In this study, the hydrodynamics and thermodynamics of a fluidyne heat machine having three columns are analysed systematically. The mathematical model of the system is considered in three parts, that is liquid, vapour, and interfacial regions. The liquid and vapour phases are separated by an interfacial surface where evaporation and condensation occur. It is assumed that heat input and output only take place at the interfaces so that the liquid and vapour phases can be considered as lumped open systems. While the major and minor losses are considered in the liquid phase, the state of the vapour phase changes isentropically. The proposed mathematical formulation of the system is solved by a Runga-Kutta method and compared with the experimental data of a previous study. The results of the solution are in good agreement with the experimental data. It is shown that work will not be produced by the system considered in this study, and that the system only overcomes the major and minor losses.