Heat Conduction Lab Report 11345d

Heat Conduction 1. Abstract The objective of this experiment is to study the conduction of heat along a composite bar and to evaluate the overall heat transfer coefficient. This experiment focus on the heat conduction for the cylindrical metal bar arrangement. The experimental overall heat

transfer coefficient will be compared to the overall heat transfer coefficient calculated. 2. Introduction Thermal conduction is the transfer of heat energy in a material due to the temperature gradient within it. It always takes place from a region of higher temperature to a region of lower temperature. A solid is chosen for the experiment of pure conduction because both liquids and gasses exhibit excessive convective heat transfer. For practical situation, heat conduction occurs in three dimensions, a complexity which often requires extensive computation to analyze. For experiment, a single dimensional approach is required to demonstrate the basic law that relates rate of heat flow to temperature gradient and area.

3. Experiment Methods and Materials The apparatus used in the experiment are heat conduction apparatus consist of an electricity heated module mounted on a bench frame. The module contains a cylindrical metal bar arrangement for a variety of linear conduction experiments. The test section is equipped with an array of temperature gradient. First, an intermediate position was selected for the heater power control and sufficient time for a steady state condition to be achieved was allowed before recording the temperature at all six sensor points and the input power reading on the wattmeter. After each change, sufficient time to achieve steady state conditions was allowed. 10 minutes was waited before the reading for 6W is read, 5 minutes was waited before the reading for both 9W and 12W are read. All the results was recorded and tabulated under the table below. Calculation for the overall heat transfer coefficient is done using: U =

Q A(THS −TCS )

The values calculated is then compared to the value calculated using the thermal geometry equation: 4. Data Analysis Wattmeter, THS Q (watts) (0C) 6 9 12

42.9 56.3 70.6

X X X 1 = H + S + C U KH KS KC

T1 ( C)

T2 (0C)

T3 (0C)

T7 (0C)

T8 (0C)

T9 (0C)

TCS

( C)

U (W/m2K)

43.5 55.9 70.2

43.7 55.5 68.7

44.1 56.3 69.8

29.4 29.6 30.1

29.4 29.6 29.9

29.1 29.2 29.6

28.8 28.8 29.1

866.89 666.71 589.07

0

K = 117 W/mK (Brass - 60% Copper and 40% Zinc) K = 25 W/mK (Stainless Steel)

0

X X X 1 = H + S + C U KH K S KC 0.04 m 1 = U 117W/mK

+

0.03 m 25W/mK

0.04 m + 117W/mK

2

U = 530.85 W/m K

Graph Heater's Temperature versus Distance 80 70 60

0C) Temperature(

50 6 W att

40

9 W att

30

12 W att

20 10 0 0

5

10

15

20

Distance(mm )

25

Graph of Cooler's Temperature versus Distance 30.2

30

29.8 6W att

0C) Temperature ( 29.6

9W att 12W att

29.4

29.2

29 0

10

20

30

40

50

Distance (mm)

60

70

80

90

5. Discussion Based on the graph, it shows that when the input power, Q (watt) increase, the overall heat transfer coefficient, U (W/m2K) will decrease. When calculating the heat transfer coefficient using the thermal geometry equation, the thermal conductivity, K used is for the Brass (60% Copper and 40% Zinc) is 117W/mK and the stainless steel is 25W/mK. When compared the U calculated using U =

Q A(T HS −TCS )

experimental results and the theoretical U calculated using

based on the

X X X 1 = H + S + C , U KH K S KC

there are differences between the values. This may because the theoretical U take only the distance and thermal conductivity without considering the input power and temperature. 6. Conclusion Varying the input power will affect the heat transfer coefficient. When the input power, Q

(watt) increases, the overall heat transfer coefficient, U (W/m2K) will decrease. There will be difference between U calculated from the experiment and U calculated theoretically because of the difference in variables (input power, area, temperature, distance and thermal conductivity) used.