calculate temperature of saturated steam discharged to atmosphere via leak 2

[BigChungus]

If saturated steam at a pressure of 5 bar leaks out of a pipe, there is a visible cloud of condensate. How do you calculate the temperature of the condensate at a distance of 1m from the leak?

 

[Snickster]

Once the steam enters the atmosphere it is at 14.7 psia and will condense at 212 F. It is initially superheated and loses heat then reaches 212 F and condenses this may or may not be at 1 meter from leak.

 

[Snickster]

Also condensation will occur only if the air is saturated with water vapor. If the steam disperses well into the air and the air remains above dew point then no steam will condense.

 

[georgeverghese]

See if you can get this jet plume thermal dispersion simulation done on a program like PHAST or similar. Its going to cost you some.

 

[goutam_freelance]

After a leak the surrounding air becomes saturated with water vapor and excess vapor condenses in small droplets, forming a cloud-like zone. Of course, this happens after the steam loses its' superheat due to mixing with air and heat loss to surroundings. The exact temperature can be predicted using a CFD software.

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[LittleInch]

"Leaks out" is very vague.

Jet plume from a large hole or very small leak from s flange or a valve stem?

How big is the plume? If it's 1.5m then it's probably 100C or close to it.

If the plume is 10m diameter it could be higher. Details matter.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BigChungus]

Sorry everyone, I'm new here and forgot to reply. Thanks to everyone for responding to my question.

More details:

My workplace implemented a "safe working distance" of 1m from steam pipes. I am not sure how to estimate if that really is safe or not. If there was a small orifice of 5mm diameter, how could I approximate the temperature of the steam/condensate cloud? Can I assume the temperature drop is primarily due to adiabatic expansion, similar to this video (since heat transfer and mixing with atmospheric air happens on a much longer timescale than expansion)?

Link (not sure how to embed a youtube video)

 

[georgeverghese]

Ok, agreed, immediate transient would adiabatic - isentropic expansion

 

[LittleInch]

What does safe working distance mean in practice in terms of restrictions etc?

For a 5mm hole 1m seems reasonable as being a distance where if this hole suddenly appeared would be ok to have people working close by.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[pierreick]

Hi,
The first barrier should be insulation to prevent people to get burnt (skin contact or steam leak).
Note: there will be a thermal equilibrium between the steam leak and air.
My 2 cents
Pierre

 

[goutam_freelance]

It will be proper to run a physical test with the required pressure and diameter of the hole. Necessary temperature and distance measurements can be done easily.

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[pierreick]

Hi,
I will consider the flow as choked flow and isenthalpic to get the temperature of stream at the discharge point to atmosphere.
Having said that:
5 Bars A, the steam temperature is 151.84 C, h = 2748.1 Kj/Kg
At 1 bars A and h= 2741.8 Kj/Kg he corresponding temperature is 135.7 C
Definitely sufficiently high to burn someone at 1 meter distance.
The skin contact temperature must be below 60 C.
Pierre

 

[FMJalink]

Hi BigChungus,
I am afraid your question is a difficult one to be solved. The first cooling will be from the expansion in the jet leaving the hole in the wall or at a gasket, but straight afterwards the mixing with ambient air starts and leads to condesation which will be the determining factor for cooling down to an allowable temperature.
There are publications with differential equations to be solved to get an impression of the temperature development, but they are rather heavy stuff and ask quite somewhat programming. Could be that a commercial numerical software package can simulate this condensing jet. If so, a party could provide you with the information.
A first approach could be looking at a non condensing free jet, but I have the feeling that condesation has a large impact on the temperature development along the jet streamline.
Just look a5 pictures or videos of steam engines releasing steam, you see there first a jet and then a cloud is generated, which is much wider.
Success

 

[goutam_freelance]

If an approximate but quick estimation is require please refer results from a CFD study(Ref Prediction of Turbulent Temperature Fluctuations in Hot JetsJames R. DeBonis∗NASA John H. Glenn Research Center, Cleveland, Ohio 44135DOI: 10.2514/1.J056596)

x=distance from jet origin.
D[sub]j[/sub]=Diameter of jet (5 mm assumed)
T[sub]inf[/sub]=atmospheric temperature=30[sup]o[/sup]C (assume)
ΔT[sub]j[/sub]=Jet temp-atmospheric temperature=135-30=105 K
So at about 15*5=75 mm distance the temperature is about 0.4*105+30=72[sup]0[/sup]C

Therefore it is expected that at 1 m distance the temperature will be much less than 60[sup]0[/sup]C

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[crshears]

Here are related but tangential questions for OP:

[1] Are all valves motor operated with controls [and possibly even the power actuators themselves] located > 1 metre from any steam line?

[2] If there are hand-operated valves, is each provided with an extension to keep the operator > 1 m from any steam line, or are there a limited number of "reach rods" the operators must carry around and engage with the handwheel of the valve to be operated to provide the necessary extension needed to respect the limit of approach?

I certainly hope operators aren't considered expendable and thus exempt from the > 1 m rule . . .

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[MortenA]

Hi Big,

You need to know stuff about thermodynamics specificalle for steam! Or get someone you know (and preferrably pay) to tell your. You get good advice here but if something is wrong are you just going to say "well the guys at this website said...."?

Anyway, also check out checalc. They have a free steam table:

https://checalc.com/

specifically

https://checalc.com/calc/steam.html

First calculate the temperature of saturated steam at the given pressure (5 barg), note down the enthalphy (2757 kJ/kg)

The leak will be equvalent to an isenthalpic expansion - so entalhphy stays the same. Now switch to pressure&temperature and enter the atm pressure (0 barg) and try with some different temperatures above 100 C e.g. 140ºC - when the enthalphy is the same that will be the temperature of your steam. The steam will cool as it mixes with air and water will condense. My numbers are sligthly off if you consider 5 bar to be 5 bara - but most people referring to "5 bar" (rather unprecise) means 5 barg.

Best regards, Morten



--- Best regards, Morten Andersen

 

[BigChungus]

Hi everyone,

Thank you all for responding. I'm away on vacation so I hope to read and reply properly when I'm back next month.

Apologies for my late reply

 

[TBP]

Steam leaks will entrain air - at whatever temperature - from countless tiny vortices, 360* in the steam plume, along it's length. This cools the steam VERY rapidly. I have direct experience in the type of situation described by the initial poster. There was a steam leak in a 30 PSIG (2 barg) building heating line in a plant I worked in. We were in the middle of a cold spell (minus 40 degrees) which is typical for a couple of weeks every winter here. We were not shutting the building heating system down under these conditions unless it was a very dire situation. I had made this clear to everyone I spoke with. The production people were quite excited, and got the safety manager involved. He & I went to the "scene of the crime", and I reached up, and put my bare hand into the outer edge of the visible "steam" plume, about 3 feet (1 metre) from the leak. His eyes widened. I told him that it was cold. I slowly moved my bare hand into the plume. A foot or so from the leak, the condensing steam was still COLD on my hand. Note that I DID NOT put my bare fingers very close to, or actually ON the leak. I invited the safety manager to try it - he looked horrified, and declined - even when I held my hand up for him to see that I was fine. We waited until the cold spell passed, then shut the system down, and repaired the leak. The production people carried-on working - and grumbling - during that time.

I'm an old steam guy - and this is my personal experience - take from it what you will. If you want a real world temperature of the leak at "whatever" distance from the pipe, fasten a thermometer to a suitable piece of rod, and hold it in the "steam" plume at various distances from the point of leakage. Read the temperatures, and take whatever course of action you deem necessary for the circumstances - physical and/or political - that you're dealing with.

 

[BigChungus]

Steam leaks will entrain air - at whatever temperature - from countless tiny vortices, 360* in the steam plume, along it's length. This cools the steam VERY rapidly. I have direct experience in the type of situation described by the initial poster. There was a steam leak in a 30 PSIG (2 barg) building heating line in a plant I worked in. We were in the middle of a cold spell (minus 40 degrees) which is typical for a couple of weeks every winter here. We were not shutting the building heating system down under these conditions unless it was a very dire situation. I had made this clear to everyone I spoke with. The production people were quite excited, and got the safety manager involved. He & I went to the "scene of the crime", and I reached up, and put my bare hand into the outer edge of the visible "steam" plume, about 3 feet (1 metre) from the leak. His eyes widened. I told him that it was cold. I slowly moved my bare hand into the plume. A foot or so from the leak, the condensing steam was still COLD on my hand. Note that I DID NOT put my bare fingers very close to, or actually ON the leak. I invited the safety manager to try it - he looked horrified, and declined - even when I held my hand up for him to see that I was fine. We waited until the cold spell passed, then shut the system down, and repaired the leak. The production people carried-on working - and grumbling - during that time.

I'm an old steam guy - and this is my personal experience - take from it what you will. If you want a real world temperature of the leak at "whatever" distance from the pipe, fasten a thermometer to a suitable piece of rod, and hold it in the "steam" plume at various distances from the point of leakage. Read the temperatures, and take whatever course of action you deem necessary for the circumstances - physical and/or political - that you're dealing with.

thank you, yes i have noticed this too

 

[BigChungus]

Hi BigChungus,
I am afraid your question is a difficult one to be solved. The first cooling will be from the expansion in the jet leaving the hole in the wall or at a gasket, but straight afterwards the mixing with ambient air starts and leads to condesation which will be the determining factor for cooling down to an allowable temperature.
There are publications with differential equations to be solved to get an impression of the temperature development, but they are rather heavy stuff and ask quite somewhat programming. Could be that a commercial numerical software package can simulate this condensing jet. If so, a party could provide you with the information.
A first approach could be looking at a non condensing free jet, but I have the feeling that condesation has a large impact on the temperature development along the jet streamline.
Just look a5 pictures or videos of steam engines releasing steam, you see there first a jet and then a cloud is generated, which is much wider.
Success

Thanks FMJalink, I suspected this to be the case...