Chris,
Now you have me curious... Time to drag out the old fluid dynamics texts
and the CDC book. ;-) I am thinking that gases *are* fluids of very low
density. I'm a meteorologist and we apply the same laws to the atmosphere
that hold for fluids. Some adjustment to the equation for density of the
fluid ("rho" which would be Mass / unit Volume) gives one P =(rho)RT. Now
you can make the fluid dense and turn it to liquid if you wish and P is
still inversely related to T, right?
I'll look this up tonight. It's been a very long time since I messed with
this and you've made me curious...
Cheers!!
Jim
On 5/25/07, Chris King <cbking@alum.rpi.edu> wrote:
>
> Uh, Jim, I'm not sure you can really apply the Ideal Gas Law to a
> liquid...
>
> But the system is pressuized, to either 7psi or 15 psi, depensing on the
> rating of the radiator cap. This pressure effectively raises the boiling
> point of the liquid, a good thing, since you don't want your coolant turning
> to steam, since steam doesn't cool as well :)
>
> With the system open, you're just measuring the temp of the liquid, and as
> long as it's less than 212F (at sea level), evaporation for this test should
> be negligible. So since we have a liquid in the first case (closed,
> pressurized system), and the second case (open system), I think that the
> thermometer method is a valid way to see if the temp gauge is reasonably
> accurate.
>
> If, for some reason, there's vapor in your cooling system, then the ideal
> gas law will come into play (partial pressures and all that), but by that
> time I'm sure you've got bigger things to worry about! :)
>
> Cheers!
>
> -=Chris
>
> Chris King
> http://home.comcast.net/~kvcbk/ <http://home.comcast.net/%7Ekvcbk/>
> <-----Original Message----->
> *From: Jim Johnson [bmwwxman@gmail.com]*
> Sent: 5/25/2007 2:17:56 PM
> To: abcoz@hky.com
> Cc: bugi1960@gmail.com;spridgets@autox.team.net
> Subject: Re: Overheating woes > Water Wetter
>
> Bud wrote:
>
> Years ago, I stuck a
> > thermometer in the radiator tank, with the engine starting from cold,
> > idle, and just noted what the thermometer read, compared to the gauge,
> > as the engine warmed up. Pretty easy to do, and it won't puke much
> > coolant out of the open filler plug hole, while idling.
>
> Bud.... This also won't give you an accurate temperature! Recall:
>
> PV = nRT
>
> Temperature (T) is inversely proportional to P (pressure) and V
> (volume). If you leave the radiator cap off, the system is not
> pressurized thus Temperature will be different than if the system is
> pressurized as it normally would be.
>
> Big question which I alluded to the other day when Frank had his
> problem - "Is a spridget cooling system pressurized??" If it isn't,
> you are okay, but I'm thinking it has to have at least some pressure
> in it due to expansion from heat and the fact that the system is
> closed.
>
> Cheers!!
> Jim - 68 Midget in Dodge City
>
>
> .
>
--
1964 R60/2 BMW
1968 MG Midget
1976 R90/6 BMW
1990 K100LT BMW
Thomas Huxley - "It is not who is right, but what is right, that is of
importance."
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