The study considers transient laminar heat transfer of a rotating disk heated to a constant initial temperature and sudden subjection to unsteady cooling by still air. Both numerical simulations of conjugate heat transfer inside the disk and convection between the disk and air, as well as a self-similar solution show that the heat transfer coefficient becomes time independent very quickly and equal to its value at steady-state conditions. It appeared that the widely employed solution of unsteady one-dimensional heat conduction in a semi-infinite plate overestimates significantly the disk temperature and consequently the heat transfer coefficient calculated from this solution using known experimental instant disk surface temperature. (C) 2004 Elsevier Ltd. All rights reserved.