A thermodynamic system may be defined as: a particular quantity of a thermodynamic substance (normally a compressible fluid such as a vapour or gas) that is surrounded by an identifiable boundary.
We often talk about the system boundary as the control surface, where the control surface encloses a region in space, the control volume, as follows:
- a) Inside the space there is a fixed mass of fluid whose behaviour is being investigated.
- b) Across the space there may be a mass transfer of fluid at the inlet and outlet whose thermodynamic state is changing and is under investigation. ...