Week 5: July 10 - July 14
The calibration mold that I had left to cure over the weekend came out excellently. Having completed it, this week I decided to undertake other projects in between observing Rafael continue to perform his PIV tests that I thought would be useful. This week turned out to be one of the best so far. In addition the the projects I completed and tests I performed ending up with good results, I was also able to observe the success of others.
Calibration Mold
Even before removing the mold from its box, I could see through the transparent walls that it had turned out fantastically. The silicone had completely cured and there were no bubbles, resulting in stressful experience as I took off the walls and removed the 3D-printed part as I did not want to ruin the mold. Luis and Armando also saw success with a complete silicone stenosis model that only needed to have the metal core melted out. Rafael actually made us wear gloves all day until the models found a secure home because he didn't want any of them to be tainted with fingerprints.
Index of Refraction of Cured 3D Printing Resin
While working on silicone models, I noticed that Luis and Armando had also 3D-printed the same models. I asked them about it and they said they were interesting in seeing if the 3D-printed models also provided data as good (or maybe even better) as the silicone models. Remembering that the models required a fluid with a matching refractive index to be run through them, I asked what solution they would use when performing PIV tests on the 3D-printed models. They said a solution for the 3D-printed models hadn't been created yet. Luis then remarked that they weren't actually sure what the refractive index of the resin was. We did some research, but couldn't find a paper that listed it; all we found was an informal post that said it was around 1.5. I remembered doing a lab in Physics this past year where we found the refractive indices of and realized what a great opportunity this would be to apply what I learned in the classroom to the real-world, so I volunteered to perform tests on the resin to find its index of refraction.
In the Physics lab, we filled up half-cylinder containers with various materials that allowed light to pass through and shot a laser pointer at these half cylinders, measuring the angle that the light would bend. To repeat this lab, I 3D-printed a half-cylinder to use. I could not find a laser pointer in the lab at ME (where I performed the tests), but was able to find an infrared thermometer (an Etekcity Lasergrip) that has a low-powered laser to help the user aim it at objects. I measured out angles in 10 degree increments up to 90 degrees from the normal (a line perpendicular to the barrier between the two mediums that light is passing though) and shot the laser both through the resin and toward the resin at these angles, measuring the angle that the light was refracted at when moving from the resin to the air and the air to the resin, respectively. After taking the average of my data, the index of refraction that I found was 1.52, which Rafael told me was consistent with that of a paper he had read.
Volumetric Flow Rate
The pump Rafael is using for PIV has a dial that can be used to adjust the volumetric flow rate of the fluid its pumping. It shows a number in liters per minute of volumetric flow rate if it is pumping water, but since Rafael is using a water-glycerol solution, the actual volumetric flow rate differs from this number. As a result, Rafael asked me to test the flow rate of the pump to see what dial setting corresponds with what flow rate of the water-glycerol solution.
I told Rafael I hadn't learned about flow rate yet, so he gave me a quick summary of what I needed to know at lunch one day. He showed me the equation for volumetric flow rate and also summarized the process I would go through when testing. In short, I turned on the pump, set the dial at a certain point, and then timed how long it took the pump to push through 500 mL of the solution. I then input the data I got into an Excel spreadsheet and used it to find the volumetric flow rate at each setting I tested. I found that the data was very linear when plotted on a graph, so I used Excel to find the equation for the line of best fit which can be used to find the flow rate at any given dial setting. Not only did I give Rafael data that was useful for his experiments, but I had learned something new in the process.
A Random Idea
On Wednesday, I was looking at a failed (as it was full of bubbles) stenosis silicone model that Luis had cut in half when it occurred to me that it might usable for casting another metal core. I taped the two halves together and poured the low-melting point metal in. After waiting an hour, I came back and took the metal core out. It had come out great. There numerous spots where there had been bubbles in the silicone that resulted in bumps on the metal core, but overall it was smooth and didn't have holes in it. It gave me an idea for an adjustment to the way we had been producing silicone models, which I pitched to Rafael. Essentially, my idea was to start by 3D-printing the core, glue it in a box, and then pour silicone in. After the silicone cures, the walls of the box can be removed, and the 3D-printed part can be cut out, producing two halves of a silicone mold that can be used to produce metal cores. I thought there would be two main benefits to this: the first is that the silicone is clear, so a thin object can be used to stir the metal and get rid of any gaps that can be seen; the second is that the silicone is flexible, making it very easy to separate the two halves of the mold and take out the metal core. Using the unclear and rigid 3D-printed objects as molds for the metal core forced Armando and Luis to hope that no holes had formed in the metal and to bang the mold against a table until the metal core popped out, putting the molds at risk for breaking. Rafael told me it was a good and interesting idea and encouraged me to go through the process with a stenosis model to see how it turns out.
The compliment, however, ended up being more of a teaching moment for me. In his compliment, Rafael reiterated something he had told me previously, but didn't really sink at the time; now, it made perfect sense. He told me that real science doesn't follow a straightforward procedure, but it requires ideas along the way which help you adjust and improve the path you take to get results. It's not like in the classroom where your teacher gives you step-by-step instructions; you have to develop the methods your self, constantly taking notes and revising them. You can never expect the results you get to be perfect, but with careful attention, you can always expect the process to improve as you go.
