ok these may sound stupid, and as if i'm answering myself, but i've just been thinking, and want to know if i'm correct in what i'm thinking. here goes.

so your cooling system is designed to work at a certain psi. in my HELMs, it says the "pressure cap opening pressure" is 11-15psi. does that mean that pressure builds up to 15psi during operation, or that it's 10psi and below?

regardless, my next question...now that certain psi is achieved using the proper amount of coolant mixture. in my case 1.5 gallons. and pressure rises in the system higher and higher as less and less coolant is used, correct? does the water pump act as a compressor, when minimal amount of coolant is used, because it's pushing more air around than liquid? hence the amount of steam pouring out of everywhere it can when the car overheats?

does plain water (no coolant added) evaporate within the system at a higher rate than a coolant/water mixture would?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">regardless, my next question...now that certain psi is achieved using the proper amount of coolant mixture. in my case 1.5 gallons. and pressure rises in the system higher and higher as less and less coolant is used, correct? does the water pump act as a compressor, when minimal amount of coolant is used, because it's pushing more air around than liquid? hence the amount of steam pouring out of everywhere it can when the car overheats? </TD></TR></TABLE>

I'm not sure I understand moat of what you're saying, but....

The water pump does not act as a compressor. The pressure rise is throughout the whole system, before and after the water pump. Therefore, the pump does no more work.

I don't understand the part with mimimal coolant. Are you talking about running a drained cooling system?

 

The coolant does turn into gas. It does not evaporate though because that is what is pressurizing your cooling system. If there are no leaks in the cooling system as the car heats up the water in the coolant goes above heat of vaporization. This turns it into stem. However there is nowhere for the steam to go except to expand the area that is surrounding it, thus creating pressure. Make sense? And since the pressure is high, that keeps the water from boiling because pressure has a large effect on heat of vaporization "PV=nRT" P is pressure, and T is temp... they are inversly related so high pressure will resist higher temp changes...

And that is my chemistry lesson for today

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Black 2K &raquo;</TD></TR><TR><TD CLASS="quote">The coolant does turn into gas. It does not evaporate though because that is what is pressurizing your cooling system. If there are no leaks in the cooling system as the car heats up the water in the coolant goes above heat of vaporization. This turns it into stem. However there is nowhere for the steam to go except to expand the area that is surrounding it, thus creating pressure. Make sense? And since the pressure is high, that keeps the water from boiling because pressure has a large effect on heat of vaporization "PV=nRT" P is pressure, and T is temp... they are inversly related so high pressure will resist higher temp changes...

And that is my chemistry lesson for today </TD></TR></TABLE>
very interesting.

so when there's no coolant at all in the system, just straight water, will it evaporate or is it the same as you've described...?

the steam of overheating and the situation of just water in the system. is that from pressure built from the higher temperature trying to vent out, or...is it because there isn't enough water in the system, and all that extra air is somewhat "compressed" from being pushed through the cycle over and over?

am i making sense...i can't describe it well...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Black 2K &raquo;</TD></TR><TR><TD CLASS="quote">The coolant does turn into gas. It does not evaporate though because that is what is pressurizing your cooling system. If there are no leaks in the cooling system as the car heats up the water in the coolant goes above heat of vaporization. This turns it into stem. However there is nowhere for the steam to go except to expand the area that is surrounding it, thus creating pressure. Make sense? And since the pressure is high, that keeps the water from boiling because pressure has a large effect on heat of vaporization "PV=nRT" P is pressure, and T is temp... they are inversly related so high pressure will resist higher temp changes...

And that is my chemistry lesson for today </TD></TR></TABLE>
Wow...

Well, evaporation MEANS turning into a gas. Either it does or it doesn't. Hint: it doesn't. Boiling point depends on pressure as well as chemical composition, so at 15 psig the boiling point is high enough so it doesn't boil. Unless your radiator cap is bad.

Now, your quiz questions for today are:
1 - What's the difference between temperature & heat?
2 - What's the difference between boiling point & heat of vaporization?
3 - Why can't you use the ideal-gas equation for water at normal automotive conditions?

 

I'm not sure whether coolant changes the boiling point of water. However, pressure built up in the cooling system will raise the boiling point of water. I doubt water with no coolant will evaporate under normal conditions.

An interesting side note, water by itself is actually much better at cooling than water and coolant.

Air is not compressed by being cycled through the water pump, and I don't see how it would be cycled through the water pump.

 

Non-water based coolants actually have such a high boiling point that the system never really runs under any pressure. The downside to havig water boil in your system is that pockets of water vapor in your water jacket prevent coolant from dissipating the heat in that area. This situation in turn creates hotspots in your engine that can cause detination and damage from overheating.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Lsos &raquo;</TD></TR><TR><TD CLASS="quote">An interesting side note, water by itself is actually much better at cooling than water and coolant.</TD></TR></TABLE>
are you referring to general situations, or specifically a honda's cooling system?

because my helms says that water dosen't protect against corrosion as well as a coolant/water mixture. and obviously water would freeze without the anti-freeze/coolant. but i'm in Arizona, i'm not worried about that.

the helms is **** though. it says too much water in the mixture introduces the problems above. but with too much coolant, it dosen't cool as efficeintly. are these things REALLY something to worry about...?

i'd much rather run just water though, it's a pain in the *** to me to mix exactly half...

 

I'm referring to general situations, as well as Honda's system. Water is the best for pure cooling, but like Helms says you need to use coolant to prevent corrosion and freezing. You might not have to worry about freezing, but corrosion is a definite concern and hence you should use a recommended water/ coolant mixture. I'm sure it doesn't need to be exaxt, but you should at least make an attempt at a proper mixture.

 

'Coolant' is whatever fluid you put in there, whether that's water or 50% ethene glycol or dog drool.

Using just water as a coolant gives better convective heat transfer, but doesn't inhibit corrosion. Anti-freeze lowers the freezing temperature, but I believe it also raises the boiling temperature. Maintaining higher pressure certainly raises the boiling temperature. The designers know the heat transfer properties of 50% ethene glycol, and the cooling system is designed for it.

Surface temperatures in the water-jackets in the head get pretty high, and you want to suppress boiling. Local nucleate boiling is an incredibly powerful heat transfer mechanism, but nucleation & collapse of the bubbles does damage so you don't want much of that to happen.

If you're in Florida or Arizona where it never(?) freezes, you can probably get away with less than 50% anti-freeze, but then you get less corrosion inhibitors, too. Remember that the anti-freeze is always there, but the corrosion inhibitors get 'used up'. Measuring specific gravity doesn't tell you about how much of the corrosion inhibitors are still there.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Hriday &raquo;</TD></TR><TR><TD CLASS="quote">Non-water based coolants actually have such a high boiling point that the system never really runs under any pressure. The downside to havig water boil in your system is that pockets of water vapor in your water jacket prevent coolant from dissipating the heat in that area. This situation in turn creates hotspots in your engine that can cause detination and damage from overheating.
</TD></TR></TABLE>
If that were water vapor it would condense. More likely it's pockets of air which were originally dissolved in the water. They don't condense, and at operating temperature they don't go back into solution.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JimBlake &raquo;</TD></TR><TR><TD CLASS="quote">
Now, your quiz questions for today are:
1 - What's the difference between temperature & heat?
2 - What's the difference between boiling point & heat of vaporization?
3 - Why can't you use the ideal-gas equation for water at normal automotive conditions?
</TD></TR></TABLE>

#1. Temperature is the measurement of individual atoms bouncing around, heat is the transfer of energy from one thing to another. ie heat is changing from the cylinder walls of your engine to the coolant, which increases the molecules of coolant moving around which we measure as temperature.

#2. Heat of vaporization is the energy required to vaporize 1 mole of liquid at a pressure of 1 atm, whereas the boiling point is is the temperature at which the vapor pressure of a liquid is exactly 1 atm.

#3. Why you cant use the ideal gas law under car conditions... My best guess as to why you think you couldnt use it is becasue the pressure is constantly changing. But i dont see a problem in using it... if you look at specific times

 

Cool, I wasn't sure anybody'd take that seriously! I was kinda bored when I wrote it.

#1 Good! But heat is energy, and it's still there whether it's being transferred or not.

#2 Almost. Heat of vaporization and boiling point will change with pressure, and they are still called the same thing when they're given at other pressures. For water, when you increase the pressure, the boiling point goes up and the heat of vaporization goes down.

#3 That equation breaks down as a singularity at saturated conditions; that's when you have boiling or any 2-phase mixture. The volume can change a lot without any change in pressure or temperature. So if you're talking about heat of vaporization in the first place, the equation doesn't even deal with that.

Anywhere near saturated conditions, the state isn't close to what you'd get from that equation. A simple way of looking at it is that the equation only works when the gas is so sparse that the distance between molecules is way bigger than the size of the molecules. Like air for example.

You originally said high pressure keeps water from boiling - that's correct. Pressure has an effect on heat of vaporization, but I think you meant to say it has an effect on boiling temperature. But the ideal gas equation doesn't have anything to do with either one. The relation between pressure & boiling point isn't linear anyway.

Cheers

 

So how does that additive (forget the name) that is supposed to lower the coolant temp by x degrees work? Supposedly, by improving the heat transfer between the cylider jacket and coolant.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by PupaScoopa &raquo;</TD></TR><TR><TD CLASS="quote">So how does that additive (forget the name) that is supposed to lower the coolant temp by x degrees work? Supposedly, by improving the heat transfer between the cylider jacket and coolant.</TD></TR></TABLE>

I don't know, but if the coolant temperature does drop, the thermostat will close and bring it back up again.

Running cooler temperatures is not necessarily better. An internal combustion engine runs more efficiently if it runs hotter, which is why they design the cooling system to keep the engine at as high a temperature as possible within material limitations.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by PupaScoopa &raquo;</TD></TR><TR><TD CLASS="quote">So how does that additive (forget the name) that is supposed to lower the coolant temp by x degrees work? Supposedly, by improving the heat transfer between the cylider jacket and coolant.</TD></TR></TABLE>
Water-Wetter?? I don't know & I'm kind of curious, too. The name implies wetting characteristics, which is about surface tension. But changing surface tension doesn't do you any good if you don't have any vapor interface.

I don't know how much you can change the thermal conductivity or heat capacity with an additive in small concentrations.

Maybe changing the viscosity to increase turbulence intensity. You'd have to lower the viscosity to raise the Reynolds number, but I don't know if that's what that stuff is all about.