Experiment8 Fluid Mixing

CCB 2092 Unit Operation Laboratory 1May 2012

Experiment:8: Fluid MixingGroup:2Group Members:Cheng Yee Yin14213Chua Lin Kiat14384Debra Adelina Chia Siew Fen15261Derek Lai Chai Zern 14233Kew Wen Ting14317

Lab Instructor:Nguyen Van ThienDucDate of Experiment:12/07/20121.0 ABSTRACTFor the fluid mixing experiment, we have done six sub experiments to study the flow patterns under various conditions and the objectives for the six sub experiments are stated according:a. To determine various flow patterns exhibited by different type of impellers. (mixing tank without baffle)b. To determine various flow patterns exhibited by different type of impellers. (mixing tank with baffle)c. To determine the influence of impeller position to rate of dispersion of solid in liquid. (tank without baffle)d. To determine the influence of impeller position to rate of dispersion of solid in liquid. (tank with baffle)e. To determine the power consumed by a mixer at different operation speed, using different impeller, with or without baffles.f. To determine power consumed by a mixer at different operating speed, using different impeller, with or without baffles.Basically, we are to determine the flow patterns based on two different choices of flow patterns which are axial and radial. The flow patterns are determined by observing how the mixture is flowing in the tank, either flowing parallel to the axis turbine or along the radii of rotation in the tank. These flow patterns depend on the type of impellers used and their position.Besides determining the flow patterns, we are required to calculated the rate of dispersion of solid in liquid first in the presence of baffle and secondly, without. In addition to that, power consumed at different operating speed, using different impeller, in the presence and absence of baffle is also calculated. The power can be calculated in the form of power number which will further be discussed. For experiments a, b, c and d, we have determined that different impellers indeed exhibit different flow patterns. The presence or absence of baffle in the mixing tank also influences the flow pattern. Pictures showing the differences in flow patterns are attached in the results section of the report.For experiment e, the power consumed by the mixer is calculated whereas for experiment f, the respective Reynolds number is calculated. The results obtained for these two sub-experiments are interpreted in the form of graphs. For experiment e, we are able to see the relation between power and the angular speed. On the other hand, the graphs for experiment f portray the relationship between the power and the Reynolds number. As we all know, there will still be errors in the experiments. The results obtained are definitely not a 100% accurate. Therefore, we also added suggestions and recommendations to further improve the accuracy of the experiments in order to avoid errors as much as possible.2.0 INTRODUCTION AND THEORY2.1 Basic ConceptFluid is mixed for numerous purposes; it depends on the objectives of the processing steps. The purposes could be the suspending solid particles, blending miscible liquids, dispersing a gas through the liquid in the form of small bubbles, dispersing a second liquid, immiscible with the first, to form an emulsion or suspension of fine drops, and promoting heat transfer between the liquid and a coil or jacket. The result of mixing process is highly influenced by the impeller flow patterns. The flow pattern depends on the impeller type. Various flow patterns are exhibited by different type of impellers. The presence of baffle in the mixing tank would influence the flow pattern as well. It can increase the amount of top to bottom circulation. It contributes to turbulence by preventing swirl of the contents as a whole and elimination of vortexes. There are mainly two types of flow patterns with top-entering mixers, which are axial and radial. The differences in the flow patterns can cause variations in distribution of shear rate and energy dissipation rate within the mixing tank.In this experiment, not only the flow patterns of the fluid is determined, but also the rate of dispersion of solid in liquid and the power consumed by a mixer at different operating speed, using different impeller and with or without baffles. The position of the impeller is a factor that influences the rate of dispersion of solid in liquid.

Figure above shows some commonly used impellers: (a) Flat-blade turbine, (b) Pitched-blade impeller, (c) Marine-type propeller, (d) Paddle, (e) Anchor impeller, (f) Helical impeller.

2.1.1 Axial flowAxial flow is the pattern that the fluid or gas is flowing parallel to the axis turbine. There are many impellers that produce axial flow. They include propeller, pitched blade turbines, and hydrofoils. An axial flow propeller produces a flow pattern throughout the entire tank volume as a single stage. It imposes essentially bulk motion, and is used on homogenization processes, in which increased fluidvolumetric flow rateis essential.2.1.2 Radial flowRadial flow is the pattern that the working fluid flowing mainly along the radii of rotation in the tank. Radial flow impellers produce two circulating loops, one below and one above the impeller. Mixing occurs between the two loops but less intensely than within each loop. These impellers impose essentiallyshear stressto the fluid, and are used to mix immiscible liquids or in general when there is a deformableinterfaceto break. Besides, they are used for the mixing of very viscous fluids.

Figure above shows the axial flow impeller (left) and radial flow impeller (right).

2.1.3 Power consumed The power input is influenced by the geometry of the equipment and also the properties of the fluid. The flow pattern and the degree of turbulence are key aspects of the quality of mixing. The power input P to an impeller of diameter D driven at a rotational speed N in a fluid of density and viscosity can be expressed in terms of a dimensionlessPower number, . This is a form of drag coefficient and is a function of the mixing Reynolds number . The vs. Re function is always in the same form for a given pattern of impeller.2.2 Relevant Equations

2.2.1 Nomenclature D = Diameter of impeller F = Force recorded on spring balance N = Rotational speed, rpm = Reynolds number of agitator P = Power consumed by the motor = Power number r = Length of torque arm

2.2.2 Greek Letters = Absolute viscosity of liquid = Density of liquid = Rotational speed, = Torque

2.3 Industrial Application Use in paint mixer industrial. Use in washing machine where the impellers are used in it to agitate the laundry. Use in wastewater treatment Use in drilling oil and gas as a drilling mud mixer

3.0 METHODOLOGYExperiment 8a: Determination of various flow patterns exhibited by different type of impellers (Mixing tank without baffle)1. The mixing tank is filled up to without baffle with water (up to 250mm height).2. A small quantity of yellow beads is added into the tank.3. The impeller is attached on the end of the shaft. It is tighten using the chucky key.4. The impeller is set to 123mm from the based. (It is measured from the bottom of the scale on the mixing tank to the bottom of the impeller.)5. The MIXER CONTROLLER is switched on. (Switch is at the back of the apparatus.) The meter light turns on.6. RPM is pressed and the initial speed is set to 100 rpm y pressing either up or down button.7. START button is pressed. The impeller is started to rotate.8. The impeller speed is increased to 50-rpm increment. Always press the RMP button to increase the RPM.(Notice that the up or down button is pushed without pressing the "RPM" first, the reading will not change). [NOTE: BEWARE OF RJGOROUS MIXING! Ensure the mixing is not too rigorous that could damage the equipment and induce splashing of liquid].9. The movement of the particles and flow pattern are observed.10. The experiment is stopped by pressing the "STOP" button on the "MIXER CONTROLLER",11. Step 5to 10 are repeated by using different type of impeller.12. The flow pattern from front view and top view is drawled.Experiment 8b: Determination of various flow patterns exhibited by different type of impellers (Mixing tank with baffle)Procedures:1. The baffle is installed into the mixing tank.2. Step 1-12 are repeated from Experiment 8a.Experiment 8c: Determination the influence of impeller position to rate of dispersion of solid in liquid (tank without baffle)Procedures:1. The mixing tank is filled up to without baffle with water (up to 2500mm height).2. A layer of particles is sprinkled (example: green peas) on the base of the tank to approximately 10 mm thickness.3. Step 3-10 from experiment 8a is repeated.4. The lifting capacity, dead spots and movements of the sand particles are observed.5. The experiment is repeated at the setting as follows:a. Lower impeller height.b. Higher impeller height.c. Impeller install at right-hand-side/left-hand side of the original position.d. Impeller inclined at an angle.6. The experiment is repeated using different type of impeller.7. The effectiveness of each configuration of impeller is discussed.8. The best configuration for this application and at what recommended speed are determined.Experiment 8d: Determination the influence of impeller position to rate of dispersion of solid in liquid (tank with baffle)Procedures:1. The baffle is installed into the mixing tank.2. Step 1-8are repeated from Experiment 8c.Experiment 8e: Determination of the power consumed by a mixer at different operating speed, using different impeller, with or without baffles.Procedures:1. The mixing tank is filled up to without baffle with water (up to 250mm height).2. A layer of particles is sprinkled (example: green peas) on the base of the tank to approximately 10 mm thickness.3. The impeller is attached on the end of the shaft. It is tighten using the chucky key.4. The impeller is set to 123mm from the based. (It is measured from the bottom of the scale on the mixing tank to the bottom of the impeller.)5. The MIXER CONTROLLER is switched on. (Switch is at the back of the apparatus.) The meter light turns on.6. RPM is pressed and the initial speed is set to 100 rpm y pressing either up or down button.7. START button is pressed. The impeller is started to rotate.8. The impeller speed is increased to 50-rpm increment.9. The movement of the articles and flow pattern are observed.10. While the experiment is running, TORQUE button is pressed and the reading is recorded (kg-cm). [NOTE: BEWARE OF RJGOROUS MIXING! Ensure the mixing is not too rigorous that could damage the equipment and induce splashing of liquid].11. The speed and torque value from the computer is recorded.12. The "RPM" button is pressed again to increase the speed.13. The experiment is stopped by pressing the "STOP" button on the "MIXER CONTROLLER.14. Step 3 to 13 is repeated by using different type of impeller.15. The experiment is repeated with baffles installed in position.16. The graph of Power vs. Angular speed (RPM) is plot as instructed by the Lab Instructor.

NOTE: Some impeller usage will give zero torque reading. This is normal operating condition considering the decimal point of the METER CONTROLLER is limited to one decimal point. However, for record purposes, zero reading is considered valid.Experiment 8f: Determination of the power consumed by a mixer at different operating speed, using different impeller, with or without baffles.Procedures:1. The mixing tank is filled up to without baffle with water (up to 250mm height).2. The impeller is attached on the end of the shaft. It is tighten using the chucky key.3. The impeller is set to 123mm from the based. (It is measured from the bottom of the scale on the mixing tank to the bottom of the impeller.)4. The MIXER CONTROLLER is switched on. (Switch is at the back of the apparatus.) The meter light turns on.5. RPM is pressed and the initial speed is set to 100 rpm y pressing either up or down button.6. START button is pressed. The impeller is started to rotate.7. The impeller speed is increased to 100-rpm increment.8. The movement of the articles and flow pattern are observed.9. While the experiment is running, TORQUE button is pressed and the reading is recorded (kg-cm). [NOTE: BEWARE OF RJGOROUS MIXING! Ensure the mixing is not too rigorous that could damage the equipment and induce splashing of liquid].10. The speed and torque value is recorded.11. The "RPM" button is pressed again to increase the speed.12. The experiment is stopped by pressing the "STOP" button on the "MIXER CONTROLLER.13. Step 2 to 11 is repeated until air is entrained at the center of the paddle or the liquid gets near to the top of the tank.14. The graph Power number, Po, vs. Reynolds number, Re, for all configurations of impeller and baffles are plotted.15. The experiment by using different type of impeller is repeated.16. The experiment with baffles installed in position is repeated.

NOTE: Some impeller usage will give zero torque reading. This is normal operating condition considering the decimal point of the METER CONTROLLER is limited to one decimal point. However, for record purposes, zero reading is considered valid.

4.0 RESULTSImpeller used: Disc Mounted Flat Blade ImpellerExperiment 8e: Determining the power consumed at different operating speed, using different impeller and without baffle

experiment 8e (without baffles)

Angular Speed(rpm)Angular Speed, (rotation/sec)torque(kg-cm)Torque(Nm)Power(W)

1001.660.000.000.00

3005.000.110.010.06

5008.330.800.080.67

Graph 4.1: Graph of Power (W) against Angular speed (rpm), without baffle fixed

Experiment 8e: Determining the power consumed at different operating speed, using different impeller and with baffle

experiment 8e(with baffle)


1001.750.300.030.05

3005.201.000.100.52

5008.333.200.322.67

Graph 4.2: Graph of Power (W) against Angular speed (rpm), with baffle fixed

Experiment 8f: Determining the power consumed at different operating speed, using different impeller and without baffle

experiment 8f (without baffles)

Angular Speed(rpm)Angular Speed, (rotation/sec)Torque(kg-cm)Torque(Nm)Power(W)PoReVelocity(m/s)

1001.710.000.000.000.0052000.000.52

3005.010.100.010.050.04157000.001.57

5008.330.700.070.580.10262000.002.62

Graph 4.3: Graph of Po against Reynold number, Re, without baffle fixed

Experiment 8f: Determining the power consumed at different operating speed, using different impeller and with baffle

experiment 8f(with baffles)


1001.710.200.020.030.6452000.000.52

3005.011.000.100.500.40157000.001.57

5008.333.300.332.750.50262000.002.62

Graph 4.4: Graph of Po against Reynold number, Re, with baffle fixed

Impeller used: Hub Mounted Flat Blade ImpellerExperiment 8e: Determining the power consumed at different operating speed, using different impeller and without baffle

experiment 8e(without baffles)


1001.710.200.020.03

3005.010.000.000.00

5008.330.000.000.00

Graph 4.5: Graph of Power (W) against Angular speed (RPM), without baffle fixed

Experiment 8e: Determining the power consumed at different operating speed, using different impeller and with baffle

experiment 8e(with baffles)


1001.710.200.020.03

3005.010.000.000.00

5008.330.100.010.08

Graph 4.6: Graph of Power (W) against Angular speed (RPM), with baffle fixed

Experiment 8f: Determining the power consumed at different operating speed, using different impeller and without baffle

Experiment 8f(without baffles)


1001.710.100.010.021.9428860.000.39

3005.010.000.000.000.0085840.001.16

5008.330.000.000.000.00143560.001.94


Experiment 8f: Determining the power consumed at different operating speed, using different impeller and with baffle

experiment 8f(with baffles)

Angular Speed(rpm)Angular Speed, (rotation/sec)torque(kg-cm)Torque(Nm)Power(W)PoReVelocity(m/s)

100.001.710.200.020.032.9028860.000.39

300.005.010.000.000.000.0085840.001.16

500.008.330.100.010.080.06143560.001.94


5.0 DISCUSSIONIn general, when the hub-mounted flat blade impeller and disc-mounted flat blade impeller are placed vertically in the middle of the tank, it produces a swirling flow pattern, where the flow swirls radially.At 100 rpm and 200 rpm, there is not much of movement of beads is observed. The beads accumulate at the circumference of the mixing tanks bottom. This is due to the radially swirling flow pushes away the beads far to the circumference of the tank. The movement of the agitator does not produce significant mixing of the fluid. There is also no significant lifting capacity at lower RPM of the impeller. However, as the RPM increases, the beads will concentrate at the bottom middle of the mixing tank. This is because the current is most intensified at the centre of the tank. At 300 to 600 rpm, the flow of water and the movement of beads start to increase. This shows that when the speed increases, the flow will also increase. The patterns of the beads movements starting to be change slowly from radial pattern flows to axial pattern flows.While collecting the data, some torque value gives zero reading. For the value of torque that equal to zero, the actual value of it is not absolute zero, but approaching to zero. Due to the low sensitivity of Meter Controller, the values only take up to only one decimal point. Thus, the reading zero is considered valid.For Impeller 1 - Disc mounted flat blade impeller, Graphs 4.1 and 4.2 show that, when the baffle is present as well as when there is no baffle, the power increases as the angular speed increases. The presence of baffle increases the power of the system compared to the system without baffle. Graph 4.3 shows that when there is no baffle, as the Re increases, the Po increases. However, Graph 4.4 shows that when the baffle is present, Po decreases from 100 to 300 rpm and then increases from 300 to 500 rpm.For Impeller 2 - Hub mounted flat blade impeller, Graph 4.5 shows that when there is no baffle present, the power decreases from 0.02 Watts to 0 Watts, when from 100 to 300 rpm. At 300 rpm, the power reaches 0 Watts. No power is used for the angular speed above 300 rpm. Graph 4.6 shows that when the baffle is present, the power decreases from 100 to 300 rpm. At 300 rpm, the power reaches 0 Watts. The power then increases from the angular speed of 300 to 500 rpm, which is from 0 Watts to 0.8 Watts. When the power is 0W, it is because torque is 0Nm due to no moment of force as the beads are just lumped together without displacement. Graph 4.7 and 4.8 show that when the baffle is present as well as when there is no baffle, the value of Po decreases as the Re increases. This is because the impeller required energy to exert power to move beads inside the tank to move. Po reaches 0 when Re = 85840. There is a slight increase in Po as the value of Re increases after that.

RecommendationThe following recommendations can be taken into consideration while conducting the experiment:1. Ensure that the position of the impeller is being situated at the centre of the mixing tank.2. Ensure that the beads used to study the flow pattern are be accumulated in the middle of the tank. These would ensure that the observation can be made more easily. By putting the beads randomly at the bottom of the mixing tank, the formation is unclear especially at low rotational speed.3. Fix the agitator properly at the intended position. Avoid parallax error while fixing the agitators position. This would ensure that the agitator is fixed properly and the intended positioning of the impeller is achieved.4. Make sure that at least 25 cm of the tank is filled with water. This would ensure that the flow of the water (beads) can easily be seen. 5. Make sure that for each of the experiments, the beads are arranged back accordingly on the bottom layer of the tank. This would ensure that the flow pattern of the beads are not due to the previous experiments final position and is solely due to the observed flow pattern.6. Ensure that the rotations of the impellers are not too high. This will damage the equipment and induce splashing of liquid.

6.0 CONCLUSIONFrom this experiment, we can conclude that the pattern flow of water is affected by the type of impellers used as well as the numbers of rotation per minute of the impellers itself. The angular speed is affected the value of torque and later will affected the value of power consumed by the mixer. The presence of baffles will also affect the flow pattern of water. The yellow beads spread throughout the tank when baffle is present. The values of Reynolds Number justify the type of the flow of the water whether it is laminar or turbulent.

7.0 REFERENCESCremer, H. W., Chemical Engineering Practice, Vol. 8, Butterworths Scientific Publications, London, 1965.Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd edition, Vol. 19, John Wiley & Sons, USA, 1982.Paul, E.L., Atiemo-Obeng, V.A. and Krest, S.M., Handbook of Industrial Mixing, John Wiley & Sons, INC., Publication, 2003.Perry, R. H. and D. Green., Perrys Chemical Engineers Handbook, 6th edition, McGraw Hill, 1987.Smith, J. M., Chemical Engineering Kinetics, 3rd edition, McGraw-Hill, 1987.Petersen, E. E., Chemical Reaction Analysis, Prentice Hall Inc., USA, 1965.Mixing and Agitation. (n.d.). Retrieved 28 July, 2012 from http://www.pacontrol.com/process-information-book/Mixing%20and%20Agitation%2093851_10.pdfMixing of Fluid. (n.d). Retrieved 28 July, 2012 from http://chemical.eng.usm.my/ekc291/exp_manuals/EKC%20291_12_mixing%20characteristics.pdfSmith, J.M. (2011). Agitation Devices. Retrieved July 28, 2012 from http://www.thermopedia.com/content/549/

8.0 APPENDICESExperiment 8a: Determination of various flow patterns exhibited by different type of impellers (mixing tank without baffle)Impeller used: Shromed flat bladeSpeed: 100 rpm

Speed: 200 rpm

Speed: 300 rpm

Speed: 400 rpm

Speed: 500 rpm

Speed: 600 rpm

Impeller used: Hub mounted flat blade impellerSpeed: 100 rpm

Speed: 200 rpm

Speed: 300 rpm

Speed: 400 rpm

Speed: 500 rpm

Speed: 600 rpm

Experiment 8b: Determination of various flow patterns exhibited by different type of impellers (mixing tank with baffle)Impeller used: Shromed flat bladeSpeed: 100 rpm

Speed: 200 rpm

Speed: 300 rpm

Speed: 400 rpm

Speed: 500 rpm

Speed: 600 rpm

Impeller used: Hub mounted flat blade impellerSpeed: 100 rpm Speed: 200 rpm Speed: 300 rpm Speed: 400 rpm Speed: 500 rpm Speed: 600 rpm