The article considers the processes of modeling the flow of a refrigerant and presents the results of numerical simulation of freon evaporation in a tubular evaporator. The results show the effect of convective heat transfer and bubble formation on the heat transfer coefficient. It is assumed that this technology can be used, among other things, as an element for water desalination. The possibility of using heat pumps and the organic Rankine cycle in the scheme of water desalination is considered. The authors propose to design such energy-technological complexes, starting from the stage of numerical simulation. The modeling results and the developed schemes presented to the attention of readers are part of a unified methodology for heat pumps and desalination systems.