[Mechanical Engineering Laboratory 4]

SEGi University

EXPERIMENT 10: HEAT CONDUCTION

Candidate’s Name: Shaheer Qamar

Student ID: SCM – 027739

Lecturer/Supervisor: Dr. Vinod

Date of Experiment: 23/11/2015

Date of Submission: 30/11/2015

FACULTY OF ENGINEERING & BUILT ENVIRONMENT

SUBJECT: EME3431 LABORATORY INVESTIGATIONS 4

EXPERIMENT 10: HEAT CONDUCTION

ABSTRACT:

In the experiment carried out, the conduction of heat along a composite bar and the

overall heat transfer coefficient. The experiment was successfully carried out with the

conductive compounds of steel and brass as sample. The experiment was prone to

some systematic and random errors which contributed to some deflected readings.

The experiment showed that different material have different value of thermal

conductivity and also that the overall heat transfer coefficient is dependent to the

input power.

OBJECTIVE:

To:

- Study the conduction of heat along a composite bar.

- Evaluate the overall heat transfer coefficient.

APPARATUS:

PROCEDURES:

1. An intermediate position for the heater power control was selected.

2. Sufficient time was allowed for a steady state condition to be achieved before

recoding the temperature (T) at all nine sensor points and the input reading on the

wattmeter (W).

3. This procedure was repeated for other input powers.

4. After each increment of power, sufficient time was allowed to achieve steady state

conditions.

5. The results were tabulated in table 1

6. Step 1 was repeated with a second test sample.

7. The steps from 2-5 were then repeated and the results tabulated in table 2.

RESULTS:

Table 1: Temperature distribution along test sample 1

Test

No.

Wattmeter Q

(watts)

T1

(0C)

T2

(0C)

T3

(C)

T4

(C)

T5

(C)

T6

(0C)

T7

(0C)

T8

(0C)

T9

(0C)

1 4 41.7 39.9 38.6 33.5 30.3 31.5 28.5 28.2 27.9

2 8 42.6 40.8 39.5 34.1 30.7 31.9 28.6 28.3 28.0

3 12 45.2 43.2 41.8 34.9 31.1 32.4 28.6 28.3 28.0

4 16 57.3 53.4 51.0 38.4 33.0 34.8 28.7 28.3 28.0

Distance (m) 0.005 0.015 0.025 0.035 0.045 0.055 0.065 0.075 0.085

𝑇@4 𝑊𝑎𝑡𝑡 = (T 1+T 2+T 3)

3 =

(41.7+39,9+38.6)3

= 40.07 0C

𝑇@8 𝑊𝑎𝑡𝑡 = (T 1+T 2+T 3)

3 =

(42.6+40.8+39.5 )3

= 40.97 0C

𝑇@12 𝑊𝑎𝑡𝑡 = (T 1+T 2+T 3)

3= (45.2+43.2+41,8)

3= 43.4 0C

𝑇@16 𝑊𝑎𝑡𝑡 = (T 1+T 2+T 3)

3= (57.3+53.4+51)

3= 53.9 0C

𝑇@4 𝑊𝑎𝑡𝑡 = (T 7+T 8+T 9)

3 =

(28.5+28.2+27.9)3

= 28.2 0C

𝑇@8 𝑊𝑎𝑡𝑡 = (T 7+T 8+T 9)

3 =

(28.6+28.3+28.0 )3

= 28.3 0C

𝑇@12 𝑊𝑎𝑡𝑡 = (T 7+T 8+T 9)

3=

(28.6+28.3+28.0 )3

= 28.3 0C

𝑇@16 𝑊𝑎𝑡𝑡 =(T 7+T 8+T 9)3

= (28.7+28.3+28.0 )

3= 28.33 0C

Watt (W) THS - Average (K) TCS - Average (K) THS - TCS (K)

4 313.07 301.2 11.87

7 313.97 301.3 12.67

12 316.4 301.3 15.1

16 326.9 301.33 25.57

𝑈 = Q

A (THS−TCS)

Where;

Q = heat transfer rate (W)

U = Overall heat transfer coefficient (W/(m²·K))

A = Heat transfer surface area (m2)

T = Temperature (K)

- Diameter of the sample = 0.025 m

- Surface Area of sample = 𝜋𝑟2 = 0.00049 𝑚2

𝑈@4 𝑊𝑎𝑡𝑡 = 4

0.00049(11.87) = 687.722 W/(m²·K)

0.005 0.015 0.025 0.035 0.045 0.055 0.065 0.075 0.0850

10

20

30

40

50

60

70

f(x) = − 1.875 x + 42.7194444444444

Temperature vs length

4 watt Linear (4 watt) 8 watt12 watt 16 watt

Length

Tem

pera

ture

oC

Values to find thermal conductivity for Steel

Q = 4 Watt

dTdx = -1.875 Km-1

𝑘 = −Q

A (dTdx

)

𝑘 = −4

0.00049(−1.875) = - 4353.74 W m∙ −1 K ∙ −1

Table 2: Temperature distribution along test sample 2

Test

No.

Wattmeter Q

(watts)

T1

(0C)

T2

(0C)

T3

(0C)

T7

(0C)

T8

(0C)

T9

(0C)

1 4 54.3 51.8 50.2 28.5 28.2 28.0

2 8 53.7 51.3 49.6 28.5 28.2 28.0

3 12 54.0 51.4 49.8 28.5 28.2 28.0

4 16 55.7 52.8 50.9 28.5 28.2 28.0

0.005 0.015 0.025 0.065 0.075 0.0850

10

20

30

40

50

60

f(x) = − 6.4 x + 62.5666666666667

Temperature vs length

4 watt Linear (4 watt) 8 watt12 watt 16 watt

Length

Tem

pera

ture

oC

Values to find thermal conductivity for Brass

Q = 4 Watt

dTdx = -6.4 Km-1

𝑘 = −Q

A (dTdx

)

𝑘 = −4

0.00049(−6.4 ) = - 1275.5 W m∙ −1 K ∙ −1

DISCUSSION:

For different materials, the thermal conductivity varies. It is because for each and

every material the atomic configuring varies and thus the heat transfer. For example

Heat moves very quickly through a metal spoon, leaving one end of a spoon in boiling

water will make the entire spoon hot very quickly. The entire spoon becomes hot, not

just the spot in the boiling water. On the other hand, heat moves very slowly through

the insulation in your house. This fact can also be seen from the above calculations

since the brass and steel have different thermal conductivities.

The experiment carried out was prone to both systematic and random errors. In the

experiment carried out, the percentage errors for the overall heat transfer coefficient

‘U’ lies beyond acceptable limit. However, the heat conductivity ‘k’ for brass and

steel were quite accurate. The reason for deflected reason may have been;

The shallow shoulder in the nylon housing were not perfectly matched.

The surface of the conductive compounds in contact were not very smooth thus

causing contact resistance to add in.

The adhesive used to attach the conductive compound too may have added to the

contact resistance.

The wattmeter scale was very sensitive and was thus difficult to set it at the

desired exact power input

The temperatures from the conductive compounds fluctuated too much.

The following improvements could be made to the experimental procedure to

improve the overall accuracy and the precision of the experiment.

Make sure that the shallow shoulder in the nylon housing is perfectly matched

Use a conductive compound that is smooth and less adhesive to reduce the

contact resistance.

The instrument should have a selector to set the sensitivity of the device as

desired.

Perform the experiment thrice and take the average of the temperatures.

REFERENCES:

i) Adam Zofka. (2011). Methods of Heat Transfer. Available:

http://www.physicsclassroom.com/class/thermalP/Lesson-1/Methods-of

HeatTransfer.

ii) Baumeister, Theodore; Marks, Lionel S., eds. (1967), Standard Handbook for

Mechanical Engineers (Seventh ed.), McGraw-Hill.

iii) Charlie Dalton. (2012). CONDUCTION ALONG A SIMPLE BAR. Available:

http://www.engr.iupui.edu/~mrnalim/me314lab/lab01.html.