The document summarizes an experiment to determine the relationship between speed of rotation, diameter, and power requirement for baffled and unbaffled tanks. Data showed that power number decreases as Reynolds number increases, and is higher for baffled tanks than unbaffled tanks under turbulent conditions. The power requirement increases with impeller size but operating at very high speeds can lead to inefficiency through vortex formation.

1. 1
ABSTRACT
The objective of the experiment is to determine the relationship of the speed of rotation
and diameter on power requirement for Baffled and unbaffled tanks. The experiment of
agitation is mostly recording the data obtained using a tachometer to measure or determine the
speed of rotation of the impeller and use this data to determine the objectives require in the
experiment. The data that was gathered showed that for increase of speed of rotation, that also
increases the Re, the power number decreases. This is also true for the diameter since Reynolds
number is proportional to the diameter of tank.

2. 2
1. Introduction
Agitation is the induced motion of a material or a mixture in a specific way, usually
in a circulatory pattern inside some sort of container. In the chemical and other processing
industries, many operations are dependent on effective agitation and mixing fluids. There are
a number of uses of agitation, some of these are blending two miscible liquids, dispersion of a
gas in a liquid as fine bubbles, it also helps heat distribution through the mixture or process.
Thus, agitation is not only used in experiments but also in industry. In production, the use of
the agitation systems through the vessel manufacturing improves the product quality by
eliminating uneven distribution of chemicals or components of the product. This is however,
not limited in materials, this also is commonly used in the application of food, dairy, water and
waste water, wine and mineral processing.
Equipment used in agitations usually consists of a container or a tank to hold the liquid
in place while the process is going on, one or more impellers to provide the shear flow, and a
motor to drive the impeller. In order for the impeller to rotate mechanical energy is required,
which in turn transmits this energy to the fluid.
This experiment seeks to understand the relationship between the power number
against Reynold’s number and the effect of speed rotation on power requirement for baffled
and unbaffled tanks. And to know the effect of impeller diameter on power requirement of
Agitation on baffled and unbaffled tanks.

3. 3
2. REVIEW OF RELATED LITERATURE
Liquids are agitated in a cylindrical vessel which can be closed or open to the air. There
are many factors which may affect the flow patterns in an agitated tank. These factors depend
on the fluid’s properties, the components in the fluid, types of baffles in the tanks, the geometry
of the tank, and the agitator itself. Inside a tank, a propeller or agitator is mounted in the center
of a tank with no baffles. By this usually a swirling flow pattern develops during agitation.
Agitators can be combined with other in tank mixer types. Agitator that is used in large
batches but are not very effective outside of producing flow, promoting heat transfer and
maintaining in-tank uniformly. An agitator cannot work without impeller, which imparts force
to the material being mixed. There are different examples of impellers namely propellers,
turbines, gates, anchors and paddles. Agitators is designed from both mechanical, such as the
design of motor, gear reducer, seal, shaft, and impellers.
Power Number is a dimensionless parameter used for estimating the power consumed
by the agitating impeller. It is also one of the most important parameters in mixing and also
used to predict power consumption. Power number can be calculated by:
𝑁𝑝 =
𝑃
𝜌𝑁3 𝐷5
This power number is a function of impeller type, Reynold’s number, and the impeller
diameter to tank diameter ratio. From the equation of Np, it can be observed that if the power
number for a given system is known, the power consumption, P, can be predicted from the
fluid density, 𝜌, impeller diameter, D, and rational speed, N.
Power number data for different type of impellers/turbines, under a give set of conditions are
documented in various technical literature. Typical values of power number (Np) are:

4. 4
• Axial flow impellers, such as marine, helical: 0,25 to 0,75
• Mixed flow impellers, such as kidney, pitch: 0,75 to 2,0
Power Number decreases with an increase in Reynolds number.
The Reynold’s number can be used to classify the impeller operations regimes. If
laminar flow, the power number is inversely proportional to Reynold’s number; if turbulent,
the power number is constant in fully baffled tanks and it is also proportional to the density of
the liquid, to the third diameter. The Reynold’s number can be calculated by:
𝑁𝑟𝑒 =
𝜌𝑁𝐷2
𝜇
As the Reynold’s number increases, the baffled tanks’ power number is evidently
greater compared to the unbaffled tanks.

5. 5
3. EQUIPMENT AND MATERIALS:
3.1 Equipment
• Agitator, 2 – blade paddle or square – pitch propeller (three sizes)
• Baffle strips (removable)
• Dynamometer
• Tachometer
• Container (10” diameter, 18” deep transparent)
3.2 Procedure
1. The container was filled with water to almost 14 inches.
2. The impeller was attached to the agitator.
3. The impeller was then immersed in the water inside the container such that the elevation
is about 4 inches.
4. With the dynamometer attached to the shaft, the power requirement was measured for
the different speed of rotation. The speed was measured using a tachometer.
5. The baffle was then placed in the container. Steps 3 and 4 were repeated.

6. 6
4. RESULTS AND DISCUSSIONS
4.1 Table 1. Recorded speed using the tachometer.
Size of Impeller Trial Without Baffle With Baffle
3.5 inches
1 252.1 308.1
2 230.4 259.4
3 115.9 211.8
2.75 inches
1 495.5 269.5
2 485.7 301.4
3 564.2 305.6
2.25 inches
1 1123.0 776.9
2 1482.1 802.0
3 1009.6 605.0

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4.2 Table 2. Computed values of NRe and NP
Size of
Impeller
Reynold’s Number Power Number
Trial
No.
With Baffles
Without
Baffles
With Baffles
Without
Baffles
1 198773.80 162644.84 11.32 20.66
3.5
inches
2 167354.50 148644.86 18.97 27.07
3 136644.89 74774.04 34.84 212.64
1 173870.62 319676.78 16.91 2.72
2.75
inches
2 194451.22 313354.21 12.09 2.89
3 197160.90 363999.27 11.60 1.84
1 501224.80 724514.68 0.71 0.23
2.25
inches
2 517418.32 956191.64 0.64 0.10
3 390321.80 651353.54 1.49 0.32
As for the data gathered, all Reynold’s number of baffled and unbaffled are over 4000
so the flow of the experiment is turbulent. As the Reynold’s number increases, the power
number of baffled and unbaffled decreases. This is because as the speed of the impeller was
increased, the power requirement decreases. But increasing the size of the impeller will also
increase the power requirement; however, it doesn’t mean that as an impeller operates ate high
speed is operating efficiently as it can lead to a vortex. All power number are based on the
specification of the dynamo which is 350 MW.

8. 8
5. CONCLUSION
Based on the results the power number of baffled and unbaffled tanks decreases as the
flow of the agitation becomes more turbulent. The calculated value of power numbers for the
baffled and unbaffled with a Reynolds number beyond 500000 is near to the typical power
number of common impeller (see in chapter 3). The experiment encountered many errors so
with the variations. However, as the Reynolds number increases, the power number of baffled
is greater than that of the unbaffled thus it can be said that unbaffled impellers consume much
power than that of the baffled under very turbulent circumstances.
6. RECOMMENDATIONS
Since the sticker used in the experiment is not liable, the students who will be
performing this experiment in the future shall use any sticker which reflect light or shiny
stickers.

9. 9
7. REFERENCES
1. Geankoplis C.J. 2012, Principles of Transport Processes and Separation Processes,
Pearson Education, Inc. pg. 929.
2. (Kenven010. (n.d.). Experiment-No.-12 - Experiment No 12 AGITATION 1
Objective... Retrieved from https://www.coursehero.com/file/13245615/Experiment-
No-12/
8. APPENDICES
Appendix A. Raw data
Size of Impeller Trial Without Baffle With Baffle
3.5 inches
1 252.1 308.1
2 230.4 259.4
3 115.9 211.8
2.75 inches
1 495.5 269.5
2 485.7 301.4
3 564.2 305.6
2.25 inches
1 1123.0 776.9
2 1482.1 802.0
3 1009.6 605.0

10. 10
Appendix B.
Formula used:
3. 𝑁𝑝 =
𝑃
𝜌𝑁3 𝐷5
4.
5. 𝑁𝑟𝑒 =
𝜌𝑁𝐷2
𝜇