In this study, the behavior and main properties of a heat exchanger was evaluated when operated with different working fluids. It was first considered as the water, which was later replaced by nanofluids. For this it was necessary to improve and simulate through the ESS software, a pre-existing mathematical model that evaluates the thermal and hydraulic characteristics of a heat exchanger and also a subroutine for the modeling of thermo-physical characteristics of nanofluids. The model input data relating to the condenser inlet point, are mass flow and temperature of the working fluid, condensing pressure, temperature and mass flow of the coolant. For evaluation of other working fluids, it was necessary to improve the model for the heat exchanger and use a subroutine to provide the thermo-physical properties of nanofluids for the simulations. For the simulated cases changed the types of nanoparticles used for nanofluid composition and the volume concentration. The nanoparticles were considered to consist of aluminum oxide, titanium dioxide and copper, with a diameter of 10 nm. The variation of the volume concentration of the nanoparticles is between 0 and 1 percent, increasing by 0.1 percentfor each new case evaluated. Considering the variation of the concentration of the nanoparticles in the composition of nanofluids, the results were evaluated the main termo-physical properties of nanofluids used. About condenser analyzed the total rate of heat transfer and the total pressure drop across the water side and nanofluids.