Experimental investigation of the steam condensation heat transfer in the presence of non-condensable gas inside a vertical tube

A condensation inside a vertical tube was experimentally studied under both pure steam and air-steam mixture conditions ranging 100–750 kPa of the pressure, 7.5–50 kg/m2s of the inlet steam mass flux, and the inlet air mass fraction up to 0.5. The detailed distributions of the local heat flux, condensation heat transfer coefficient, and air mass fraction were measured and analyzed along the radial and axial directions according to the axial change in steam quality. The effect of the inlet steam mass flux, pressure, and air mass fraction on the local heat transfer coefficient was comprehensively discussed in relation to the accumulation of the condensate film and air layer. Based on the present data, a new prediction model for the film condensation heat transfer coefficient was proposed with the empirical correlation factors accounting for the entrance effect, condensate convection, and degradation of condensation by the non-condensable gas. The proposed model showed 4.0 % and 6.6 % of relative mean absolute errors for pure steam and air-steam mixture condition, respectively. It also provided a satisfactory accuracy with overall 28–37 % of relative mean absolute errors in the evaluation including the existing experimental data (D = 7.5–47.5 mm, Pin = 0.031–7.46 MPa, Gs.in = 1.3–456 kg/m2s, wnc.in = 0–0.42), showing a noticeable improvement over the existing empirical models. •Detailed distribution of local air mass fraction and heat transfer coefficient.•Non-condensable gases tend to accumulate near the wall and outlet regions.•The condensation heat transfer enhances with increasing steam mass flux.•The pressure effect is insignificant except for the low-pressure conditions.•A new film condensation model outperformed other existing empirical correlations.