Numerical study of wet-steam flow in Moore nozzles

Abstract

Wet-steam flow is a two-phase mixture of vapor and tiny liquid droplets that occurs in the final stages of low pressure (LP) steam turbine process. These liquid droplets are formed by the non-equilibrium condensation of steam. This condensation of steam releases a significant amount of latent heat to the flow. As a result, the flow velocity is reduced and it affects the efficiency of the steam turbine. Since it is extremely difficult to perform numerical studies with the non-equilibrium condensation for turbines, they are usually done in convergent-divergent nozzles. In this paper, the effect of area ratio of the well-known Moore nozzles on the non-equilibrium condensation of steam is investigated numerically. The mathematical model for the non-equilibrium condensation is based on the classical homogeneous nucleation theory corrected with non-isothermal effects and Hill’s droplet growth law. The numerical results are successfully validated with the experimental data for Moore nozzle B. The numerical results represent that with increasing area ratio, the intensity of condensation decreases and the residue amount of liquid mass fraction in the flow field increases. Therefore, while designing the area ratio of the nozzle, the influences of both the condensation intensity and liquid mass fraction should be considered.