Electron beam evaporation of high-purity liquid metals is characterized by vigorous (turbulent) convection in the melt pool resulting in unwelcome heat losses. This convective motion is exclusively driven by thermocapillary forces. We exploit this unique feature to measure the Nusselt number in liquid iron for Marangoni numbers up to 10(8). The experiments are carried out in a real-to-life test facility for electron beam evaporation. We compare the results of our investigations with findings of a recent scaling analysis. Moreover. we perform direct numerical simulations employing a 2D model. The numerical results demonstrate the turbulent character of the flow as well as the dominance of thermocapillarity over buoyancy. (C) 2000 Elsevier Science Ltd. All rights reserved.