The two-phase flow in the corrugated gap created by two adjacent plates of a plate heat exchanger was investigated experimentally. One setup consisting of a transparent corrugated gap was used to visualize the two-phase flow pattern and study the local phenomena of phase distribution, pressure drop and void fraction. Saturated two-phase R365mfc and an air-water mixture were used as working fluids. In a second experimental setup, the heat transfer coefficients and the pressure drop inside an industrial plate heat exchanger during the condensation process of R134a are determined. Both experimental setups use the same type of plates, so the experimental results can be connected and a flow pattern model for the condensation in plate heat exchangers can be derived. In this work the results of the flow pattern visualization, the two-phase pressure drop in the corrugated gap and the void fraction analysis by measurement of the electrical capacity are presented. A new pressure drop correlation is derived, which takes into account different flow patterns, that appear during condensation. The mean deviation of the presented pressure drop model compared to the experimental data and data from other experimental works is 18.9%. 81.7% of the calculated pressure drop lies within +/- 30% compared to the experimental data. (C) 2017 Elsevier Ltd. All rights reserved.