# P R O B L E M # 1 5 BLOWING BUBBLES - PhysLab 2018-08-10¢  bubbles produced from single soap film and

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• I Y P T 2 0 1 8

P R O B L E M # 1 5

BLOWING BUBBLES T EA M PA K I S TA N

I F R A H M A H M O O D

• PROBLEM STATEMENT

• When blowing on a soap film in the ring, a bubble may be formed. The liquid film may pop or continue to exist. Investigate how the number of bubbles produced from a single soap film and the characteristics of the bubbles depend on the relevant parameters.

2

• 3

3

PRELIMINARY OBSERVATIONS

ANALYSIS

THEORY

EXPERIMENTAL SETUP

CONCLUSION

3

• 4

PRELIMINARY OBSERVATIONS

• 5

Preliminary Observations

• Soap film is formed due to the surfactant.

• Increasing detergent concentration reduces surface tension and large number of bubbles are blown.

• Number of bubbles reaches peak around 100%concentration of detergent.

• 10% of surfactant exhibits a small number of bubbles.

• We took many concentrations and observe the number of bubbles.

5

Relation of concentration with number of bubbles

• 6

0

5

10

15

20

25

30

0 20 40 60 80 100 120

N U

M B

ER O

F B

U B

B LE

S

PERCENTAGE CONCENTRATION OF DETERGENT%

number of bubbles

As the concentration increases the number of

bubbles increase

Relation of concentration with number of bubbles

• 7

• The film formed from the solution with maximum concentration (80%surfactant and 20%water) exists for 19.5s(approx.)

• Whereas the film formed from the solution of (20% surfactant and 80% water ) exists for 6.04s(approx.)

• Similarly the solution with concentration(50% surfactant and 50%) exists for long time 22.02s (approx.)and produce maximum bubbles per second.

• On other hand the film formed from the solution of minimum concentration (1%surfactant and 99%) lasts for 5.54s(approx.)

Preliminary Observations

7

Relationship of concentration of soap film with duration of soap film

• 8

0%

20%

40%

60%

80%

100%

5.54s 7.02s 22.02s 22.37s

C O

N C

ER N

TR A

TI O

N O

F D

ET ER

G EN

T

TIME PERIOD OF SOAP FILM

Relation of concentration with duration of soap film

• 9

Preliminary Observations Relationship of concentration of soap film with flowrate of air

14.03 15.67 16.44 17.79 19.01

0

20

40

60

80

100

120

0 1 2 3 4 5 6

Pe rt

en ta

ge c

o n

ce n

tr at

io n

o f

d et

er ge

n t

Flowrate of gas

concentration of detergent flowrate of air Linear (flowrate of air)

As the concentration increases the flowrate increases

• 10

Preliminary Observations

Proper surface tension is needed to produce soap bubbles

Water

Soap molecules

Soap molecules

Hydrophobic tail

• Soap film is formed due to Marangoni effect • Soap lower the surface tension of water

• 11

Preliminary Observations

Proper surface tension is needed to produce soap bubbles

• Soap film is made from soap and water

Water

Soap molecules

Soap molecules

• 12

Preliminary Observations Bubble is always spherical

Surface tension

• Surface tension is pulling the water molecules in all directions and creating net inward force

• Hydrostatic equilibrium between the internal pressure and surface tension. One of it is trying to expand spherically the other to contract spherically.

• Moreover the air pressure present inside the soap bubble opposes this and equilibrium is obtained Moreover the air pressure present inside the soap bubble opposes this and equilibrium is obtained

• 13

P o p p i n g o f b u b b l e

BURST

• Internal pressure increases

• Elastic membrane become thin

Surface tension

• 14

Hypothesis

• 15

Soap bubbles are produced when the gas blowing velocity exceeds threshold vg (i.e. vg> vc)

BELOW THRESHOLD ABOUT THRESHOLD ABOVE THRESHOLD

vg> vcvg< vc

vc vc vg

Dimple is formed

It becomes greater as the speed increases

Hypothesis 1

• 16 16

1/2pgvg 2 = 4ˠ /Ro

Dynamic pressure of gas jet

Laplace pressure of the cavity

P= density of gas(kgm-2)

Vg= velocity of gas flow (m.s -1)

𝛾= surface tension of the solution(N\m)

δ = 0 Energy transport

Dynamic pressure of gas jet

Laplace pressure of the cavity

• 17 17

𝑣g = √ 8𝛾 /𝜌𝑔𝑅o for δ = 0

P= density of gas(kgm-2)

Vg= velocity of gas flow (m.s -1)

𝛾= surface tension of the solution(N\m)

Threshold velocity Distance between the

soap film and nozzle

δ = 0 Energy transport

• 18 18

Hypothesis 2 First bubble is generated when the radius of ring become

equal to the curvature of bubble (Rc=Rg)

vg

Rc=curvature of bubble Rg=radius of ring

Rc=Rg

Rc

• 19

Hypothesis 3 Pressure inside the soap bubble is greater than the pressure

outside the soap bubble(Pi>Po)

P(inside) − P(outside) = 4Ɣ/R

Pressure difference Radius of the bubble

Pi=pressure inside Po=pressure outside R= radius of the bubble

pressure inside

pressure outside

• 20

Hypothesis 4

productivity(p is the number of bubbles one soap film can produced per second.

P=ΠR0vg/4/3ΠR ,3

Number of bubbles single film can produced Gas flow velocity

• 21

N=p*∆t

Number of bubbles

T=time P=number of bubbles one film can produced per second

• 22 22

Characteristics to be discussed with respect to parameters:

•Size of bubbles

•Number of bubbles(productivity)

•life span of bubbles

• 23 23

Parameters: •Velocity of the gas

•Distance of nozzle from the ring

• Surface tension of the solution

• Temperature of the solution

• Thickness of film

• 24

Experimental setup

• 25

nozzle

Flow meter

compressor

Experimental setup

• 26

Experiment 1 Number of bubbles

Flowrate of gas Surface tension of solution Temperature of soap film Thickness of soap film

• 27

Experiment 1 Number of bubbles

(single bubble analysis)

Control variables:  Radius of ring : 1.6cm  Diameter of nozzle:0.6cm  Distance of nozzle from ring:

δ:1.3cm  Concentration of surfactant :50%  Density of gas:1.225 kg/m3

Independent variables: • velocity of gas

 Dependent variable : number of bubbles

• 28

Experiment 1 Number of bubbles

(single bubble analysis)

Results :  Bubbles start forming

at 10L/m  Maximum number of

bubbles are formed at 14L/m

0

5

10

15

20

25

1 2 4 6 8 10 12 14 16 18

N u

m b

e r

o f

b u

b b

le s

Velocities of air

Bubbles start forming

Maximum number of bubbles are formed

• 29

Experiment 2 Concentration and f lowrate of

air

Control variables:  Radius of ring : 1.6cm  Diameter of nozzle:0.6cm  Distance of nozzle from

ring: δ:1.3cm  Density of gas:1.225 kg/m3

Independent variables: • flowrate of gas • Concentration of surfactant

 Analysis : number of bubbles and radius of bubbles

• 30

25

2019.5

12

7 4

1.1 1.4

1.7

2.3 2.6

3.1

0

0.5

1

1.5

2

2.5

3

3.5

0

5

10

15

20

25

30

0 20 40 60 80 100 120

n u

m b

e r

o f

b u

b b

le s

percentage concerntration 0f detergent

flowrate (L/m)of air

number of bubbles

Experiment 2 Radius and Number of bubbles

(Different concentrations)

As the concentration increases the flowrate increases and number of number also increases

Due to increases in flowrate of air the radius of bubble decreases

• 31

Experiment 3 Temperature of soap fi lm

Control variables:  Radius of ring : 1.6cm  Diameter of nozzle:0.6cm  Distance of nozzle from ring:

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