EXPERIMENTAL INVESTIGATION ON CONDENSATION IN CORRUGATED LOW FINNED TUBES IN PRESENCE OF NONCONDENSABLE GAS

The phenomenon of condensation with noncondensable gas widely exists in many industrial processes. In this paper, the effect of noncondensable gas on condensation heat transfer inside corrugated low finned tubes is investigated experimentally. Air is mixed into steam playing the role of noncondensable gas. The effects of gas mixture inlet conditions and condensation tubes structural parameters are investigated. The results show that the influence mechanism inside corrugated low finned tubes is similar with that inside smooth tubes. The heat transfer coefficient decreases as noncondensable gas fraction increases. However, the decreasing rate is gradually reduced. Increasing inlet mass flux could enhance the heat transfer coefficient especially at small heat transfer rate. And the heat transfer coefficient decreases with the increase of inlet pressure. The heat transfer coefficients inside smaller pitches tubes are higher than that inside larger pitches tubes, and the declining rate is also slightly faster. When the noncondensable gas fraction is large enough, the difference of heat transfer coefficients between different enhanced tubes can be ignored. Tube with the largest protrusion height has the highest heat transfer coefficient. And the gap of heat transfer coefficients between different protrusion heights is larger than that between different pitches. This shows that the protrusion heights have greater influence on condensation compared with pitches.