Solar Autoclave Team – February Update

March 3, 2015

By Jessica Allen, Ryan Bartoszek, Victoria Cheng,Isa Ferrall, Robinson Ford, Taylor Lane, and Jordan Thomas

This month predominantly consisted of construction of our first prototype and preparing for the Prototype Design Review (PDR). At the beginning of the month we constructed the 3’ x 3’ wooden frame using wood glue and wood screws. After the frame was constructed, a Mylar sheet was stretched and taped onto the frame. This was one of the most meticulous aspects of construction since it took so much time to stretch and tape the sheet as well as immense attention to ensure no rips or tears in the sheet that would nullify the vacuum. After installing the sheet, we sealed the frame with caulk, and nailed and sealed plywood backing on the rear side of the frame.

While doing the prototype a few of the engineers in the group did SolidWorks drawings and drop tests as well as heat transfer calculations. Two drop tests were done on the frame. The first was a drop test on the bottom edge from a height of 3 feet from the center; the maximum displacement of the edge was .1013 inches at the center of the edge. The second was a drop test on the lower left corner at a height of 3 feet from the center; the maximum displacement was .006174 inches at the center of the left and bottom edges. Thus our wooden frame will withstand some wear and tear in travel, which was one of the criteria set by Grupo Fenix. In the heat transfer analysis, the biggest discovery was losses due to wind speeds that in March are at a daily maximum of 17mph. With wind speeds at this velocity, even with the sun at its highest possible intensity for the region, it would take far too long to heat the autoclave and possibly not even reach the required temperature (121°C). Our proposed solution is building a foam “hat” insulator for our pressure cooker that will mitigate heat loss from the top of the receptacle.

Lastly, we tested the pressure cooker on an electric stove to time how long it takes to reach desired temperature and pressure on a conventional kitchen range. On the high heat setting, the cooker took about 20 minutes to heat up the water to required heat. This time concerns us, and has now got us reworking our prototype to possibly integrate more than one solar mirror in addition to looking at options for round aluminum prefabricated frames instead of wooden frames.

The next step in our timeline is to present the preliminary prototype the first week of March, get feedback, and continue solving both the expected and unexpected complications cropping up as we begin testing the first prototype. As the end of the semester begins to approach, we are hoping to quickly redesign the autoclave’s mirror system so that we have time to test it in late March or April.