Analysis of moisture condensation during air expansion in turbines

Water is always present in the atmospheric air in the form of vapour. As air of low temperature expands through the turbine condensation may occur. Condensation gives rise to several problems in materialization of the air cycle as it results in temperature rise thus to different conditions than the expected at the turbine exit. Also in most air cycle applications, liquid water must be removed from the air stream before it gets to the cooled space. In the case that turbine exit temperature is very low; there is the possibility of ice particles formation. A method allowing the evaluation of air properties when condensation occurs is required in order to examine its effect on the cycle and optimize the operating envelope. The present paper describes a thermodynamic equilibrium method for predicting the occurrence of condensation and calculating the mixture properties once condensation has occurred. The method has been validated against the experimental results from a turbocharger turbine. The experimental results show that condensation can cause significant alteration to the turbine exit conditions. It is demonstrated that condensation can be predicted and the mixture properties after condensation can also be accurately evaluated.