E46 BMW Social Directory E46 FAQ 3-Series Discussion Forums BMW Photo Gallery BMW 3-Series Technical Information E46 Fanatics - The Ultimate BMW Resource BMW Vendors General E46 Forum The Tire Rack's Tire Wheel Forum Forced Induction Forum The Off-Topic The E46 BMW Showroom For Sale, For Trade or Wanting to Buy

Welcome to the E46Fanatics forums. E46Fanatics is the premiere website for BMW 3 series owners around the world with interactive forums, a geographical enthusiast directory, photo galleries, and technical information for BMW enthusiasts.

You are currently viewing our boards as a guest which gives you limited access to view most discussions and access our other features. By joining our free community you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is fast, simple and absolutely free so please, join our community today!

If you have any problems with the registration process or your account login, please contact contact us.

Go Back   E46Fanatics > E46 BMW > General E46 Forum

General E46 Forum
This is the place to get answers, opinions and everything you need related to your E46 (sedan, coupe, convertible and wagon) BMW!

 
 
Thread Tools Search this Thread Rating: Thread Rating: 10 votes, 4.60 average. Display Modes
Prev Previous Post   Next Post Next
Old 10-07-2012, 02:54 PM   #11
TerraPhantm
Registered User
 
Join Date: Feb 2008
Location: Mountain Top
Posts: 5,996
My Ride: 2005 M3 Coupe
Quote:
Originally Posted by mkodama View Post
lol, your posts are much longer than they need be.

So for your ideal gas law, you are only acknowledging the air within the expansion tank, and your variables are:

P=variable you're solving for
V=?
n=?
R=?
T=coolant temperature

I think we are all in agreement that if you completely top off the expansion tank with coolant, you will get the 2bar relief pressure on the expansion tank cap?
R is the gas constant. You don't need to solve for R. You can also treat n as constant since it wouldn't change in a closed system (which it is until it starts venting).

If you set up an equation for both states, you get the following:
P1V1 = nRT1
P2V2 = nRT2

P1V1/T1 = nR
P2V2/T2 = nR

P1V1/T1 = P2V2/T2

Now you need to make some assumptions. For our purposes, it's reasonable to assume that starting temperature and pressure will be 20C and 1atm respectively. We know the final temperature gets to about 95C. Now if we assume that the system does indeed reach 3 bar, we can calculate how much the volume changes on relative terms.

V1/V2 = P2T1/P1T2
V1/V2 = 3 * 293 / 368
V1/V2 = 2.38 and V2/V1 = ~0.42

That means for the pressure to reach 3 bar, the volume of air must decrease to 42% of its starting value. If we know the volume of air in the ET when cold, we can verify whether or not this actually happens by calculating how much coolant expands during operation. If it's enough to create 3 (or more) bar, then we know the cap does something.
__________________

Last edited by TerraPhantm; 10-07-2012 at 05:23 PM.
TerraPhantm is offline   Reply With Quote
 

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Censor is ON





All times are GMT -5. The time now is 04:55 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
(c) 1999 - 2011 performanceIX Inc - privacy policy - terms of use