Use of the international association for the properties of water and steam (IAPWS) formulations, IAPWS-95 & IAPWS-IF97: Making of Mollier diagram and T-s diagram of water and steam

•Calculation of thermodynamic properties of saturated liquid water and water vapor in saturation line of near-critical region.•Procedures to plot different lines of Mollier diagram and T-s diagram of water and steam by combining the IAPWS-IF97 with IAPWS-95.•Use in designing and in calculating the main equipment of thermal power plants. It is very important to correctly calculate the thermodynamic properties of water and steam needed for design and operation of the main equipment of the power industry such as boilers and steam turbines. On the other hand, the Mollier diagram and T-s diagram of water and steam are widely used to study or review thermodynamic cycles as well as expansion processes of steam turbines and steam power equipment in the power industry. Presented in this paper are the method and procedures to exactly construct the diagrams. The diagrams involve several lines, including the saturation line, and constant pressure, temperature and vapor fraction lines. In the paper, a method is proposed for correctly calculating other thermodynamic properties of saturated liquid water and water vapor in saturation line of near-critical region by using the basic equation of region 3 of IAPWS-IF97 and iteration. Then, the procedures to plot the lines are presented by combining the method with IAPWS-95 and IAPWS-IF97, and the Mollier diagram and T-s diagram made in MS-Excel are shown. The method and procedures in the paper can be used not only in making the Mollier diagram, T-s diagram and steam tables, but also in accurately calculating the thermodynamic properties of saturated liquid water and water vapor.