A nonconventional thermodynamic converter, called thermogravimetric system, capable of generating mechanical-electric energy is described in the present work. Such plant is basically an interesting application of a liquid-vapor two-phase flow, evolving in elevated vertical ducts of a large diameter The most significant plants-those working with liquid lead/steam and liquid lead/PP 50 (C5F12)-have been analyzed in more detail. Plant height Z, power W (0.5-4 MW), and overall efficiency eta(0) have been evaluated through an appropriate calculus code, particularly regarding the two-phase flow behavior.