Vapor free convection film condensation heat transfer in the presence of non-condensable gases with smaller molecular weights than the vapor

Abstract

Non-condensable gases seriously reduce the free convection film condensation heat transfer on surfaces with greater reductions when the gas molecular weight is smaller than that of the vapor (MNG < Mv) than when MNG > Mv. Thus, existing approximate heat transfer models for MNG > Mv cannot accurately predict the heat transfer for MNG < Mv. In this study, R11 free convection film condensation heat transfer on a horizontal tube outside surface was experimentally investigated in the presence of three non-condensable gases, N2, CO2 and R22, whose molecular weights are all smaller than that of R11. The results show that the heat transfer is sharply reduced at very low gas concentrations with smaller reductions at increasing gas concentrations. The condensation heat transfer reduction due to the gases with MNG < Mv is much stronger than that with MNG > Mv at low gas concentrations. The reductions for the two types of gases get closer with increasing gas concentrations. A heat transfer correlation was developed with 95% of the predictions within ±20% of the experimental data.