Heat Pipes Relevant Questions

QUESTION 1: For the modules that we have, what size heat pipes are best and what are our options for buying them?

Answer: Considering the dimensions of our battery box, the best sized heat pipe options are probably --- The best options for buying heat pipes would be on DigiKey/Amazon websites as they provide a wide variety of typically copper heat pipes. Below will be linked a couple of options that could be viable for our size and application constraints:

QUESTION 2: How are we going to attach the heat pipes to the battery modules and in what orientation is the best to put them in the bb?

Answer: The heat pipes can be attached to the battery box modules by having dissipating plates (typically aluminum/nickel) with grooves in them to fit in the heat pipes. With these grooves, the heat pipes can be soldered (best way) or epoxied in (2nd best way) and can be placed above the battery modules and provide cooling through that way. In general, the best orientation for heat pipes is to be horizontal positioned (however many specific heat pipes can work in vertical conditions just as well) because you want to limit the effects of gravity. For heat pipes to properly work, the evaporation side has to be equal to OR above the condenser side, which is our main restricting condition. Considering the lengthy/rectangular dimensioning of our battery box, the way we want to attach the heat pipes to the battery box, and also the fact that it would be easier to design horizontal heat pipes versus vertical heat pipes, we should look towards a horizontal orientation. With a horizontal orientation, we would possibly have to consider an inclination angle (typically between 60-75 degrees), which can be defined through further ANSYSS and CFD testing.

QUESTION 3: How many heat pipes are we going to need to cool the battery box properly?

Answer: v

QUESTION 4: What's the best way to cool the heat pipes?

Answer: The best way to having a cooling heat pipe system is having copper heat pipes with inner wicks and water as the liquid from 25-150 Celsius. In addition, the heat pipes can be attached to fins which will provide a better way to dissipate the thermal conductivity. Essentially, the heat pipes would be routed through the grooved dissipating plates within the battery box and go out at the outtake section of the battery box. At the end, the heat pipes would be attached to fins that will allow the fans to push the hot air out and into the exterior duct.

Heat Pipes Questions 2nd Part:

https://www.mdpi.com/1996-1073/12/9/1698

Heat Pipe Design Guide | Celsia

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?

Answer: To get the heat pipes set into the heat plate, we should solder the pipes. In order to do this, we need to first nickel plate the aluminum plate which provides it with corrosion and wear resistance (most likely just buy an aluminum plate that has been nickel plated, basically just makes it an aluminum alloy). To actually solder the heat pipes into the grooved plates, we need a solder material (most likely lead-free) and have a blowtorch to make it a sort of paste. This paste should be create a super thin layer in the grooves and the heat plates should be placed on top like a press fit. The maximum temperature we can solder at is around 138 degrees C and the heat pipes cannot exceed 250 degrees C in general or else the water inside will boil and explode the heat pipe.

Assuming the dissipating plates are aluminum, how are we going to put grooves in it for the heat pipes?
Typically, for EV battery boxes, and assuming we're going with a horizontal orientation, at what angle are the pipes usually at? We will probably have to bend the heat pipes, what's the safest method for bending these pipes without damaging them? (assume we're using copper heat pipes with water inside)

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 manufacturable within 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. 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 round sintered heat pipes (what we will most likely use). 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.

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.

Answer:

Battery Box Current Dimensions: 600 mm x 100 mm x 370 mm

Cost range based on size:

Ease of machining of on and usability:

Working Temp with 70 C

Additional Constraints (will continue to grow):

Constraints	Does it meet? Yes/No

Constraints	Does it meet? Yes/No
Fits Battery Box Dimensions
Within Abstract Budget Consideration
Machine/Usability
Temperature Constraints
Additional Constraints

Given the new modules on bild, sketch or cad your heat pipe design.