This would be a good project for someone who has taken the heat transfer class, but you could get by with the knowledge from general physics and chemistry. There's also maybe an opportunity to do some FEA.
This is mostly a design task with some testing and machining. It would be a good project for a couple MME sophomores or juniors.
problem description
One concern for the fin can is the heat from the motor. The epoxy matrix in the carbon fiber shell can't go above 350 F. We don't really know how hot the motor gets though. The motor pushes up against the bottom of the rocket with an aluminum flange (see diagram). This is how the thrust of the motor actually gets transferred to the rocket. At the top of the motor, there's the spider ring, which keeps the motor from falling out of the rocket before and after firing. The spider is not load-bearing.
The idea behind this phase change plate is to have a material with a melting point below 350 F between the thrust flanges. Thus, when the motor's thrust flange goes above that melting point, the temperature will level out, since heat will be going into the phase change of the plate rather than its temperature. This will buy us a little time before the epoxy matrix starts to overheat.
We can't simply make an annular disc of our phase change material (PCM) and stick it between the flanges. If we did that, the spider would become the load-bearing part as the PCM begins to melt. Neither the spider ring nor the holes it mounts to are designed to take the whole 9x the weight of the rocket and could break. So, there will need to be some additional structure to transfer the load between the flanges (perhaps concentric aluminum rings). We also don't want the PCM to leak out and catch fire (again, concentric aluminum rings might work).
diagram
(The dash-dot line is the axis of the rocket. Only half of the rocket is shown, for laziness.)
requirements
must
use a PCM that melts below 350 F
continue to transfer the load through the thrust flanges after the PCM has completely melted, in a way that does not damage the thrust flange or the spider ring
completely contain the PCM after melting so that it does not spill out or catch fire
should
give some indication of the temperature the motor flange reached (color change paint? different PCM layers?)
perform a test using a static load up to 400 F
suggested action
Make a list of possible PCMs including melting temperature, latent heat of fusion, density, viscosity, ignition temperature.
Obtain dimensions for the flange of the Cesaroni 21062-O3400-IM and Cesaroni N1975-GR. (Try to arrive at a design that is compatible with both.)
Check out the FEA done by the 2014 team (pester @joedang if it's not in the repo) and determine if using aluminum rings around the PCM ring will damage the rocket's thrust flange. (Maybe use a third ring?) If need be, modify their FEA model to address these concerns.
Use the OR model and whatever data you can find about the motors (or similar motors) to get a model / general idea of the heat flow through the PCM.
Choose dimensions and PCM. (Or narrow down to a few)
Perform a test in the oven in EB 480 with weight similar to the thrust at launch. (Be careful your weight does not act as a heat sink!) Determine how long it will take your PCM to melt with your expected maximum temperature. (If your expected max temp is below 400 F, try a test at 400 F.)
Iterate on your design so that it does not leak PCM when melted.
This would be a good project for someone who has taken the heat transfer class, but you could get by with the knowledge from general physics and chemistry. There's also maybe an opportunity to do some FEA.
This is mostly a design task with some testing and machining. It would be a good project for a couple MME sophomores or juniors.
problem description
One concern for the fin can is the heat from the motor. The epoxy matrix in the carbon fiber shell can't go above 350 F. We don't really know how hot the motor gets though. The motor pushes up against the bottom of the rocket with an aluminum flange (see diagram). This is how the thrust of the motor actually gets transferred to the rocket. At the top of the motor, there's the spider ring, which keeps the motor from falling out of the rocket before and after firing. The spider is not load-bearing.
The idea behind this phase change plate is to have a material with a melting point below 350 F between the thrust flanges. Thus, when the motor's thrust flange goes above that melting point, the temperature will level out, since heat will be going into the phase change of the plate rather than its temperature. This will buy us a little time before the epoxy matrix starts to overheat.
We can't simply make an annular disc of our phase change material (PCM) and stick it between the flanges. If we did that, the spider would become the load-bearing part as the PCM begins to melt. Neither the spider ring nor the holes it mounts to are designed to take the whole 9x the weight of the rocket and could break. So, there will need to be some additional structure to transfer the load between the flanges (perhaps concentric aluminum rings). We also don't want the PCM to leak out and catch fire (again, concentric aluminum rings might work).
diagram
(The dash-dot line is the axis of the rocket. Only half of the rocket is shown, for laziness.)
requirements
must
should
suggested action