Design of electric stirrer.

We have designed this electric stirrer in for calorimeter of the refrigeration test rig. Also, this is cost efficient and effective in working.

1. Report of Minor Project

In

Uniform distribution of heat in calorimeter in
Refrigeration Test Rig.

By

Rohan R. Deshmukh (TYB-03)
Swapnil R. Mahajan (TYB-32)



Submitted in partial fulfillment of the requirement for

Degree of Bachelor of Technology
(Mechanical Engineering)

Of

Dr. Babasaheb Ambedkar Marathwada University,

Aurangabad.






Department of Mechanical Engineering,

Maharashtra Institute of technology,
Aurangabad.
2018-2019

2. CERTIFICATE


This is to certify that the Minor Project Report
Submitted by



Rohan R. Deshmukh (TYB-03)
Swapnil R. Mahajan (TYB-32)



Is completed as per the requirement of Dr. Babasaheb Ambedkar
Marathwada University, Aurangabad in partial fulfillment of


Degree of Bachelor of Technology (Mechanical Engineering)
For the academic Year 2018-2019









Prof. Irfan A. Syed Dr. A. J. Keche Dr. S. P. Bhosle
Guide Head of Department Principal

3. ACKNOWLEDGMENT

The satisfaction that accompanies the successful completion of this minor project would
be incomplete without the mention of the people who made it possible, without whose constant
guidance and encouragement would have made of efforts go in vain. We consider our self-
privileged to express gratitude and respect towards all those who guided us through the
completion of this minor Project.

Our guide Prof. Irfan A. Syed provided we lot of knowledge of this Minor Project also
gives the meaning of Minor Project and said the increase world’s technology towards do
something. It is chiefly to their untiring efforts and an analytical guidance which encourages us
at every step during Minor Project work.

We are grateful to Dr. A. J. Keche, Head of the Mechanical Engineering Department for
giving us support and encouragement that was necessary for the completion of this Minor
Project.

We express our deepest regards towards our Principal Dr. S.P.Bhosle and library for
providing required books time to time.

4. INDEX
1. Abstract…………………………………………………1
2. Introduction…………………………………………….2
3. Objectives………………………………………………3
4. Literature Survey…………………………………..….4
5. System Development…………………………………..5
5.1 Test Rig Basics………………………………….5
5.2 Problem Identification ………………………….8
5.3 Problem Solution Method……………………….8
6. System Analysis………………………………………11
6.1 Design parameters………………………………11
6.2 Selection of Motor………………………………11
6.3 Johnson Geared DC motor Description……….12
6.4 Geometric Location………………………….…14
6.5 Flow Pattern …………………………………….16
6.6 Electrical Supply and Connections……………..18
6.7 Working ………………………………………….19
7. Advantages And Disadvantages ………………………20
8. Conclusion………………………………………………21

5. 9. Reference ……………………………………………..22

6. List Of Figures
Figure 5.1 Refrigeration Test Rig
Figure 5.3(a) Pneumatic stirrer
Figure 5.3(b) Magnetic Stirrer
Figure 5.3(c) Electric Stirrer
Figure 6.2(a) Input Output of electric motor
Figure 6.2(b) DC motor
Figure 6.3(a) Johnson Geared Motor
Figure 6.3(b) Wireframe diagram of motor
Figure 6.4 Location of Stirrer
Figure 6.5(a) Tangential flow pattern
Figure 6.5(b) Radial flow pattern
Figure 6.5(c) Axial flow pattern
Figure 6.6 Electrical Component Circuit
Figure 6.7 Actual Stirrer

7. Table List
Table 6.3 Specification of Johnson DC motor

8. 1

ABSTRACT

In this minor project we are designing an electric stirrer to attain uniform distribution of
heat in water of calorimeter in refrigeration test rig.

In a calorimeter provided to us the water heater and the evaporator coil of VCC system
are located. Both are submerged in water. Both the devices (i.e. water heater and evaporator coil)
operates at the same time. Due to upside location of heater in the calorimeter in test rig; the heat
distribution by water inside it is not uniform in nature. When fluids (liquids) are heated, they
expand and therefore become less dense. Any object or substance that is less dense than a fluid
will float in that fluid, so hot water rises (floats) in colder water. Often it affects the precise
reading of temperature by thermocouple.

Agitation field find its application along wide range of industries like food, laboratories
and chemicals etc. Agitation is putting into motion by shaking or steering to achieve mixing.
consisting of electric motor, impeller shaft, impeller blades and calorimeter carrying water. So it
is designed to operate in such environment. The electricity is supplied to electric Johnson DC
geared motor which runs at 500 rpm.

This project will present an electric stirrer / agitator which is able to improve precise
working of calorimeter.

9. 2


INTRODUCTION

Test Rig enables students to study and understand Vapour Compression Cycle, its
components, principle and working. All the components are mounted on rigid steel frame.

The trainer consists of a hermetically sealed compressor; forced convection air-cooled
condenser, filter / drier, flow meter, expansion device and shell & coil type evaporator. Separate
pressure gauges are provided to record suction and discharge pressures and digital temperature
indicators for various temperatures. The refrigerant used is R-134a, which is environment
friendly. The calorimeter consists of an insulated stainless steel tank. The evaporator tubes are
made of refrigerated grade annealed copper tubes. This is a direct expansion type evaporator.
The heat absorbed by the refrigerant is balanced by heater input. The heater is immersion type
resistive water heater. This project is focused on improvement in working of the calorimeter.

A calorimeter is an object used for calorimetry, or the process of measuring the heat of
chemical reactions or physical changes as well as heat capacity. In a calorimeter provided to us
the water heater and the evaporator coil of VCC system are located. Both are submerged in
water. Both the devices (i.e. water heater and evaporator coil) operates at the same time. The
heater generates the heating effect in water and evaporator coil produces cooling effect in water
at the same time. Thus uniform distribution of heat or exchange of heat is done by the stirrer.

Thermocouple are located in the calorimeter to monitor the temperature reading.
Due to upside location of heater in the calorimeter in test rig; the heat absorption by water inside
it is not uniform in nature as hot water rises or floats in cold water due to its less density.
Ultimately it is affecting the precise reading of thermocouple.

This system can be used to avoid this error in reading by designing an
agitator/stirrer to attain uniform absorption of heat in water of calorimeter.

10. 3


OBJECTIVES

• The objectives of this project is to design and implement an electric stirrer which will
improve the precise working of calorimeter.
• To develop an electric stirrer to attain uniform absorption of heat in water of
calorimeter in refrigeration test rig.
• To obtain precise reading by avoiding error due to uneven heat distribution of heat in
water of calorimeter.

11. 4


Literature Survey
• Kevin J. Myers [1] of University Of Dayton in February 2002 presents a research
paper on “Optimize Mixing By the proper Baffles”.
When the high velocity streams come into contact with stagnant or slower
mowing liquid, momentum transfer occurs. Baffles promote better flow in an agitated
vessel but how to apply them and what kind to use takes some ingenuity.
Agitation field find its application along wide range of industries like food,
cosmetics, chemical and pharmaceutics etc. According to Kevin J. Myers the
momentum transfer phenomenon can be used shear action is necessary in fluids.
• Joanna Karcz [2] of Department of chemical engineering Present research paper “An
effect of impeller position on dispersion of floating particles in an agitated vessel”.
Key findings are, in order to avoids the floating of low density particles at the
top of vessel and in order to achieve the proper mixing.
• Julian fasano [3], Eric E. Janz, Kevin Myers in 2012 present a research article on
“Design Mixers To Minimize Effects of Erosion and Corrosion Erosion”.
The research paper focused on various static and dynamic factors that affect
the rate of erosion. Key findings are, in order to achieve the proper mixing blade
position should be 0.67*H

12. 5

5.System Analysis
5.1Test Rig Basics
5.1.1 Refrigeration Test Rig
The experimental Refrigeration Cycle Test Rig consist of a compressor unit, condenser,
evaporator, cooling chamber, controlling devices and measuring instruments those are fitted on
a stand and a control panel. The test rig is used to study Refrigeration Cycle, to determine Co-
efficient of Performance of Cycle.

Figure 5.1 Refrigeration Test Rig

13. 6

The Refrigeration Test Rig works on vapour compression cycle. The refrigeration (i.e.
process of maintaining a closed space temperature below ambient temperature) is
accomplished by continuously circulating, evaporating and condensing a fixed supply of
refrigerant in a closed system. Evaporation occurs at a low temperature and low pressure
while condensation occurs at a high temperature and pressure. Thus it is possible to transfer
heat from an area of low temperature (in this case evaporator) to an area of high temperature
(the surroundings). The compressor pumps the low-pressure refrigerant from the evaporator
through the accumulator, increases its pressure, and discharges the high-pressure gas to the
condenser. The accumulator prevents liquid refrigerant entering the compressor. In the
condenser, the refrigerant rejects its heat to the surroundings by passing air over it. At that
pressure, the refrigerant loses its latent heat and liquefies. Then the refrigerant passes through
the drier/filter where any residual moisture or foreign particles present, these are plugged.
The flow of refrigerant into the evaporator is controlled by expansion device where its
pressure and consequently temperature is lowered to the saturation temperature at the
corresponding pressure. The low temperature refrigerant enters the evaporator where it
absorbs heat from the surrounding medium and evaporates. The compressor sucks the cold
vapours and the cycle repeats. The required instrumentation is provided to measure the
various parameters at different points. This includes pressure gauges, temperature indicators
and controller, energy-meters, heater for applying load and flow meter to measure the
refrigerant flow. The calorimeter consists of an insulated stainless steel tank. The evaporator
tubes are made of refrigerated grade annealed copper tubes. This is a direct expansion type
evaporator. The heat absorbed by the refrigerant is balanced by heater input. Our project is
mainly focused on effective working of calorimeter.
5.1.2 Calorimeter
A calorimeter is an object used for calorimetry, or the process of measuring the heat of
chemical reactions or physical changes as well as heat capacity. Differential scanning
calorimeters, isothermal micro calorimeters, titration calorimeters and accelerated rate
calorimeters are among the most common types. A simple calorimeter just consists of a
thermometer attached to a metal container full of water suspended above a combustion
chamber. It is one of the measurement devices used in the study of thermodynamics,
chemistry, and biochemistry.
5.1.3 Adiabatic calorimeters
An adiabatic calorimeter is a calorimeter used to examine a runaway reaction. Since
the calorimeter runs in an adiabatic environment, any heat generated by the material sample
under test causes the sample to increase in temperature, thus fuelling the reaction. No

14. 7

adiabatic calorimeter is fully adiabatic - some heat will be lost by the sample to the sample
holder. A mathematical correction factor, known as the phi-factor, can be used to adjust the
calorimetric result to account for these heat losses.

5.1.4 Reaction calorimeters
A reaction calorimeter is a calorimeter in which a chemical reaction is initiated within
a closed insulated container. Reaction heats are measured and the total heat is obtained by
integrating heat flow versus time. This is the standard used in industry to measure heats since
industrial processes are engineered to run at constant temperatures.[citation needed] Reaction
calorimetry can also be used to determine maximum heat release rate for chemical process
engineering and for tracking the global kinetics of reactions.
5.1.5 Constant-pressure calorimeter
A constant-pressure calorimeter measures the change in enthalpy of a reaction
occurring in solution during which the atmospheric pressure remains constant. An example is
a coffee-cup calorimeter, which is constructed from two nested Styrofoam cups and a lid with
two holes, allowing insertion of a thermometer and a stirring rod. The inner cup holds a
known amount of a solvent, usually water, that absorbs the heat from the reaction.
5.1.6 Thermocouple
A Thermocouple is a sensor used to measure temperature. Thermocouples consist of
two wire legs made from different metals. The wires legs are welded together at one end,
creating a junction. This junction is where the temperature is measured. When the junction
experiences a change in temperature, a voltage is created. Thermocouples are placed in the
calorimeter to obtain temperature reading.

15. 8

5.2 Problem Identification

In a calorimeter provided to us the water heater and the evaporator coil of VCC system
are located. Both are submerged in water. Both the devices (i.e. water heater and evaporator coil)
operates at the same time. The heater generates the heating effect in water and evaporator coil
produces cooling effect in water at the same time. Thus uniform distribution of heat or exchange
of heat is done by the stirrer. Due to upside location of heater in the calorimeter the heat
absorption by water inside in it is not uniform in nature. When fluids (liquids and gases) are
heated, they expand and therefore become less dense. Any object or substance that is less dense
than a fluid will float in that fluid, so hot water rises (floats) in colder water. When fluids are
cooled, their molecules contract and therefore become more dense. Any object or substance that
is more dense than a fluid will sink in that fluid, so cold water sinks in warmer water. Due to this
the heat distribution in the evaporator tube in contact with hot water is not uniform.

5.3 Problem Solution Methods

5.3.1 Design of heating coil at the bottom of calorimeter
We can design heating coil arrangement fixed at the bottom of calorimeter. As we can
mount the heating coil at the bottom of container such that water gets heated from lower
direction. Thus we can avoid the problem of non-uniform heat distribution of water. But this is
not feasible solution as it is difficult to mount it due to leakage issue of water. This solution
requires a lot of changes in the original calorimeter which is not cost efficient.
5.3.2 Design of stirrer
In industrial process engineering, mixing is a unit operation that involves manipulation of
a heterogeneous physical system with the intent to make it more homogeneous. liquid. A rotating
agitator produces high velocity liquid streams, which move through the vessel. When the high
velocity streams come into contact with stagnant or slower mowing liquid, momentum transfer
occurs.
5.3.3 Pneumatic Stirrer
Pneumatic mixers sometimes called air-mix mixers or air-drive mixers are mixers that
uses compressed air or air bubbles instead of electricity to mix or homogenize materials or
powders. The blender consists of a mixing silo and in some cases a central conveying tube with
an inverted conical deflector at the top for spreading material. Pneumatic blenders are equipped
with aerators mounted around a housing cone. Compressed air or gas is introduced intermittently
at high velocities through nozzles present at the bottom or side of the silo, to mix powder
materials that exhibit expansion characteristics when aerated.

16. 9



Figure 5.3(a) Pneumatic Stirrer
5.3.4 Magnetic Stirrer
A magnetic stirrer or magnetic mixer is a laboratory device that employs a rotating magnetic
field to cause a stir bar (or flea) immersed in a liquid to spin very quickly, thus stirring it. The
rotating field may be created either by a rotating magnet or a set of stationary electromagnets,
placed beneath the vessel with the liquid. Because of its small size, a stirring bar is more easily
cleaned and sterilized than other stirring devices. They do not require lubricants which could
contaminate the reaction vessel and the product. Magnetic stirrers may also include a hot plate or
some other means for heating the liquid.


Figure 5.3(b) Magnetic Stirrer
5.3.5 Electric Stirrer
Propeller stirrer are used to thoroughly stirring(mingling) of water throughout the
calorimeter cylindrical water tank. The propeller stirrer mainly works on the principle of

17. 10

shearing force. It has the capacity to mix low viscosity emulsions. The stirrer is driven by the
electric motor. It includes propeller shaft and propeller blades.


Figure 5.3(c) Electric Stirrer

18. 11

6. System Development
6.1 Design Parameter
Depending on purpose of the operation carried out in a mixer, the best choice for the
geometry of the tank and impeller type can vary widely. Different materials require different
types of impellers and tank geometries in order to achieve the desired product quality. The flow
field and mixing process even in a simple vessel are very complicated. The fluid around the
rotating impeller blades interacts with the stationary baffles and generates a complex, three-
dimensional turbulent flow. The other parameters like impeller clearance from the tank bottom,
proximity of the vessel walls, baffle length also affect the generated flow. The presence of such
a large number of design parameters often makes the task of optimization difficult.

6.1.1 Factors to be considered while designing
a. Type of agitator
b. Circulation pattern
c. Location of agitator in the basic equipment
d. Shape and size of tank
e. Diameter and width of agitator
f. Power required for agitation
g. Shaft overhang
h. Types of stuffing box or seal, s, drive systems etc.

6.2 Selection Of Motor
6.2.1 DC Motor
The DC motor is a rotary electrical machine which converts electrical energy (direct
current energy) into mechanical energy. They uses electric field produced by the conductor
which is responsible for the rotary motion of the rotor. DC motors are used to drive the stirrer.

Figure 6.2(a) Inputs and outputs of electric motor
Input
Voltage and
Current
Electric motor
Output
Torque and RPM

19. 12


6.2.3 Operating Principle of DC motor
A machine that converts DC power into mechanical power is known as a DC motor. Its
operation is based on the principle that when a current carrying conductor is placed in a
magnetic field, the conductor experiences a mechanical force. The direction of this force is
given by Fleming’s left hand rule and magnitude is given by;

F=BIL


Figure 6.2 (b) DC Motor
6.2.3 Working of DC motor
An electric current carrying wire in a magnetic field experiences force. The direct current
convert electrical energy into mechanical energy through the interaction of two magnetic field.
One field is produced by a permanent magnet assembly, the other field is produced by an
electrical current flowing in the motor winding. These two field interact with each other result
in torque with tend to rotate the rotor. The direction of rotation is given by the Flemings left
hand rule.

6.3 Johnson Geared DC motor description

A Johnson Geared motor is a simple DC motor with gear box attached to the shaft of the
motor which is mechanically commutated electric motor powered from direct current (DC).
This motor is known for their compact size and massive torque-speed characteristic. The
Johnson Motor comes with side shaft also known as an off-centered shaft and six M3 mounting
holes. The shaft of the motor equips metal bushes which makes these DC gear motors Shaft
wear resistant. The shaft of the motor has a hole for better coupling.

20. 13



Figure 6.3(a) Johnson Geared Motor

6.3.1 Johnson DC motor Specification


Rated RPM 600
Operating Voltage(VDC) 6 to 18
Nominal Voltage (V) 12
Rated Torque(kg-cm) 1.2
Stall Torque(Kg-Cm) 5.2
No-Load Current 350mA
Shaft Diameter * Length in (mm) 6*280
Max. stirring capacity (Water) 20Litre

Table 6.3 Specification of Johnson DC motor

21. 14




6.3.2 Wireframe Diagram of Johnson DC motor




Figure 6.3(b) Wireframe Diagram

22. 15

6.4 Geometric Location Of Stirrer

For sake of convenience we are placing stirrer motor (Johnson DC motor) 8CM away
from the heating coil arrangement on the calorimeter lead. Thus it will be isolated from the coil
arrangement and the physical damage to the stirrer and propeller shaft can be circumvented.
Following is the wireframe diagram representing the heater and motor arrangement which is
prepared with Auto Cad software.





Figure 6.4 Location of stirrer on Lead of calorimeter
(All dimensions are in CM)








Stirrer
Motor
Heater
Coil

23. 16

6.5 Flow Patterns in Stirred Vessel
According to the main directions of the streamlines in the vessel, there are three principal
types of flow. These are tangential flow, radial flow and axial flow.

6.5.1 Tangential flow
Where the liquid flows parallel to the path is shown in fig . When the flow is
predominantly tangential, discharge of liquid from the impeller to the surroundings is small.
Tangential flow takes place in a paddle type impeller running at a speed, which is not sufficient
to produce a noticeable action of the centrifugal force.


Figure 6.5(a) Tangential Flow Pattern


6.5.2 Radial flow
The liquid discharges from the impeller at right angles to its axis and along a radius.
figure shows the flow pattern of a impeller with its axis coinciding with that of the vessel and
producing radial flow. In this case it is apparent that the impeller produces two flow sections;
one is in the bottom part of the vessel it entrains the liquid in the upward direction and displaces
it at right angles to the axis of the impeller; the other is in the upper part of the vessel, the
impeller entrains the liquid downwards, displacing it like perpendicular to the impeller axis.

24. 17


Figure 6.5(b) Radial Flow Pattern



6.5.3 Axial flow
Axial flow, in which the liquid enters the impeller and discharges from it parallel to it
axis as shown in figure.


Figure 6.5(c) Axial flow Pattern

25. 18



6.6 Electrical supply and Components

Basically Johnson motor is DC motor so we have to design a adapter or SMPS to provide
12V DC supply to the motor. 12V DC is the safe voltage to operate the motor. Thus SMPS or
AC/DC adapter plays a vital role in all electric component. Following is the circuit diagram of
the circuit.









Figure 6.6 Electric Component Circuit







Ac/Dc
Adapter
230V
AC
12V Dc
Supply
Johnson
Motor
+
-

26. 19

6.7 Working
It consists of motor (500rpm, 12V DC) impeller shaft with lock arrangement and
impeller (3 Blade type). The impeller is connected to the impeller shaft with the help of
fastening glue. When motor is started by providing 12V DC supply, it rotate at 500RPM. This
speed is transmitted to impeller through impeller shaft. Because of this Impeller rotate at
designed speed, so that proper mixing of is carried out. So that homogeneous mixing is
achieved with minimum vibrations.
In a calorimeter provided to us the water heater and the evaporator coil of VCC system are
located. Both are submerged in water. Both the devices (i.e. water heater and evaporator coil)
operates at the same time. The heater generates the heating effect in water and evaporator coil
produces cooling effect in water at the same time. Thus uniform distribution of heat or
exchange of heat is done by the stirrer.


Figure 6.7 Actual Stirrer

27. 20


7. Advantages And Limitations.

7.1 Advantages
• Low noise and vibration so no need of vibration isolator.
• Required less maintenance.
• No need to provide baffles.
• Low cost due to less number of accessories
• It achieves various chemical properties and dilute solution is obtained.
• It is energy efficient.
• As sufficient turbulence is achieved in the mixing chamber, hence homogeneous mixing
is obtained.

7.2 Limitations
• Able to work in particular range of viscosity
• Limited capacity.
• Designed for particular application.

28. 21




8. Conclusion

Thus the system is prepared by designing and manufacturing the components, and
assembled these components with standard available parts. The machine setup is then tested to
ensure its satisfactory performance. During the testing it is found that, the machine is able to
work with specified rpm and sufficient turbulence is created inside the calorimeter. The
vibrations created during running condition are much less. These all results in homogenous
mixing of contents in the calorimeter , which are our main objectives. The problem is that the
machine is able to work in particular range of viscosity and it is able to handle the limited
capacity for which it is previously designed. For given conditions the performance of machine
is found to be satisfactory. In future for large capacity tanks concept of baffling, sensors and
concept of square vessel are also suggested.

29. 22

Reference

1. D. Chitra of VIT India in April-June 2014. Present a research article on “Effect of Impeller
Clearance and Multiple Impeller Combinations on solid Suspension in a Standard Flat
Bottom Agitated Vessel”.
2. “Design of Machine Elements”, V.B. Bhandari, Tata McGraw Hill, Third edition.
3. “A Textbook of Fluid Mechanics and Hydraulic Machines” ,R.K. BANSAL.
4. “FLUID MECHANICS (SIE)”, Frank M. White ,Tata McGraw Hill.
5. “Refrigeration And Air Conditioning”, C.P. Arora.