Properties of metastable supercooled steam

To calculate some thermal processes, mainly the processes of steam expansion in turbines, it is important to know properties of metastable supercooled steam in the region adjoining the region 2 of formulation on the side of right boundary curve. As there is no experimental data of thermodynamic properties of supercooled water steam, its calculation can only be made by extrapolation of equation of state formed for a stable superheated steam to that region. An analysis of several equations such as the main equation for region 2 of the formulation, equation of a superheated steam from formulation IFC-67 and International equation of state for general and scientific application IAPWS-95, shows that results of its extrapolation are considerably different. Such situation is typical for complicated equations containing a lot of constants. Therefore, as initial datum for equation of state of a metastable supercooled steam were taken that obtained from simpler equation that was formulated as auxiliary for International equation of state IAPWS-95 [1].

To calculate metastable region of supercooled steam the equation given in [3] is used. List of functions for property calculation of supercooled metastable steam is given here.

The equation is applicable for the metastable steam region from the upper boundary curve to a line of 5% humidity of steam in equilibrium h, s - chart at pressure up to 10 MPa. The following datum define adjustment of calculated values on the saturation line with the main equation for region 2:

v|max = 0.014 % s|max = 0.082 J/(kg·K)
h|max = 0.043 kJ/kg g|max = 0.023 kJ/kg
cp|max = 0.78 % w|max = 0.05 %

The equation for metastable steam region converts to the equation for region 2 in discrete steps along the 10 MPa isobar in the field of metastable steam, but that is not of essential practical importance.

The monitoring values of thermodynamic properties of metastable supercooled steam are given in tab. 1.

Table 1. Thermodynamic properties of a metastable supercooled steam
Property t = 450 K, P = 1 MPa t = 440 K, P = 1 MPa t = 450 K, P = 1.5 MPa
v, m3/kg 0.192516540 0.186212297 0.121685206
h, kJ/kg 0.276881115·104 0.274015123·104 0.272134539·104
u, kJ/kg 0.257629461·104 0.255393894·104 0.253881785·104
s, kJ/(kg·K) 0.656660377·101 0.650218759·101 0.629170440·101
cp, kJ/(kg·K) 0.276349265·101 0.298166443·101 0.362795578·101
w, m/sec 0.498408101·103 0.489363295·103 0.481941819·103