In external vapor condensation with noncondensable gases (NCG) present, horizontal tubes are preferred to vertical ones because they minimize condensate film resistance, thus mitigating somewhat the negative impact of NCG. Heat transfer correlations are available for forced [1] or free convection [2] flows. However, no equivalent correlations exist for the important mixed convection regime. In this work, we aim at developing and validating such a correlation.
As mixed convection data are scarce, we first present a detailed CFD model with which we verify the integral correlation. The CFD predictions are validated against databases [3, 4] which include some tests where buoyancy effects are important. Excellent agreement between the CFD model and the data is observed. Subsequently, we present an integral solution which generalizes the correlation by Rose [1] for pure forced flows. The correlation is validated with the CFD model, and very good agreement is found. Finally, our solution is compared to the free convection correlation [2] in dominant buoyancy flows with Richardson numbers >5. The solution converges accurately to the free convection correlation, highlighting its consistency and generality. Our correlation can thus be used over laminar flow regimes spanning free convection up to pure forced flows.