Abstract
In the previous chapters the law of energy conservation has been thoroughly discussed. By this, it was possible to evaluate thermodynamic systems energetically. A distinction has been made between closed and open systems. However, next to thermal state values, such as pressure p or temperature T, that can be measured easily, a new category of state values has been introduced: These state values, i.e. specific internal energy u and specific enthalpy h for instance, can not be determined by a sensor and thus need to be calculated.
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Notes
- 1.
Such as \(\left[ u\right] ={1}{\frac{\text {kJ}}{\text {kg}}}\) and \(\left[ h\right] ={1}{\frac{\text {kJ}}{\text {kg}}}\).
- 2.
The indices at the brackets indicate, that this variable is kept constant!
- 3.
At constant specific volume v.
- 4.
At constant pressure p.
- 5.
The thermodynamic proof is given in Sect. 12.3.2.
- 6.
To be honest, it is even difficult to find a physical meaning of the internal energy. Though you probably have accepted its existence by now.
- 7.
Known as integrating factor!
- 8.
Similar to the first law of thermodynamics: The state value internal energy is influenced by process values work and heat!
- 9.
For the Gibbs free enthalpy there is a physical motivation for chemical reactive systems, e.g. fuel cells or Lithium Ion batteries. This will be handled in part III of this book, see Sect. 24.3!
- 10.
With the assumptions, that \(c_{v}=\text {const.}\) and \(c_{p}=\text {const.}\)
- 11.
Indicated by the v-subscript.
- 12.
Indicated by the p-subscript.
- 13.
Very slow is a synonym for no turbulence inside, see also Theorem 7.25.
- 14.
Gravity constant g is not relevant, since the piston is operated horizontally.
- 15.
The change of kinetic energy can be ignored, since the change of state is quasi-static! There is no change of potential energy, since the cylinder is horizontal!
- 16.
According to \(V=\frac{mRT}{p}\).
- 17.
Mind, that \(H=mh\).
- 18.
Fluid motion would need to be initiated, e.g. by a moving piston.
- 19.
Mind, that \(U=mu\).
- 20.
This part is for the advanced readers, who are already familiar with the T, s-diagram, see Sect. 13.4.
- 21.
Assuming, that \(c_{p}=\text {const.}\)!
- 22.
For the calculation a temperature difference is required, so it does not make any difference, if you apply \(\Delta \vartheta \) or \(\Delta T\), see Eq. 12.175!
- 23.
The specific enthalpy remains constant!
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Schmidt, A. (2019). Caloric Equations of State. In: Technical Thermodynamics for Engineers. Springer, Cham. https://doi.org/10.1007/978-3-030-20397-9_12
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DOI: https://doi.org/10.1007/978-3-030-20397-9_12
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