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Special equations of state for water and steam

Strzelczyk F., Wawszczak A.

Archives of Thermodynamics

2002

Vol. 23, no 1-2

69-99

Demand for on-line calculation in contemporary simulation models of power engineering units, microcomputer measurement systems and automatic control rendered the necessity to develop approximation functions, which enable to determine thermodynamic prperties of water and steam in time, which is several times shorter than that using the reference functions. In the work presented have been approximation functions of thermodynamic properties of water and steam for different independent variables. These are the algebraic polynomials of low order with simple scaling functions and minimal numbern of non-linear parameters, hence, due to their simplicity, very simple in conding in. Classical method of mean square approximation have been used in the development of these functions - a simultaneous approximation of several dependent variables with given weighting functions. Presented have been the distribution of errors as well as calculation times, when using such functions, and the results have been compared against the reference functions IAPWS-IF97. Presented in the paper equations enable, in the assumed range, to calculate thermodynamic parameters of water and steam with a given (required) accuracy.