Gas Dynamics of real gases I/II

 

This lecture shows which phenomena occur in gases and gas flows if the conditions are far outside of the validity range of ideal gases. Processes are discussed as they are typical for very high temperatures, besides the fact that in classical thermodynamics the expression "real gas effects" is used for phenomena taking part at low temperatures and high pressures.

Flows with high temperature regions for example occur in the stagnation region of hypersonic vehicles and during the reentry of space planes into the earth atmosphere. The bow shock around the vehicle heats the air to such high temperatures that molecular excitation, dissociation and even ionization occur. The last reaction is responsible for the "black out" which takes some minutes during reentry. For this time no radio contact to the space plane is possible. The aim of this lecture is to describe the phenomena from the thermodynamical point of view. This is done incorporating the kinetic gas theory as well as statistical mechanics.

The lecture "Gas Dynamics of Real Gases I" is related to processes in thermodynamic and chemical equilibrium, whereas nonequilibrium reactions are subject of the lecture "Gas Dynamics of Real Gases II". After a short introduction listing different molecular models to describe intermolecular forces the kinetic gas theorie is used to derive the Maxwellian Distribution. An other approach uses statistical mechanics and results in the Boltzmann distribution of the particles over the possible energy levels. In combination of the Boltzmann relation this allows to determine the thermodynamic properties of a gas at high temperatures. The determination of equilibrium gas properties for high temperatures including dissociation and ionization reactions follows next. In the last chapter it is shown how the results achieved are used to compute gas flows in chemical and thermodynamic equilibrium. This is done for the flow through shocks, nozzles and the Prandtl-Meyer flow.