Process variable
A process or operation variable is a physical variable that occurs only when there is a change in state and describes the process of the change in state. Therefore process variables are dependent on the path of change. Process variables describe how one state changes into another state.
This is in contrast to the state variables , which only depend on the respective state and for which it is of no importance in which way this state has occurred.
A thermodynamic system experiences a change of state through the supply or removal of energy . The work W performed here and the heat Q exchanged are therefore process variables.
An infinitesimal change in a process variable (e.g. heat) is identified by a δ (e.g. δ Q ), which indicates an inexact differential . In contrast, infinitesimal changes in a state variable, e.g. B. entropy , marked with ad (z. B. d S ).
Individual evidence
- ↑ Dorothea Lüdecke, Christa Lüdecke: Thermodynamics: Physico-chemical basics of thermal process engineering . Springer-Verlag, 2013, ISBN 978-3-642-56988-3 ( google.de [accessed April 8, 2019]).