Film condensation in inclined tubes with noncondensable gases: An experimental study on the local heat transfer coefficient

An experimental investigation on the role of noncondensable gases during condensation of steam inside inclined tubes is presented. In a condenser, noncondensable gases flowing with steam cause reduction of condenser performance and efficiency. Many researchers have investigated in-tube condensation for vertical heat exchangers, but very few works have been performed to study condensation in inclined tubes with noncondensable gases. In the paper, experiments dedicated to this situation are described, with reference to the following conditions: tube internal diameter: 12.6 mm, 20 mm and 26.8 mm; tube inclination: 7°, 15°, 30° and 45°; inlet noncondensable gas mass fraction ωin = 2%–42%; inlet mixture Reynolds number Rem,in = 5000–20000; local noncondensable gas mass fraction ω = 2%–70%; local mixture Reynolds number Rem = 400–21000; local condensate Reynolds number Rel = 10–290; saturated steam at atmospheric pressure; and gravity controlled flow regime. A limited influence of the inclination angle on heat transfer coefficient has been observed. Correlations to evaluate the local heat transfer coefficient along inclined tubes, in a gravity controlled flow regime, have been developed and they are in good agreement with the experimental results.