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uct.mines.eduuct.mines.edu
Experimental Study on Foam Generation in Tunneling Industry
Scott Jarriel, Dhrupad Parikh, Yuanli Wu, Dr. Mike Mooney, Dr. Nils Tilton
Foam in Tunneling2
Why condition soil?
Soil conditioning refers to the mixing of soil and conditioning agents, like foam, at the cutter head of the TBM to alter the soil properties.
Control face pressure
Reduce torque
Reduce wear of metallic parts
Improve workability
Reduce clogging
Image courtesy of BASF
Foam Generation
Image courtesy of BASFImage courtesy of BASF
3
Foam Generation: The Foam Gun
Air
Water + Surfactant
Inlet
Foam
Outlet
Air and Liquid Mixing
Beads or other filling
Foam Gun
4
Desired foam properties
“If the foam sticks to the palm of your hand while it is facing the ground that is great foam.”
• Operator’s Idea of Good Foam
5
• Qualitative Analysis of Good Foam Thewes et al. (2012) has defined certain requirements of foams
• High stability• Homogenous bubble size
However, little literature exists on the mechanical system that
generates the foam.
Motivation and Objectives
• The mechanics of foam generation are not fully understood.• Most studies assume foam is generated by turbulent
mixing.• Role of porous material not understood.
6
Motivations
Objectives• Understand the mechanisms of foam generation.
• Quantify the influence of system parameters on foam quality.
• Investigate competing role of turbulence and porous material on the creation of foam.
Image courtesy of BASF
Experimental Study on Foam Generation
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Foam generation system:
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Foam gun:
Qair
Q(water + surfactant)
Foam
Porous Material: Bead Diameter Pore Size Permeability
Geometry of the Foam Gun
• Length = 11 cm• Diameter = 1.5 cm
Outlet Inlet
Experimental Study on Foam Generation
Experimental Study on Foam Generation
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Porous media used for experiments Beads (1 mm, 2 mm)
2 mm1 mm
Experimental Study on Foam Generation
Pressurized Air In
Air Mass Flow Controller
Liquid Flow Controller
Tank Containing Water and Surfactant
Foam
G
un
Air to Pressurize Tank
Foam
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Measurement of Foam Properties
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Foam Bubble Size and Distribution:
Measure the foam bubble size and distribution under pressure
Foam Expansion Ratio (FER)
•We use an FER of 15, as an industry.
𝐹𝐸𝑅0=𝑉 𝑓𝑜𝑎𝑚
𝑉 𝑙𝑖𝑞𝑢𝑖𝑑¿𝑄𝑎+𝑄𝑙
𝑄𝑙
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Hypothesis• Many parameters affect foam generation, • Here, we focus on the influence of bead size and
flow rate on the bubble size distribution and foam stability.
• Initial Hypotheses:▫ Increased flow rates should decrease bubble size due to
turbulent mixing.▫ Increased bead size should increase bubble size.▫ Foam stability increases with decreasing bubble size.
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Bubble Size Analysis
• Distributions are “noisy.”
• 1mm beads produce a Gaussian (normal) distribution of bubbles.
• 2mm beads produce a Weibull distribution.
• Weibull distribution possibly due to foam gun edge effects.
0 0.1 0.2 0.3 0.4 0.5 0.60.0%
5.0%
10.0%
15.0%
20.0%
25.0%
30.0%
35.0%
40.0%Frequency distribution for 2mm beads
Qa2.6Qa3.8Qa5.8Qa7.4Qa8.3Qa9.7Qa10.7Qa12.5Qa13.8Qa15.5
Avg. Bubble diameter (mm)
Freq
uenc
y (%
)
-0.4 0.1 0.60.0%
5.0%
10.0%
15.0%
20.0%
25.0%
30.0%
35.0%
40.0%Frequency distribution with 1mm beads
Qa2Qa4Qa6Qa6.6Qa7.5Qa7.8Qa8.5Qa9.7Qa10.9Qa12.5Qa13.5Qa15.5
Bubble Diameter (mm)
Freq
uenc
y (%
)
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Bubble Size Analysis1 mm Bead Size Results
2 4 6 8 10 12 14 16 18-5.55111512312578E-17
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Avg. Bubble diameter VS Air flow rate for 1mm beads
1mm beads
Linear (1mm beads)
Air flow rate (slpm)
Avg.
Bub
ble
diam
eter
(mm
)
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Bubble Size Analysis1 mm Results vs 2 mm Results
0 2 4 6 8 10 12 14 16 18-5.55111512312578E-17
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Avg. Bubble diameter VS Air flow rate for 1mm & 2mm beads
1mm beads
Linear (1mm beads)
2mm beads
Linear (2mm beads)
Air flow rate (slpm)
Avg.
Bub
ble
diam
eter
(mm
)
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Stability of Foam
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Foam Half-Life [ t50 ]
Depends on: Surfactant Concentration Foam Expansion Ratio Surface Tension, Viscosity & Film Thickness
Time required for 50 % liquid to drain from the foam
Measured using a funnel.
Experimental Results: Foam Stability
0 2 4 6 8 10 12 14 16 184
5
6
7
8
9
10Half of foam for 1mm and 2mm beads
Half life 2mm beadsHalf life 1mm beads
Air flow rate (SLPM)
Hal
f lif
e (m
ins)
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Conclusions•Bead size significantly affects the bubble
size distributions.
•Flow rates have little to no effect.
•Both bead size and flow rates have an effect on foam stability.
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Looking Forward• Future tests will explore:▫Foam gun geometry (diameter and length)▫Foam gun filling▫Effect of higher pressures encountered in
underground conditions▫FER▫Surfactant concentrations
• Long term, we hope to eventually tailor foam properties to varying soil conditions and allow for more efficient and effective underground tunneling.
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Thank you