CONCLUSIONS

Liquid film properties such as viscosity and surface tension affect the liquid mass separation of a shear-driven liquid film at the sharp corner through changes in LAW forma- tion and film inertia. Liquid film separation from the corner is then due to two mechanisms:

1) the force imbalance between inertial force and restoring forces such as surface tension and gravity at the point of separation, and 2) formation of LAWs at the interface with considerable mass content with respect to the mean film layer, which results in more liquid mass separation .

For constant gas and liquid flow rates, increasing the viscosity decreased the liq- uid mass separation at the sharp corner. Higher viscosity decreased the inertial force and consequently the force imbalance at the corner by influencing liquid film mean properties. Also, the LAW mass content at the interface prior to the corner decreased by increasing the viscosity due to wave attenuation.

The surface tension influence on the liquid mass separation was more complex. First, the decrease in surface tension resulted in dramatically higher F R values compared to the viscosity test. This occurred since for the large corner angles, the dominant restoring force was the surface tension. The liquid mass separation results showed that despite the fact that LAW formation was weaken by decreasing the surface tension, the liquid mass separation increased. This may be explained by the increase in the mean film inertia as demonstrated in the F R at the corner. Finally, while a reduction in surface tension reduced LAW formation, those that did form grew faster with axial position.

These results clearly show that neither the inertia of the uniform film layer nor the formation of LAWs can fully describe the film separation at the corner. Liquid mass sep- aration models must consider both the mean film as well as the wavy layer in considering the impact of liquid properties on liquid film separation.

NOMENCLATURE

U Velocity Û

Qf Liquid Volume Flow Rate hf Liquid Film Mean Thickness Wf Film Width

72 Re Reynold number ρ Density µ Viscosity σ Surface Tension W e Weber number f liquid film g gas REFERENCES

Alekseenko, S. V., Cherdantsev, A. V., Cherdantsev, M. V., Isaenkov, S. V., Kharlamov, S. M., and Markovich, D. M., ‘Formation of disturbance waves in annular gas- liquid flow,’ in ‘Proc. of 17th International Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon,’ 2014 .

Andreussi, P., Asali, J., and Hanratty, T., ‘Initiation of roll waves in gas-liquid flows,’ AIChE journal, 1985, 31(1), pp. 119–126.

Arai, T. and Hashimoto, H., ‘Disintegration of a thin liquid sheet in a concurrent gas stream,’ Heat Fluid Flow, 1985, 20, pp. 507–512.

Bacharoudis, E., Bratec, H., Keirsbulck, L., Buchlin, J.-M., and Labraga, L., ‘Simpli- fied Model for the Prediction of the Occurrence of Film Atomization in Corner Geometries,’ International Journal of Multiphase Flow, 2014, 58, pp. 325–337. Bruno, K. and McCready, M., ‘Origin of roll waves in horizontal gas-liquid flows,’ AIChE

journal, 1988, 34(9), pp. 1431–1440.

Craik, A. D., ‘Wind-Generated Waves in Thin Liquid Films,’ Journal of Fluid Mechanics, 1966, 26(2), pp. 369–392.

Friedrich, M. A., Lan, H., Wegener, J., Drallmeier, J., and Armaly, B. F., ‘A Separation Criterion with Experimental Validation for Shear-Driven Films in Separated Flows,’ Journal of Fluids Engineering, 2008, 130(5), p. 051301.

Hanratty, T., ‘Interfacial Instabilities Caused by Air Flow Over a Thin Liquid Layer,’ Waves on Fluid Interfaces, 1983, 11(1), pp. 221–259.

Hoogendoorn, C., ‘Gas-liquid flow in horizontal pipes,’ Chemical Engineering Science, 1959, 9(4), pp. 205–217.

Nakamura, H., ‘Slug Flow Transitions in Horizontal Gas/Liquid Two-Phase Flows (De- pendence on Channel Height and System Pressure for Air/Water and Steam/Water Two-Phase Flows),’ Research/Japan atomic energy research institute (Tokyo), 1996, 96, p. 022.

O’rourke, P. and Amsden, A., ‘A particle numerical model for wall film dynamics in port- injected engines,’ Technical report, SAE Technical Paper, 1996.

Owen, I. and Ryley, D., ‘The Flow of Thin Liquid Films around Corners,’ International Journal of Multiphase Flow, 1985, 11(1), pp. 51–62.

Pereira, A. and Kalliadasis, S., ‘Dynamics of a falling film with solutal Marangoni effect,’ Physical Review E, 2008, 78(3), p. 036312.

Setyawan, A. et al., ‘The effect of the fluid properties on the wave velocity and wave frequency of gas–liquid annular two-phase flow in a horizontal pipe,’ Experimental Thermal and Fluid Science, 2016, 71, pp. 25–41.

Shedd, T. A., ‘Characteristics of the liquid film in horizontal two-phase flow,’ Technical re- port, Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign., 2001.

74

Thwaites, G., Kulov, N., and Nedderman, R., ‘Liquid film properties in two-phase annular flow,’ Chemical Engineering Science, 1976, 31(6), pp. 481–486.

Wang, Y., Wilkinson, G., and Drallmeier, J., ‘Parametric Study on the Fuel Film Breakup of a Cold Start PFI Engine,’ Experiments in Fluids, 2004, 37(3), pp. 385–398. Wegener, J., Experiments and Modeling of Shear-Driven Film Separation, MS Thesis,

Missouri University of Science and Technology, Rolla, MO, 2009.

Weisman, J., Duncan, D., Gibson, J., and Crawford, T., ‘Effects of fluid properties and pipe diameter on two-phase flow patterns in horizontal lines,’ International Journal of Multiphase Flow, 1979, 5(6), pp. 437–462.

Whitaker, S., ‘Effect of surface active agents on the stability of falling liquid films,’ Industrial & Engineering Chemistry Fundamentals, 1964, 3(2), pp. 132–142.

Wittig, S., Himmelsbach, J., Noll, B., Feld, H., and Samenfink, W., ‘Motion and evaporation of shear-driven liquid films in turbulent gases,’ in ‘ASME 1991 International Gas Turbine and Aeroengine Congress and Exposition,’ American Society of Mechanical Engineers, 1991 pp. V003T06A017–V003T06A017.

Zadrazil, I., Matar, O. K., and Markides, C. N., ‘An Experimental Characterization of Down- wards Gas-liquid Annular Flow by Laser-Induced Fluorescence: Flow Regimes and Film Statistics,’ International Journal of Multiphase Flow, 2014, 60, pp. 87–102. Zhang, Y., Jia, M., Duan, H., Wang, P., Wang, J., Liu, H., and Xie, M., ‘Experimental and

numerical study of the liquid film separation and atomization at expanding corners,’ Technical report, SAE Technical Paper, 2017.

Zhao, Y., Markides, C. N., Matar, O. K., and Hewitt, G. F., ‘Disturbance Wave Development in Two-Phase Gas-Liquid Upwards Vertical Annular Flow,’ International Journal of Multiphase Flow, 2013, 55, pp. 111–129.

III. EXPERIMENTAL MASS SEPARATION MAP FOR SHEAR-DRIVEN LIQUID