NITROUS OXIDE ( nos / n2o ) advice forum

It's worth figuring out.

Somebody guess it right please, it's doing my head in!

If we mean airlock as opposed to vapour-lock, then would the tiny amount of water in air (which freezes at 0 degrees) be of any consequence?

My only other randon guess is that air might create a sort of damping effect on the liquid as it's compressible?

Mike
If you have air in the nitrous delivery line there would be a problem.

There IS air in the supply pipe any time the pipe is vacated of nitrous, however the effect I'm talking about is the same regardless of it being air or nitrous vapour.

Anyone who has any ideas may like to PM me with them and anyone who wants to know the answer could also PM me, as this is something I don't want to make general knowledge yet.

errrr can i have the question please?
cuz it seems like another langfield riddle that i cant figure out before i can even answer
this could be a job for "common sense" da da daaaaa

Common sense is ALWAYS the way to a greater understanding, because as I've said a number of times, that's all I have to call on myself.

However, there is no question as such, it was just a passing comment made by somebody on the thread previously which wasn't quite right. Might I suggest you read the other guys posts to work out the plot.

this maybe a very silly question but why cant the flow be straight ?

""There IS air in the supply pipe any time the pipe is vacated of nitrous, however the effect I'm talking about is the same regardless of it being air or nitrous vapour.""

I can see there being air in the line if you blow the gas off, like when you change a bottle.
Which is when I use my purge solenoid, after fitting a new bottle.

I can see there being nitrous vapour in the line when you havent used it for a while as the engine bay temp will cause the liquid to expand to a vapour and cause liquid migration back to the bottle if the valve is open. But if the bottle valve is shut, surely you just end up with a high pressure liquid in the line. Maybe even an emulsion.

On my old holley system this was evident as nitrous lag when I hit the loud pedal. Very noticeable too, approx 2-3 seconds which blew my 1/4 times out of the water. This is why I fitted the purge system. I only use it for showing off now though. Because I know when my bottle is up to 900 psi I dont seem to get lag when I hit the loud pedal.

Going back to Daves graphic of a 90 degree bend, I would have thought it would look more like a full head of liquid down the vertical runner right into the back of the elbow. And then as it turns off to the right I would have thought it would be more like a dense liquid at high velocity along the bottom of the pipe with more turbulence of phase change going on in the upper half of the horizontal pipe.

For what its worth.

Mostly right but I'm with Dave on the elbow flow and I think even Dave has been "generous".

Here's a clue to the cause & effect of the "issue" we're discussing, have you ever looked at the consistency of the flow (or lack of it) for the first second or so after a solenoid is first opened??

Yes.
Its a little unstable until you have a full head of liquid into the guts of the pulsoid so the jet can do its job of metering liquid instead of vapour. The vapour plume seems to move a lot quicker than a liquid plume. And as the liquid tarts to exit the open end of the pipe on a test you seem to get more of Newtons 3rd law (I think it is) going on. The pipe tries to push in the opposite direction more violently when you have liquid at the outlet.
Which seems ok to me. And this would still be nitrous lag wouldnt it??

Yes there is nitrous lag going on but "there is more to it than your original explanation".

If it was just vapour/gas build up at the solenoid end of the pipe, the transition from gas to liquid would be more clear cut but it isn't, it has fits and starts.

I just thought the fits and starts were caused by the vapour being compressed by the inrush of liquid which sets up some sort of shockwave as the vapour gets hit hard by a column of liquid and gets squashed / compressed, but then fights back as it does like the be bullied by the liquid. Until eventualy the liquid forces some of the vapour out and absorbs some of it by condensation until the liquid wins. ( I love a good ending)

I suppose if the conditions were right you could have saturated vapour or small pockets of liquid hiding here and there. This would give the effect of vapour with lumps in it coming out the end of the pipes wouldnt it. We just call this flash gas in the fridge game. Where you want a column of liquid, but due to conditions not being correct in the system you get either liquid with pockets of vapour, or vapour with pockets of liquid. The visual result is similar. The discharge spits like an old espresso coffee machine spout until you have established enough liquid at the right pressure to make the flow rate correct for the size of the outlet.

I dont know what you would call this effect. I shall refer to it as the Cappucino Theory.

What a tease artist

I suppose if we are talking about pockets of vapour in the liquid line while its flowing. We go back to the effect that non smooth internals in the flow line can cause minute pockets of phase change gas all the time the liquid is flowing.

Like Daves Elbow drawing. I suppose once the obstacle in the line has caused this pocket / area of phase change, it will continue to do so at a fixed rate (assuming pressure and flow are constant) and the result will be the spitting / Cappucino effect at the outlet.

You certainly know how to get me thinking Trev. I'm supposed to be writing up quotes. I'll pop back in later.

as youve highlighted liquid with vapour in perry post im guessing thats what your thinking lol
adiabatic compression would cause pockets of gas in the nos line, but only when flowing
otherwise any gas formed with in the lines would have to be due to expansion of the static liquid

i think its been said, but couldnt inertia be part of the problem?
the moment the pulsoid is openned the liquid/gas in the line will instantly expand to escape to atmos ( or inlet )
the liquid nos behind that will have to be accelerated to match to escaping liquid/gas infront of it
and so the coughing and farting (cappachino effect) until the liquid nos is travelling at the same velocity as whats infront of it

id say there is a distinst velocity per volume that has to be flowing before the outlet can become liquid nos only
below that the liquid nos is still "travelling" too slow to create a pressure that prevents gas pockets from forming?

So Moo!!
You thinking about some sort of reversion or shockwave effect in the supply line when pulsing?

Both VERY GOOD potential causes which may well exist and contribute but not the cause/subject that started the whole discussion.

I'm taking Moo to mean the "time" factor (that I keep mentioning that others ignore to their cost) and the stretch / concertina effect of gas flow as a consequence, which is a particular issue with a liquid gas and exaggerated by that fact.

So let me think out loud now.
I'm visualising a cross section of pipe say.
There is a full head of liquid up to a point where there is an exit point.
The liquid flows at X feet per second in a uniform state with stable pressure etc.
I'm seeing the liquid flashing off to vapour in its run for freedom out of the hole at the end.
Could this phase change at an outlet cause a pressure drop local to the outlet to the point that it starts to accelerate in the last inch or so of the pipe. But it may be accelerating to a speed which is faster than the pipe run can support. Would you then see a sort of push / pull effect as the outlet pressure dropped and the resultant acceleration got to a point where the outlet was starved of liquid for a millisecond, at which point the expansion slowed down and allowed the liquid to catch up again??

This may be all complete crap of course. But I shall call this "The Slinky effect"

Reading back again.
Trev said.

""If it was just vapour/gas build up at the solenoid end of the pipe, the transition from gas to liquid would be more clear cut but it isn't, it has fits and starts.""

Are you talking about the discharge line from the solenoid to the nozzles?
If so, do you think air / moisture in the outlet side up to the nozzles could momentarily freeze somewhere along the way to the nozzles.

Just thinking out loud as usual.

""liquid with pockets of vapour""
Now I wonder where they come from?

From Daves Elbow and similar fittings in the supply line I would assume??

"Some" may be as a result of that but there is a more major cause and you're not going far enough back in this thread, to the statement that started this line of thinking, to close the loop.