Origin of droplet size underprediction in modeling of low pressure nucleating flows of steam

This article examines deficiencies in nucleation rate and droplet growth models that impair modeling of low pressure (LP) nucleating flows of steam. It is shown that classical nucleation theory (CNT) exhibits excessive dependence on supersaturation in the operating range of LP condensing (wet-steam) flows. The complex mechanisms of the nucleation-growth model are explained with regard to discrepancies in the modeling results. The discrepancy between modeling results and LP wet-steam experiments is attributed to imprecision in CNT and inadequacies in the employed droplet growth equation. The link between the excessive dependence of CNT on supersaturation and underprediction of the mean droplet size is explained. Two examples are given demonstrating that the inverse correlation between mean droplet size and nucleation rate can be moderated by rectifying and reducing the dependence of CNT on supersaturation. Moreover, prediction of mean droplet size is improved without modifying the location and magnitude of the condensation shock.