Steam condensation in the presence of non-condensable gas inside a nearly horizontal tube under separated flow

Abstract

An experiment for steam condensation in the presence of a non-condensable gas was conducted in a nearly horizontal tube with an inner diameter of 40 mm and a downward slope of 3°. The multi-dimensional distributions of the local air–steam mixture temperature and heat transfer coefficient were measured in the stratified and annular flow regimes. The influence of the non-condensable gas on the local heat transfer coefficient was investigated by varying the inlet steam mass flux, air mass fraction, and pressure. It was found that the film-wise condensation appearing in the upper region of the tube was significantly deteriorated by the air layer near the wall, but little effect was observed in the convective heat transfer by the condensate accumulated in the lower region. The degradation effect on the condensation increased further downstream due to the air accumulation near the cold wall. In addition, an empirical correlation for the degradation factor of the condensation heat transfer coefficient was developed, and it showed a mean absolute error of 10.4% against the circumferential average heat transfer coefficient of the present experimental data. This correlation is applicable to separated flow covering inlet air mass fractions of 0.01–0.56, pressures of 1–5 bar, and inlet air–steam mixture Reynolds numbers of 7,500–166,000.