linear heat conduction
TRANSCRIPT
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Koya University Faculty of Engineering
Chemical Engineering Department
Laboratory of Heat transfer Experiment Number One Linear heat conduction
Instructor: Dr.Barham & Mrs.Anfal
Author Name: Aree Salah Tahir
Experiment Contacted on: 20/Oct/2014
Report Submitted on: 10/Nov /2014
Group:A
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List of content:
Objectives...............................................3 Introduction.. .4 Background Theory ...........5 Procedure .......6 Equipment and components used...7 Table of Reading........8 Calculation........................................9-10 Table...11-12 Discussion ......13-14 Conclusion........15 References .......16
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Objectives:
The aim of this experiment is to measurement linear thermal along z
direction conductivity and to investigate and verify Fouriers Law for linear heat conduction along z direction.
{1}
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Introduction:
Conduction is defined as the transfer of energy from more energetic
particles to adjacent less energetic particles as a result of interactions
between the particles. In solids, conduction is the combined result of
molecular vibrations and free electron mobility. Metals typically have
high free electron mobility, which explains why they are good heat
conductors. Conduction can be easily understood if we imagine two
blocks, one very hot and the other cold. If we put these blocks in contact
with one another but insulate them from the surroundings, thermal
energy will be transferred from the hot to the cold block, as evidenced by
the increase in temperature of the cold block.
This mode of heat transfer between the two solid blocks is termed
conduction.
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Background Theory:
Linear Conduction of heat along a simple bar.
If a plane wall of thickness (X) and area (A) , supports a temperature difference (T) then the heat transfer rate per unit time (Q) by conduction through the wall is found to be:
If the material of the wall is
homogeneous and
has a thermal conductivity
(k) then:
Heat flow is positive in the direction of temperature fall. What is the
effect of average temperature on the values of thermal conductivity for
brass?
The heat flow through a material can not always be evaluated at steady
state e.g. through the wall of a furnace that is being heated or cooled. To
calculate the heat flow under these conditions
it is necessary to find the temperature distribution through the solid and
how the distribution varies with time. Using the equipment set-up
described above, it is a simple matter of monitoring the temperature
profile variation during either a heating or cooling cycle thus
facilitating the study of unsteady state conduction. {2}
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Procedure:
1-Install the insert and adjust the cooling water flow rate and the heater
power.
2-Switch on the unit and adjust the desired temperature drop through the
power setting on the control and display unit.
3-When the thermal conduction process has reached a steady state
condition i.e. the temperature at individual measuring points are stable
note the measurement results at the individual measuring points and the
electrical power supplied to the heater.
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Equipment and components used:
1-display and control unit,
2-measuring object,
3-experimental set-up for radial heat conduction,
4-experimental set-up for linear heat conduction {3}
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Table of Reading:
Temperature of barrel is 23.2 c
Q T1 T2 T3 T4 T5 T6 T7 T8
30 0 100.6 97.9 X 89.2 88.9 X 73.2
60 0 91.2 89.6 X 86.1 85.7 X 74.8
Q T1 T2 T3 T4 T5 T6 T7 T8
30 0 100.6 97.9 93.6 89.2 88.9 81.1 73.2
60 0 91.2 89.6 87.9 86.1 85.7 80.3 74.8
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Calculation:
At Q= 30 watt
For No 2:
Diameter for (brass and steel) =25mm = 0.025m
Q= 30watt T2=100.6 T3=97.9 T=T2 T1 =2.7 K
X=10 mm = 0.01m
A=
4d2 =
4 (0.025)2 =4.910 -4
Q=KA (X
T) K=
Q
A(
X
T)
K =30(0.01)
4.9104(2.7) = 226.5
W
m.C
The same way for others.
No. X (m)
T
() T
( ) K
(
. )
1 ------- ------- ------ -------
2 0.010 373.6 2.7 226.75
3 0.020 370.9 4.3 142.38
4 0.030 366.6 4.4 139.14
5 0.040 362.2 0.3 2040.8
6 0.050 361.9 7.8 78.49
7 0.060 354.1 7.9 77.49
8 0.070 346.2 ------ -------
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At Q= 60 watt
For No 2:
Diameter for brass and steel = 25mm = 0.025m
Q= 60 watt T2=91.2 T3=89.6 T=1.6 K
X=10 mm = 0.01m
A=
4d2 =
4 (0.025)2 =4.910 -4
Q=KA (X
T) K=
Q
A(
X
T)
K =360(0.01)
4.9104(1.6) =
KW
m.K
The same way for others.
No. X (m)
T
( ) T
( ) K
(
. )
1 ----- ----- ------- ------
2 0.010 364.2 1.6 756.3
3 0.020 362.6 1.7 720.3
4 0.030 360.9 1.8 680.2
5 0.040 359.1 0.4 3061.2
6 0.050 358.7 5.4 226.7
7 0.060 353.3 5.5 222.6
8 0.070 347.8 ----- ------
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Table:
2.7
4.3 4.4
0.3
7.8 7.9
0
1
2
3
4
5
6
7
8
9
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
Tem
per
atu
re (
K)
distance(m)
Plot between Temperature & distanceQ=30
1.6 1.71.8
0.4
5.4 5.5
0
1
2
3
4
5
6
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07
Tem
per
atu
re (
K)
distance(m)
Plot between Temperature & distanceQ=60
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Discussion: 1-
Here are the factors that affect the rate of conduction
A) Temperature difference
B) Cross-sectional area
C) Length (distance heat must travel)
D) Time
2-
The thermal conductivity of an object is dependent on its composition and
dimensions(cross-sectional area and length).
for two connected objects of the same dimension connected to hot and
cold reservoirs, the higher the temperature drop, the lower the thermal
conductivity
3-
In contact point will make error because when we join the peace of
material will make a space that cause to heat losses.
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4-
To measure the temperature distribution for steady-state conduction of
energy through a composite plane wall and determine the Overall Heat
Transfer Coefficient for the flow of heat through a combination of
different
materials in series
5-
By increasing area and T thermal conductivity decrease:
But by increasing X, thermal conductivity increase
6-
Why we neglect the first rate of temp. ?
Because of the distance is zero and read temp.as minus.
7-
What is the advantage of cooling water?
To make the difference between the temp.
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Conclusion:
In this experiment we proved that K is inversely proportional with T, and we have many errors in our experiment that made the result not clear.
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References:
1-
www.me.uprm.edu/o_meza/.../Heat%20Transfer%20
Experiment-1.doc
2-
http://www.d.umn.edu/~dlong/exhtcond.pdf
3-
www.gunt.de/static/s3684_1.php?p1=0&p2=&pN=se
arch;Volltext;linear%20heat%20conduction