In this thesis, a thermodynamic analysis of plate heat exchanger with brazed was performed. The influence of two different designs of plate geometry on the coefficients of convection heat, fluid temperature and total heat transfer was analyzed. The problem was defined as a stationary, threedimensional convection-diffusion heat transfer between two fluids. Paper in the first part contains a theoretical insight into the thermodynamic basis of heat transfer, classification of heat exchanger in general, detailed description of the plate heat exchanger characteristics, and the basics of mathematical modeling. The second part of the paper describes a mathematical model for the observed problem, a description of the numerical method used and its calculation method, and the procedure for using Ansys Fluent and Solidworks computer programs. In the last part, the results were presented and a comparison was made for two analyzed cases with different geometry. The assumption was that there will be a greater heat exchange in the cast of geometry with a larger surface for heat transfer, and this was proven right, as shown by the graphic results of the temperature distribution and the analysis of the output temperature, the convection heat transfer coefficients and the total heat transfer, which are compared with diagram for both cases.