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Due to time constraints, we were unable to alter pot quantity or placement and instead measured change of convection over varying temperature. During the experiment, we had a thermal sink of a black pot with 5 lbs. of water in the center of the oven. The field of view covered the right side of the oven from the bottom black plate to the pot on the left side. In order for the camera to be able to view inside the oven from the front, the plywood door had to be removed and a piece of glass was duct taped into place. Additionally, the back of the oven is covered with reflective sheet metal. This had to be covered with a piece of cardboard duct taped into place. We assume these changes had a negligible effect on oven performance.
Figure 1 - PIV schematic
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Figure 2 - Picture of PIV setup in DeFrees lab.
An Aragon Ion laser was used at a wavelength of 488 nm. This wavelength was chosen because it provided the highest emission from the particular laser and also was imaged brighter on our particular camera than the other principal emission wavelengths. In order to spread the beam into a laser sheet, a cylindrical lens was placed above the oven and the sheet was dispersed through the top glass sheets.
Thermocouples were placed in the pot of water, on the black plate at the bottom of the oven, and on the inside of the glass at the top of the oven. The thermocouples were sampled at a rate of .1 Hz with a DaqPro Data Logger.
The oven was heated with 15 halogen lamps located 24" from the top of the oven in an array of:
Figure 3 - Lighting arrangement of halogen lamps above PIV setup.
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Once the images were obtained, some data processing had to be performed in order to get the desired results and filter out erroneous data. Image pairs were processed with a subwindow size of 16pix x 16pix. This size was somewhat arbitrary, but was hoped to capture high image correlation between pairs. This choice of subwindow size resulted in a map of mean displacements in each subwindow. Using an image of a ruler to calibrate distance as well as knowing that the camera image rate was 30 Hz, these displacements were then converted to velocities by the equation:
The 
The U and V displacement matrices were also run through a simple band pass filter that set a tolerance for upper and lower bounds of displacement and cut out background noise. Histograms of U and V data for each temperature data set were examined and upper and lower bounds were chosen based on visual inspection. If a data point appeared outside of these bounds, the data point was set to the mean value at that data point.
Figure 6 - Band Pass Filter schematic and generic Matlab code used to process the data.
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We also note that these PIV results generally agree with the heating mechanism isolation tests. Of the three mechanisms, we can only expect that energy gained from radiation will remain constant from the beginning of heating through all temperatures. As the black plate gets hotter relative to the pot, we expect that conduction's role in heating would increase. And finally, as convection cell strength increases (as is seen in PIV) we expect the role of convection to also increase. While the contribution of the three mechanisms was more uniform across temperatures than we might think, there was a definite decrease in radiation's contribution at high temperatures.
Figure 7 - Vector map of mean displacements at 30°C.
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Figure 8 - Vector map of mean displacements at 50°C.
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Figure 9 - Vector map of mean displacements at 70°C.
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