Unsteady steam condensation flow patterns inside a miniature tube

Unsteady steam condensation inside a single miniature tube has been studied. The visualization of different instantaneous and periodically two-phase flow is conducted for different experimental conditions. The two-phase flow characterization is obtained using the image processing. Annular, slug bubbly, spherical bubbly, and wavy flows are observed by varying the steam inlet pressure and cooling heat transfer. The cycle of the periodically flows are compared. It is shown that increasing the cooling heat flow rate reduces the number of the instabilities and the injected bubbles. The axial vapor velocity decreases during the waves growth. The local distribution of the condensate film thickness is analyzed. It is shown that the liquid film becomes thinner near the meniscus-like interface because of the surface tension effect. The reverse annular flow is observed at the end of each periodic flow when the bubbles leave the channel. It can be concluded from experimental results that the stratification effect is not significant during the condensation inside the miniature tube. The capillary pressure evolution is measured. The maximum values are obtained in the waves locations and near the meniscus of the annular flow.