The main topic of this master’s thesis is thermodynamic analysis of cogeneration plant cycle and thermodynamic analysis of water heater in the given cogeneration power plant. Respectively, thesis is combined from two parts. First part consists of the description of cogeneration plant “Slavonija OIE”, with the emphasis on the steam generator and its basic devices. Also, all the necessary power plant components schematics are attached. Furthermore, thermodynamic calculation of cogeneration plant cycle was conducted using the “Engineering Equation solver” (EES) computer program. The main goal of the thermodynamic calculation of plant cycle is the analysis of thermal efficiency of the plant, which was increased by the means of cogeneration. In the second part of the thesis, numerical simulation of flow and heat transfer through a single curved pipe with smooth walls was conducted as a compromised solution for the water heater (ECO3), which represents the actual heat exchanger used in the given cogeneration plant. Geometry and boundary conditions were defined, finite volume mesh was generated and mathematical model of flow and heat transfer was set up to perform the numerical simulation of flow and heat transfer and for the results to be analyzed. Also, numerical simulation of flow and heat transfer through a single smooth pipe and a single finned pipe was performed to examine the effect of fins on the heat transfer efficiency and therefore the heat exchanger efficiency. Numerical calculations are based on finite volume method and numerical simulation software “ANSYS” was used. Heat fluxes, mass flow rates, dimensionless wall distances in geometric grid and temperature and velocity fields were analyzed as results of numerical calculations.