See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/354059818
MCEN3005 Applied Thermodynamics and Heat Transfer Laboratory Report:
Convection Heat Transfer
Experiment Findings · August 2021
DOI: 10.13140/RG.2.2.30176.40960
CITATIONS
READS
0
2,247
1 author:
Mohamed Adnan Azmie
Curtin University
6 PUBLICATIONS 0 CITATIONS
SEE PROFILE
All content following this page was uploaded by Mohamed Adnan Azmie on 22 August 2021.
The user has requested enhancement of the downloaded file.
Curtin University Dubai
Discipline of Mechanical Engineering
MCEN3005 Applied Thermodynamics and Heat Transfer
Laboratory Report: Convection Heat Transfer
Prepared by: Mohamed Adnan Azmie
Student ID No: 19382425
Date Due: 19/05/2021.
Table of Contents
Introduction ................................................................................................................................ 3
Objectives .................................................................................................................................. 4
Nomenclature ............................................................................................................................. 4
Theory ........................................................................................................................................ 4
Apparatus ................................................................................................................................... 6
Armfield HT10XC ................................................................................................................. 6
Steel Tube .............................................................................................................................. 6
Thermocouples ....................................................................................................................... 6
Test Article............................................................................................................................. 7
Electric Fan ............................................................................................................................ 7
Procedure ................................................................................................................................... 7
Results ........................................................................................................................................ 8
Discussion ................................................................................................................................ 10
Conclusion ............................................................................................................................... 11
References ................................................................................................................................ 11
Appendix 1 ............................................................................................................................... 12
Appendix 2 ............................................................................................................................... 13
Appendix 3 ............................................................................................................................... 15
List of Figures
Figure 1: Armfield HT10XC heat transfer service unit. Digital Image. Reproduced from:
https://www.dksh.com/global-en/products/ins/armfield-heat-transfer-ht10xc-computercontrolled-heat-transfer-teaching-equipment. ............................................................................ 6
Figure 2: Schematic diagram (AutoCAD) ................................................................................. 7
Figure 3: Experimental and theoretical heat transfer coefficients plotted against the air velocity.
.................................................................................................................................................. 10
Figure 4: Steam table consisting of dry air values (Engineering ToolBox 2005). .................. 12
Figure 5: Key features of Armfield HT10XC Digital Image. Reproduced from:
https://www.dksh.com/global-en/products/ins/armfield-heat-transfer-ht10xc-computercontrolled-heat-transfer-teaching-equipment. .......................................................................... 16
List of Tables
Table 1: Respective A and B values for different Re numbers.................................................. 5
Table 2: Measurements of apparatus ......................................................................................... 8
Table 3: Experimental readings to calculate experimental ℎ𝑒 ................................................... 9
Table 4: Steam Table values (Dry Air) @ 300K ....................................................................... 9
Table 5: Theoretical heat transfer coefficient values and the required parameters needed. .... 10
Introduction
Heat is a form of energy that can be transferred through three different modes. The total heat
transferred from a body is the sum of all three modes: conduction, convection, and radiation.
The conductive mode of heat transfer takes place through solids and requires a medium for the
heat to distribute. Convective mode of heat transfer takes place through fluids such as air,
water, and others. Lastly, radiation is the mode of heat transfer that can take place in the
absence of a medium (vacuum) (smlease design n.d.).
Transfer of heat within thermally conductive bodies or between thermally contacted bodies is
known as conduction. This mode of heat transfer depends heavily on the material, size, and
other characteristics of the body. The rate of heat transfer is directly proportional to the material
thermal conductivity.
The transfer of heat from one body to another through electromagnetic waves (mostly infrared)
is known as radiation (smlease design n.d.). Media are not required for this mode of heat
transfer. An example of radiation is the heat transfer from the sun to the earth’s surface.
The transfer of heat from one place to another through the movement of fluids is known as
convection (smlease design n.d.). There are two different types of convection heat transfer,
which are natural and forced convection. Natural convection is the heat transfer caused by
buoyancy forces (smlease design n.d.) while forced convection is the heat transfer caused by
an external force (smlease design n.d.). Many experimental studies involving flow around a
body initiated by cross-flow have demonstrated that the convective heat transfer of the body is
dependent on material type, size, temperature difference, fluid properties, velocity, the surface
roughness of the body and other factors (Ezzat and Zghaer 2013).
The convective heat transfer coefficient is a useful quantity, describing the heat transfer during
this mode of heat transfer. Higher the heat transfer coefficient, the higher the heat transfer
during convection. It allows for the determination of the rate of heat transfer for any given
surface of unit area and unit temperature difference.
The principles of heat transfer are also used in food processing such as pasteurisation.
Pasteurisation is a heat treatment similar to sterilization but less drastic. It neutralises diseaseproducing organisms (Unitops n.d.). Pasteurisation was originally meant to counter Bovine
tuberculosis, an infectious disease of cattle, in milk. A combination of temperature and time is
needed to sufficiently kill most species of bacteria or enzymes under consideration (Unitops
n.d.). For example, Mycobacterium tuberculosis is inhibited through heating at high
temperatures of 62.8 ̊C, 71.7 ̊C and 126.7 ̊C at their respective times of 30 min, 15 secs, 4 secs
(Unitops n.d.). An enzyme, phosphatase is also destroyed under similar conditions as
Mycobacterium tuberculosis (Unitops n.d.).
The heat transfer around a cylinder is important in applications such as heat exchangers, nuclear
reactor fuel rods, cooling towers and sensors (Hamad 2017). Heat exchangers are a system
used to transfer heat between fluids in both cooling and heating processes. Heat exchangers
utilize the heat transfer coefficient to determine the appropriate set-up and the necessary work
needed to reach the target temperature (Unitops n.d.). Common examples of heat exchangers
are internal combustion engine, where the incoming air cools the coolant by carrying the heat
away and heat sinks, where the heat generated is transferred to a fluid medium.
Heat transfer principles are used in air conditioning systems. Air conditioners are key
components in the HVAC systems, that cool a space through the removal of heat and transfer
it elsewhere (Afework, et al. 2018). They act similarly to a heat pump but follow a cooling
cycle. A cool liquid known as the refrigerant absorbs heat from the warmer area, cooling it
down. The refrigerant is then put through a compressor, after changing to the gaseous state, to
increase the temperature. The refrigerant passes through condenser coils cooling down while
transferring heat to the atmosphere. It cools to temperatures below room temperature and is
brought back only to repeat the process (Afework, et al. 2018).
Heat transfer principles are also used in refrigerators. Refrigerators are an open system that
removes heat from a closed space to a warmer area, usually to a kitchen. Through the removal
of heat, food can be kept at cool temperatures. Similar to heat pumps but instead of heating a
region, it cools a region (Afework, Hanania and Heffernan, et al. 2018). A refrigerator achieves
its results by compressing a coolant to increase its temperature and allowing the heat to escape
into the atmosphere thus reducing the temperature of the coolant (Afework, Hanania and
Heffernan, et al. 2018). The coolant expands and causes the temperature to reduce below the
temperature inside the refrigerator, where the heat is then removed as the cooler coolant passes
through (Afework, Hanania and Heffernan, et al. 2018).
Objectives
•
•
•
•
To determine the amount of heat carried by an open crossflow.
To determine the heat transfer coefficient using experimental values.
To estimate the heat transfer coefficient theoretically.
To compare and evaluate both predicted and experimental heat transfer coefficient
results.
Nomenclature
Symbol
ρ
μ
V
Re
Q
Pr
P
Nu
A
L
I
D
Cp
𝑇𝑤
𝑇∞
ℎ𝑒
ℎ𝑝
Name
Density
Dynamic viscosity
Voltage
Reynold’s number
Heat transfer
Prandtl’s number
Power
Nusselt number
Area
Length
Current
Diameter
Specific heat
Temperature of cylinder
Upstream temperature
Experimental heat transfer coefficient
Theoretical heat transfer coefficient
Unit
kg/m^3
kg/m s
V
W
W
m^2
M
Amps
m
kJ/kg K/
C
C
W/K m^2
W/K m^2
Theory
The convective heat transfer coefficient describes the transfer of heat through convection. The
convective heat transfer is directly proportional to the area (A) involved in the heat transfer
and the temperature difference ∆𝑇 between the bodies. Using the two relationships indicated,
the heat transfer by convection is given by the equation below.
𝑄 = 𝐴ℎ𝑒 ∆𝑇
The convective heat transfer coefficient for forced convection systems is governed by
temperature dependant parameters evaluated at a reference temperature.
𝐹𝑜𝑟𝑐𝑒𝑑 𝑐𝑜𝑛𝑣𝑒𝑐𝑡𝑖𝑜𝑛: 𝐺𝑜𝑣𝑒𝑟𝑛𝑖𝑛𝑔 𝑣𝑎𝑟𝑖𝑎𝑏𝑙𝑒𝑠 [ℎ, 𝑉, 𝐿, 𝜌, 𝜇, 𝑐𝑝 , 𝑘]
ℎ𝑝 𝐷
𝑘
𝜌𝑈𝐷
𝑅𝑒 =
𝜇
𝑁𝑢 =
𝑃𝑟 =
𝜇𝐶𝑝
𝑘
Where 𝑁𝑢 = Nusselt Number, 𝑅𝑒 = Reynold’s number and 𝑃𝑟 = Prandtl number.
Using the governing variables, a correlation is drawn using the Buckingham Theorem (S. and
R.J. 2004).
𝑁𝑢 = 𝐴 ∙ 𝑅𝑒 𝐵 𝑃𝑟 𝐶
where A, B, and C are semi-empirically determined constants. The correlation devised for
1
forced convection across a cylinder is known to have 𝐶 = 3, with the respective calculated A
and b for different Reynold’s number.
1
𝑁𝑢 = 𝐴 ∙ 𝑅𝑒 𝐵 𝑃𝑟 3
Table 1: Respective A and B values for different Re numbers
Re
40 − 4000
4000 − 40000
40000 − 250000
A
0.683
0.193
0.0266
B
0.466
0.618
0.805
The heat transfer correlation for a heated cylinder in a crossflow used in this laboratory was
determined by Churchill in 1977 (Churchill and Bernstein 1977). Through experimentation and
satisfying the needed boundary conditions, the correlation was established to fit for a heated
cylinder in a crossflow.
1
1
𝑁𝑢 = 0.3 + (0.62𝑅𝑒 2 𝑃𝑟 3 ) (1 + (
2
3
−
0.4
) )
Pr
1
4
5
8
4
5
𝑅𝑒
(1 + (
) )
282000
Apparatus
Armfield HT10XC
Armfield HT10XC is a computer-controlled service unit, allowing integration with a range of
small accessories for demonstration into the modes of heat transfer (Armfeild n.d.). The
corporation between facilities and safety features allow it to remotely control and shut down
the experiment in an event of communication failure (Armfeild n.d.). It also has the necessary
connections to incorporate the reading of temperatures using thermocouple wires. Additional
features can be found in appendix 3.
Figure 1: Armfield HT10XC heat transfer service unit. Digital Image. Reproduced from:
https://www.dksh.com/global-en/products/ins/armfield-heat-transfer-ht10xc-computercontrolled-heat-transfer-teaching-equipment.
Steel Tube
A cylindrical steel tube of about 1 meter in height is connected to the electric fan, test article,
anemometer, and the necessary thermocouples.
Thermocouples
Thermocouples are sensors that are used to measure temperature consisting of 2 wires of
different materials. The wires are connected at one end creating a junction where the
temperature is measured (REOTEMP 2011).
Test Article
A heated cylinder placed at the end of the steel tube with a thermocouple attached to the
surface. It is heated by coils inside the cylinder and powered by the Armfield HT10XC.
Electric Fan
An electric fan powered by an electric motor is used to divert air into the steel tube. The amount
of air can be varied by opening the door of the electric fan.
Figure 2: Schematic diagram (AutoCAD)
Procedure
•
•
•
•
•
Measure and note the dimensions (length and diameter) of the heated cylinder.
Ensure all safety procedures are taken; begin the experiment by turning on the electrical
motor and setting the air velocity to 0.5 m/s.
Supply a voltage of 15V and wait till the system becomes steady. Make sure the
cylinder thermocouple is at θ = 0 position.
Record the readings of voltage (V), current (A), upstream air velocity (U), upstream
temperature (𝑇∞ ), and cylinder temperature (𝑇𝑤 ) from the Armfield HT10XC by
turning the dial to the required parameter needed.
Increase the air velocity in increments of 1.0m/s until 6.5m/s. Record the readings for
each increment allowing sufficient time (>5min) for the system to become steady.
•
•
•
•
•
Increase the voltage to 20V, while maintaining the air velocity at 6.5m/s and record the
readings as done before.
Using the voltage and current, calculate the power supplied by the heater.
Using the upstream and cylinder temperatures, calculate the change in temperatures.
Calculate the area of the cylinder exposed to the crossflow.
Using the calculated power, change in temperature and area, calculate the heat transfer
coefficient.
Results
The recorded measurements of the heated cylinder are shown in table 2.
Table 2: Measurements of apparatus
Diameter
Length
Area
Measurements
0.01
0.07
0.00219911
m
m
m^2
The readings taken were then used to calculate the power and the change in temperature as
shown below. The recorded readings can be seen in table 3, along with the power and change
in temperature results. The sample calculations of power and change in temperature can be
found in appendix 2.
The area of the cylinder was calculated using the equation given below.
𝐴 = 𝜋𝑟𝐿
The power was calculated using the equation given below.
𝑄 = 𝑃 = 𝑉𝐼
The temperature change was calculated using the following equation.
∆𝑇 = (𝑇𝑤 − 𝑇∞ )
The experimental ℎ𝑒 can be calculated using the heat transfer rate equation.
𝑄 = ℎ𝑒 𝐴∆𝑇
ℎ𝑒 =
𝑄
𝐴∆𝑇
The experimental ℎ𝑒 for different air velocities are shown in table 3. Further explanation
regarding the calculation of the values presented in table 3 is shown in appendix 2.
Table 3: Experimental readings to calculate experimental ℎ𝑒
Air
Velocity
0.5
1.5
2.5
3.5
4.5
5.5
6.5
6.5
Voltage
Supplied
15
15
15
15
15
15
15
20
Current
Supplied
2.43
2.44
2.45
2.46
2.46
2.46
2.47
3.28
Power
Supplied
36.45
36.60
36.75
36.90
36.90
36.90
37.05
65.60
Cylinder Wall
Temperature
300
242
205
181
164
151
141
219
Ambient
Temperature
30.4
30
29.5
29.2
28.7
28.6
28.4
28.3
ΔT
He
269.6
212.0
175.5
151.8
135.3
122.4
112.6
190.7
61.48
78.50
95.22
110.54
124.02
137.09
149.62
156.42
The theoretical ℎ𝑝 is estimated using the heat transfer correlation.
1
1
𝑁𝑢 = 0.3 + (0.62𝑅𝑒 2 𝑃𝑟 3 ) (1 + (
where 𝑁𝑢 = average Nusselt number =
number =
𝜇𝐶𝑝
𝑘
ℎ𝑝 𝐷
𝑘
2
3
−
0.4
) )
Pr
1
4
5
8
4
5
𝑅𝑒
(1 + (
) )
282000
, 𝑅𝑒 = Reynold’s number =
𝜌𝑈𝐷
𝜇
, 𝑃𝑟 = Prandtl
.
The properties for the parameters in 𝑁𝑢, 𝑅𝑒 & 𝑃𝑟 are taken at the upstream temperature (𝑇∞ ).
Utilising steam tables in appendix 1, the parameters are seen in table 4 after taking the
temperature to be at 300 Kelvin.
Table 4: Steam Table values (Dry Air) @ 300K
ρ
μ
k
Cp
Steam Table Dry Air
1.177
0.00001846
0.00002624
1.0049
kg/m^3
kg/m s
kW/m K
kJ/kg K
The theoretical ℎ𝑝 is then estimated using the heat transfer correlation as shown in appendix 2,
within the above-established parameters. Table 5 consists of the predicted Nusselt number and
the predicted heat transfer coefficient.
Table 5: Theoretical heat transfer coefficient values and the required parameters needed.
Air
Velocity
0.5
1.5
2.5
3.5
4.5
5.5
6.5
6.5
Re
Pr
A
B
C
318.80
956.39
1593.99
2231.58
2869.18
3506.77
4144.37
4144.37
0.707
0.707
0.707
0.707
0.707
0.707
0.707
0.707
9.86
17.08
22.05
26.09
29.58
32.71
35.56
35.56
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
1.01
1.02
1.03
1.04
1.05
1.05
1.06
1.06
Nu
Predicted
9.06
15.64
20.26
24.09
27.44
30.48
33.29
33.29
Hp
23.7638
41.0292
53.1737
63.2109
72.0149
79.9848
87.3427
87.3427
After determining both experimental and theoretical heat transfer coefficients, they were
plotted against the air velocity as seen in the figure 3.
Heat Transfer Coefficient
180
160
140
120
100
80
60
40
20
0
0
1
2
3
4
5
6
7
Air Velocity
Experimental He
Theoretical Hp
Figure 3: Experimental and theoretical heat transfer coefficients plotted against the air
velocity.
Discussion
It is seen that the experimental heat transfer coefficient values are much larger than the
theoretical heat transfer coefficient values. This could result from the assumption that
experimental heat transfer (Q) is solely convective during the estimation of the theoretical heat
transfer coefficient values. Failure to account for the heat radiated by the heated cylinder could
cause these deviations between the theoretical and experimental results. Furthermore, the
estimation of the theoretical coefficients does not account for the temperature of the cylinder
as it is known that heat radiates more quickly when the difference in temperatures between the
surrounding and surface is greater. This is seen in table 5 as the last theoretical heat transfer
coefficient is the same as the previous one, whereas the experimental heat transfer coefficient
is higher as seen in table 4 for a greater voltage. This is further emphasised by figure 3 where
it is seen at an air velocity of 6.5 m/s, there are 2 heat transfer coefficients for the experimental
data set and only one for the theoretical data set, indicating that there was no change in the
theoretical heat transfer coefficient with an increase in power.
The uncertainty of measurement of the quantities used to calculate the experimental heat
transfer coefficient would produce a source of error. As it is not known what measuring tool
was used to determine the length and diameter of the steel pipe, the uncertainty found in these
measurements is unknown. Whereas the measurement device for the temperatures has a
resolution of <0.15 C. This produces very little error within the results. Another source of error
would be the time allowed for the system to become steady. Therefore, the accuracy of the
readings will be higher if more time should be given for the system to stabilise.
Conclusion
The laboratory set out to determine the heat transfer coefficient experimentally and
theoretically and to compare both heat transfer coefficient values. The experimental heat
transfer coefficient was calculated using the parameters recorded during the experiment:
power, area, and the temperature difference between the upstream and heated cylinder surface.
The theoretical heat transfer coefficient values were determined using the correlation
established by Churchill (Churchill and Bernstein 1977). The experimental and theoretical
values were then plotted against the air velocities to determine the discrepancies between the
results. The causes of these discrepancies were discussed, and potential errors were identified.
Resolving these errors would improve the accuracy of the results. In conclusion, this laboratory
has successfully met the objectives set out at the beginning.
References
Afework, Bethel, Jordan Hanania, Braden Heffernan, James Jenden, Ellen Llyod, Kailyn
Stenhouse, Karen Street, Jasdeep Toor, and Jason Donev. 2018. Energy Education Refrigerator.
Accessed
May
5,
2021.
https://energyeducation.ca/encyclopedia/Refrigerator.
Afework, Bethel, Jordan Hanania, Kailyn Stenhouse, and Jason Donev. 2018. Energy
Education
Air
conditioner.
Accessed
May
5,
2021.
https://energyeducation.ca/encyclopedia/Air_conditioner.
Armfeild. n.d. Armfield - Heat Transfer - HT10XC Computer Controlled Heat Transfer
Teaching Equipment. Accessed May 5, 2021. https://www.dksh.com/globalen/products/ins/armfield-heat-transfer-ht10xc-computer-controlled-heat-transferteaching-equipment.
Churchill, S. W., and M. Bernstein. 1977. “A Correlating Equation for Forced Convection
From Gases and Liquids to a Circular Cylinder in Crossflow.” J. Heat Transfer 300306.
Engineering ToolBox. 2005. Dry Air Properties. Accessed May
https://www.engineeringtoolbox.com/dry-air-properties-d_973.html.
5,
2021.
Ezzat, Akram, and Hassan W. Zghaer. 2013. “Forced Convection Heat Transfer around Heated
Inclined Cylinder.” International Journal of Computer Applications 5-11.
doi:10.5120/12759-8631.
Hamad, Faik. 2017. “Heat Transfer from a Cylinder in Cross-Flow of Single and Multiphase
Flows.” 2nd International Conference on Fluid Dynamics & Aerodynamics. Rome:
ResearchGate.
REOTEMP. 2011. Welcome to ThermocoupleInfo.com! Accessed May 5, 2021.
https://www.thermocoupleinfo.com/#:~:text=A%20Thermocouple%20is%20a%20sen
sor,temperature%2C%20a%20voltage%20is%20created.
S., Sanitjai, and Goldstein R.J. 2004. “Forced convection heat transfer from a circular cylinder
in crossflow to air and liquids.” International Journal of Heat and Mass Transfer Pages
4795-4805.
smlease design. n.d. Modes of Heat Transfer: Conduction, Convection and Radiation.
Accessed May 5, 2021. https://www.smlease.com/entries/thermal-design/modes-ofheat-transfer-conduction-convection-radiation/.
Unitops. n.d. Chapter 6 - Heat Transfer Application.
Appendix 1
Dry Air steam table (Engineering ToolBox 2005).
Figure 4: Steam table consisting of dry air values (Engineering ToolBox 2005).
Parameter values used to estimate the theoretical heat transfer coefficient were taken at a
temperature of 300 K.
Appendix 2
Area calculation:
𝐴 = 𝜋𝐷𝐿
𝐴 = 𝜋 ∙ 0.012 ∙ 0.07 = 0.0021991𝑚2
Power calculation:
𝑃 = 𝑉𝐼
𝑃 = 15 ∙ 2.43
𝑃 = 36.45𝑊
Change in temperature calculation.
∆𝑇 = (𝑇𝑤 − 𝑇∞ )
∆𝑇 = (300 − 30.4)
∆𝑇 = 269.6 𝐶
Experimental heat transfer coefficient ℎ𝑒 calculation
ℎ𝑒 =
ℎ𝑒 =
𝑄
𝐴∆𝑇
36.45
0.0021991 ∙ 269.6
ℎ𝑒 = 61.48 𝑊 ⁄𝑚2 𝐾
Reynold’s number.
𝑅𝑒 =
𝑅𝑒 =
𝜌𝑈𝐷
𝜇
1.177 ∙ 0.5 ∙ 0.01
1.846 × 10−5
𝑅𝑒 = 318.80
Prandtl’s number
𝑃𝑟 =
𝜇𝐶𝑝
𝑘
1.846 × 10−5 ∙ 1.0049
𝑃𝑟 =
2.624 × 10−5
𝑃𝑟 = 0.707
Predicted Nusselt number.
1
1
𝑁𝑢 = 0.3 + (0.62𝑅𝑒 2 𝑃𝑟 3 ) (1 + (
−
2
3
0.4
) )
Pr
1
1
4
1
1
𝐴 = (0.62(318.8)2 (0.707)3 ) = 9.86
2
3
−
0.4
𝐵 = (1 + ( ) )
Pr
1
4
4
5
𝑅𝑒
(1 + (
) )
282000
𝐴 = (0.62𝑅𝑒 2 𝑃𝑟 3 )
1
5
8
−
2
3
0.4
) )
𝐵 = (1 + (
0.707
1
4
= 0.88
5
8
4
5
𝑅𝑒
) )
𝐶 = (1 + (
282000
𝐶 = (1 + (
5
8
4
5
318.8
) ) = 1.01
282000
𝑁𝑢 = 0.3 + (𝐴 ∗ 𝐵 ∗ 𝐶)
𝑁𝑢 = 0.3 + (9.86 ∗ 0.88 ∗ 1.01) = 9.06
Calculation of theoretical heat transfer coefficient ℎ𝑝 .
ℎ𝑝 = 𝑁𝑢 ∙
ℎ𝑝 = 9.06 ×
𝐷
𝑘
0.01
= 23.7638 𝑊 ⁄𝑚2 𝐾
−5
2.624 × 10
Appendix 3
Armfield key features were taken from the Armfield site (Armfeild n.d.).
Figure 5: Key features of Armfield HT10XC Digital Image. Reproduced from:
https://www.dksh.com/global-en/products/ins/armfield-heat-transfer-ht10xc-computercontrolled-heat-transfer-teaching-equipment.
View publication stats