Thermodynamic machine and method for the operation thereof
The invention relates to a thermodynamic machine having a circulation system in which a working fluid, in particular a low-boiling working fluid, circulates alternately in a gaseous and a liquid phase, a heat exchanger, an expansion machine, a condenser, and a fluid pump. The invention also relates to a method for operating the thermodynamic machine. According to certain embodiments of the invention, in the flow line of the fluid pump, a partial pressure increasing the system pressure is applied to the liquid working fluid by adding a non-condensing auxiliary gas. Compact ORC machines can be implemented, preventing cavitation in the liquid working fluid.
1. A thermodynamic machine with a cyclic system, in which an organic Rankine working fluid circulates alternately in a gaseous phase and a liquid phase, with a heat exchanger, with an expansion machine, with a condenser, and with a liquid pump, wherein a partial pressure, which increases the system pressure, is applied to the liquid phase of the working fluid in the head of the liquid pump by the addition of a non-condensing auxiliary gas.
2. The thermodynamic machine as claimed in claim 1 , wherein the partial pressure which results by the addition of the auxiliary gas is sufficiently high so that the pressure at the head of the liquid pump does not drop below the saturation vapor pressure of the working fluid during operation of the liquid pump.
3. The thermodynamic machine as claimed in claim 1 , wherein the head height of the liquid pump lower than a minimum necessary head height based on the net positive suction head (NPSH) value and a subcooling of the liquid working fluid.
4. The thermodynamic machine as claimed in claim 1 , wherein a point of introduction for the auxiliary gas is provided between the expansion machine and the liquid pump.
5. The thermodynamic machine as claimed in claim 1 , wherein the condenser is designed for entrainment of the auxiliary gas in the flow direction of the working fluid, as an air condenser or by means of plate-type heat exchange elements.
6. The thermodynamic machine as claimed in claim 1 , wherein the expansion machine is a positive displacement machine.
7. The thermodynamic machine as claimed in claim 1 , wherein a sensor for detecting the auxiliary gas concentration is arranged in a header tank of the liquid working fluid.
8. The thermodynamic machine as claimed in claim 1 , wherein the thermodynamic machine is a mobile plant for a motor vehicle, and wherein the heat exchanger is thermically connected to a waste heat source of the motor vehicle.
9. A method for the operation of a thermodynamic machine, wherein, in a cyclic system, an organic Rankine working fluid circulates alternately in a gas phase and a liquid phase, and
wherein the working fluid is heated, expanded, condensed, and delivered by pumping of the liquid, wherein a partial pressure, which increases the system pressure, is applied to the liquid phase of the working fluid in the head of the liquid pump by the addition of a non-condensing auxiliary gas.
10. The method as claimed in claim 9 , wherein the partial pressure which results by the addition of the auxiliary gas is sufficiently high so that the pressure at the head of the liquid pump does not drop below the saturation vapor pressure of the working fluid during operation of the liquid pump.
11. The method as claimed in claim 9 , wherein the auxiliary gas is added to the expanded, gaseous working fluid.
12. The method as claimed in claim 9 , wherein the auxiliary gas is further transported, principally in the flow direction, during the condensing of the working fluid.
13. The method as claimed in claim 9 , wherein the working fluid is expanded in a positive displacement machine.
14. The method as claimed in claim 9 , wherein waste heat of a motor vehicle is used for heating and/or evaporating the working fluid.