APPROXIMATE RELATIONSHIPS FOR DETERMINING THE ENTHALPIES OF WATER AND STEAM IN THE CALCULATIONS OF HEAT EXCHANGER DEVICES OF STEAM TURBINE INSTALLATIONS (PART II – DETERMINATION OF THE ENTHALPY OF WATER STEAM)

The conducted studies are the II part of a complex work on creating a methodological approach for determining the enthalpy of water and water vapor in the calculations of heat exchange equipment for operational control of the operating modes of large power steam turbines, when the use of tables of thermodynamic properties of working media in the "manual" mode is not successful. The current part II of the work, in contrast to part I, where the determination of the enthalpy of water is considered, is devoted to the determination of the enthalpy of water vapor. A methodological approach of obtaining approximating equations for determining enthalpy from the values of changing steam parameters is proposed, similar to what was done for water in рart I. In order to ensure the necessary approximation accuracy, the zone of the studied characteristics is divided by pressure into two regions - the vacuum region (1 kPa ≤ Р ≤ 100 kPa) and the overpressure region (0.1 MPa ≤ Р≤ 6 MPa), which in turn is divided into 3 regions (0.1 MPa ≤ Р ≤ 1 MPa, 1 MPa ≤ Р ≤ 3 MPa, 3 MPa ≤ Р ≤ 6 MPa). Since the effect of temperature in the area of the studied parameters is more significant than pressure, there was a need to introduce a significantly larger number of intervals in terms of temperature: 4 – in the vacuum area and15 – in the overpressure area. As a result, a system of approximating equations is proposed, which is characterized by sufficient accuracy in determining the enthalpy in the entire studied range of changes in the superheated steam parameters – pressure and temperature. To demonstrate the obtained results, an example of the application of the proposed methodology to the calculation of a specific heat exchange device is made in the work. The determination of the superheated steam consumption in the conditions of the thermal scheme of the T-250/300-240 heating turbine operated at the CHP, in relation to the PVТ-8 high-pressure heater for one of the operating modes, is given. As a result, it was found that the discrepancy between the value of the consumption of heating steam, determined according to the table values, and the consumption determined according to the obtained approximating dependencies, is 2.2 %, which is quite acceptable for practical needs in the operation of steam turbine plants.