I Y P T 2 0 1 8

P R O B L E M # 1 5

BLOWING BUBBLEST 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

NU

MB

ER O

F B

UB

BLE

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

CO

NC

ERN

TRA

TIO

N O

F D

ETER

GEN

T

TIME PERIOD OF SOAP FILM

Relation of concentration with duration of soap film

9

Preliminary ObservationsRelationship 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

Pert

enta

ge c

on

cen

trat

ion

of

det

erge

nt

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

Hydrophilic head

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 ObservationsBubble 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

1/2pgvg2 = 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)

R0 = radius of nozzle

δ = 0Energy transport

Dynamic pressure of gas jet

Laplace pressure of the cavity

17 17

𝑣g = √ 8𝛾 /𝜌𝑔𝑅ofor δ = 0

P= density of gas(kgm-2)

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

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

R0 = radius of nozzle

Threshold velocity Distance between the

soap film and nozzle

δ = 0Energy transport

18 18

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

equal to the curvature of bubble (Rc=Rg)

vg

Rc=curvature of bubbleRg=radius of ring

Rc=Rg

Rc

19

Hypothesis 3Pressure 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 insidePo=pressure outsideR= 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

Ro= radius of the nozzleR , =radius of bubble

Number of bubbles single film can produced Gas flow velocity

21

N=p*∆t

Number of bubbles

T=timeP=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

• Radius of the nozzle

•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 1Number of bubbles

Flowrate of gasSurface tension of solutionTemperature of soap filmThickness of soap film

27

Experiment 1Number 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 1Number 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

Nu

mb

er

of

bu

bb

les

Velocities of air

Bubbles start forming

Maximum number of bubbles are formed

29

Experiment 2Concentration 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

74

1.11.4

1.7

2.32.6

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

nu

mb

er

of

bu

bb

les

percentage concerntration 0f detergent

flowrate (L/m)of air

number of bubbles

radius of bubbles(cm|)

Linear (radius ofbubbles(cm|))

Experiment 2Radius 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 3Temperature of soap fi lm

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

δ:1.3cm Flow rate of gas:16.1(L/m) Concentration of detergent : 50% Density of gas:1.225 kg/m3

Independent variables:• Temperature of soap film

analysis: number of bubbles

32

0 5 10 15 20

4

10

20

30

40

50

NUMBER OF BUBBLES

TEM

PER

ATU

RE

OF

SOA

P F

ILM

°C

Experiment 3Number of bubbles

Maximum number of bubbles are formed at 30°C

Conclusion: Cohesive forces

decrease with the increase of molecular thermal activity

Surface tension decrease when temperature increases.

33

Experiment 4Thickness of soap fi lm

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:• Amount of glycerin

Analysis : number of bubbles

34

0

2

4

6

8

10

12

14

16

18

9.7 16.79 21.1 28.96 33.3

Nu

mb

er o

f b

ub

ble

s

Percentage % concentration of glycerin

Experiment 4Thickness of soap fi lm

Conclusion: Higher the

concentration of glycerin lower the number of bubbles

Maximum number of bubbles are formed at 9.7%

35

Experiment 5Size of bubbles at different f lowrates

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

Analysis :size of bubbles

36

1.11.4

1.7

2.32.6

0

0.5

1

1.5

2

2.5

3

0 5 10 15 20

Rad

ius

of

bu

bb

les

Flowrate of air

As the flowrate increases the radius of the bubble decreases

Experiment 5Size of bubbles at different f lowrates

37

conclusion

0

5

10

15

20

25

30

0 50 100 150

NU

MB

ER O

F B

UB

BLE

S

PERCENTAGE CONCENTRATION OF DETERGENT%

number ofbubbles

As the concentration

Relationship between the concentrations of detergents and the number of bubbles produced from single soap film and the duration of soap film

How and why the soap film is produced and the role of surface tension in bubble formation

Concentration of detergent and its affects on flowrate of gas

0%

20%

40%

60%

80%

100%

5.54s 7.02s 22.02s 22.37s

CO

NC

ERN

TRAT

ION

OF

DET

ERG

ENT

TIME PERIOD OF SOAP FILM

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

14.03 15.67 16.44 17.79 19.01

0

20

40

60

80

100

120

0 1 2 3 4 5 6

Pert

enta

ge c

on

cen

trat

ion

of

det

erge

nt

Flowrate of gas

concentration of detergent flowrate of air

Linear (flowrate of air)

38

conclusion

Surfactant and its role in formation of bubble Popping of bubble

39

conclusion Discuss some hypothesis above the bubble formation

40

conclusion

The relationship between the velocity of jet and the pressure inside the bubble

Characteristics of bubbles with respect to parameters The radius and the number of bubbles at different

concentration and flowrate

41

conclusion

Number of bubbles by varying the temperature of soap film

The relation between the thickness of soap film and the number of bubbles

42

conclusion

• Radius of bubbles on different flow rates

43

44

concentration flowrate radius bubbles

100 19.01 1.1 25

80 17.79 1.4 21

60 16.44 1.7 19.5

40 15.67 2.3 12

20 14.03 2.6 7

10 13.98 3.1 4

45

0

5

10

15

20

25

4 4.5 4.5 5 19 19.5 19.8 19.9 22 25

FLO

WR

ATE

OF

GA

S (L

/M)

NUMBER OF BUBBLES

Experiment 1Number of bubbles

Maximum number of bubbles are formed22.01(L/m) (100%

concentration) Conclusion: Higher the

concentration greater the bubbles blown out

46

Hypothesis 5

Duration or stability of soap bubbles(amount of time in which bubbles are produced from the film)

∆tR’

vg

T=amount of time that film keep generating bubblesVg=gas flow velocity

UNSTABLE