cantdrv65

iTrader: (3)

Chemical Formula N2O
Molecular Weight 44.013
Boiling Point -88.56ºC (-127.4ºF)
Melting Point -93.06ºC (-131.5ºF)
Vapor Pressure 5,238 kPa @ 21.1ºC (759.7 psia @ 70ºF)
Specific Gravity (air = 1) 1.53
Gas Density (21.1ºC (70ºF) @1atm) 1.836 kg/m3 (0.1146 lb/ft3)
Liquid Density (saturation pressure at 0ºC) 0.913 kg/l (57.0 lb/ft3)
Specific Volume (21.1ºC (70ºF) @ 1atm) 0.5447 m3/kg (8.738 ft3/lb)
Critical Temperature 36.4ºC (97.6ºF)
Critical Pressure 7,254 kPa (1,052.2 psia)



Supercritical fluids are produced by heating a gas above its critical temperature or compressing a liquid above its critical pressure. The critical temperature of a substance is the temperature above which a liquid phase cannot exist, regardless of pressure.


Critical temperature and pressure
The errors in ideal gas predictions become most striking as you approach the gases critical conditions.

DEFINITION
At higher temperatures and/or higher pressures the difference between a gas and a liquid eventually disappears(!) and a supercritical fluid is formed. The point at which this happens is called the critical point

DEFINITION
The highest temperature at which a species can coexist as a liquid and a vapor is termed its critical temperature, Tc.

DEFINITION
The highest pressure at which a species can coexist as a liquid and a vapor is termed its critical pressure, Pc.



DEFINITION
A supercritical fluid is a substance which is above its critical temperature, Tc and pressure, Pc.

cantdrv65

iTrader: (3)

The above facts make me want to keep my bottle BELOW 1052.2 psia - 14.7 = 1037.5 psig and below 97 degrees F....Maybe thats why nitrogen push works so well. I seem to like about 1000psi and definitely below 95 degrees now...

Am I flawed in my thinking?

NXJeremy

Not sure about the Tc, but you are right about the critical pressure so I would think that the Tc would also hold true. Keep the pressure below 1052.2psia and you should be ok.

cantdrv65

iTrader: (3)

But thats just it...It doesnt matter what pressure you are at if you exceed the 97.6 degree critical Temp you are going to have problems getting liquid to the solenoids, being that the N2O in the bottle will be in a gaseous state...

cantdrv65

iTrader: (3)

Controlling the pressure of your N2O bottle at 1050psig which is 1064.7psia and achieving that pressure by way of adding heat (bottle heater) puts you at or above the critical temp of N2O at 97.6 degrees. This would be at above the point the N2O would be in a completely gaseous state in the bottle, provided the entire bottle was above that temp (albeit highly unlikely)... Nevertheless if controlling the pressure by temp Id definitely lower bottle pressure to 950 to 1000psig for better performance. It only makes sense!

NXJeremy

I was agreeing with you, sort of. I had not read about Tc until now, I only knew about Pc. But if Pc is true (which it is), then it only makes sence that Tc would hold true as well.

That being said, at 97 degrees bottle temperature it doesn't necessarily mean that the substance inside the bottle is at 97 deg. as well. That's why I never really paid any attention to temperature, just Pc. However, even if you pass the point of Pc at the bottle I don't know if the N2O doesn't revert back to liquid form at some point down the line due to a drop in pressure once it reaches the solenoid or nitrous jet.

cantdrv65

iTrader: (3)

Right but....

the material is at 97 degress or better when the pressure is a direct result of heat added. The critical pressure is what you get when you heat N2O in an enclosed cylinder to the exact point of the critical temp without changing volume of the container or adding material.

So if you heat your bottle up and go from 800psi to 1050psi you've passed the critical temp of N2O....

The only way to return to a liquid is if the temp drops back below 97.6... that may not happen in a Texas summer.

cantdrv65

iTrader: (3)

I was mistaken here...If the bottle presure is raised to 1050psi by way of a heater the N2O is already beyond critical temp....

MrDude_1

iTrader: (4)

psst.. thats at atmospheric pressure... at actual bottle pressure, the temp is MUCH higher.

cantdrv65

iTrader: (3)

Refer to this rule: The critical temperature of a substance is the temperature above which a liquid phase cannot exist, regardless of pressure.




H2O for example this would occur at 705 degrees F...

NXJeremy

Just heat the bottle to no higher than 1035psia and you won't have to worry about Pc. Plus, once you get the N2O moving (through the lines and eventually the jet) the temp of it is going to go down. So the Tc shouldn't be an issue either.

Robert56

iTrader: (2)

I have 95* electro thermastats, which heat the bottle to 1150. Now this is below your 97* critical point, comments please. Also, a buddy ran a 11.48 on n2o from a baseline 12.6x and his bottle (from parked in the sun) was at about 1500psi. It was jetted for about 100rwhp and a dry hit, comments please. I was there and seen this, so I conclude if it was just vapor the 1-sec plus would not have been taken off his ET?
Robert

NXJeremy

Robert, I think it would be a better idea to see what the temp and/or pressure of the N2O is at the point that it leaves the jet. I say this because the N2O is going to get colder as soon as you get it moving (read - either opening the bottle valve or opening the solenoid), but by how much I don't know (and we haven't done any testing for this either). I'm trying to talk Ricky into doing this test, but we are pretty slammed with projects (read - custom jobs) right now.

Robert56

iTrader: (2)

That's probably why my Cobalt gauge reads diff than the on bottle gauge. Cobalt sending unit is right at my noid array. IIRC, the gauge at noids reads a little lower than the bottle gauge, does this sound correct? I allways thought to myself gauge tolerance diff.
Robert

NXJeremy

Yea, the difference in pressure is because the N2O dropped in temp just in the short length that it travelled from the bottle to the solenoid. I would like to see how much the temp/pressure drops at the exit of the nozzle/plate when the system is activated and there is a constant flow of N2O.

cantdrv65

iTrader: (3)

Id lower the bottle pressure and try it out Robert. What actually happened to your friends trap speed with the N2O hit? He may have gained more from a lower bottle pressure?... Im not sure? Thats why I brought this up for discussion. Above the critical point N2O is classified as neither a gas or liquid but a supercritical fluid which displays the properties of both. That may even be desirable, I have access to a Phd research scientist Ill ask him and post the results. It just seems to me observing the properties of N2O that I myself have tried to run too much pressure in the past, when I should have just jetted up.

Robert56

iTrader: (2)

On the dry hits we have been for a while upping the pressure to fool jets into thinking they are bigger. Seems to work, allthough it looks like there is a limit to a percent gain compared to upping jets instead. Good stuff to think about.
Robert