A new calculation method is presented for heat transfer in coupled convective-conductive fluid-wall systems under periodical intensity oscillations in fluid flow. It is demonstrated that the true steady-state mean value of the heat transfer coefficient has to be multiplied by a newly defined coupling factor. This correction factor is always smaller than one and depends on the coupling parameters Biot number, Fourier number as well as dimensionless geometry and oscillation parameters. For characteristic periodic heat transfer problems, analytical solutions are given for the coupling factor. To facilitate engineering application, the monograph also presents the analytical results in accompanying tables and diagrams.