COLLEGE OF AERONAUTICAL ENGINEERING
(DEPARTMENT OF AEROSPACE ENGINEERING)
Heat Transfer
ME-305
LAB NO 08
Assessment No 08
LAB: To study the heat transfer from an extended surface resulting from convection and
Radiation mode of heat transfer.
1.
INTRODUCTION. The Heat Transfer Service Unit is utilized in the subject experiment.
The details are discussed below:
2.
HEAT TRANSFER SERVICE UNIT (H111).
The Hilton Heat transfer service unit
H111 is a benchtop unit designed to support and instrument various optional heat transfer
experiments to demonstrate one or more fundamental methods of heat transfer. It consists of:(a)
Steel fabricated console which contains main input and a variable voltage 0-240
Volts at 2 amps, and a power outlet point for connecting optional equipment.
(b)
12 Type K input sockets for thermocouples. These are connected using miniature
plugs which are suitable for temperatures in the range of 0-999.9 oC.
(c)
It has a 30mA residual current circuit breaker for disconnecting the system from
the mains in case of current leakage.
3.
EXTENDED SURFACE HEAT TRANSFER SERVICE UNIT (H111E).
The
Hilton
Extended surface heat transfer H111E accessories allow the investigation of one-dimensional
conduction from a pin. A small diameter metal rod is heated at one end and the remaining
exposed length is allowed to cool by natural convection and radiation. This results in a
dimensioning temperature distribution along the bar that is measured by regularly spaced
thermocouples. The H111E is designed to be used with and installed alongside the heat transfer
service unit service H111.
(a) The accessories compare a 10mm diameter brass rod of approximately 250mm
effective length mounted horizontally with support at the heated end and a mounting at
the opposite end.
(b) Inside an insulated hosing is a 240 Volt electric heater in direct contact with the
brass rod. The heater has a normal power rating of approximately 30 Watts at 240 Volts
AC. The power supplied to the heated cylinder is provided by the heat transfer service
unit H111. The transfer service unit H111 also allows the operator to vary the power input
to the heater by controlling the voltage supply to the heater element.
1|Page
Lab Handout
COLLEGE OF AERONAUTICAL ENGINEERING
(DEPARTMENT OF AEROSPACE ENGINEERING)
Heat Transfer
ME-305
LAB NO 08
Assessment No 08
(c) For safety purposes, a thermostat limits the maximum temperature of the heater
to approximately 150 °C.
(d) Eight thermocouples are located at 50mm intervals along the rod to record the
surface temperature. These are connected to the heat transfer service unit H111 through
the miniature plugs. The thermocouples are attached to the rod to minimize errors from
conduction effects. An additional thermocouple is mounted on the unit to record the
ambient air temperature.
(e) To protect the thermocouple from damage, all lead termination is mounted firmly
into turning and conduit. Also, the rod is coated with a heat resistant matt black paint to
provide a constant radiant emissivity close to 1.
4.
INSTALLATION OF EXTENDED SURFACE HEAT TRANSFER UNIT H111E WITH
HEAT TRANSFER SERVICE UNIT H111.
Assuming that the basic INSTALLATION AND
COMMISSIONING procedures for the heat transfer service unit H111 have been completed,
following steps ensure that the proper connection between the service unit and H111E.
(a)
Ensure that the main switch is in the OFF position.
(b) Place the Radial Heat conduction unit on a flat surface adjacent to the Heat transfer
Service Unit H111.
(c) Connect the nine miniature thermocouples plugs from temperature sensors to the
sockets marked T1 to T9 in the front of the heat transfer service unit H111. Note that
each thermocouple plug has a cable marker for identification.
(d) Set the heater voltage controller on the front of the heat transfer service unit to
zero (Turn anti-clockwise).
(e) Connect the power lead from the heated cylinder to the eight-pole socket on the
front panel of the heat transfer service unit H111.
5.
GENERAL OPERATING PROCEDURE
Experiment 6
2|Page
Lab Handout
COLLEGE OF AERONAUTICAL ENGINEERING
(DEPARTMENT OF AEROSPACE ENGINEERING)
Heat Transfer
ME-305
LAB NO 08
Assessment No 08
(a)
Objective:
(i)
To study the heat transfer from an extended surface resulting from
convection mode of heat transfer.
(ii)
(b)
To compare the results with the theoretical analysis.
General Procedure.
Following procedure is to be adopted for the experiment:-
(i)
Ensure that the main switch is in the OFF position (the digital displays
should not be illuminated), and ensure that the residual current circuit breaker on
the rear panel is in the ON position.
(ii)
Turn the voltage controller anti-clockwise to set the AC voltage to a
minimum and ensure the extended surface Heat Transfer Service Unit H111E has
been connected to the Heat Transfer Unit H111 as described above.
(iii)
Ensure that the heated cylinder is located inside the hosing before turning
ON power to the unit.
(iv)
Turn on the main switch and the digital display should illuminate the
temperature selector display T1. Rotate the voltage controller to increase the
voltage approximately to 120 volts.
(v)
After adjusting the heater voltage ensure that T1 (the temperature of the
thermocouple closer to the heater) varies by the sense of adjustment i.e. if the
voltage is increased, the temperature T1 should also increase. Also, if the voltage
is reduced the temperature T1 should also reduce. Note that if T1 is close to 100°C
and the current (Amps) displays zero, it may be that the safety thermostat has
been activated. Reduced the voltage and wait for the thermostat to reset.
(vi)
Monitor the temperature regularly and allow the system to reach stability
until T1 reaches approximately 80°C then reduce the heater voltage to
approximately 70 volts. This procedure will reduce the time taken for the system
to reach a stable operating condition.
3|Page
Lab Handout
COLLEGE OF AERONAUTICAL ENGINEERING
(DEPARTMENT OF AEROSPACE ENGINEERING)
Heat Transfer
ME-305
LAB NO 08
Assessment No 08
(vii) When T1 through T8 has reached a steady-state temperature, record the
temperatures from T1 to T9, Voltage ‘V’ and current ‘I’.
(viii) Increase the voltage controller to give 120 volts reading, monitor T1 for
stability and repeat the readings.
(ix)
Once readings have been completed, the voltage may be reduced to zero
to allow the rod to cool. Finally, turn off the main switch.
(x)
Perform calculation using the formula given at the end and write down the
results of calculations in the attached table, and plot the measured and calculated
values of temperature in degree Celsius vs. distance from T1 in meters.
Notes:
• During operation the heated rod will be operating up to 100 °C. Treat the unit
with caution and observed operating procedures as there is a burn hazard if the
cylinder is touched.
(c)
Theory.
(i)
A pin of length L diameter D and cross-sectional area A (Perimeter P) and
thermal conductivity K is heated at one end. It has a total surface area As and is in
ambient temperature Ta as shown in the Figure 1.
Figure 1: Experimental Setup
4|Page
Lab Handout
COLLEGE OF AERONAUTICAL ENGINEERING
(DEPARTMENT OF AEROSPACE ENGINEERING)
Heat Transfer
ME-305
LAB NO 08
Assessment No 08
(ii) Due to the heat input from one end, the temperature of the bar is raised above
that of the surroundings, and heat is convected and radiated away from the surface.
As the heater input is from one end only and the bar is thermally conductive, the
temperature will vary along the bar from T1 at the hot end to T8 at the other end. It is
assumed that the bar is sufficiently long for there to be negligible heat transfer from
the tip. At any distance X from the heated end, the temperature of the material is Tx.
(iii)
The heater is convected and radiated away from the bar with an overall
conviction coefficient of ‘h’.
(iv)
From the above condition, it is possible to develop the following deferential
equation to describe conditions along the bar.
d2 Tx / dX2 – hP/kA (Tx – Ta) = 0
where perimeter
P = dAs / dx
by introducing
θ = Tx – Ta
The equation becomes
d2θ / dX2 – hP/KA θ = 0
If we introduce
m2 = hP/KA
Then the equation can be written as
d2θ / dX2 – m2 θ = 0
(v)
It can be shown that the general solution to this equation may be written as
θ = C1 e(mx) + C2 e (-mx); where C1 and C2 are constant of integration.
(vi)
The following boundary conditions may be applied.
At X = 20 (The heat input)
Tx = T1
At X = L (The end of the rod) d θ / dx = 0; (if there is no heat transfer at the tip this
implies there is no temperature gradient between the tip and the surroundings).
(vii)
5|Page
By applying boundary conditions, it can be shown that
Lab Handout
COLLEGE OF AERONAUTICAL ENGINEERING
(DEPARTMENT OF AEROSPACE ENGINEERING)
Heat Transfer
ME-305
LAB NO 08
Assessment No 08
(Tx –Ta) / (T1 – Ta) = coshm (L –x)/ coshmL
where m = √
(viii)
hP
KA
Therefore, the equation may be re-written as
(Tx –Ta) / (T1 – Ta) = cosh√
hP
KA
(L –x)/ cosh√
hP
KA
L
(xi)
The mathematical development of the above theory is greatly simplified and
more detailed derivations may be found in typical textbooks on heat transfer.
(d)
Calculation.
(i)
Results can be calculated using the following formulae and useful data
Heated Rod diameter
Heated Rod effective length
Heated Rod effective cross-sectional area
Heated Rod surface area
Thermal Conductivity of heated rod material
Stefan Boltzmann Constant
D = 0.01m
L = 0.35m
As = 7.854 x 1010 m2
A = 0.01099 m2
K = 121 W/mK
𝜎 = 5.67 x 10-8 W/m2K4
(ii)
The problem in the further calculations is the unknown value of the overall
heat transfer coefficient ‘h’. Therefore, it is necessary to calculate the values
iteratively in this instance. This is a simple but lengthy process and the following
steps will simplify the process.
(iii)
Assume any value of ‘m’, but a starting value of m = 7.4 will reduce the
number of iterations.
(iv)
Calculate (Tx –Ta) / (T1 – Ta) and coshm (L –x) / coshmL for number of
temperatures and compare these results.
6|Page
Lab Handout
COLLEGE OF AERONAUTICAL ENGINEERING
(DEPARTMENT OF AEROSPACE ENGINEERING)
Heat Transfer
ME-305
LAB NO 08
Assessment No 08
(v)
Based upon the result, change the assumed value of ‘m’ remembering that
reducing the value of ‘m’ will increase the value of coshm (L –x) / coshmL.
(vi)
Repeat the steps (iv) and (v), till a reasonably accurate value of ‘m’ has
been achieved, then Tx can be calculated using the following equation
Tx = (T1 – Ta)
(vii)
coshm (L –x)
coshmL
+ Ta
Compare the calculated and observed values these should match.
(viii) Once ‘m’ has been determined to a reasonable degree of accuracy such
that the errors between the equations are minimized, the equation relating to heat
transfer from the fin i.e. Q̇x = KAm (T1 – Ta) tanh(mL) can be used and Q̇x can be
calculated.
(ix) Compare the calculated heat transfer rate with measured one and comment
on the difference.
6.
SAFETY PRECAUTIONS:
(a)
Know locations of laboratory safety showers, eyewash stations, and fire
extinguishers. Safety equipment may be located in hallway near laboratory entrance.
(b)
Know emergency exit routes.
(c)
Avoid distracting or startling persons working in the laboratory.
(d)
Use equipment only for its designated purpose.
(e)
Determine the potential hazards and appropriate safety precautions before
beginning any work.
(f)
Avoid working alone in a building. Do not work alone in a laboratory if the
procedures being conducted are hazardous.
7|Page
Lab Handout
COLLEGE OF AERONAUTICAL ENGINEERING
(DEPARTMENT OF AEROSPACE ENGINEERING)
Heat Transfer
ME-305
LAB NO 08
Assessment No 08
(g)
All equipment should be regularly inspected for wear or deterioration.
(h)
Designated and well-marked waste storage locations are necessary.
(i)
7.
Avoid wearing jewelry in the lab as this can pose multiple safety hazards.
LAB ASSESSMENT RUBRICS (PLO-5, P3)
SNO
Assessment
Parameters
1
Safety Procedures
(x1.5)
2
Equipment Handling
and Operations
(x1.5)
3
Group Participation
(x1)
4
Individual Performance
(x 6)
5
Methodology adopted
(x5)
6
Accuracy and Critical
Analysis of Results
(x5)
8|Page
Outstanding
(05)
Good
(04)
Average
(03)
Below
Average
(02)
Poor
(01)
Lab Handout
COLLEGE OF AERONAUTICAL ENGINEERING
(DEPARTMENT OF AEROSPACE ENGINEERING)
Heat Transfer
ME-305
LAB NO 08
Assessment No 08
TABLE OF OBSERVED VALUES
Ambient Temperature T9 or Ta
Sample No
1
2
Distance from T1 (m)
V
Volts
-
I
Amps
-
T1
T2
°C
°C
0
0.05
T3
°C
0.1
T4
T5
T6
T7
°C
°C
°C
°C
0.15
0.2
0.25
0.30
T8
°C
0.35
TABLE FOR CALCULATED DATA
Ambient Temperature T9 or Ta
Measured
Temperature
(°C)
9|Page
°C
°C
Distance (𝐓𝐱 − 𝐓𝐚) 𝐜𝐨𝐬𝐡𝐦 (𝐋 – 𝐱)
x from T1
𝑻𝟏 − 𝑻𝒂
𝐜𝐨𝐬𝐡𝐦𝐥
(m)
T1
0
T2
0.05
T3
0.1
T4
0.15
T5
0.2
T6
0.25
T7
0.30
T8
0.35
Calculated
Heat
transferred
(Watt)
Measured
Heat
transferred
(Watt)
Lab Handout