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https://www.mdpi.com/1996-1073/12/9/1698
https://celsiainc.com/heat-sink-blog/heat-pipe-design-guide/
What's the procedure for soldering the heat pipes on a heat plate? What materials do we need? what type of solder? What temperature can we solder at without damaging the heat pipes and vaporizing the liquid inside the pipes?
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Answer: The best way we can put grooves in our cold plates of aluminum is to make them in our machine shop. We can create the grooves in the aluminum plate through the Mill machine (or any other applicable machine we have). Because the overall design premise is to have heat pipes within the grooves of the cold plate, the angle of the pipes should be minimal (below 10 degrees) to provide the battery box with enough thermal conductivity benefits and also be able to fit into the grooves. The most important element is to have the condenser at or above the evaporator, which would mean looking into having the heat pipes vertically oriented. To have the best optimization, we would want to have Assuming we are using copper heat pipes with water inside, we can most likely just use a pipe bender to bend the pipes to fit within the grooves. This method of bending should work with flat round sintered heat pipes (what we will most likely use) and round sintered heat pipes. While using the pipe bender, it may be necessary to also anneal the heat pipes (heating them up) so that they can be easier to bend. When doing this, the working liquid should not be inside the pipe and we need to be careful of the copper hardening, which can make the heat pipe explode (because of all the working chemicals inside). It is important to note that increasing the angle of our bends will gradually reduce the thermal conductivity of the heat pipes. However, considering our application where the heat pipes will not need much of an angle within the heating/dissipating plates, this should not be much of an issue.
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Should we be using round or flattened heat pipes?
Decide on a specific type of heat pipe we should use and say why (probably CCHP right?)
Answer: We should be using round heat pipes compared to flattened heat pipes because they provide better thermal conductivity compared to flattened heat pipes. Additionally, using grooved cold/dissipating plates is more applicable for round heat pipes as flat heat pipes would be used with flat cut plates. The trade off is that we will be giving up more surface area contact by using rounded heat pipes, but with the tight space we have and the amount of patterns within the grooved plate, I believe the inherit better thermal conductivity is more valuable. For our application, Constant Conductance heat pipes (CCHP) would be best because of their fixed thermal conductance in the condenser and evaporator (we need to value thermal conductance, but most importantly a common temperature of conductance across the heat pipes). It is also known that CCHP are commonly used for electronic applications which fits our profile.
Come up with a broad list of selected heat pipes and plates/fins we can buy given the following parameters: battery pack shape, cost, viability and possible to work with, working temp up with 70C, goal is to keep the cells <40C, there's a lot more things we need to take into account such as heat generation of cells but we haven't calculated those yet.
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