Thermodynamics of moist air: contribution to error estimates

In several articles and books on thermodynamics, equations describing the behaviour of unsaturated moist air are available. On the other hand, to our best knowledge, a summary of the thermodynamic functions together with all their derivatives is lacking. Individual equations contained in the list of equations in this article are useful for numerous applications in the field of heat transfer and thermodynamic processes of humid air. They can also be applied to other examples, e.g. to construct diagrams which describe various classes of other vapours, such as of solvents. In particular, the derivatives yield a solid basis for error estimates of the related thermodynamic processes. An example—describing a dew point measurement to determine the relative humidity of moist air—is discussed. It demonstrates how the theory can be applied by readers who are interested in applying the results to interpret their experimental data.