Coolant plumbing...
Turbo Mini Forums

Colin, I dont get your second point,

no probs, I've been at the beer, somprbably cant count lol

"Saturated water in a closed container has a saturated pressure of 525.8mmhg at 90c. This is a vacuum."


mm of mecury mean naff all to me, but that statmunt sugets that if yo heat water t0 90 deg you get a decrease in volume.

Ok

If you have a container such as a cylinder, that contains water, which does not completely fill the cylinder, and then remove all the air, the cylinder only contains water as a liquid and a vapour, at its saturated pressure. If the water temperature is 90c, its saturated pressure in the cylinder would be 525.8mmhg, which is roughly equivelant to 0.7 bar absolute, or -0.3 bar gauge >> a vacuum.

If you heated the water to 100c, the pressure inside the cylinder would be 1 bar absolute, or zero bar gauge. meaning that you could open the cylinder at sea level and nothing would enter or exit the cylinder.

Edited by Sprocket on 5th Feb, 2011.

When you fill your rad and put the cap on you do not remove all the air from the system! When you heat the water to about 90 degC the SVP will be about 9 or 10 psi. This is the amount the internal pressure is above the external, i.e. atmospheric. If you remove the cap at 90 deg I can assure you air will not be sucked in, very hot vapour will come out!

Geoff

Colin,

You may have 90 Deg C water in the rad.

But you may have a hot cylinder head that will cause localised boiling as you release the pressure. The only reason that it has not been boiling until the moment you remove the cap is that is is held under pressure.

This thread needs a health warning and a TM disclaimer

Edited by Paul S on 6th Feb, 2011.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

So we are dismissing the fact that the pump is raising the pressure in the block and head, against the restriction of the thermostat?

sorry, still not convinced

I did not say that water boils at 90 deg C!!! The vapour pressure of water rises exponentially with temperature until it reaches 760mm of Hg when it boils, assuming an open container.
For those who do not understand what happens when you heat water, have a look at this:
http://www.chemguide.co.uk/physical/phasee...apourpress.html

Edited by h4887 on 6th Feb, 2011.

Geoff

Colin,

Well, run your engine until the gauge shows 90 and then remove the cap. But be sure to make a video of it so we can all see you get burned by the hot coolant gushing out. Or not...

Jean

Edited by jbelanger on 6th Feb, 2011.

http://www.jbperf.com/

Water does NOT need to be heated to a uniform 100C to produce vapour if there are local hotspots (like a kettle element) to produce local temperatures above 100C.

It just needs to be at an average of 100C to BULK boil at atmospheric pressure.

But it can easily be pressurised at less than 100C if vapour is being produced by localised boiling, even if the vapour bubbles collapse in the sub-cooled fluid.

Try putting a lid on a kettle and taping it up so the vapour space is sealed and then turning it on (before it boils).

Just type DNBR into Google to see what I mean.

And, like Jean, I would strongly NOT recommend taking the expansion/rad cap off your engine at 90C running.
Just squeeze the hoses instead to feel the pressure.



BUT.....

Back to my original point, pumps raise pressure to produce flow - another basic law of thermodynamics and fluid flow....

Irrespective of temperatures and "boiling points", if the pump doesn't create a pressure rise, there will be no flow (apart from the small amount produced by density changes, ie, thermosyphon).

Edited by Rod S on 6th Feb, 2011.

Schrödinger's cat - so which one am I ???

OK im done.

Bye

:)