Determination of flow regimes and heat transfer coefficient for condensation in horizontal tubes

This study explores condensation of FC-72 in horizontal tubes. Using high-speed video motion analysis, dominant condensation flow regimes are identified for different combination of mass velocities of FC-72 and cooling water. Additionally, detailed heat transfer measurements are used to explore both axial and circumferential variations of the condensation heat transfer coefficient. Four different regimes are identified: stratified, stratified-wavy, wavy-annular with gravity influence, and wavy-annular without gravity influence. In the latter regime, which is achieved at high FC-72 mass velocities, annular film transport is dominated by vapor shear with negligible gravity effects. Using different types of regime maps, prior relations for transitions between regimes are assessed, and new, more accurate transition relations developed. The heat transfer coefficient is shown to be highest near the inlet, where quality is near unity and the film thinnest, and decreases gradually along the condensation length because of axial thickening of the liquid film. This study also explores the predictive capabilities of prior heat transfer correlations and a control-volume-based annular flow model. The experimental data of both the local and average condensation heat transfer coefficients show fair to good agreement with predictions of prior and popular correlations. But superior predictions in both trend and magnitude are achieved with the annular flow model.