Stratified flow model for convective condensation in an inclined tube

Abstract

Experimental data are reported for condensation of R134a in an 8.38 mm inner diameter smooth tube in inclined orientations with a mass flux of 200 kg/m²s. Under these conditions, the flow is stratified and there is an optimum inclination angle, which leads to the highest heat transfer coefficient. There is a need for a model to better understand and predict the flow behaviour. In this paper, the state of the art of existing models of stratified two-phase flows in inclined tubes is presented, whereafter a new mechanistic model is proposed. The liquidvapour distribution in the tube is determined by taking into account the gravitational and the capillary forces.The comparison between the experimental data and the model prediction showed a good agreement in terms of heat transfer coefficients and pressure drops. The effect of the interface curvature on the heat transfer coefficient has been quantified and has been found to be significant. The optimum inclination angle is due to a balance between an increase of the void fraction and an increase in the falling liquid film thickness when the tube is inclined downwards. The effect of the mass flux and the vapour quality on the optimum inclination angle has also been studied.

The influence of inclination angle on void fraction and heat transfer during condensation inside a smooth tube

“…The experimental system (Figure 1) was inherited from past research work in which detailed descriptions and explanations have been provided (Adelaja et al, 2014a(Adelaja et al, , 2014bCanière et al, 2007;Lips and Meyer, 2012a, 2012b, 2012cMeyer et al, 2014;Suliman et al, 2009;Van Rooyen et al, 2010). Therefore, only a brief overview will be provided in this section.…”

An Empirical Model to Predict the Transition Between Stratified and Nonstratified Gas–Liquid Two-Phase Flow in Horizontal and Downward Inclined Pipes

“…The recent void fraction modeling work of Bhagwat and Ghajar [11] shows that their flow pattern-and pipe orientationindependent model accurately predicts the void fraction for all flow patterns except the stratified flow. On a similar note, Lips and Meyer [12] identified the shortcomings of the existing twophase flow models and justified a need of stratified flow patternspecific model to determine two-phase heat transfer coefficient in convective condensation in downward inclined tubes.…”

Condensation heat transfer in smooth inclined tubes for R134a at different saturation temperatures

“…Lips and Meyer [14][15][16], in their study of convective condensation of R134a in a smooth tube of inner diameter of 8.38 mm, mean vapour qualities of 0.1 -0.9, mass flux of 200 -400 kg/m 2 s for the whole range of inclination angles at saturation temperature of 40°C, reported a significant influence of inclination angle on heat transfer especially at low mass fluxes and low mean vapour qualities. In their study, optimum inclination angles of -15° and -30° (downward flow) were obtained.…”

“…In summary, the most comprehensive work of convective condensation in inclined tubes was done by Lips and Meyer [14][15][16]. At different inclination angles they reported experimental measurements of heat transfer coefficients, pressure drop, mean vapour qualities, mass fluxes, and photos of the flow regimes.…”