A DROPLET MODEL IN DROPWISE CONDENSATION WITH THE PRESENCE OF NON-CONDENSABLE GASES

A droplet model is proposed with respect to molecular clustering to describe the state of steam molecules before condensing on the cooled solid surface in steam condensation process, and also the model is used to account for the mechanism of steam dropwise condensation in the presence of non-condensable gases (NCG). The mathematical model is presented based on the Dillmann and Meier's homogeneous nucleation theory. Correction of surface tension term is conducted to match the physical and chemical characteristics of condensation process, and the heat transfer model considering the effect of interfacial effects was used to calculate the mean temperature of clusters. The model predicted results of Gibbs free energy at different subcooling degrees and different saturated temperatures were given. And the ratio of heat transfer coefficient with to that without NCG with different fractions of NCG was also obtained. The results show that the non-condensable gases reduce the condensation rates in the same way as shown by experimental results in the literature. That confirms the validity of the model.