## RTy0 yo yr nr

where n = p/p and r = T*/ Twith R given by Eq. (1).

The equation for the ideal-gas part yo is identical with Eq. (16) except for the values of the two coefficients no and n 2, see Table 10. For the use of Eq. (16) as part of Eq. (18) the coefficients no and n 2 were slightly readjusted to meet the high consistency requirement between Eqs. (18) and (15) regarding the properties h and s along the saturated vapor line; see below.

The equation for the residual part yr reads

where n = pip* and t = T*/ T with p* = 1 MPa and T* = 540 K. The coefficients n and exponents and J of Eq. (19) are listed in Table 16.

Note: In the metastable-vapor region there are no experimental data to which an equation can be fitted. Thus, Eq. (18) is only based on input values extrapolated from the stable single-phase region 2. These extrapolations were performed with a special low-density gas equation [11] considered to be more suitable for such extrapolations into the metastable-vapor region than IAPWS-95 [3].

i |
Ii |
Ji |
ni |

1 |
1 |
0 |
- 0.733 622 601 865 06 x 10"2 |

2 |
1 |
2 |
- 0.882 238 319 431 46 x 10"1 |

3 |
1 |
5 |
- 0.723 345 552 132 45 x 10"1 |

4 |
1 |
11 |
- 0.408 131 785 344 55 x 10"2 |

5 |
2 |
1 |
0.200 978 033 802 07 x 10"2 |

6 |
2 |
7 |
- 0.530 459 218 986 42 x 10"1 |

7 |
2 |
16 |
- 0.761 904 090 869 70 x 10"2 |

8 |
3 |
4 |
- 0.634 980 376 573 13 x 10"2 |

9 |
3 |
16 |
- 0.860 430 930 285 88 x 10"1 |

10 |
4 |
7 |
0.753 215 815 227 70 x 10^2 |

11 |
4 |
10 |
- 0.792 383 754 461 39 x 10"2 |

12 |
5 |
9 |
- 0.228 881 607 784 47 x 10"3 |

13 |
5 |
10 |
- 0.264 565 014 828 10 x 10^2 |

All thermodynamic properties can be derived from Eq. (18) by using the appropriate combinations of the ideal-gas part yo, Eq. (16), and the residual part yr, Eq. (19), of the dimensionless Gibbs free energy and their derivatives. Relations between the relevant thermodynamic properties and y0 and yr and their derivatives are summarized in Table 12.

All required derivatives of the ideal-gas part and of the residual part of the dimensionless Gibbs free energy are explicitly given in Table 13 and Table 17, respectively.

Table 17. The residual part yx of the dimensionless Gibbs free energy and its derivatives a according to Eq. (19)

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