New calculation method for thermodynamic properties of humid air in humid air turbine cycle – The general model and solutions for saturated humid air

• Our new model is suitable to calculate thermodynamic properties of humid air in HAT cycle.
• Fundamental behaviors of dry air and water vapor in saturated humid air are explored in depth.
• Local-Gas-Constant describes existing alone component and Improvement Factor describes interaction between different components.
• The new model proposes and verifies the relationship between total gas mixture pressure and component pressures.
• It solves saturated humid air thoroughly and deviates from experimental data less than 0.1%.

The article proposes a new calculation method for thermodynamic properties (i.e. specific enthalpy, specific entropy and specific volume) of humid air in humid air turbine cycle. The research pressure range is from 0.1 MPa to 5 MPa. The fundamental behaviors of dry air and water vapor in saturated humid air are explored in depth. The new model proposes and verifies the relationship between total gas mixture pressure and gas component pressures. This provides a good explanation of the fundamental behaviors of gas components in gas mixture from a new perspective. Another discovery is that the water vapor component pressure of saturated humid air equals PS, always smaller than its partial pressure (f·PS) which was believed in the past researches. In the new model, “Local Gas Constant” describes the interaction between similar molecules. “Improvement Factor” is proposed for the first time by this article, and it quantitatively describes the magnitude of interaction between dissimilar molecules. They are combined to fully describe the real thermodynamic properties of humid air. The average error of Revised Dalton's Method is within 0.1% compared to experimentally-based data.