[en] The flow regimes inverse annular film flow and the change to dispersed droplet flow have been studied through measurements of void fraction and heat flux. Equipment for measuring the mean void fraction by the γ-ray absorption method has been developed. Measurements are presented of the axial void fraction distribution, the low flow inverse film boiling heat transfer, and the heat transfer to the dispersed droplet flow. The experiments were performed in a heated glass tube with a nitrogen gas-liquid two-phase flow at 1 bar. The inlet mass flux was varied through a 10 to 120 kg/m²s range. Furthermore, a few measurements are presented of void fraction during inside reflood of a single heated steel tube with water. The experimental data from the series of experiments using nitrogen as coolant have been compared with calculations with the one-dimensional, six-equation computer code RISQUE-N2. (author)