Quote:
Originally Posted by lucid
Hey Swamp, thanks for the comparison. I'll respond to your post(s), just busy. At a first glance, 2 clarification questions:
1. Why is the iron rotor volume less than the CC rotor volume given they seem to have the same thickness? (this will actually strengthen your argument if it is a simple data entry error). If this is not an error, does it have to do with the vent geometry?
2. Why did you pick c=800 J/kgK for the CC rotor? Were you able to verif that was the spec for the P-car back in 2004? I assume you went with the data on the SGL website (I don't know how up to date that is). However, their 2006 SAE presentation is referencing 1350 J/kgK, and 2005 Krenkel paper is stating 1200 J/kgK for the Brembo rotors.
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Good questions.
1. Yup, typo and vents, great guesses. When looking at rotors I wanted to properly model the volume due to the vents. My approximation, which I think is very good is to consider the annular friction surface part to be three sections, two outer ones solid and an inner one, all of equal thickness. For the inner one I figured it had 1/2 the material removed for vents. This places a 5/6 factor in the volume equation which was then missing for the CSiC case. It raised the 534 temperature figure significantly to a whopping 637.
However, the quoted weight savings spec from Porsche of 18 kg for all four rotors is the way I backsolved for the rotor ID. taking the above into account changes the ID and again worsens the case for the CSiC. A revision is included below that fixes both issues.
2. Again I used numbers from SGL website for current SGL materials. SGL was and is the supplier for Porsche. If their specific heats are better now than then this again would only show worse performance for the PCCB set up back in 2004. A value as high at 1350 would bring the temp way down to 386, just a hair higher than the iron.