Control of ORC processes by injecting unevaporated fluid

A method for operating a thermodynamic Organic Rankine Cycle (ORC) process, said method comprises the following steps:

• preheating a working medium with a preheater;
• further preheating, evaporating and superheating a first mass flow of the preheated working medium with an evaporator;
• expanding the evaporated and superheated first mass flow of the working medium in a volumetric expansion machine;
• condensing the working medium exiting said volumetric expansion machine with a condenser;
• pumping condensed working medium to said preheater with a feed pump;
• and
• supplying a second mass flow of the preheated working medium to the partially expanded first mass flow of the working medium in an expansion chamber of said volumetric expansion machine, wherein the second mass flow is supplied to the expansion chamber during a time period in which there is no first mass flow into or out of the expansion chamber.