A flow regime map for condensation in macro and micro tubes with non-equilibrium effects taken into account

• Published in: International journal of heat and mass transfer 2019-03, Vol.130, p.893-900
• Main Authors: Xiao, Jiange, Hrnjak, Pega
• Format: Article
• Language: English
• Subjects: Condensation; Dimensionless numbers; Flow control; Flow mapping; Flow regime map; Flow regime transition mechanism; Heat transfer; In-tube condensation; Microchannels; Non-equilibrium; Shear forces; Surface tension; Tubes
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2018.10.081

•Flow regime transitions described and modeled.•A new flow regime map developed for macro and micro tubes.•Advantages over a conventional flow regime map elaborated.•Flow visualizations are found to be in good agreement with the flow regime map. A flow regime map for condensation from superheated vapor is proposed in this paper. The flow regime map takes the non-equilibrium effects into account by following the development of liquid film from the real onset of condensation to the end. It can be applied to both conventional tubes and microchannels. The transition mechanism between annular and stratified-wavy flow is determined to be the force balance between the shear force, gravity and surface tension. The transition mechanism from annular to intermittent flow is found to be the comparison between wave heights and tube diameter. The transition mechanism for stratified-wavy and fully-stratified is kept the same as elaborated by Xiao and Hrnjak (2017). The connections between the dimensionless number We, Fr and Bo and the transition criteria are analyzed. The flow regime map is validated by the experimental data in Xiao and Hrnjak (2017) and some current visualizations, which includes diabatic visualizations of R134a, R1234ze(E), R32, R245fa and R1233zd(E) condensing at 30 and 50 °C in 1, 4 and 6 mm tubes.