The paper presents the results of an experimental investigation of heat transfer at flow boiling of water and n-pentane/water and freon-11/water emulsions in a horizontal minichannel with a hydraulic diameter of 1.1 mm. The flow conditions of two-phase flows have been visualized at the exit from an evaporator with the use of high-speed video filming. At bubble and slug flow conditions of a two-phase flow the mean coefficient of heat transfer from the channel wall to emulsions has proved to be higher than to water. The results of a synchronous measurement of variations in the liquid temperature at the channel inlet and outlet and the excess pressure in the system at the instability of a two-phase flow have been examined. (C) 2018 Elsevier Ltd. All rights reserved.