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Five tests were run to characterize the new, larger oven. Tests 1 and 2 were run using the two older 30"x30" box cookers, and Tests 3, 4, and 5 were run using the new 1-D scale up of the original ovens. The tests involved heating a measured amount of water in the solar ovens and observing the time it took to heat from 40°C to 95°C. The pots used to contain the water had a top diameter of 8 inches and were 5 inches tall. With an upper lip thickness measured to be ¼ inches, the inner diameter of the pots was calculated to be 7.5". The pots' exterior and their lids were painted black, and can be seen in the picture below.
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Figure 1. Black pots used for heating water in the solar oven tests.
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The testing was done using the lighting system, where the insulation from the halogen lamps give approximately the same amount of energy as the sun does on a bright, clear day in Nicaragua. A pyranometer was used to measure the insulation during the five tests. During Test 1 and 2, the pyranometer was placed at the center of the lighting system, straddling the tops of the two older ovens. For Tests 3, 4, and 5, the pyranometer was moved to the back left corner of the new oven, where insulation was weaker. However, the amount of insulation recorded was similar for each position, and probably did not change between testing of the older and new ovens. Figure 2 shows the pyranometer reading for each test, though the data was interpreted by the program reading results from the thermocouples, and the units of the pyranometer output, which were converted from the pyranometer voltage output to °C, do not make sense. However, this graph shows that the insulation was relatively constant when the pyranometer was placed in the center for the first two tests, and that it was relatively constant when the pyrometer was placed in the corner of the light bed during the last three tests.
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Figure 2. Insolation during the five tests in °C units converted from voltage output.
Images of the test set up can be seen in Figure 3 to 6.
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Figure 3. A view of the oven interior from the door opening.
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Figure 4. New oven during Test 4.
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Figure 5. New oven being tested using the light system.
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Figure 6. Computer used to log temperature data with new oven being tested in the background.
Test 1 involved the two older ovens, each with approximately 2.7 kg of water in a single pot. Test 2 also involved the two older ovens, but each with approximately 4 kg of water divided into two pots. Test 3 involved the newly constructed oven with approximately 8 kg of water divided into four pots. Test 4 and 5 involved the new oven with approximately 4 kg of water divided into two and four pots, respectively. These results are illustrated in Figures 7 to 11, and a consolidated table of test details and results are in tables following the figures.
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Figure 7. Test 1 temperature results. Note that probes T2 and T3, which read the temperature of the black plate in each oven, became detached at different points in the run.
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Figure 8. Test 2 temperature results.
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Figure 9. Test 3 temperature results.
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Figure 10. Test 4 temperature results.
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Figure 11. Test 5 temperature results.
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Even though the amount of time required to heat from 40°C to 95°C increases as the mass of water heated increases, the difference in time required decreases. This suggests that there is a fixed amount of energy used to heat the oven, since the relationship is not linear, as can be seen in Figure 12 below.
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Figure 12. Time required to heat water from 40°C to 95°C as a function of the total mass of water.
This is further evidenced by the decrease in per kilogram heating time as the total mass of water being heated, as illustrated in Figure 13.
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Figure 13. Per kilogram heating time as a function of the total mass of water.
While this data suggests that the time required to heat all the water from 40°C to 95°C is heavily dependant of the total mass of water being heated, more testing is needed to fully understand the affect of other variables, such as the surface area of the water touching metal painted black. However, this data does indicate that the surface area of the pots in contact with the black plate on the bottom of the oven does not have much influence on the heating time. To get a complete understanding of the best way to heat large amounts water, which will help give an understanding of the best way to cook large amounts of food, testing needs to be done using pots of different sizes, which were not available at the time of testing.
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