DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY
Faculty of Engineering and Built Environment
UNIVERSITY OF JOHANNESBURG
Doornfontein Campus
HEAT EXCHANGER
By
B Dube
220092592
Refrigeration and Air Conditioning 3B (RACMIB3)
B.ENG TECH: Mechanical Engineering
LECTURER: Dr. C. Anghel
Date: 27/09/2023
Statement of Originality
I, Banele Dube, state that this written report is my own original analysis. The secondary materials
used, whether electronic or written, have been carefully defined and referenced according to the
type of reference used by the Department of Mechanical and Industrial Technology of the
University of Johannesburg.
Signed: B.Dube
Date: 27/09/2023
Table of Contents
Objective ......................................................................................................................................... 4
Theory/background ....................................................................................................4
Apparatus: ..................................................................................................................6
Procedure....................................................................................................................7
Observations...............................................................................................................7
Analysis of Results: ...................................................................................................8
For Counter Flow Srl 1: ..........................................................................................8
For Counter Flow Srl 2: ..........................................................................................9
For Parallel Flow, Srl 1:........................................................................................ 11
For Parallel Flow, Srl 2:........................................................................................12
Results ......................................................................................................................14
For Counter Flow: ................................................................................................14
For Parallel Flow: .................................................................................................14
Discussion/Conclusion .............................................................................................15
REFERENCES.........................................................................................................16
Objective
To demonstrate indirect heating and/or cooling by the heat transfer from one fluid to another.
Theory/background
Heat exchangers are an essential component of any manufacturing facility since they may
significantly lower fuel use, prices, and carbon emissions on their own. The efficiency of the
plant can be impacted by the heat exchangers, and as industries develop, so does the demand for
enhanced and more efficient heat exchangers. We must therefore educate ourselves on the
background of these devices and how they have changed over time. [1]
“The recorded history of Heat Exchangers can be traced around the 1880s, their major
applications being the food and beverage industries. It is widely recognized that the first
recorded patent for a Plate heat exchanger was awarded to Albrecht Dracke of Germany in
1878. However, the first modern and commercial examples of Heat Exchangers would be
observed in the early 1900s.” [3]
A heat exchanger is a device that moves heat from one medium to another. For example, a
swimming pool heat exchanger warms the water in the pool by using hot water from a boiler or a
solar heated water circuit. [2] Through the materials of the exchanger, which separate the
working media, heat is transported through conduction. A shell and tube heat exchanger moves
fluids over and through tubes, whereas an air-cooled heat exchanger cools a liquid by moving
cool air through a core of fins.[4]
Shell & tube heat exchanger:
This type of heat exchanger has a bundle of tubes enclosed in a shell, usually cylindrical. The
tubes are arranged parallel to the shell axis. One fluid stream is passed through the bundle of
tubes, while the other fluid stream flows through the shell over the tubes. [Figure 1] Overall heat
transfer between the fluid streams is enhanced using multiple shell & tube passes. With the use
of baffles, the shell-side fluid stream is re-routed and made to flow back-and-forth over the tubes.
[3]
Figure 1: Shell and Tube Heat exchanger
The temperature efficiency is a valuable indicator of heat exchanger performance. The maximum
temperature difference between the two streams is compared to the temperature change in each
stream (hot and cold). This could only happen in an infinitely large, perfect heat exchanger with
no external gains or losses. [1]
The temperature efficiency of the hot stream:
ηHot =
𝑇1−𝑇2
𝑇1−𝑇3
The temperature efficiency of the cold stream:
ηCold =
𝑇4−𝑇3
𝑇1−𝑇3
The mean temperature efficiency:
ηMean =
ηHot+ ηCold
2
The LMTD is a logarithmic average of the temperature difference between the hot and cold fluid
streams at each end of the heat exchanger. The larger the value of LMTD, the higher heat is
transferred.[1]
The LMTD can be calculated using the formula stated below:
LMTD =
𝑑𝑇𝑚𝑎𝑥−𝑑𝑇𝑚𝑖𝑛
=
ln
𝑑𝑇𝑚𝑎𝑥
𝑑𝑇𝑚𝑖𝑛
(𝑇1−𝑇4)−(𝑇2−𝑇3)
ln(
𝑇1−𝑇4
)
𝑇2−𝑇3
All the equations above were taken from
Apparatus:
Figure 2: Heat Exchanger used in lab experiment.
Where:
T1: Hot water inlet to the heat exchanger
T2: Hot water outlet from the heat exchanger
T3: Cold water inlet to the heat exchanger
T4: Cold water outlet from the heat exchanger
Procedure
1. The machine was set to counter flow.
2. The water inlet pipe was connected to supply the cold water from the pump.
3. The main switch and heater were switched on.
4. The hot water temperature controller was set to 60º C.
5. Cold water flow rate was set to (V cold) 15 g/sec.
6. Hot water flow rate was set to (V hot) 50 g/sec.
7. The temperature of the streams was monitored to ensure that they remain close to the
original.
8. Measurements T1-T6 were taken.
9. Cooling water flow rate was adjusted to 30 g/sec whilst hot water flow rate remained at
50g/sec.
10. Measurements T1 – T4 were taken again.
Observations
For Counter Flow
Srl
1
2
T1 °C
30.1
29.5
T2 °C
28.8
27.8
T3 °C
12.1
12.1
T4 °C
18.4
16.9
V cold
15 g/s
30 g/s
V hot
50 g/s
50 g/s
T2 °C
31.6
30.3
T3 °C
11.8
11.9
T4 °C
14.5
16.6
V cold
15 g/s
30 g/s
V hot
50 g/s
50 g/s
For Parallel Flow
Srl
1
2
T1 °C
34.4
32.6
Analysis of Results:
For Counter Flow Srl 1:
Reduction in hot fluid temperature: T1 – T2 = 30.1 – 28.8
= 1.3 ºC
Increase in cold fluid temperature: T4 – T3 = 18.4 - 12.1
= 6.3 ºC
The temperature efficiency of the hot stream:
𝑇1−𝑇2
ηHot = 𝑇1−𝑇3
30.1−28.8
= 30.1−12.1
= 0.07022 x 100
= 7.22 %
The temperature efficiency of the cold stream:
𝑇4−𝑇3
ηCold = 𝑇1−𝑇3
18.4−12.1
= 29.5−12.1
= 0.3620689 x100
= 36.21 %
The mean temperature efficiency
ηMean =
ηHot+ ηCold
2
=
0.07022+0.36206
2
= 0.21613
= 21.613 %
The power emitted from the hot stream ( Qhot):
Q = Vhot x phot x cphot x (T1 – T2)
= (0.05) (0.9852) (4.183) (303.1 – 301.8)
= 0.267 kW
The power absorbed by the cold stream ( Qcold)
Q = Vcold x pcold x cpcold x (T3– T4)
= (0.015) (0.9975) (4.18) (291.4 – 285.1)
= 0.394 kW
The Logarithmic Mean Temperature difference (LMTD):
LMTD =
𝑑𝑇𝑚𝑎𝑥−𝑑𝑇𝑚𝑖𝑛
ln
𝑑𝑇𝑚𝑎𝑥
𝑑𝑇𝑚𝑖𝑛
=
(𝑇1−𝑇4)−(𝑇2−𝑇3)
=
(30.1−18.4)−(28.8−12.1)
ln(
𝑇1−𝑇4
)
𝑇2−𝑇3
30.1−18.4
)
28.8−12.1
ln(
= 14.05 ºC
For Counter Flow Srl 2:
Reduction in hot fluid temperature: T1 – T2 = 29.5 – 27.8
= 1.7 ºC
Increase in cold fluid temperature: T4 – T3 = 16.9 – 12.1
= 4.8 ºC
The temperature efficiency of the hot stream:
𝑇1−𝑇2
ηHot = 𝑇1−𝑇3
29.5 − 27.8
= 29.6 − 12.1
= 0.11494 x 100
= 11.494 %
The temperature efficiency of the cold stream:
𝑇4−𝑇3
ηCold = 𝑇1−𝑇3
16.9−12.1
= 29.5−12.1
= 0.27586 x100
= 27.59 %
The mean temperature efficiency:
ηMean =
ηHot+ ηCold
2
=
0.11494+0.27586
2
= 0.1954
= 19.54 %
The power emitted from the hot stream ( Qhot):
Q = Vhot x phot x cphot x (T1 – T2)
= (0.05) (0.9852) (4.183) (1.7)
= 0.35 kW
The power absorbed by the cold stream ( Qcold)
Q = Vcold x pcold x cpcold x (T3– T4)
= (0.03) (0.9975) (4.18) (4.8)
= 0.6 kW
The Logarithmic Mean Temperature difference (LMTD):
LMTD =
𝑑𝑇𝑚𝑎𝑥−𝑑𝑇𝑚𝑖𝑛
ln
𝑑𝑇𝑚𝑎𝑥
𝑑𝑇𝑚𝑖𝑛
=
=
(𝑇1−𝑇4)−(𝑇2−𝑇3)
𝑇1−𝑇4
)
𝑇2−𝑇3
ln(
(29.5−16.9)−(27.8−12.1)
29.5−16.9
)
27.8−12.1
ln(
= 14.093 ºC
For Parallel Flow, Srl 1:
Sr.no 1
Reduction in hot fluid temperature: ∆T hot = T1 - T2
= 34.4 – 31.6
= 2.8 ºC
Increase in cold fluid temperature: ∆T cold = T4 - T3
= 14.5 – 11.8
= 2.7 ºC
The temperature efficiency of the hot stream:
𝑇1−𝑇2
ηHot = 𝑇1−𝑇3
34.4−31.6
= 34.4−11.9
= 0.1244 x 100
= 12.44 %
The temperature efficiency of the cold stream:
𝑇4−𝑇3
ηCold = 𝑇1−𝑇3
14.5−11.8
= 34.4−11.8
= 0.11946 x100
= 11.95 %
The mean temperature efficiency
ηMean =
ηHot+ ηCold
2
=
0.1244+0.11946
2
= 0.12195 x 100
= 12.195 %
The power emitted from the hot stream ( Qhot):
Q = Vhot x phot x cphot x (T1 – T2)
= (0.05) (0.9852) (4.183) (2.8)
= 0.577 kW
The power absorbed by the cold stream ( Qcold)
Q = Vcold x pcold x cpcold x (T4– T3)
= (0.015) (0.9975) (4.18) (2.7)
= 0.1689 kW
The Logarithmic Mean Temperature difference (LMTD):
LMTD =
𝑑𝑇𝑚𝑎𝑥−𝑑𝑇𝑚𝑖𝑛
ln
𝑑𝑇𝑚𝑎𝑥
𝑑𝑇𝑚𝑖𝑛
=
(𝑇1−𝑇3)−(𝑇2−𝑇4)
=
(34.4 −11.8)−(31.6 −14.5)
𝑇1−𝑇3
)
𝑇2−𝑇4
ln(
34.4−11.8
)
31.6 − 14.5
ln(
= 19.722 ºC
For Parallel Flow, Srl 2:
Sr.no 2
Reduction in hot fluid temperature: ∆T hot = T1 - T2
= 32.6 – 30.3
= 2.3 ºC
Increase in cold fluid temperature: ∆T cold = T4 - T3
= 16.6 – 11.9
= 4.7 ºC
The temperature efficiency of the hot stream:
𝑇1−𝑇2
ηHot = 𝑇1−𝑇3
32.6−30.3
= 32.6−11.9
= 0.11111 x 100
= 11.11 %
The temperature efficiency of the cold stream:
𝑇4−𝑇3
ηCold = 𝑇1−𝑇3
16.6−11.9
= 32.6−11.9
= 0.22705 x100
= 22.71 %
The mean temperature efficiency
ηMean =
ηHot+ ηCold
2
=
0.1111 + 0.22705
2
= 0.1691 x 100
= 16.91 %
The power emitted from the hot stream ( Qhot):
Q = Vhot x phot x cphot x (T1 – T2)
= (0.05) (0.9852) (4.183) (2.3)
= 0.4739 kW
The power absorbed by the cold stream ( Qcold)
Q = Vcold x pcold x cpcold x (T4– T3)
= (0.03) (0.9975) (4.18) (4.7)
= 0.5879 kW
The Logarithmic Mean Temperature difference (LMTD):
LMTD =
𝑑𝑇𝑚𝑎𝑥−𝑑𝑇𝑚𝑖𝑛
ln
𝑑𝑇𝑚𝑎𝑥
𝑑𝑇𝑚𝑖𝑛
=
(𝑇1−𝑇3)−(𝑇2−𝑇4)
=
(32.6−11.9)−(30.3−16.6)
𝑇1−𝑇3
)
𝑇2−𝑇4
ln(
32.6 − 11.9
)
30.3 −16.6
ln(
= 16.96 ºC
Results
For Counter Flow:
srl
Reduction
Increase in Temperature Temperature
Mean
Power
Power Logarithmic
in hot fluid
cold fluid
efficiency
efficiency temperature emitted absorbed
Mean
temperature temperature.
of the hot
of the cold
efficiency
from
by cold Temperature
(ºC)
(ºC)
stream
stream
(%)
the hot
stream
(LMTD)
(%)
(%)
stream (Qcold)
(ºC)
(Qhot)
(kW)
(kW)
1
1.3
6.3
7.22
36.21
21.613
0.267
0.394
2
1.7
4.8
11.494
27.59
19.54
0.35
0.6
For Parallel Flow:
srl
Reduction
Increase in Temperature Temperature
Mean
Power
Power Logarithmic
in hot fluid
cold fluid
efficiency
efficiency temperature emitted absorbed
Mean
temperature temperature.
of the hot
of the cold
efficiency
from
by cold Temperature
(ºC)
(ºC)
stream
stream
(%)
the hot
stream
(LMTD)
(%)
(%)
stream (Qcold)
(ºC)
(Qhot)
(kW)
(kW)
1
2.8
2.7
12.44
11.95
12.195
0.577
0.1689
2
2.3
4.7
11.11
22.71
16.91
0.4739
0.5879
Discussion/Conclusion
Counter flow:
It can be seen that the power emitted from the hot stream and the power absorbed by the cold
stream are almost the same with the difference being 0.127. This difference can be accounted for
either heat lost to the atmosphere or human error in taking the measurements.
When the water flow rate of the cold water is increased the overall temperatures decreased. The
temperature efficiency of the hot stream increased whilst the temperature efficiency of the cold
stream decreased. A conclusion can be made that the flow rate of the cold water is inversely
proportional to the power absorbed by the cold water when the flow rate of the hot water remains
constant.
When the flow rate of the cold water was increased both the power emitted and absorbed by the
hot and cold stream respectively increased.
Parallel flow:
For parallel flow a similar observation can be seen with regards to the increase in flow rate of the
cold water, the temperature efficiency of the hot water decreases slightly whilst the temperature
efficiency of the cold-water increases.
When the flow rate of the cold water was increased the power emitted by the hot water dropped
slightly and power absorbed by the cold stream increased.
CHECK THIS -- Meanwhile the Logarithmic Mean Temperature difference (LMTD) increases
with the increases of the cold-water flow rate which is the opposite of what happens with the
counter flow.
The experiment was successfully completed, and it successfully showed the flow in a heat
exchanger. Additionally, the experiment's objectives were achieved.
It can be concluded that the experiment was successful, and the objective was achieved.
REFERENCES
1. Khurmi, R.S. and Gupta, J.K., 2008. A textbook of thermal engineering. S. Chand
Publishing.
2. Kern, D.Q. and Kern, D.Q., 1950. Process heat transfer (Vol. 871). New York: McGrawHill.
3. Kakac, S. and Liu, H., 2002. ″Heat Exchangers Selection, Rating and Thermal Design ″,
Dept. of Mech. Eng. Univ. of Miami, Coral Gables, Florida.
4. Kays, W.M. and London, A.L., 2016. Compact heat exchangers.
5. Cornelissen, R.L. and Hirs, G.G., 1999. Thermodynamic optimization of a heat
exchanger. International journal of heat and mass transfer, 42(5), pp.951-960.