Plate heat exchangers (PHE's) with "chevron" or "herringbone" corrugation have been extensively and successfully used in many industrial applications. Designers of these exchangers have paid a great deal of attention to the optimisation of plate geometry such as size of the plates, shape of the corrugation, inclination angle of corrugation and corrugation depth and pitch. By improving the geometry, the heat transfer can be increased and the pressure drop can be reduced. In this paper, the details of a research project dealing with this topic is provided. The paper contains experimental data concerning the fluid velocity, temperature and pressure, and the analysis of the flow patterns obtained through experiments with commercial PHEs of different geometries. This information can help to better understand the flow behaviour in the channels between corrugated plates, and to estimate the heat transfer therein. The experimental set-up, test procedures and analysis techniques are described. Also, a brief description of the numerical investigations undertaken for this study with some typical results are included.