Entrainment vs carry-over

[jflsys]

"entrainment" vs "carry-over"

Hi,

these two terms seems to be used interchangeably, but I would like to make sense of of them.

Some sources seem to imply that they are the same, some say that entrainement is a subset of carry-over. Some say just the reverse.

Usually, they are both used to describe droplets of water or condensate being carried in steam lines, but at least one source says that entrainment is "minerals dissolved in the carryover".

If anybody could help me make sens of this apparent randomness, I would be extremely grateful.

Thanks in advance!

JF Lussier

http://www.systhermique.com

 

[Artisi]

I would suggest that it depends on where / what you are describing. For me, entrainment implies (usually) that something is already in the product prior to the point of reference, ie, the water contained entrained air introduced at the pump sump - whereas carry over implies something is introduced at the very last moment or "carried-over" right at the reference point, ie, the wig-wam valve was supposed to eliminate any water being "carried over" into the gizmo.

It's all a bit semantic any way - the main thing is to ensure there is no mis-understanding, if important it's better to describe what is happening in clear language.

 

[jflsys]

Thanks Artisi,

the thing is I need to write technical documents sbout the carry-over/entrainment phenomenon in steam systems, so it's important that I use the right language.

I'm afraid your interpretation is yet another way to use these two words...





JF Lussier

http://www.systhermique.com

 

[katmar]

I think most of us use these terms inter-changeably, but if I had to split hairs and try to make a distinction between the two then I would have to disagree with your source which discussed mineral carry-over.

In my mind entrainment generally carries the connotation of the kinetic energy of the primary flow causing the flow of the secondary fluid. For example, in a steam ejector we talk of the motive steam "entraining" the low pressure gas or vapour.

If fast flowing steam causes droplets of condensate to flow with it, I would term that entrainment. Similarly, in a liquid drain system if the flow of liquid is too fast it "entrains" air into the flowing stream.

On the other hand, I would generally think of carry over as something that was always in the fluid, and just being carried along with it. An example would be an effluent stream carrying over contaminants into the river system.

On this basis I would turn your quoted reference on its head and say "the minerals were carried over in the droplets entrained in the steam".

You will unfortunately get as many different definitions as the number of engineers you ask to define it. As long as you ensure that the meaning is clear in the context of your documentation I don't believe this definition is going to be the make-or-break factor in determining the quality of your document.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[jflsys]

Hi katmar,

I didn't give much credit to the source that says entrainment is "minerals dissolved in carry-over" since it appears to be an isolated point of view.

After all I read here, I think I will simply opt for the word that is more commonly used, which is "entrainment", since it's a webpage I'm working on : it's always best to use the words used by people doing searches.

I think it's simpler than trying to figure out in which situation each of the two words applies best.

Thanks a lot, folks!

JF Lussier

http://www.systhermique.com