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Old 10-05-2012, 10:01 AM   #79
TerraPhantm
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Join Date: Feb 2008
Location: Mountain Top
Posts: 5,837
My Ride: 2005 M3 Coupe
Quote:
Originally Posted by SeanC View Post
Terra, I know the algebra, but thanks for laying it out for those who may not. Technically it is a called special case of the ideal gas law when n and V are constant. It is not called a "simplified" version. If you insist on writing it for 2 different conditions, you need to have the knowledge of 3 of the 4 unknowns in the form that you write it (1 equation 4 unknowns). That means you first have to use the PV=nRT twice to get to those 3 unknowns (actually you'd know all 4 by then). How's this for simplified?
I meant it's a simplification in that it's an algebraic simplification by definition. If you assume volume and molecules of gas are constant, you can simplify the equations by canceling the terms out. I realize that it is a special case and doesn't apply in every situation. No one is saying that the ideal gas law always simplifies to that form.


Quote:
Originally Posted by WDE46 View Post
I'm glad we have come to the same conclusion. I can think of no engineering justification for the 2 bar cap . I also don't think a 1 bar cap will help with the longevity of the ET. I think it WILL help prevent a headgasket failure in the event of an overheat, but in day to day operation, the system never runs over 1.4 bar and that is generous. I will continue to try to justify a 2 bar cap, but I don't think I ever will.
I think it's time one of us measures the pressure and see if the theory matches the reality. The only thing I can think of is that if you reach atmospheric pressure while the heatercore is running, and then subsequently shut off the heat, the coolant level will rise a bit and decrease the volume for air. I don't know if that would be enough to bring the pressure to 2 bar (let alone 3) in any circumstance though.


I should probably mention - I'm just a senior in college, not majoring in engineering or chemistry, so my knowledge will have gaps compared to both of yours. But nonetheless, this has been fun
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Last edited by TerraPhantm; 10-05-2012 at 10:10 AM.
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