Fluid Mixing.docx

UNIVERSITI TEKNOLOGI MARA FAKULTI KEJURUTERAAN KIMIA THERMOFLUIDS LABORATORY CGE 536 STUDENT’S NAME ID

:1) ABU BAKAR BIN ZULKIFLI 2) KAMA AMIRA BINTI KAMALUDIN 3) SHAZAATUL SHUHADHA BINTI MOHD KHAIRI 4) MOHAMAD SYAFIQ IZUDDIN BINMOHAMED ELHAM : EH243 3B (GROUP 1) : FLUID MIXING : 8/3/2019 : 20/3/2019 :3 :MISS SURIATIE

GROUP EXPERIMENT DATE PERFORMED DATE SUBMITTED SEMESTER LECTURER No

Title

Allocated Marks

1

Abstract/ Summary

5

2

Introdction

5

3

Objectives

5

4

Theory

5

5

Material and Apparatus

5

6

Matedology

10

7

Data and Result

20

8

Discussion

20

9

Conclusions

10

10

Recommendations

5

11

References

5

12

Appendices

5 Total

100

Remarks: Checked by: ___________________ Date: 1

Marks

TABLE OF CONTENT Abstract/ Summary................................................................................................................

3

Introduction............................................................................................................................

4

Objectives .............................................................................................................................

6

Theory ...................................................................................................................................

6

Material and Apparatus..........................................................................................................

9

Methodology..........................................................................................................................

10

Data and Result ....................................................................................................................

11

Discussion.............................................................................................................................

15

Conclusion.............................. .............................................................................................

17

Recommendation ................................................................................................................

17

References ..........................................................................................................................

18

Appendices...........................................................................................................................

18

2

1.0 ABSTRACT

Fluid mixing experiment contains 2 sub experiments. The objective for the first experiment is to observe the flow pattern of the fluid by using different impellers with inclusion of baffle. Objective for second experiment is to determine the power consumption of a mixer varies with speed, type of impeller, and inclusion of baffle. As observed from the first experiment, the flow pattern of the fluid is affected by the presence or absence of baffle and type of impeller used during the experiment (turbine impeller and flat paddle).

The photos of the flow patterns for the first

experiment are attached at the result section in this report. As for the second experiment, power consumption is calculated by using calculation that has given in lab manual. This calculation is interpreted in the form of graph and the relation between the power consumed and angular speed is shown. The result that obtained during this experiment is not 100% accurate since the torque that we have used is very sensitive with external forces and this will be discussed in the report later on. As for that reason, we also added some recommendations to improve this machine to avoid any error as much as possible and to get more accurate result.

3

2.0 INTRODUCTION

Mixing of liquid-liquid system or the solid-liquid system is a complex operation. In order to analyse the formation and choose the right mixer, a lots of variables need to be considered including the degree of the bulk movement and also the shear mixing properties. To predict fullscale requirements, it is necessary to model the system and apply dimensional analysis. Fluid mixing mechanism is the most commonly used in the mixing process regarding to its simplest operation which by rotating an impeller in the liquid confined tank. Mixing impeller are designed to pump fluid through the impeller and produce turbulence which this effect is vital in mixing operations. These produces fluid velocity and fluid shear respectively. Fluid velocity produces movement throughout the mixing vessel, intermixing material in one part of the tank with another and prevents solids from setting out and produces flows. Fluid shear in the form of turbulent eddies is essential to micro-mixing within the large velocity streams breaking up gas bubbles or immiscible liquids into small droplets. All mixing impellers produce both fluid velocity and fluid shear but different types of impellers produce different degrees of flow turbulence. However, the limitation of these kind of operation could predict a possible waste in term of input energy waste if the wrong kind of impeller is used. The particular purposes of impeller in this experiment are to make a uniform mixture or flow pattern in confined vessel. There are two types of impeller have been used which are flat paddle and turbine impeller. Both impeller have their own pros and cons. Flat paddle is usually used for low to medium viscosity of fluid. Meanwhile, turbine which operates in low speed are usually used for chemical reactions, suspension solid and miscible liquid mixing due to its excellent feature in designing the flow pattern. Figure 1 shows two main types of flow pattern which are axial and radial flow pattern. The differences in the flow patterns can cause variations in distribution of shear rate and energy dissipation rate within the mixing tank. The presence of baffle in mixing tank would influence the flow patterns as well. It can increase the amount of top to bottom circulation which contributes to turbulence by giving out some obstacles for the mixture to swirl as a whole and elimination of vortexes.

4

Figure 1. Axial impellers and Radial impellers

Axial flow is the patterns where the fluid is flowing parallel to the axis turbine. An axial flow impeller exhibits a flow pattern throughout the entire tank volume as a single stage. It imposes necessarily bulk motion, and is used to on homogenization processes, in which increased volumetric flow rate is necessary. Radial flow is the pattern that the working fluid flowing mainly along the radius of rotation in the tank. Radial flow impellers produce two circulating loops, one below and above the impeller. Mixing occurs between the two loops but less intensely than within each loop. These impellers impose necessarily shear stress to the fluid, and are used to mix immiscible liquids or generally, when there is a deformable interface to break. Besides, they are used for the mixing of very viscous fluid.

5

3.0 OBJECTIVES

Experiment 1: 

The objective of this experiment is to observe the flow patterns that can be achieved by using different impellers with and without the use of baffles.

Experiment 2: 

The objective of this experiment is to show how the power consumed by a mixer varies with speed, types of impeller and with the inclusion of baffles.

4.0 THEORY

An impeller is the rotating component of a centrifugal pump that transfer energy from the motor and accelerate the fluid outwards from the centre of the rotation. The velocity achieved by the impeller is transfers into pressure when the outward movement of the fluid is confined by container. In short, impellers in confined tanks are used to mix fluids or slurry in the tank. Two types of impeller were used in this experiment such as flat paddle and turbine impeller. These two types of impeller were observed next to achieve the objective which are to observe the flow patterns of two fluids with various viscosity when different impellers used with and without baffle in liquid tank and also to study how power affect the force, torque, angular speed and flow pattern by changing the speed of mixer. In this experiment, baffle in Figure 2 are needed to stop the swirl in mixing tank. Most of common baffle used are straight flat plate of metal that run along the straight sides of vertically oriented cylindrical tank. Baffles are attached to the inside vertical walls of the tank by means of welded brackets. Four equally spaced baffles are usually sufficient to prevent liquid swirling and vortex formation.

6

Figure 2. Baffle in Fluid Mixing Tank

There is a tendency for a swirling flow pattern to form in the tank without the baffles regardless the type of the impellers. A vortex is produced owing to centrifugal force acting on the rotating liquid but there is a limit to the rotational speed that may be used, since one the vortex reaches the impeller and the severe air entrainment might be occur. The swirling mass of the liquids normally created an oscillating in tank that might create a large fluctuating force acting on the mixer (Figure 3).

Figure 3. Baffle attached to the wall for low viscosity liquid

7

The modes of flow behaviour exist in a mixer laminar and turbulent flow. Both these flow conditions may be described dimensionally but for turbulent flow its behaviour is less significant. In particular, the power number becomes independent of Reynolds number beyond a certain turbulence range. In laminar flow (NRE<10), the same power were used by the impeller. The flow pattern may be effected by the baffle but it not favorable. To allow the fluid circulate and produce axial deflection we may need the baffle. In transitional flow (10
8

5.0 MATERIALS AND APPARATUS



Fluid Mixing Apparatus



Flat paddle



Turbine impeller



Speed controller



Force indicator



Baffle



Tank



Motor



Water

9

6.0 METHODOLOGY

1 General start-up procedure 1. The power was switch on. 2. The tightening screws were fastened. 3. The shaft was lifted up and down by using lifting chain and attached it to the shaft before started the experiment. 2 Experiment 1. The general start-up procedure was performed. 2. The tank was filled with 30 liters of water. 3. A turbine impeller was attached at the end of the shaft. 4. The angular speed of the impeller was set up to 50 rpm, 100 rpm, 150 rpm, 200 rpm, 250 rpm and 300 rpm. 5. The flow pattern of the water was observed at every angular speeds and the torque was recorded. 6. Step 4 and 5 was repeated by replacing the turbine impeller with flat paddle impeller. 7. Step 3 to 5 was also repeated by replacing baffles inside the tank with each turbine impeller and flat paddle impeller. 8. The angular speed, force and power consumed for each speed were calculated.

3 General shut-down procedure 1. Liquid inside the tank was removed through the outlet valve. 2. The tank was washed and rinsed several times. 3. The impeller was removed and placed at the right place after used it. The power was shut down.

10

7.0 RESULTS

Experiment 1: A) Water flow pattern without baffle inside the tank. Types of impeller

Flow pattern

Observations 

The impeller created a deep whirlpool at the centre of the

Flat Paddle Impeller

tank water that moves at a very high velocity in circular motion. The angular paddle played a role in increasing the velocity of the whirlpool.



The impeller created a shallow whirlpool at the center of the tank water that moves at a

Turbine Impeller

lower velocity in circular motion compared to the Flat Paddle Impeller. The Turbine impeller created less whirlpool due to its flat design and less surface area acting on the direction of the force (small fin).

Table 1: The water flow pattern without baffle inside the tank using different type of impeller.

11

B) Water flow pattern with baffle inside the tank. Types of impeller

Flow pattern

Observations 

The baffle acted as a restrain to the water flow.



When the water that flow at a certain velocity hits the baffle, its

Flat paddle

flow

turbulence

breaks

causing

and

uneven

circulation. 

Therefore,

the

moved

scatter

in

water at

flow high

velocity.



The baffle acted as a restrain to the water flow.



When the water that flow at a certain velocity hits the baffle, its

Turbine Impeller

flow

turbulence

breaks

causing

and

uneven

circulation. 

Therefore,

the

moved

scatter

in

water at

flow high

velocity. 

However, the turbulence of water flow in this test was lesser compared to the Flat Paddle Impeller with baffle.

Table 2: The water flow pattern with baffle inside the tank using different type of impeller

12

Experiment 2 Type of impeller

Angular speed (rpm)

Force (N)

Torque (N.m)

Power (watts)

50

Angular speed, ω (rad/s) 5.236

0

0.0

0

100

10.472

0.33

0.1

10

150

15.708

0.66

0.2

30

200

20.944

1.33

0.4

80

250

26.180

1.67

0.5

129

300

31.416

1.67

0.5

150

50

5.236

1.33

0.4

20

Flat paddle

100

10.472

1.67

0.5

50

Impeller

150

15.708

8

2.4

360

200

20.944

20

6.0

1200

250

26.180

36.67

11.0

2750

300

31.416

50

15.0

4500

Turbine Impeller

Table 3: Water with baffle inside the tank.

Power against Speed with Baffle 5000 4500 4000 3500

Power,W

3000 2500

turbine

2000

flat

1500 1000 500 0 0

5

10

15

20

25

30

Angular speed, ω Graph 1: Power against speed with baffle.

13

35

Type of impeller

Angular speed (rpm)

Force (N)

Torque (N.m)

Power (watts)

50

Angular speed, ω (rad/s) 5.236

0

0

0

100

10.472

0.33

0.1

10

150

15.708

0.33

0.1

15

200

20.944

1.33

0.4

80

250

26.180

0.33

0.1

25

300

31.416

1

0.3

90

50

5.236

1

0.3

15

Flat paddle

100

10.472

1.67

0.5

50

Impeller

150

15.708

2

0.6

90

200

20.944

2.67

0.8

160

250

26.180

3

0.9

225

300

31.416

4

1.2

360

Turbine Impeller

Table 4: Water without baffle inside the tank.

Power against Speed without Baffle 400 350

Power,W

300 250 200

Turbine

150

Flat Paddle Blade

100 50 0 0

5

10

15

20

25

30

35

Angular speed,ω

Graph 2: Power against speed without baffle.

14

8.0 DISCUSSION

In this fluid mixing experiment, it consists two part of experiments, 1 and 2. For experiment 1, the flow patterns of water with different types of impeller are observed. Four set of flow patterns are shown with the use of two different impellers with and without the baffle. Based on the observation, the flow pattern of water is depend on the type of impeller used. As for water flow pattern without baffle inside the tank, for flat paddle impeller, the impeller created a deep whirlpool at the center of water that moves at a very high velocity in circular motion. Next, for turbine impeller, the impeller created a shallow whirlpool at the center of tank water that moves at a lower velocity in circular motion. For water flow pattern with baffle inside the tank for flat paddle impeller and turbine impeller, the baffle acted as a restrain to the water flow. When the water flow hits the baffle, its flow breaks causing turbulence and uneven circulation for both type of impellers. However, the turbulence of water flow for turbine impeller was lesser compare to flat paddle impeller. As for experiment 2, the material used is water and the manipulated variable is the mixing tank with baffle or without baffle. The tank were filled with 3 liter of water. First and foremost, the tank used flat paddle without baffle experiment, the result of torque,T (Nm) were 0.3, 0.5, 0.6, 0.8, 0.9 and 1.2 when the angular speed (rpm) is 50, 100, 150, 200, 250 and 300 respectively. The value of force,F (N) that have been calculated were 1, 1.67, 2, 2.67, 3 and 4 when the angular speed (rpm) 50, 100, 150, 200, 250 and 300 respectively. Next, the value of power,P (W) that have been calculated were 15, 50, 90, 160, 225 and 360 when the angular speed, (rad/s) is 5.236, 10.472, 15.708, 20.944, 26.18 and 31.416 respectively. For the water using flat paddle and with baffle experiment, the result of torque,T (Nm -2) value were 0.4, 0.5, 2.4, 6.0, 11.0 and 15.0 when the angular speed (rpm) is 50, 100, 150, 200, 250 and 300. The value of force, F (N) that have been calculated were 1.33, 1.67, 8, 20, 36.67 and 50 when the angular speed (rpm) 50, 100, 150, 200, 250 and 300 respectively. Then, the value of power, P (W) that have been calculated were 20, 50, 360, 1200, 2750, and 4500 when the angular speed, (rad/s) is 5.236, 10.472, 15.708, 20.944, 26.18, and 31.416 respectively.

15

For experiment using turbine impeller and without baffle, the result of torque,T (Nm) were 0, 0.1, 0.1, 0.4, 0.1 and 0.3 when the angular speed (rpm) is 50, 100, 150, 200, 250 and 300 respectively. The value of force, F (N) that have been calculated were 0, 0.33, 0.33, 1.33, 0.33 and 1 when the angular speed (rpm) is 50, 100, 150, 200, 250 and 300 respectively. Then, the value of power, P (W) that have been calculated were 0, 10, 15, 80, 25 and 90 when the angular speed, (rad/s) is 5.236, 10.472, 15.708, 20.944, 26.18 and 31.416. For the water using turbine impeller and with baffle experiment, the result of torque,T (Nm) value was 0, 0.1, 0.2, 0.4, 0.5 and 0.5 when the angular speed (rpm) 50, 100, 150, 200, 250 and 300 respectively. The value of force, F (N) that have been calculated were 0, 0.33, 0.66, 1.33, 1.67 and 1.67 when the angular speed (rpm) is 50, 100, 150, 200, 250 and 300 respectively. Next, the value of power, P(W) that have been calculated were 0, 10, 30, 80, 129 and 150 when the angular speed, (rad/s) is 5. 236, 10.472, 15.708, 20.944, 26.18 and 31.416.

16

9.0 CONCLUSION

In this experiment, the purpose is to observe the flow patterns that can be achieved by the use of different type of impellers, with and without baffles. In a baffled tank, flat paddle produced radial flow pattern while turbine propeller produced axial flow pattern. For a tank without baffle in the tank, it can be concluded that both types of impellers produced the same flow pattern which is tangential flow pattern and vortex will be formed depends on the rpm. Based on the results and graphs obtained for the second part of the experiment, it can be seen that power consumed increases as the speed increases. It also can be observed that the power consumed in a baffled tank is higher than the tank without baffle. By that, it can be concluded that the baffle prevent the formation of vortex in the tank which is not very desirable for the process of liquid mixing.

10. 0 RECOMMENDATION

Due to the experiment that has been done, there are few recommendations that should be considered during the experiment in order to get the best result needed throughout the experiment. First of all, the impellers should be attached firmly onto the shaft. This is to prevent the impellers from falling off while the machine is being operated. Also, loosely installed impellers will affect the flow pattern. Next, all the experimental equipment need to be in good shape as they are used frequently. Some maintenance work should be done if the machine has been used for a while to avoid an inaccuracy of data when collected. Last but not least, the eyes must be perpendicular to the scale of the tank during refill the tank with water to avoid parallax error. Always make sure that the water does not spill out of the tank by increasing the speed way too much.

17

11.0 REFERENCES

1. Light, M. (2011, Nov 9). Scribd. Retrieved from Experiment 2 Fluid Mixing: https://www.pdfcoke.com/doc/72158398/Exp3-Fluid-Mixing 2. Noor, S. (n.d.). Coursehero. Retrieved from https://www.coursehero.com/file/8491168/L8-Fluid-Mixing/

L8

3. Wikipedia. (n.d.). Retrieved from Mixing (Process https://en.wikipedia.org/wiki/Mixing_(process_engineering)#References

Fluid

Mixing:

Engineering):

4. Glimm J., Lindquist W.B. (1993) A Theory of Fluid Mixing. In: Donato A., Oliveri F. (eds) Nonlinear Hyperbolic Problems: Theoretical, Applied, and Computational Aspects. Notes on Numerical Fluid Mechanics (NNFM), vol 43. Vieweg+Teubner Verlag 5. Thermofluids Laboratory Manual, Fluid Mixing Experiment.

12.0 APPENDICES

18