Bubbly Flow

Bubbly Flow

Bubbly Flow

Interaction between bubble and background liquid is a canonical but still fascinating problem. Especially, we are mainly focused on the effects of agitation induced by bubble on mass, momentum and heat transfer which are existing in Energy and Propulsion System (e.g., nuclear power plant), Processing System (e.g., liquid chemical reactor, bioreactor, air-lift system), and Biological and Environmental System (e.g., waste water treatment, weather change, destratification of lake). Understanding their physics is very important because of the significant impact on the safety and efficiency of the thermal-fluid and environmental systems listed above.

1. Dual-nozzle Atomization

Experiment setup for upward bubbly pipe flows.

Experimental techniques for visualizing the flow structure of the turbulent bubbly flow

- Laminar flows

Vortical structures in upward laminar bubbly flows and bubble path

Mean vertical velocity of liquid phase in upward laminar bubbly flows

- Turbulent flows

Analysis of turbulence induced by bubbles using Discrete wavelet transfrom (DWT)

Turbulence statistics of upward turbulent bubbly flows.

Scale-wise energy transfer for the pipe flow

2. Turbulence and fluid mixing induced by bubble plume

Bubble plume is a common system in nature and industry. It has been used for chemical reactor and oil mixing. Also, it is found in natural gas seeps and underwater oil spill.

To achieve a better understanding of the system and establish a model which describes a relation between initial gas condition and the resultant liquid turbulence and fluid mixing, we experimentally and theoretically study the turbulence and fluid mixing induced by bubble plume.

We are answering questions as below :

  1. What determines the mixing type?

  2. What is the effect of the individual bubble motion and collective plume motion?

  3. What is the relation between the bubble motion and resultant fluid mixing?

  • We are answering questions as below :

  1. What begins collective plume motion?

  2. What is the effect of the individual bubble motion and collective plume motion?

  3. What is the relation between the bubble motion and resultant liquid turbulence?

  • We are answering questions as below :

  1. What determines the mixing type?

  2. What is the effect of the individual bubble motion and collective plume motion?

  3. What is the relation between the bubble motion and resultant fluid mixing?

3. Turbulent bubble-swarm external flows

Experimental setup for bubbly flow over a circular cylinder and bubble generation system

Instantaneous two-phase flow contour of the normalized vorticity around a circular cylinder (D=20mm); volume void fraction of 0.6%(Left) and 1.1%(right)

Contour of time-averaged void distributions in the cylinder (D=20mm) wake

Turbulent nature of the pure bubble-induced turbulence in (a),(c) streamwise and (b),(d) transverse directions, measured (a),(b) inside and (c),(d) outside the wake behind the cylinder

4. Micro-size bubble dynamics in viscous fluid

Experimental setup ( bubbles with a size of 20-3000μm in water or glycerol/water mixture having a viscosity 1-100cP in a vertical circular tube)

Equilibrium radial positions of bubbles in water. The predicted equilibrium radial positions indicated by dashed lines

5. Development bubble detecting/measuring sensor

(a) Schematic diagram of the test-section with a single-layer wire-mesh sensor(WMS); (b) Actual picture of the WMS

Temporal variation of normalized conductance(g/go) signal induced by a millimeter- (solid) and a micro-sized bubble (dotted), contacting at the position near (T1,R4) and (T5,R4) nodes

(a) Schematic diagram of the test-section with a single-layer wire-mesh sensor(WMS); (b) Actual picture of the WMS

Temporal variation of normalized conductance(g/go) signal induced by a millimeter- (solid) and a micro-sized bubble (dotted), contacting at the position near (T1,R4) and (T5,R4) nodes

5. Development bubble detecting/measuring sensor

Experimental setup

Interface according to colliding angle

Colliding angle vs. escape time, interface hight (10cP silicone oil)

PIV result according to colliding anlge

7. Bubble chain

Experimental setup

Bubbles trajectories

Pdf for oscillation trajectories of bubbles

PIV raw image for 2-dimensional bubble chain; 45mm<z<100mm(left), 140mm<z<200mm(middle), 310mm<z<370mm(right)

Raw image of bubble shadowgraphy for 3-dimensional bubble chain with various bubble generation frequency(single – 30Hz)

8. The rising bubble dynamics

Experiment setup for the rising bubble dynamics

Vortical structures behind a deformable rising bubble near the wall

The trajectory of a rising bubble

8-1. Heat transfer by a single bubble wake rising near vertical heated wall

Experimental setup and representative raw image from 2-phase PIV and definition of bubble geometry

Temporal variation of wall Nusselt number and corresponding 2-phase flow at S*(normalized bubble-wall distance)=1.5

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