Degree of reaction

The reaction rate r is the ratio of the enthalpy that the rotor is converted, to the total in the turbomachine unreacted enthalpy. The degree of reaction can be specified both for an entire turbomachine and for individual stages of a multi-stage turbomachine.

formula

The degree of reaction is calculated as follows:

${\displaystyle r={\frac {\Delta h_{2s}}{\Delta h_{1s}+\Delta h_{2s}}}={\frac {\Delta h_{2s}}{\Delta h_{s}}}}$

where the following sizes are used:

${\displaystyle r}$= Degree of reaction

${\displaystyle \Delta {h_{2s}}}$= Enthalpy gradient across the rotor

${\displaystyle \Delta {h_{1s}}}$= Enthalpy gradient over the tail unit

${\displaystyle \Delta {h_{s}}}$= Enthalpy gradient over the entire turbomachine

The degree of reaction is a dimensionless key figure that can assume a value between zero and one. It cannot exceed 1, since the enthalpy gradient of the medium in the rotor blades cannot be greater than the total enthalpy gradient of the turbomachine. ${\displaystyle r}$

application

Example of a positive pressure turbine with degree of reaction r = 1

Constant pressure turbines have a degree of reaction , which means that the tail unit converts the entire static pressure into kinetic energy and no further conversion of enthalpy takes place in the rotor. The entire enthalpy gradient is converted into flow energy in the guide vanes, the static pressure in the rotor blades of the stage remains constant. As peer pressure turbines described usually have still a small overpressure share why such turbines to still regarded as direct pressure turbines. Furthermore, it should be noted that the blades of larger turbines are twisted, which increases the degree of reaction towards the outside. ${\displaystyle r=0}$ ${\displaystyle r=0.2}$

Overpressure turbines have a degree of reaction , which means that part of the energy is converted in the tail unit and another part in the rotor. Usually a degree of reaction of 0.5 is achieved in steam and gas turbines , which means that half of the pressure reduction occurs in the tail unit and the other half in the rotor. Overpressure turbines with one degree of reaction are not used industrially. In this type of turbine, all of the static pressure is converted into kinetic energy using a nozzle on the rotor. ${\displaystyle r>0}$ ${\displaystyle r=1}$

literature

• Adolf J. Schwab : electrical energy systems. Generation, transport, transmission and distribution of electrical energy. Springer, Berlin 2006, ISBN 978-3-540-29664-5 , pp. 102-107. ( Online )
• Ernst Schmidt: Thermodynamics, ninth edition. Springer-Verlag Berlin-Heidelberg GmbH, 1962, ISBN 978-3-662-23813-4 , pp. 307f. ( Online )

Individual evidence

1. ↑ ^{a b} Gunt (Ed.): Turbines for gaseous fluids . Hamburg ( gunt.de [PDF]).