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Explain "you can't pump steam" 1
- Thread starter ghensky
- Start date
Steam is created in a Boiler under pressure. Some of it is at very high pressure.
When steam is released from the Boiler it will travel a very long distance with out any supplemental boost. This is because there is more steam coming along behind the first release.
You need to study the science of Steam before you go on: You also need to stop listing to the Beauregard Gustsafisan's of this world (Look is up).
Sometimes its possible to do all the right things and still get bad results
When steam is released from the Boiler it will travel a very long distance with out any supplemental boost. This is because there is more steam coming along behind the first release.
You need to study the science of Steam before you go on: You also need to stop listing to the Beauregard Gustsafisan's of this world (Look is up).
Sometimes its possible to do all the right things and still get bad results
Compositepro
Chemical
This is mainly a question of semantics. A pump is used to move liquids not gases. I would say that the statement is poorly worded but not absolutely wrong.
MikeHalloran
Mechanical
Steam is a gas.
The most common form of pump, the centrifugal pump, works great with liquids, and not so great with gases. Once primed, they can lift water a few feet. ... unless the water flashes to steam or delivers a big bubble of some other gas, then the pumping stops.
(
Centrifugal compressors are topologically similar to centrifugal pumps, but run at much higher speeds, have smaller clearances and better balance, and do pump gas.
)
Mike Halloran
Pembroke Pines, FL, USA
The most common form of pump, the centrifugal pump, works great with liquids, and not so great with gases. Once primed, they can lift water a few feet. ... unless the water flashes to steam or delivers a big bubble of some other gas, then the pumping stops.
(
Centrifugal compressors are topologically similar to centrifugal pumps, but run at much higher speeds, have smaller clearances and better balance, and do pump gas.
)
Mike Halloran
Pembroke Pines, FL, USA
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1
- #5
You don't pump gas, because you compress the gas, then let the gas do the work of moving itself along, as it expands into regions of lower pressure downstream. Liquids are relatively incompressible and won't do much work when decompressing, so you have to move them along by pushing them out ahead of the space you are filling with more liquid.
georgeverghese
Chemical
The distinction between liquid pumping and gas compression blurs out in dense phase operation - is this what you mean ? This happens somewhere beyond P = 200barg, T= 370degC. Is this a supercritical steam boiler operation ?
- Thread starter
- #8
I would say BigInch's reply was a matter of fact - not thought provoking.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
LittleInch
Petroleum
Of course it would have helped if the "fourth law" which from my search is not clear what this is had been stated.
I think it is really semantics, "pumps" terminology is used for liquid or liquid like fluids such as dense phase gases, whereas compressors are used for gases.
The energy in steam is different from gases or liquids as the condensation and superheating nature is used.
I'm not sure BI description is correct - pressure is pressure regardless of fluid type and for any fluid to flow there needs to be a pressure difference between the two points caused by elevation or induced pressure. Gas complicates things by expanding as well but both simply move from a high pressure location to a lower pressure location.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
I think it is really semantics, "pumps" terminology is used for liquid or liquid like fluids such as dense phase gases, whereas compressors are used for gases.
The energy in steam is different from gases or liquids as the condensation and superheating nature is used.
I'm not sure BI description is correct - pressure is pressure regardless of fluid type and for any fluid to flow there needs to be a pressure difference between the two points caused by elevation or induced pressure. Gas complicates things by expanding as well but both simply move from a high pressure location to a lower pressure location.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
LittleInch
Petroleum
That's a vessel and not a pipe and nothing to do with the previous comment. It is though no different to my comment that fluids move from locations with high pressure to ones of lower pressure, in this case inside the milk bottle to outside the milk bottle. The same would apply if the bottle was full and you squeezed the bottle - Liquid would flow out of the bottle because of the pressure being exerted onto the outside of the bottle.
Your comment above about gas compression etc is related more to the energy stored in a pipeline due to pumps or compressors and I agree with that, but don't think it applies in terms of the question asked.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
Your comment above about gas compression etc is related more to the energy stored in a pipeline due to pumps or compressors and I agree with that, but don't think it applies in terms of the question asked.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
Pumps don't do useful work on gases. The difference between compression and pumping is the [highlight #EF2929]compressor does a useful amount of work on the gas or vapour[/highlight], that can be stored within the gas or vapour and used for purposes of it's own self-transportation, or other things, later. Try that with a normal, relatively incompressible, liquid and you won't get much more than a mm of movement, if that. If you close the discharge valve, not much liquid makes it even past the discharge check valve. The hi to low pressure difference exists only for a millisecond. Then liquids can't move much based on the amount of work they contain stored within. Compressors do work on the gasous fluid itself. You can't do much work on a liquid; the reason why compressors don't like even the smallest amount of liquid getting into them.
Semantics clouds the issue here, for sure.
Centrifugal pumps will not "pump" gasses; virtually impossible to add energy to gas using centrifugal pump.
Positive displacement pumps are another story however.
A good real-world example would be multiphase pumps (typically of the twin or 3-screw pump variety). They can pump gasses and liquids simultaneously and in separate slugs. Semantics comes into play here because this "pump" is really acting as a compressor when handling gas slugs, and as a true PD pump with liquids.
Don't see how this is much more than a philisophical argument.
Centrifugal pumps will not "pump" gasses; virtually impossible to add energy to gas using centrifugal pump.
Positive displacement pumps are another story however.
A good real-world example would be multiphase pumps (typically of the twin or 3-screw pump variety). They can pump gasses and liquids simultaneously and in separate slugs. Semantics comes into play here because this "pump" is really acting as a compressor when handling gas slugs, and as a true PD pump with liquids.
Don't see how this is much more than a philisophical argument.
With two phase, it's just a matter of when more useful work is done on the fluid, or on the system.
Whereas nothing changes as the result of the discussion, it is obviously totally philosophical, to the philosophers, however the physicist might be willing to argue that point too.
Whereas nothing changes as the result of the discussion, it is obviously totally philosophical, to the philosophers, however the physicist might be willing to argue that point too.
Compositepro
Chemical
There is very little difference between a blower used for gases or a centrifugal pump used for liquids, theoretical or practical. Compressibility is not a significant factor, and design differences are due to the density difference.
moltenmetal
Chemical
There are people trying very hard to "pump steam" every day, in a sense - in vapour recompression heat transfer schemes for instance- but the goal isn't really to "pump steam" . It is usually a bad idea to try to substitute thermodynamic work directly for heat, when heat alone will do- it's a poor tradeoff!
Generally, a compressor starting with a vapour saturated in some component, generates a superheated vapour. The mechanical inefficiency of the machine to some degree ensures that. However, that is not to say that trying to compress a condensable vapour which condenses at a temperature much higher than ambient, doesn't have significant issues associated with it- assuming there's an actual reason to try to do it in the first place. Compressors of many designs tend not to like to handle condensate in any quantity, at least not in the long term. The heat transfer that is often required to keep compressors durable in the long term, can tend to generate condensate at least at start-up unless it is managed properly.
Generally, a compressor starting with a vapour saturated in some component, generates a superheated vapour. The mechanical inefficiency of the machine to some degree ensures that. However, that is not to say that trying to compress a condensable vapour which condenses at a temperature much higher than ambient, doesn't have significant issues associated with it- assuming there's an actual reason to try to do it in the first place. Compressors of many designs tend not to like to handle condensate in any quantity, at least not in the long term. The heat transfer that is often required to keep compressors durable in the long term, can tend to generate condensate at least at start-up unless it is managed properly.
georgeverghese
Chemical
An example of how a gas can be boosted up with a pump to a higher pressure is in ammonia based liquid absorption chillers. Water is the solvent to dissolve NH3, and the resulting rich ammonia is then pumped up to a higher pressure. Ingenious way to get a gas to a higher pressure.
Mixed refrigerants in LNG plants do something similar; a heavier solvent dissolves the lighter ends under pressure after compression, and the light ends are later released at lower pressure for chilling at the low temp end of the cooling profile.
So to make something like this happen for steam, you'll need to find a suitable solvent for steam ?
Mixed refrigerants in LNG plants do something similar; a heavier solvent dissolves the lighter ends under pressure after compression, and the light ends are later released at lower pressure for chilling at the low temp end of the cooling profile.
So to make something like this happen for steam, you'll need to find a suitable solvent for steam ?
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