When I open a valve, there is initially a high pitched sound?

[EpicOfMan]

When I open a valve and gas escapes, there is initially a high pitched sound, then the sound eventually goes to just a normal hum. Why does this occur?

[MacM]

When I open a valve and gas escapes, there is initially a high pitched sound, then the sound eventually goes to just a normal hum. Why does this occur?

Can you give more detail?

What is the source? i.e. A compressor storage tank?

What is the pressure.

What is the size of the line?

What is the capacity - if known (tank) or is it unlimited such as a gas line.

I am expecting a whistle from high initial velocity which ceases to whistle as the pressure, hence flow rate decreases.

If you are exposed to this frequently you should wear ear plugs or muffs. High pitch noise will damage your hearing fairly quickly.

[EpicOfMan]

It's just more of a general question. It was actually a liquid nitrogen tank. It was quite large, and when you open the valve there is initially a high pitched noise, and I was just wondering why this occurs.

[MacM]

It's just more of a general question. It was actually a liquid nitrogen tank. It was quite large, and when you open the valve there is initially a high pitched noise, and I was just wondering why this occurs.

Of course it is hard to assess the issue from here and what is being offered is just a guess based on some experience in that area.

It sounds like the sound is brief in terms of the overall release of gas. That is it disappears even though the pressure has not decreased substantially and there is still a high volume of gas being released.

If so, I think the affect may be due to the turbulance of the initial rush of air where high pressure gas is filling each and every creavess and cranny, bend and orifice obstructions until the flow has smoothed out.

That is the initial rush is more turbulant than the stabilized flow once gas has been forced into these stagnant points in the flow channel.

After all a whistle is created by causing turbulant air flow and laminar flow is a quiet Shsssss or rushing sound.

Anybodyelse have an idea?

[Yuriy]

EpicOfMan,
Are you keeping liquid nitrogen into a closed tank?
(Not giving it's vapor a single way to escape?)

[EpicOfMan]

EpicOfMan,
Are you keeping liquid nitrogen into a closed tank?
(Not giving it's vapor a single way to escape?)

Yeah, the tank is closed.

[QuarkHead]

Yeah, the tank is closed.Then stand clear

[Yuriy]

Yeah, the tank is closed.
It sounds very strange to me... But, it is not my business...
In this case the answer on your question, dear EpicOfMan, depends upon facts:
1. Where is located the entrance hole of the tube: in liquid or in gaseous phase of nitrogen?
2. Where is located valve on the tube: in its beginning, middle part or on its end?
Can you answer those questions?

[EpicOfMan]

There is a tube at the top and a valve at the end of the tube. I suppose it would be at the gaseous phase.

[Yuriy]

As you have describe the situation, I think this effect
there is initially a high pitched sound, then the sound eventually goes to just a normal hum
is a simple jump down of a huge preassure that take plase in your tank due to accumulated heat from outside during two consecutive use of this valve.

[MacM]

As you have describe the situation, I think this effect

is a simple jump down of a huge preassure that take plase in your tank due to accumulated heat from outside during two consecutive use of this valve.


It would seem we agree on something at least. From my first post:


I am expecting a whistle from high initial velocity which ceases to whistle as the pressure, hence flow rate decreases.

Epicofman,

Just curious.

1 - How frequently do you vent the tank?

2 - Is the venting done in response to some pressure reading?

3 - Why does not the tank have a PRV (Pressure Relief Valve)?

4 - or does it have one but the setting is much higher and is just backup for safety?

5 - I sounds to me like the process for which this is being used wants to maintain something higher than the inherent temperature should the tank be left to evaporate continuously.

6 - It also sounds like they could use a bit of automatic instrumentation to establish a more stable result.

7 - Can you tell use what the tanks function is? That is what process does it support?

FYI: Be aware (if you aren't) what your employeers are having you do.

http://webs.wichita.edu/facsme/nitro/safe.htm

and

zero: -459.67 ° F or -273.15 °C

Liquid Nitrogen: -320F.

Your pinky or pecker will simply freeze and summarily break like glass and fall to the floor shattering into fragments. Humpty Dumpty will never be whole again. Be careful.

[QuarkHead]

Well I am a moron. So forget clever-dick comments like Then stand clear
Of course - the only way way to keep your gas liquid is to allow pressure to build. Sure a PRV might be wise, but read the following.
Here's a question for all you number crunchers
Suppose I have a sealed tank volume V, and insert into it a gas-tight removable partition exactly to divide it in two. I now fill the lower half, allow to equilibrate, and then remove the partition. Liquid gas will "boil" off to form a gas phase and thus provide pressure to keep the liquid gas liquid.
Q: What is the residual volume of liquid as a fraction of V?
Alternatively (it amounts to the same thing)
Q: what is the minimum fractional volume I need to fill with liquid gas so I am left with at least some liquid?
Use any simplifying assumptions you care to specify. I suggest the following:
*the system is adiabatic
*the gas is ideal
*liq N₂ = 90K, ambient = 290K
*there is no temperature gradient across the gas phase

No - it's not a riddle. I don't know the answer (I don't do numbers)

[MacM]

Well I am a moron. So forget clever-dick comments like
Of course - the only way way to keep your gas liquid is to allow pressure to build.

I doubt you are a moron. :D The point is if the liquid is allowed to boil off, what liquid you have remains at the -320F temperature.

If you want or can use a higher temperature then your tank can regulate that temperature by controlling the pressure at which it relieves. So the safety depends on the design of the tank and your pressure setting.

It really depends on the application. In cryogenics you generally allow the tank to slowly vent maintaining the lowest possible temperature.

[Yuriy]

QH,
If you indeed are interesting in the theory of evaporation (which by necessity contains the physics of equilibrium “vapor-liquid” in closed vessels), you should read “The Scientific Notes” volume #1, where I for the first time gave an exact equations of the kinetic of evaporation. (BTW, I count the idea how to get the rate of evaporation of liquid, which I published for the first time in that volume, as the most beautiful one in whole my career as physicist…)
But if you are not interested and only one what wonders you is to know the answer on you question, please, explain it to me, what you meant saying “thus provide pressure to keep the liquid gas liquid” because I can not imagine what means “liquid gas” which should be kept … liquid?

[QuarkHead]

QH,
If you indeed are interesting in the theory of evaporation ....... please, explain it to me, what you meant saying “thus provide pressure to keep the liquid gas liquid” because I can not imagine what means “liquid gas” which should be kept … liquid?Well - I was throwing down a challenge to our members who prefer to use numbers rather than equations. But as you ask...
I am assuming that liquified gas can only remain liquid under pressure. Right?
I am also assuming that, as long as the container is not completely full, then there will be some sort of equilbrium between gas phase and liquid phase.
Am I wrong to assume that that, at equilibrium, pressure from the gas phase will maintain the liquid phase as liquid gas? Hence...“thus provide pressure to keep the liquid gas liquid”

[Yuriy]

QH,
1. Any phase is the same natural for a given matter as any others. When we say “to liquefy gas” or “to evaporate liquid” or “melting of crystal” we simply emphasize the initial thermodynamic state (phase) of a matter. (Pay attention: we can get the same liquid “liquefying gas” or “melting crystal”; we can sometime get gas … evaporating crystal, skipping liquid phase).
2. The transits between phases that we are talking about are so called phase transitions of the first type (there are also so called the second type, third type phase transitions, and even types with none integer number transitions). The major feature of those transitions is that all they require some specific energy to transform a unit of matter from one phase into another – so called latent specific energy. The most thermodynamic phase transitions of a first type, PT-1, are happening at the constant temperature – the temperature of phase transition.
3. This temperature indeed depends upon pressure of liquid or gas (Pay attention – I do not specify which one: internal or external, because due to the Pasquale law in the rested liquid and gas out of external fields, like gravitational, the pressure is equal in any point!). So we can say that T = T(P). On the plate (T, P) this line is called the phase transition line.
4. And now exactly about evaporation of liquid nitrogen. In open vessel (i.e. connected with some atmosphere – a huge reservoir of some, usually - alien - gas with its own pressure and temperature – the ambient pressure Po and ambient temperature To) above a free surface of the liquid nitrogen we will have vapor of nitrogen (some ensamble of the nitrogen molecules in gaseous phase that consist of both – already being in atmosphere and already evaporated from liquid nitrogen). Pay attention: we do not call this ensemble “a nitrogen gas”, but “a nitrogen vapor”. That is so because gas, which is in contact with its own liquid, is called by special term – “a vapor”. It is not because we like to create a lot of special terms, but because the physical behavior of the same ensemble of molecules is absolutely different in cases either is there a contact with liquid phase of the same matter, or is not.
5. If the temperature of liquid is far away of so called critical temperature, Tcr, at which the physical properties of liquid and gaseous phases become the same, the density of the liquid phase is much higher then the density of its vapor (even if it is a saturated one). At such conditions (typical for a liquid nitrogen in a tank opened into ambient air) the molecules of vapor no how can influent on the processes that are pushing molecules of liquid nitrogen to evaporate (the physical basis of my central idea in "The Scientific Notes” leading to the kinetic theory of evaporation). Therefore, liquid evaporates with the same rate no matter what the pressure of vapor above it is! (As far as everything stays far away the critical state!) But we know what is the rate of evaporation of liquid at thermodynamic equilibrium with its vapor! Recall the definition:
The liquid is in the dynamical equilibrium with its vapor if the rate of evaporation coincides with rate of condensation.
But the rate of condensation of molecules of the saturated vapor one can very easy find due to general gaseous laws! Therefore, we can conclude:
At any temperature that is far away of the critical one and given other conditions any liquid evaporates with the rate of the condensation of its saturated vapor at the same conditions.
This simplest and very understandable result allows us to have well defined self-consistent and complete theory of evaporation, which exactly is described in vol.#1 of “The Scientific Notes”.
In the first article there you can find all formulas that are answering on all your questions.
BTW, the essence of your question is to find what the volume of liquid will be as function of temperature at given volume V of tank and given initial pressure in it. So, you are interested to know volume of the termodynamical system Vliquid, which is an internal thermodynamic characteristic of liquid at any given external volume V of vessel.

[MacM]

Well - I was throwing down a challenge to our members who prefer to use numbers rather than equations. But as you ask...
I am assuming that liquified gas can only remain liquid under pressure. Right?
I am also assuming that, as long as the container is not completely full, then there will be some sort of equilbrium between gas phase and liquid phase.
Am I wrong to assume that that, at equilibrium, pressure from the gas phase will maintain the liquid phase as liquid gas? Hence...“thus provide pressure to keep the liquid gas liquid”

Your problem here I think is purely symantical. You should say "Liquified Gas" rather than talk about "liquid gas liquid". Also it is not only pressure that keeps it liquid but temperature and pressure combined. It takes less pressure at colder temperatures.

Yuriy,

I don't believe it is proper to say "Evaporate Crystals". The process crystal to gas or vapor is "Sublimation".

[Yuriy]

QH,
If you have some dificulties with reading that article, let me help you by direct answer on your question (it will be a light guide for you at reading):

Vliq = (Mo-V*Dsat[T])/(Dliq[T]-Dsat[T])..........(*)

where Mo - initial mass of liquid
V - volume of closed vessel
Dliq[T] - density of liquid at given temperature T.
Dsat[T] - density of saturated vapor at given T.

Dsat[T] = μ Psat[T]/RT ....................(**)

where μ is vapor's molecular waight and R is universal gas constant.
(**) is a usual tie of density with pressure (in our case - saturated pressure at T)

As you see, it works at condition that

Mo ≥ V*Dsat[T]...........................(***)

Only at that condition you will have some liquid phase remaining at equilibrium at T. Otherwise whole Mo will evaporate and we will have a pure nitrogen gas into a vassel (well known "full evaporation condition" in Gas Chromotography, for example).

The main problem is to find T, if initial temperature of liquid was To.
It can be done from the simple law of conservation of energy:

Internal enegry of liquid at initial moment = Internal energy of liquid in equilibrium + Internal energy of vapor at equilibrium

As you understand, V liquid will figure in this conservation law together with To and T. After excluding T from those two equation (conservation of energy and (*)) we will get unknown Vliq. I too tierd to do this simple but long enough calculations right now. Do it for me, please...

[QuarkHead]

Oops, missed two. I almost certainly can't "do it for you..". But I'll think about it. Got a busy weekend here.

[Yuriy]

QH,
Of course, you should not do that... I described you the logical way, how this kind problems are solved. I hope, you understood it... All further is for one, who indeed is interested in that area...

[QuarkHead]

Sorry Yuriy, I don't understand this post?????
EDIT: or maybe I do. More thinking... Yuriy, you do work us hard!
(Good - that's why we are here)

[Yuriy]

QH,
everything is very easy.
You said:
I almost certainly can't "do it for you..".
I responded:
Of course, you should not do that...
That is it...