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DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY
Faculty of Engineering and Built Environment
UNIVERSITY OF JOHANNESBURG
Doornfontein Campus
Lab report 1: Heat Exchanger
By
MATHABELA G
THERMODYNAMICS 3A (TRDMIA3)
B. ENG TECH IN MECHANICAL ENGINEERING
Engineering: Mechanical
LECTURER: Dr S.L. Gqibani
I declare that this assignment/report is my own, original work. All secondary material that I
used, whether from print or electronic sources, has been carefully acknowledged and
referenced according to the Mechanical Department requirements. I have not submitted this
work for credit previously. I understand that plagiarism is unacceptable, and I have studied
the department’s plagiarism and referencing policies as set out in the Learner guide.
Signed: Date: 16 APRIL 2021
ACKNOWLEDGEMENTS
I would like to express my deep and sincere gratitude to my lecturer Dr S.L. Gqibani, lab
technician Mr W.M. Tlali, tutor Miss L.L. Mathipa at the University of Johannesburg who
were very supportive, kind, sincere and motivative. They provided excellent guidance and
suggestions on the topic. I would also like to express my profound gratitude to all those who
indirectly guided and helped me in the preparation for this Laboratory report.
I would also like to express my special thanks of gratitude to my lecturer who provided
excellent knowledge on the topic, his passion and love for thermodynamics are inspiring.
TABLE OF FIGURES
Figure 1:Parallel flow in heat exchanger (obtained from: Applied thermodynamics and
Engineering textbook, chapter 16, p.614).................................................................................. 8
Figure 2:Counter flow in heat exchanger (obtained from: Applied thermodynamics and
Engineering textbook, chapter 16, p.614).................................................................................. 8
Figure 3:Counter current flow (Obtained from the laboratory guide provided by Dr S.L.
Gqibani)...................................................................................................................................... 9
Figure 4:Parallel current flow (Obtained from the laboratory guide provided by Dr S.L.
Gqibani).................................................................................................................................... 10
LIST OF TABLES
Table 1:Nomenclature................................................................................................................ 6
Table 2:Collected results for counter flow............................................................................... 11
Table 3:Collected results for parallel flow............................................................................... 11
Table 4:Calculated data for counter flow................................................................................. 13
Table 5:Calculated data for parallel flow................................................................................. 14
Nomenclature
Symbol Variable Units
V
cold
Cold stream flow rate g/s
V
hot
Hot stream flow rate g/s
T
1
Hot water Inlet to the heat
exchanger
T
2
Hot water outlet from the
heat exchanger
T
3
Cold water inlet to the heat
exchanger
T
4
Cold water outlet from the
heat exchanger
T
5
Hot water mid position 4
concentric tube
T
6
Cold water mid position for
concentric true
∆ T
hot
Decrease in hot fluid
temperature
K
∆ T
cold
Increase in cold fluid
temperature
K
C
P hot
Specific heat of the hot
stream
kJ / kg k
C
p cold
Specific heat of the cold
stream
kJ / kg k
ρ
Hot
The density of the host
stream
Kg/litre
ρ
Cold
The density of the cold
stream
Kg/litre
ηHotHot The temperature efficiency
of the hot stream
ηHotCold The temperature efficiency
of the cold stream
ηHotMean The mean temperature
efficiency
ηHotThermal Thermal efficiency
LMTD Logarithmic Mean
Temperature difference
K
Q
hot
The power emitted from the
hot stream
Watts
Q
cold
The power absorbed by the
cold stream
Watts
dTmax The maximum temperature
difference across the heat
K
1. INTRODUCTION
1.1 Objectives/Aims
To determine the heat transfer of fluids (water) by demonstrating indirect heating or
cooling of the heat transfer from one fluid to another, this indirect heating or cooling
is demonstrating by using parallel flow and counter flow heat exchangers.
To demonstrate the differences between counter-current flow and parallel flows and
the effect on heat transfer temperature efficiencies and temperature profiles through a
shell and tube heat exchanger.
To find the effect of the difference between a hot stream and cold stream temperatures
with counter current and parallel current flow.
1.2 Assumptions
The whole process is assumed to be adiabatic, which means there is no heat exchange
with the surroundings.
Heat transfer coefficients and thermophysical properties of fluids keep a constant
value at any time in the entire heat exchanger.
The process is assumed to be Isobaric
Parallel flow, in which fluids flow in parallel and the same direction
Counter-flow, in which fluids flow in parallel and the opposite direction
2. BACKGROUND/THEORY
Temperature can be expressed as the amount of thermal energy the substance consists
of. This thermal energy can be transferred from one fluid to another by heat
exchangers. In the process industry heat exchanges are important in ensuring that the
inlet flow streams, and the outlet flow streams are maintained to maximize efficiency.
The heat exchanger is a device that facilitates the transfer of thermal energy between
two or more fluids. For most heat exchangers, heat transfers occur indirectly this is
done via a heat transfer surface that separates the fluids ensuring they do not come
into direct contact with each other or leak. However, there are a few heat exchangers
where direct contact occurs between two fluids to exchange heat. The transfer of heat
occurs by three processes: conduction, convection and radiation. Heat is transferred
from the fluid through a solid wall of the pipe by conduction, heat is transferred from
one fluid to another by convection and radiation is not effective within heat
exchangers.
There are two type of flow distribution in heat exchangers which are parallel and
counter flow. Each experiment, with the individual heat exchangers, was carried out
twice to implement the different flow distribution. Parallel flow in heat exchangers Is
where the hot fluid supplied runs in the same direction as the cold fluid, as shown in
Figure 1 below. Counter flow is the opposite of parallel flow, where the hot fluid and
the cold fluid enter the heat exchanger from opposite ends and run in opposite
directions to each other as shown in Figure 2 below.
One of the most important processes in engineering is the heat exchanger between
flowing fluids. In heat exchangers the temperature of each fluid changes as it passes
through the heat exchanger, and hence the temperature of the dividing wall between
the fluid also changes along the length of the heat exchanger. Examples in practice in
which flow influence exchange heat our air intercoolers and preheaters, Condensers
and boilers in steam plant, condensers and evaporators in refrigeration units, and
many other industrial processes in which a liquid or gas is required to be either cooled
or heated [ CITATION Eas93 \l 1033 ].
Figure 1 :Parallel flow in heat exchanger (obtained from: Applied
thermodynamics and Engineering textbook, chapter 16, p.614)
Figure 2 :Counter flow in heat exchanger (obtained from: Applied
thermodynamics and Engineering textbook, chapter 16, p.614)
Heat Exchanger Calculations by using the following formulas:
1.Reduction in hot fluid temperature: ∆T hot = T 1
- T
2
- Increase in cold fluid temperature: ∆T hot = T 4
- T
3
3.The temperature efficiency of the hot stream:
ηHot = Hot =
T 1 − T 2
T 1 − T 3
4.The temperature efficiency of the hot stream
3.2 Set up for the parallel current
Figure 4 :Parallel current flow (Obtained from the laboratory guide provided by Dr S.L. Gqibani)
4. PROCEDURE
4.1 For counter flow
Set up the machine to counterflow (see Figure 3 for counter flow)
Connected the water inlet pipe and supply cold water from the pump
Turned the main switch and heater switch on.
Set the hot water temperature controller to 60º C
Set the cold-water flow rate to (V cold) 15 g/ sec
Set the hot water flow rate to (V hot) 50 g/ sec
Monitored the stream temperatures, the hot and cold flow rates to ensure they
remained close to the original setting.
Allowed the conditions to stabilise and took measurements from T 1
to T 6
Then Adjusted the cooling water flow to 30 g/ sec
Made sure that the hot flow rate remained at 50g/sec
Finally, allowed the condition to stabilise and took measurements from T 1
to T 6
again.
4.2 For parallel flow
Set up the machine to parallel (see Figure 4 for parallel flow)
Connected the water inlet pipe and supply cold water from the pump
Turned the main switch and heater switch on.
Set the hot water temperature controller to 60º C
Set the cold-water flow rate to (V cold) 15 g/ sec
Set the hot water flow rate to (V hot) 50 g/ sec
Monitored the stream temperatures, the hot and cold flow rates to ensure they
remained close to the original setting.
Allowed the conditions to stabilise and took measurements from T 1
to T 6
Then Adjusted the cooling water flow to 30 g/ sec
Made sure that the hot flow rate remained at 50g/sec
Finally, allowed the condition to stabilise and took measurements from T 1
to T 6
again.
5. RESULTS
5.1 For counter flow
Sr. no
T
1
T
5
) T
2
T
3
T
6
T
4
V
cold
(g/s)
V
hot
(g/s)
Table 2 :Collected results for counter flow
5.2 For Parallel flow
Sr. no
T
1
( ℃ ¿ T
5
T
2
T
3
T
6
T
4
V
cold
(g/s)
V
hot
(g/s)
Table 3 :Collected results for parallel flow
6. ANALYSIS OF RESULTS
6.1 Calculations for Counter flow
First sample from Table 2 (data collected from the 1
st
row)
Reduction in hot fluid temperature
∆ T
hot
= T
1
− T
2
¿ 1 0.5 K
Increase in cold fluid temperature
∆ T
cold
= T
4
− T
3
K
The temperature efficiency of the hot stream
ηHotHot =
T
1
− T
2
T
1
− T
3
× 100
Ave 9.35 15.65 1416.605 1926.61 16.49 27.56 22.
Table 4 :Calculated data for counter flow
From the calculated results we can note that the LMTD of counter flow is greater than that of
the parallel flow. Since counter flow has a larger LMTD, we can then conclude that it is more
efficient than the parallel flow. The temperature difference in counter flow is more uniform
throughout the entire exchanger, which reduces thermal stress that can lead to shaking or
motions that can become damaging to the equipment. Further, since the temperature
difference is more consistent, the heat exchange rate is also more consistent throughout the
exchanger.
6.2 Calculations for Parallel flow
First sample from Table 3 (data collected from the 1
st
row)
Reduction in hot fluid temperature
∆ T
hot
= T
1
− T
2
¿ 5 K
Increase in cold fluid temperature
∆ T
cold
= T
4
− T
3
K
The temperature efficiency of the hot stream
ηHotHot =
T
1
− T
2
T
1
− T
3
× 100
× 100
The temperature efficiency of the cold stream
ηHotcold =
T
4
− T
3
T
1
− T
3
× 100
× 100
The mean temperature efficiency
ηHotMean =
ηHotcold + ηHotHot
The power emitted from the hot stream
Q
hot
= C
P hot
× ρ
Hot
×V
hot
× ( T
1
− T
2
¿ 4.183 × 0.9852 × 50 × ( 7 3.5− 6 8 .5)
¿ 1030. 27 W
The power absorbed by the cold stream
Q
cold
= C
P cold
× ρ
cold
×V
cold
× ( T
4
− T
3
¿ 4.18 × 0.9975 × 15 × ( 3 8. 7 −22. 4 )
¿ 3398.18 W
The logarithmic Mean Temperature difference
LMTD =
dTmax − dTmin
ln
dTmax
dTmin
T
1
− T
4
−( T
2
− T
3
ln(
T
1
− T
4
T
2
− T
3
ln(
¿ 40.1 9 K
6.2.1 Calculated data
Sample
No.
∆ T
hot
∆ T
cold
Q
cold
Q
hot
ηHotHot ηHotcold ηHotMean
Units K K W W % % %
Ave 5.2 12.9 2293.25 1071.70 11.04 26.77 18.
Table 5 :Calculated data for parallel flow
Parallel flow
This is the type in which two fluids enter from the same end and exit from the same end
means the direction of flow is same for both the fluids i.e.travel parallel to one another when
either enter or leaves the tube. With parallel flow the temperature difference between the two
fluids is large at the entrance end, but it becomes small at the exit end as the two fluid
temperatures approach each other. The overall measure of heat transfer driving force, the log
mean temperature difference is greater for counter flow(from the calculated results we can
note that the LMTD of counter flow is greater than that of the parallel) so the heat exchanger
surface area requirement will be larger than for a counter flow heat exchanger with the same
inlet and outlet temperatures for the hot and the cold fluid.
