Calculating the caloric properties of dissociated steam at high temperatures

Abstract

Lookup tables and the hs-diagram of the caloric parameters of dissociated steam are drawn up in the temperature and pressure ranges 1250–4000 K and 0.1–10 MPa for calculating the processes in thermal power installations that use dissociated steam as working fluid. Unlike the existing tables for thermophysical properties of dissociated steam, the enthalpy presented in the proposed tables has positive values in the entire range of the considered parameters. The enthalpy of mixture includes the entire energy spent in the chemical reaction of dissociation for breaking the bonds in steam molecules. The caloric parameters are determined from the reference temperature equal to 0°C adopted in the methods for calculating the parameters of nondissociated steam, due to which it becomes possible to carry out coordinated calculations of processes in thermal power installations. Supplements to the existing tables for calculating the above-mentioned caloric parameters are developed. Dissociated steam expansion processes are calculated for the conditions with and without recombination of dissociation products at the same values of initial parameters and final pressure. It has been determined that the change of enthalpy and the work done in the expansion process without recombination are smaller than they are in the process involving recombination of dissociation products. The error of the performed calculations of caloric parameters is less than 0.1%.