The semi-analytical method for determining the temperature field in the liquid is proposed. It allows calculating the heat flux at the wall and estimating the distance, at which the equilibrium temperature is set in the film.

The results of calculations by the proposed method are in good agreement with the numerical solution of the problem by the finite-difference method. Good agreement may be found both for the case of falling films and for the cases of co-current and countercurrent gas flows.

The calculations prove that the distance of reaching the equilibrium temperature distribution depends on the direction of the gas flow. The co-current gas flow leads to an increase in such a distance, and the countercurrent gas flow results in its decrease.

The analytical solution considering shear stress on the film surface has been obtained for the thermal entry region for the classical problem of heating the laminar falling liquid film, moving under gravity and gas flow at constant wall temperature and heat transfer at the liquid-gas interface.