Equations for engineering calculations of the thermodynamic properties of high-temperature dissociated steam

A system of equations is developed to calculate the properties of dissociated steam in the temperature and pressure ranges of $1250$–$3400$ K and $0.01$–$10.00$ MPa. These equations are based on detailed tables for dissociated steam compiled for a mixture of atoms of hydrogen and oxygen, hydroxyl $\rm OH$, molecules of hydrogen and oxygen, and steam at a reference temperature of $0$ K. Since the expansion of dissociated steam in a thermal engine results in its transformation into its common form, the equations for the parameters of dissociated or nondissociated steam uses the same reference temperature, i.e., the water triple point of $273.16$ K. A system of equations for the calculation of dissociated-steam properties is derived with the generalized thermodynamic equation, which takes into account the change in the chemical potential and the composition of the mixture during steam dissociation, the Gibbs energy equation, differential thermodynamic equations, and equations for calculation the properties of nondissociated steam. To minimize the deviation of the steam properties calculated by the proposed equations from the table values, the considered temperature and pressure ranges have been divided into three regions. The deviation of the steam properties calculated by the proposed equations from the table values does not exceed $0.05$–$0.09\%$. The developed equations can be used in calculations of the processes of cooling of burners and combustion chambers during the combustion of hydrogen–oxygen mixtures, as well as cycles of heat engines that use high-temperature steam as a working fluid at temperatures over $1250$ K.