1. Experimental Characterization of Gas-Liquid Column:
Effect of nozzle orientation and pressure
by Peter Spicka
CREL group regular meeting, November 26th
CHEMICAL REACTION ENGINEERING LABORATORY

2. Objective
Study the sparger nozzle orientation effect on gas hold-up, liquid velocity and turbulence in gas-liquid column
Motivation
Only few data, i.e. liquid velocity and gas holdup, available in the literature for churn-turbulent flow regime
CARPT and CT techniques allow relatively accurate acquisition of needed data
Different pressures and UGS can be covered
Additional experimental database for CFD simulations can be created

3. Experiment 6.375” stainless steel column
Cross-sparger, two nozzle orientations: facing upward and downward
Air-water system
Dynamic height maintained at 11 D
Pressure: 1 bar and 4 bars
UGS= 5 cm/s (only CT) and 20 cm/s
CARPT setup
Typical setup, 30 detectors
Only photo peak acquisition
50 Hz sampling frequency
CT setup
5 detectors, 7 projections per view
4 axial levels: 2.5D; 3.5D; 5.5D; and 9D
20 Hz sampling frequency

4. Detector alignment and calibration
CT CARPT

5. CT Results Effect of Nozzle Orientation- Global View
Gas holdup at UGS=20 cm/s and p=1 bar
nozzles facing downward nozzles facing upward
Bubbles formed from nozzles facing upward are smaller Þ increased hold-up
Similar behavior was found for all the studied regimes

6. CT Results Effect of Nozzle Orientation and Pressure
Gas holdup profiles
UGS=5 cm/s UGS=20 cm/s
Nozzle orientation
particularly pronounced at high pressure and high UGS in the sparger zone
diminishes with axial position
Pressure
Typical increase of gas holdup magnitude

7. Axial velocity profiles Radial velocity profiles
CARPT Results
Liquid velocity
Steeper velocity profiles observed at high pressure Þ higher bubble momentum
However, effect of nozzle orientation on liquid velocity is visible only at near-sparger region

8. Comparison with Boon Cheng’s data
Liquid velocity calculation
CARPT processing algorithm considers uniform time step
However, relatively large amount of data is excluded from calculation (25% and more)
Time step is non uniform
Calculated velocity will be biased towards higher values
Comparison with Boon Cheng’s data

9. Nozzles facing down Nozzles facing up
CARPT Results
Turbulent kinetic energy
Nozzles facing down Nozzles facing up
p= 1 bar p = 4 bars p = 1 bar p = 4 bars
Turbulent kinetic energy is higher for nozzles pointing downward and at higher pressure
Nozzle effect is significant mainly at low pressure
Significant effect of bubble-induced turbulence

10. CARPT Results Reynolds stresses
u’xu’x are approximately 2.5 x higher than u’ru’r and they are weakly coupled
Magnitude of u’xu’x is comparable with the corresponding mean velocities
Highly anisotropic flow !

11. Concluding Remarks Outlook for future
Nozzle orientation
Significant effect on gas holdup and turbulent kinetic energy mainly near the column bottom
More pronounced at high UGS and high pressure
Effect on liquid velocity profiles is less significant
Uncertainty in magnitude of turbulent parameters due to gas holdup fluctuations
Outlook for future
Filtering
Elimination of gas holdup fluctuations from CARPT data
CFD
Examination of nozzle orientation effect in churn-turbulent regime