Abstract:
The objective of performing this experiment is to calculate the emissivity of both copper and aluminum and performing a comparison to the theoretical values on the basis of principles of radiation heat transfer. The plotted figure for the experimental temperature/time data for the copper cylinder shows a large variation in the position between the experimental value and the theoretical value. The theoretical emissivity value of 0.8 is very far from the experimental value and this is explained in the discussion section. The major mistake for the copper cylinder experiment was the misplacement of the thermocouple wire into the correct plug. The percentage error between the theoretical and experimental emissivity value is 25.8 %. The plot for the aluminum on the other hand yielded better results and the calculated value for the emissivity through taking the slope of Figure 4 is 0.2343 that falls in the published value of 0.20 to 0.31. This experimented displayed how important assumptions are and how it affects the results. The cylinder finish was assumed to be a grey diffuse whilst the actual finish was an oxidized surface. The oxidized surface played a role to increase emissivity.
Outline Lab Procedure:
1. Please have a briefing by the instructor in relation to the safety measured of performing this experiment.
2. Measure the cylinder's length and diameter and record it in a table in Excel.
3. Measure the cylinder's temperature when it is in the furnace by the digital thermometer.
4. Insert the copper the cylinder that is connected to the thermocouple inside the hole of the furnace door and make sure it is in a secured position by sliding the plate on the furnace door.
5. Wait for the cylinder to heat up to 400 degrees Celsius and go ahead and turn on the water cooling system to ensure a constant temperature for the container.
6. Configure the data acquisition software as necessary.
7. After reaching 400 degrees Celsius, remove the cylinder from the furnace and place it on the aluminum container and make sure it is perfectly aligned so the copper cylinder is not touching the wall.
8. Evacuate the container by turning on the vacuum pump.
9. Wait for around 10 seconds to ensure that a strong seal has been established and then close the valve and shut off the pump.
10. Click the manual trigger button to initiate the data acquisition.
11. Heat up the aluminum cylinder in the process of taking measurements.
12. After 28 scans, the data acquisition will stop and the data will be transferred to Excel.
13. Columns A and B correspond to the wall temperature and the cylinder temperature respectively, while column C can be deleted.
14. Perform steps 7 to 13 for the aluminum cylinder.
15. Make a plot of the experimental temperature/time data for the copper and aluminum cylinders through Excel and include the theoretical results to perform a comparison that will help estimate emissivity.