the difference between the exact and the obtained solution does not exceed 3 %.