DILUTE SUSPENSION FLOW: AN EXPERIMENTAL AND MODELING STUDY

Jennifer Sinclair CurtisChemical Engineering, University of Florida

Center for Particulate & Surfactant Systems (CPaSS)IAB Meeting

Columbia University, New York CityAugust 20, 2009

Relevance and Impact

Slurry flows are prevalent across a diverse range of industrial and geophysical processes• Transport lines for chemicals, minerals and ores• Debris flows and sediment transport

Non-homogeneous slurries often have problems with settled, stationary particles which can cause pipeline blockage

Current approaches to pipeline operation and design are largely empirical

Pumping systems account for nearly 20% of the world's electrical energy demand and are typically responsible for 25-50% of the energy usage in industrial plant operation

Objectives

Via a combined effort of CFD simulations and non-intrusive experimentation, the project will develop a fundamental modeling tool which can be used for:

• Prediction of the critical settling velocities in pipeline operation in dilute-phase flow leading to reduced shut down times

• Improvement in design of new slurry lines

• Increasing operating efficiency of existing lines, resulting in higher solids flow and lower energy costs

…….as a function of the particle properties of the material to be conveyed

Research Background

Fluid-particle flows involve complex interactions between fluid and particles that influence solids distribution and motion

For fluid-particle flows that are not treated as a homogeneous suspension, previous work (both experimental and modeling) has focused exclusively on extremes of viscous-dominated flow or inertia-dominated flow regime (e.g. gas-solid flows with larger particles)

Work in this project emphasizes “transition flow regime” which characterizes non-homogeneous slurries

Viscous Flow Inertial Flow

f

psdd

Viscous

Collision

2/12

2/3

222

Number Bagnold

Research Methods/ Techniques

Experimentation• Pilot-scale slurry flow facility in the Particle S&T Building high bay area• Non-intrusive flow measurements via LDV/PDPA• Can accommodate a wide range of flowrates, particle sizes and solids concentrations (refractive index matching under dense-phase conditions)

Research Methods/ Techniques

CFD Modeling• Continuum-approach for the particle phase using kinetic theory concepts to describe particle-phase stress• Good success in many gas-solid flow applications• For liquid-solid flow, particle-phase stress is modified to include influence of a viscous liquid

Results – Completed Experiments

Particles: Glass Beads, 1mm and 1.5mm

Seed Particles to Trace Fluid: 1 micron hollow glass spheres

Particle concentration: 0.7%, 1.7%, 3%

Re: 200,000, 335,000, and 500,000

Bagnold Number range: 90 – 700

Measurements

Pressure Drop

Axial Mean Fluid and Solids Velocity Profiles

Axial Fluctuating Fluid and Solid Velocity Profiles

Solid Concentration Profiles

Results – Mean and Fluctuating Velocity

r/R

U/U

fc

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

ClearFluidSolid

Ba = 94

r/R

U/U

fc

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

ClearFluidSolid

Ba = 701

r/R

u'/u

t

0 0.2 0.4 0.6 0.8 10

0.5

1

1.5

2

2.5

3

3.5

4

ClearFluidSolid

r/R

u'/u

t

0 0.2 0.4 0.6 0.8 10

0.5

1

1.5

2

2.5

3

3.5

4

ClearFluidSolid

With increasing Ba,

Increase in mean slip velocity

Increase in particle velocity fluctuations

Increase in fluid turbulence

enhancement

Results – Solids DistributionBa = 94 Ba = 701

r/R

v/v c

0 0.2 0.4 0.6 0.8 10

5

10

15

20

25

r/R

v/v c

0 0.2 0.4 0.6 0.8 10

5

10

15

20

25

Increased solids concentration at the wall, similar to gas-solid systems

Future Plans

Order and set-up of upgraded LDV/PDPA equipment

Experiments with smaller particles and slightly higher solids concentrations

Begin model testing (in-house code, MFIX, and Fluent) using experimental data

AcknowledgementsPhD students Mark Pepple & Akhil Rao

NSF & CPaSS