Below are the questions asked during the event, along with their respective answers.
Q: Do you have any of these operating in military avionics or space applications?
A: Yes. Please contact us directly for further information.
Q: Are there any concerns about using thin VCs in sub-zero operating temperatures?
A: If the VC temperature is less than zero C, it will not function as a VC. Repeated freezing and thawing of the VC will also damage the wick and reduce thermal performance. The design will have to make allowance for such performance degradation based on the number of freezing events the product will see during its expected useful life.
Q: Has the CFD smart part been correlated using empirical data?
A: This is an ongoing process. We continue to apply it to our product designs and verify that the predictions are reasonable.
Q: Have you thought of making a smart part or instructions of thin VC for Flotherm?
A: No. This would be something that Mentor Graphics would have to do.
Q: Have you done any research into thin VC’s using AL and Ammonia working fluids?
A: No. We have made aluminum-ammonia heat pipes for space applications but no vapor chambers.
Q: How well will this VC work in ground vehicle vibration and secondly if having to mount the subsystem (pc) upside down in ground vehicle vibration?
A: The frequency of such vibrations is likely high enough that the vapor chamber will not respond. Upside down orientation is not an issue. Gravity direction should be included in all analyses when considering capillary pumped devices like heat pipes and vapor chambers.
Q: What is the range of effective thermal conductivity of thin vapor chambers as compared to coldplates?
A: Typically the conductivity is very high but both conductivity and heat carrying capacity decrease rapidly when the vapor space becomes very thin. For 0.1 mm vapor space, the net conductivity of the vapor chamber could be less than 2000 W/m-K at 50 C vapor temperature. Cold plates provide a different function altogether so they cannot be compared to vapor chambers.
Q: Can VC parameters be provided under NDA to OEMs to perform preliminary assessments prior to engaging with detail design activities using tools like Flotherm or IcePak?
A: The calculations for vapor chambers based on water as the working fluid are embedded within the SmartCFD software. No explicit parameters are provided because the software you mention models such devices only as conducting solids. Just using a high value for thermal conductivity would probably be fair for an assessment of the temperatures that you might see assuming the VC works in your application. When we work closely with customers, we do provide specialized SmartCFD models which have optimized wick parameters for their application.
Q: Is there a software to design a complex-shape vapor chamber?
A: SmartCFD can help you analyze a complex-shaped vapor chamber with a uniform thickness. The next version of the software will allow more three-dimensional features to also be modeled.
Q: What maintenance or wear out would be prevalent/expected with heavy use of an instrument that is cooled by this? I am anticipating wear out in the wick’s capillary action over continued heating and cooling cycles?
A: The fluid velocities inside the vapor chambers are small enough that no wear out of wicks has ever been reported. That said, if the product operation results in frequent freezing and thawing of the vapor chamber, then the wick damage will build up and performance degradation can be expected over time.
Q: VC bendable?
A: Copper VC’s are bendable for small deflections or a one-time plastic deformation to conform to the shape of a mating part. Copper tends to work harden so continued back and forth bending or forming will damage the VC. We can take a look at what you want to accomplish and advise you further.
Q: What other alternate modeling techniques do you recommend without the Aavid SmartCFD?
A: The standard approach is to model these devices as high conductivity solids. Such a model can provide a reasonable prediction of the temperatures.
Q: Why is titanium better for making thin vapor chambers? Is the structure similar to a copper VC?
A: Titanium is attractive for applications where low weight is an important metric. Yes, the structure is similar to copper vapor chambers.