Dynamics of Evolving Fluid Interfaces DEFI, 2016 Experimental analysis of the hydrodynamics and mass transfer of Taylor flow in small channels Mohammad R. Haghnegahdar, Stephan Boden, Uwe Hampel 12.10.2016 page 1 Prof. Peter Mustermann Institute I of Institute Fluid Dynamics of xxxxx I I www.hzdr.de
Outline Introduction & Motivation Experimental setup Mass transfer calculation Results Conclusion Page 2
Taylor bubble/taylor Flow Dominant flow within a large range of flow and operating conditions Ideal flow regime to improve heat & mass transfer Liquid film Fixed gas liquid interface Narrow residence time distribution Uniformly dispersed gas bubbles Liquid slug Taylor bubble Capillary High recirculation and mixing in the liquid Low axial dispersion and back mixing along the channel Page 3
Application of Taylor flow Reaction engineering Microfluidics Monoliths Vehicle engine emission converter Catalytic combustion of methane Hydrogenation of aromatic compounds Heat transfer applications Miniaturized heat exchangers Glass microreactor, amarequip.com Diesel soot catalytic reduction device (SCR) Micromesh reactor Hessel et al. 2005 Rectangular channel (height = 70 micron) Page 4
Literature review Wide attention on the Microchannels: Bubble formation process (Fu et al., 2009; Garstecki et al., 2006; Pohorecki and Kula, 2008; van Steijn et al., 2007, ) Gas bubble and the liquid slug length (Garstecki et al., 2006; Leclerc et al., 2010; Qian and Lawal, 2006; Sobieszuk et al., 2010, ) Liquid film thickness around bubbles (Fries et al., 2008; Han and Shikazono, 2009a; Thulasidas et al., 1995, ) Phase distribution (Choi et al., 2011; Kawahara et al., 2005; Saisorn and Wongwises, 2010, ) Pressure drop (Kreutzer et al., 2005a, 2005b; Yue et al., 2009, ) Mass transfer (Sobieszuk et al., 2011; van Baten and Krishna, 2004; Vandu et al., 2005, )... Open fields Process control Optimization The relation between Mass transfer & Hydrodynamics (liquid flow field, bubble motion, ) Page 5
Objective In this study Presence of surfactant The shape and mass transfer rate of an individual Taylor bubble Measured parameters Bubble rise velocity (u b ) Bubble surface area (A b ) Bubble volume & its dynamics (V b, dv b /dt) Technique Microfocus X-ray technique High resolution Rather fast Independent on refractive index: most accurate in comparison with other conventional optical methods Allows tomography for square channels: full 3D shape determination by optical techniques is difficult Non-transparent phases & channels Page 6
Experimental Set up 6 2 1 3 5 8 M 9 4 7 10 11 1. observation section 2. microfocus X-ray source 3. flat panel X-ray image detector 4. rotary table 5. remotely controlled motorized needle valve 6. upper reservoir 7. lower reservoir 8. video camera 9. injection needle 10. fast solenoid valve 11. gas cylinder Channel: Hydraulic diameter: Cross section: Flow Regime: Liquid: Gas: Bubble motion: Gas bubble injection: Liquid flow control: Glass capillary 6 mm, 8 mm Circular, Square Single Taylor bubble De-ionised water CO 2, O 2, Air buoyancy driven Fast solenoid valve Motorized needle valve Haghnegahdar et al. 2015a Page 7
Injecttion & Adjustment of bubble position 2 1 3 5 Adjustment of bubble position 8 M 9 4 10 11 7 Pulse-controled fast solenoid injector valve Injecttion of single bubble Joystick controller of the remotly driven motorized needle valve Page 8
X-ray Visualisation Measurement of Taylor bubble shape (and their dynamics) based on X-ray visualisation techniques: X-ray Radioscopy Volume V b Bubble shape Surface area A b Investigation of Mass Transfer based on volumetric transfer rate over time Length L b Page 9
Mass transfer study for CO 2 d h = 6 mm Long term dissolution of CO 2 bubbles with different initial volumes CO 2 : High soluble gas in water time Bubble volume (cm 3 ) 0,5 0,45 0,4 0,35 0,3 0,25 0,2 0,15 V 0 = 0.347 cm 3 # 73 V 0 = 0.427 cm 3 # 71 V 0 = 0.313 cm 3 # 87 0,1 CO 2 N 2, O 2, 0,05 0 0 10 20 30 40 50 60 70 t (s) Counter-diffusion of solved gases from the liquid into the bubble Initial bubble size dictates final bubble volume Page 10
Processed bubble images Bubble images from three dimensional calculations in 6 mm circular capillary Bubble volume (cm3) d eq (mm) 9.60 V (cm 3 ) 0.463 d eq (mm) 8.66 V (cm 3 ) 0.340 d eq (mm) 7.33 V (cm 3 ) 0.206 dd eeee = 6 ππ VV bb 1 3 d eq (mm) 6.31 V (cm 3 ) 0.131 d eq (mm) 5.23 V (cm 3 ) 0.075 V b (t) A b (t) A eq (t) L b (t) dv b /dt (t) d eq (mm) 4.61 V (cm 3 ) 0.052 Page 11 0 5 10 15 20 25 30 35 time (s) d eq : sphere-volume equivalent diameter: the diameter of a spherical bubble with same volume
Mass transfer calculation Mass balance for CO 2 dddd dddd = kk llaa CC CC CO 2 Henry s law Pressure dddd dddd = kk llaa CC LLPPPP HH PPPP PP = PP aaaaaa + ρρ LL ggh + 4σσ dd eeee kk ll = 11 HH PP dddd AAAAAA CC LL PP dddd Ideal gas law dnn dtt = PP dddd RRRR dddd n: total moles of gas phase (CO 2 ) inside the bubble t: time C*: concentration of gas at interface C: concentration of gas at the liquid bulk H: Henry s constant C L : water concentration y: mole fraction of CO 2 inside of gas phase P: pressure inside of the bubble P atm : atmospheric pressure h: distance from the liquid surface R: universal gas constant T: bubble temperature K l : mass transfer coefficient V: volume of bubble Page 12
Surfactant (SURFace ACTive agant) Triton X-100 (C8H17C6H4(OCH2CH2)10OH) MW: 647 g/mol CMC: 240 mmol/m 3 detergent in laboratories Page 13
Bubble shape and movement clean contaminated Triton X-100 6.5 ppm Page 14
Bubble rise velocity 30 White and Beardmore [50] U b / mm/s 25 20 15 Clean water Contaminated water Triton X-100, 6.5 ppm 10 5 D = 7.96 mm 4.0 < d eq < 15 mm sodium dodecyl sulfate (SDS) 0 4 6 8 10 12 14 16 18 20 L b / mm Almatroushi & Borhan, 2004 Haghnegahdar et al. 2016 Page 15
Liquid film thickness- film thickening effect d h = 6 mm -1 Liquid film thickness contaminated 1 Liquid film thickness clean 3 clean contaminated 5 z (mm) 7 9-3,1 0 3,1 r (mm) 11-3 -2-1 0 r (mm) Page 16
Liquid film thickness- film thickening effect Page 17
Mass transfer coefficient k L (m/s) 4,0E-04 3,5E-04 3,0E-04 2,5E-04 2,0E-04 Triton X (6.5 ppm) Triton X (1.3 ppm) Clean water 45-58% reduction in k L 1,5E-04 1,0E-04 25-35% reduction in k L 5,0E-05 Surfactant concentration 0,0E+00 0,6 0,8 1 1,2 1,4 1,6 1,8 d eq /D SSSSSSSSSSSSSS cccccccccccccccc rrrrrrrrrr (SSSS) = interfacial surfactant concentration at equilibrium saturated interfacial surfactant concentration 1.3 ppm Triton X 6.5 ppm Triton X Se 0.75 0.94 Page 18
Conclusions A laboratory based X-ray radioscopic/tomographic measurement technique to measure bubble shape and shape dynamics has been set up Long time overall mass transfer was measured for dissolving CO 2 Taylor bubbles Significant differences in dissolution behaviour in celan and contaminated liquids were observed Data eventually will help to validate CFD models Page 19
Thank you! Page 20
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3D Tomographic reconstructions of stabilized Taylor bubbles 6 mm Channel wall bubble Liquid film V (cm 3 ) 0.196 Circular channel Page 22