Film condensation heat transfer on a horizontal tube in presence of a noncondensable gas

The double boundary layer model has been developed to study the behavior of film condensation heat transfer outside a horizontal tube in presence of air treated as a noncondensable gas. And the coupled heat and mass transfer on a smooth horizontal tube is numerically solved with the finite difference method. The local mass concentration of the noncondensable gas, the distributions of velocity and temperature in the boundary layers are presented and discussed. The numerical results have shown that the mass concentration and velocity of the noncondensable gas increase from the bulk mixture to the interface while the temperature decreases from the bulk mixture to the interface. Although the mass concentration of the noncondensable gas in the bulk mixture could be small, the reduction in average heat transfer coefficient is obvious. The comparisons of heat transfer coefficient show that the numerical predictions agree well with available experimental data.

► We develop the double boundary layer model.
► We examine film condensation heat transfer in presence of noncondensable gas.
► We present local mass concentration, velocity and temperature in boundary layers.
► Low noncondensable gas causes large reduction of condensation heat transfer.
► Good agreement for heat transfer is achieved between numerical and experimental data.