Full test soon! (Shock Tube Blog #9)

Hi all,

My next priority was engineering the diaphragm. I had to cut the a stainless steel mesh in a very specific pattern, so that the diaphragm would only heat up and break in specific places. I designed and printed two halves of a cutter using the apple slicer that I was talking about a few weeks ago. After destroying said apple slicer to get the blade section and intentionally dulling the parts of the blade I didn’t want to cut the diaphragm mesh, I was left with this:

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With my Spongebob arms and weak hammer though, I couldn’t make it actually go through and cut. What was worse was that the clamps I had got to hold the steel mesh in place just barely didn’t fit, so the mesh curved upwards where it wasn’t being cut, which would be really bad for the heat conductivity. I made some stencils, however, to cut the diaphragm into the initial circle, and they had worked really well. I could use the clamps to secure both of them to either side of the mesh, and use an Exacto knife to cut it somewhat precisely. I figured I could just use those stencils to cut out the whole pattern, so I designed and printed these ones here(still have yet to test them):

While I was working on this, I’d also picked up moving the Schlieren system components upstairs to the shock tube room and integrating it. My prior attempts while developing and testing this system a few months ago were kind of disappointing, because they were really dim and blurry(the following is footage of the hot exhaust of a candle, inverted):

Although picking up normally invisible air disturbances like this was kind of cool, I really wanted to figure out a way to make it brighter and sharper. Midway through setting it up upstairs, though, I figured I may as well just stick my iPhone camera directly looking at the light(instead of looking at the light reflecting off of a piece of paper) and I was kind of shocked by what I saw:

It was really clear and bright compared to last time with the candle, and you can see fine details of the model like the aluminum wiring. I then stuck my actual high speed camera on there, and finished the setup by aligning a razor blade in front of it at the focal point, and that worked pretty well too. To figure out if it could actually catch any air disturbances, though, I’d have to run a few tests. My first idea was to just use my mom’s hair dryer positioned in front of the lens:

However, I couldn’t really distinguish whether the slight disturbances on the image were from actual air movements or from the vibrations caused by the hair dryer. The camera was focused on the model, which was further back in the setup than the hair dryer’s air, so I think it was really out of focus and blurry. I tried cranking up the heating, because that wouldn’t affect the vibrations but would affect the air disturbances, but it was still really difficult to tell. After a while, the dryer was apparently consuming way too much power, and it triggered the circuit breaker on my power adapter. I also smelled smoke, which isn’t something you usually want to have with electronics. I figured it was about time to call it quits with this method, and instead, I decided to use a candle in front of the lens: