Visual and instrumental investigations of the processes of condensation and redistribution of a working fluid in a loop heat pipe have been carried out. This paper presents the results of an experimental investigation of the heat transfer and hydrodynamics during the condensation of water vapor in a flat gap condenser measuring 80 x 40 x 1 mm. Investigations have been conducted at a condenser cooling temperature of 20, 40 and 60 degrees C. During all operating modes a stratified two-phase flow and film condensation have been observed. The temperature field in the condenser has been measured, and the heat-transfer coefficients and the thermal resistances have been determined. (C) 2013 Elsevier Ltd. All rights reserved.