Stationary process

This article deals with the stationary process in thermodynamics, for stochastics see Stationary stochastic process .

The Joule cycle is a steady flow process

In thermodynamics, a stationary process is a process whose state variables are independent of time . Stationary processes are widespread in reality, for example in turbines in power plants , jet engines in aircraft , pumps and compressors . Many cycle processes are stationary processes. ${\displaystyle \tau }$

In balance equations such as mass balance or energy balance , the left side of the equation usually shows the change in the respective balanced state variable. For example, the following applies to the mass balance

${\displaystyle {\frac {dm(\tau )}{d\tau }}=\sum {\dot {m}}_{i}(\tau )}$

In a stationary flow process, the state variables do not change over time, so the following applies:

${\displaystyle {\frac {dm(\tau )}{d\tau }}=0}$.

The mass balance is consequently simplified to

${\displaystyle 0=\sum {\dot {m}}_{i}(\tau )}$.

The fact that the state variables are independent of time in a stationary process does not mean that a state variable within a system is always constant. For example, if you consider a turbine operating in a steady flow process, the pressure and temperature before entering the turbine are higher than after the turbine. These state variables are therefore dependent on the location, but they are constant for a fixed location.

See also

Stationary process

Individual evidence

1. ^ ^{A b} Peter Stephan, Karlheinz Schaber, Karl Stephan , Franz Mayinger: Thermodynamik. Basics and technical applications. Volume 1: One-component systems. 19th edition, Springer Verlag, Berlin Heidelberg 2013, ISBN 978-3-642-30097-4 , pp. 89-93.
2. ↑ Klaus Lucas: Thermodynamics. The laws of energy and matter conversion. 7th corrected edition, Springer Verlag, Berlin Heidelberg 2008, ISBN 978-3-540-68645-3 , pp. 115-131.