The aim of this work was to present the numerical simulation results determining the distributions of flow velocity and pressure in the individual channels of a plate heat exchanger. The simulations have been conducted by means of the Finite Volume Method (FVM) of numerical computation using the ANSYS CFX software. The computational model constituted spaces between 10 flat, straight flow type plates of the heat exchanger. The obtained results of numerical simulations confirm the presence of inhomogeneous flow conditions in the neighbouring channels between the plates. The computations enabled to point out the regions on the plates, in which insufficient flow can result in problems with their cleaning. The results of this work constitute the first part of a research leading to an assessment of cleaning conditions in plate heat exchangers.