VC-10
Topic Author
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ACM Press/Temp Graph.

Mon Dec 31, 2001 10:09 pm

In response to Essential Power's request that I explain where the energy comes from as illustrated in the P/T graph below I submit the following.



The bleed air enters the pack with the pressure & heat energy given to it by engine combustion. As can be seen in the graph this illustrated by the entry P/T of 2.6 bar/190 degs.

The air flow now passes through the primary heat exchanger where some of the press & temp energy is lost and enters the ACM centrifugal compressor at 2.5bar/90 degs. The ACM impellor adds energy by accelerateing the air flow while the compressor diffusor converts this kinetic energy into pressure/temp energy. The air leaving the compressor at 3.6bar/140degs.

The air now enters the main heat exchanger and water extractor where more heat/pressure energy is lost by radiation & conduction so by the time it enters the ACM turbine the P/T is 3.55bar/40degs. As the air passes through the turbine and has to do work in accelerating the airflow in the compressor plus overcomeing internal frictional losses further energy is lost resulting in the pack outlet P/T being 1.1bar/-10 degrees C.

So overall the energy lost through the air cond pack amount to a 200 deg C drop in temp and a 21 psi drop in pressure.

Now to answer your other points.

1. "So prior to that you weren't even aware of the concept of the bypass, or what it was for".

2. "and your ignorance of it, greatly reduces your credibility."

I refer you to:-

2001-11-06 21:16:31

One point you omitted was that the airflow doesn't have to go through the compressor on system start up. There is a by-pass valve that by-passes the air around to comp, then, as the turbine spins up and turns the compressor, the comp. delivery air back pressure closes the by-pass valve.


Which you agreed later was before you brought it up.

Furthermore during that long post you seem to have fogotten that there were times when you were asking for my support.


Finally may I wish all my readers a happy new year.
 
delta-flyer
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RE: ACM Press/Temp Graph.

Sat Jan 05, 2002 2:32 pm

Way-to-go, VC -- I could really use the P/T diagram you provided. Do you by any chance know the mass flow of air in this process during normal operation, and how many packs are working at a time to provide an "average" cabin atmosphere?

Thanks
Pete
"In God we trust, everyone else bring data"
 
VC-10
Topic Author
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RE: ACM Press/Temp Graph.

Thu Jan 10, 2002 6:27 am

Delta-flyer,

Sorry for the delay in getting back to you, I had to wait untill I was back in at work the get the data. I haop the following is what you are after.



QT= Total fresh airflow to pressurised fuselage
QF/D= Fresh a/flow to Flt Dk
QC= Fresh airflow to pax cabin
QR= Recirc a/flow fron two recirc fans.

Normally both packs are used. If the a/c is dispatched under the MEL with a singel pack operational there is an alt restriction of 31,000 Ft.

Nml 100% flow = 2.558 Kg/s on Grnd - 1.9 Kg/s at Cruise alt.

With one pack off 60% of nml flow is avail at Crz Alt.

 
delta-flyer
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RE: ACM Press/Temp Graph.

Thu Jan 10, 2002 1:25 pm

VC-10,

Yes, that's exactly what I was looking for -- THANKS!!

I am printing this out so I can study it in more detail - there is a ton (tonne) of data here.

Thanks again

Pete
"In God we trust, everyone else bring data"
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Thu Jan 10, 2002 2:00 pm

I asked you to describe where the energy comes from.
All you have did above is read the chart...Isn't that why those values are charted in the first place? Save some typing...

But I asked about enthalpy, remember???

Btw-
You should pay more attention to what you type. 2001-11-06 21:16:31 was posted by Airplay...

So Sorry....
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Thu Jan 10, 2002 2:14 pm

REf above to VC10

Btw-If you are LATENTLY "willing to concede" a bypass existed after going UNRECOGNIZED in your OWN NOTES...and took weeks just to read what a PT chart clearly shows...and finally, accuse me of something I clearly did not say, maybe you should just leave it alone, or present something with a scrap of legitimacy. Yeay, yeah you'll respond. So,

1. Describe where the energy comes from
2. Accurately identify who you are quoting
3. And as I have, apologize when necessary

Otherwise, your credibility is worse now than it was, b/c all you have proven up to this moment is that you like to argue - poorly.

 
EssentialPowr
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RE: ACM Press/Temp Graph.

Thu Jan 10, 2002 4:00 pm

VC10, One final comment as I reviewed the ACM topic.

Why would you ref 11-06 21:16:31, and then vascillate such that finding the bypass per 11-14 01:59:28 was a revelation, and then were finally "willing to concede" the existance of the bypass 11-15 06:16:37?

Why were you "willing to concede" in the first place? Did you not agree with the statement
11-06 21:16:31? You do now, but didn't then? From those contradictory statements, you didn't make a point either way.

I did ask for your input, but you ignored that request, so exactly what did you prove in any case?

Try to admit to learning one thing: That PT graph doesn't prove where "the energy comes from". It only shows pressure and temp values through the cycle.

I offerred an explantion for you in the ACM post, you ignored it, and now come back to explain that the A340 comp inlet press is around 2.5 bars @ around 90C? That's not an explanation. That's reading a graph.
 
VC-10
Topic Author
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RE: ACM Press/Temp Graph.

Thu Jan 10, 2002 4:11 pm

Yawn.........
 
VC-10
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RE: ACM Press/Temp Graph.

Thu Jan 10, 2002 8:28 pm

EP,

1. "I asked you to describe where the energy comes from. All you have did above is read the chart...Isn't that why those values are charted in the first place? Save some typeing "

Read the first sentence of the first para below the illustration That tells you where the energy comes from. As usual you just quote what suits your arguement at the time.

Enthalpy = U + PV

U = Internal energy

P = Pressure

V = Volume of the system.


Internal energy is the total of the kinetic energies of the atoms and molecules of which a system consists and the potential energies associated with their mutual interactions.

The source of that energy is the energy released by the combustion of kerosene in the engine.


2. "You should pay more attention to what you type. 2001-11-06 21:16:31 was posted by Airplay... "

Funny, I copied & pasted it like this :-

"Username: VC-10
Posted 2001-11-06 21:16:31 and read 1178 times.

Airplay,

One point you omitted was that the airflow doesn't have to go through the compressor on system start up. There is a by-pass valve that by-passes the air around to comp, then, as the turbine spins up and turns the compressor, the comp. delivery air back pressure closes the by-pass valve."

I think you should pay more attention.


2. "If you are LATENTLY "willing to concede" a bypass existed after going UNRECOGNIZED in your OWN NOTES.."

You seem to have overlooked that on the 8 Dec you agreed that I brought up the By-pass vlv first.

3. "1. Describe where the energy comes from "

See item 1 above.

4. "accuse me of something I clearly did not say"

What words have I put into your mouth ?

5. "2. Accurately identify who you are quoting "

I believe I identified all my sources - Boeing, Douglas & Airbus documentation.

6. "And as I have, apologize when necessary"

For what ?

7. "Why would you ref 11-06 21:16:31, and then vascillate such that finding the bypass per 11-14 01:59:28 was a revelation, and then were finally "willing to concede" the existance of the bypass 11-15 06:16:37? "

Once again you are up to your old trick of taking statements out of context. You will no doubt recall that Airplay was, at that time saying there was no by-pass vlv. The post you have refered to above was pointing out to Airplay the the diag he posted contained a by-pass vlv.

7. "Why were you "willing to concede" in the first place? Did you not agree with the statement
11-06 21:16:31? You do now, but didn't then? From those contradictory statements, you didn't make a point either way.
"

As usual, as it suits your arguement, you have conveniantly chosen to ignore what I was conceeding.

8. "I did ask for your input, but you ignored that request "

Because I didn't agree with you.

9. "Try to admit to learning one thing: That PT graph doesn't prove where "the energy comes from". "

See Item 1. above.


 
FDXmech
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RE: ACM Press/Temp Graph.

Thu Jan 10, 2002 9:57 pm

The bypass valve if incorporated, primary function isn't ACM startup.

Any incidental or accidental function is purely unintentional or coincidental....at best.

As VC10 stated, the energy originates from the compressor of the engine.

You're only as good as your last departure.
 
airplay
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RE: ACM Press/Temp Graph.

Fri Jan 11, 2002 3:56 am

EP,

You are demonstrating some disturbing obsessive behaviour. You're really beginning to ramble. It's difficult, if not immposible to accurately figure out "who said what and when" in the original post without re-reading the entire thread each time. We should really take the focus off of that.

It seems to me that VC-10 is just offering some supplementary information that he promised to supply. Of course according to you, all the manufacturers are idiots and the information they provide, including the subject graph is wrong, or incomplete, or has some other deficiency. Read the graph and learn...or ignore it and remain ignorant. Nobody cares anymore.

Try to put your energy into something else. You'll feel better and we'll be able to let this "dead horse" rest in peace.

 
EssentialPowr
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RE: ACM Press/Temp Graph.

Fri Jan 11, 2002 9:27 am

VC10-

1. You started this entire thread, and have the audacity to call me obsessive?

2. So, exactly what were you willing to Concede? What was your point? Why the contradiction? You still didn't even know what was in your own notes, fail to concede that fact, and blame me for your lack of clarity?

3. Glad you finally learned something from a physics text. A PV diagram doesn't really address enthalpy, does it? That was the hint I originally offerred. More directly, for the Brayton Refrigeration cycle:

The refrigeration effect Qdot (in) = h1-h4 where:

Qdot(in) = Specific heat transfered off turbine
h1 = enthalypy @ compressor inlet
h4 = enthalpy @ turbine outlet

h1 and h4 are of course, the beginning and end states of this cycle. THAT is "where the energy comes from"; THAT is the ACM equation, and THAT, therefore, is the correct answer to my question for you.
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Fri Jan 11, 2002 9:34 am

Airplay-

Stay out of it.
 
jetfixer
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RE: ACM Press/Temp Graph.

Fri Jan 11, 2002 10:05 am



 Insane

 Sleepy
 
VC-10
Topic Author
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RE: ACM Press/Temp Graph.

Sun Jan 13, 2002 12:49 am

EP,

VC10-

1. You started this entire thread, and have the audacity to call me obsessive?


Either you have a problem in understanding how to read who is the author of a post (again) or you are using the above statement to bait me. I will credit you with some intelligence and assume it is the latter. In which case I'm not going to play your game.  Smile
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Sun Jan 13, 2002 12:26 pm

You and Airplay ARE interchangeable on this topic as far as I'm concerned; starting with trying to identify a simple check valve, the lack of clarity of your position on the topic, your demand for me to identify my position, your pathetic attempt to incorrectly correlate/describe the Brayton REfrigeration CYCLE as a PT diagram (??? - thanks for reading the chart though; that was profound), your inability to admit ANY of the above...and yes, your obsessiveness that causes you to start this thread and still muck it up, still coming nowwhere close to the correct answer.

IF YOU would read things more closely, you would have found I posted this exact explanation in the orig thread...but you're clearly too arrogant for that.

You started this thread in an attempt to respond to a comment that challenged you from weeks ago, "Yawned" about it, realized you still weren't close due to my hint w/ the word enthalpy (thus the time delay) and then spent a few hours to finally offer a 10th grade definition of the word - "enthalpy".

That's great. What about the definition of the cycle? Enthalpy is present in all of them - REfrigeration or Power, Rankine, Diesel, but HOW IS IT DEFINED? Get the picture? Airplay nor you could even identify the equation that produces the cold air from the start. How do you think these things are designed? So you know it all? Hardly.

So yes, it's all the same from my viewpoint. After I apologized for my errors weeks ago, YOU can't let it go, and simply showed your ass here.
 
airplay
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RE: ACM Press/Temp Graph.

Mon Jan 14, 2002 1:39 am

EP,

You need to reread the original thread. You are the one who introduced advanced scientific principles to a somewhat simple question.

The original question was not about the existance of a bypass valve. I offered a general description of the ACM system and later further offered that I didn't know of any system that used a compressor by-pass valve.

Does that mean that none do? No.

Does that mean that there are systems that don't use them? Yes.

Does that mean that a compressor is "required" to "start" an ACM. I think there is enough information presented to say "No".

Clarification over.

Defining Enthalpy or Einstein's Special Theory of Relativity for that matter and defining all of the associated equations will help very few in this forum to understand the basic operation of an ACM as was requested in the original post. I certainly can spout off all kinds of techical jargon including discussions regarding enthalpy, but the original question can easily be dicussed without requiring a degree in physics.

Stop hiding behind your perceived intellectual superiority in an attempt to reclaim the credibility you've lost already.
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Mon Jan 14, 2002 9:33 am

Airplay,

What you perceive as pertinent content of the original thread is your business. Obviously VC10 felt some scientific content was warranted by starting this thread, which I answered, thus reproving MY point.

Yes, the def of a cycle was a component of the orig thread. You won't admit that, simply b/c you are ignorant of it, so don't define for me what the "correct" interpretation of the entire thread was.

So No, I'm not too impressed w/ your "technical" ability to interpret a schematic correctly or comprehend the concept of enthalpy. Remember, you demanded that I define the ACM cycle...b/c you couldn't.
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Mon Jan 14, 2002 12:14 pm

Airplay's completed post on the "orig" ACM thread,
11-17 06:04:03: "And what "cycle" is the most appropriate model for the ACM, in your opinion?"

So, Airplay, you didn't even know the ACM utilized a cycle, let alone how to define it.

Or another from Airplay 11-17 02:13:49: "The ACM converts heat to rotational energy."

Heat convects, conducts, or radiates. Period.

Yeah, you can sure spout technical jargon. The problem is, you just don't have a clue about what you're saying. The topic did get technical, and as proven by the comments above, you were in over your head. This isn't germane to the topic? Only from a Fool's viewpoint...
 
airplay
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RE: ACM Press/Temp Graph.

Tue Jan 15, 2002 3:05 am

EP,

I admit that out of the thousands of words I typed on that thread there are a few inaccuracies.

I began assembling a list of incorrect statements offered by you in the subject thread. Unfortunately there is far too much material for the purposes of this thread.

If I in fact was in over my head, you had drowned after your first post.

 
EssentialPowr
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RE: ACM Press/Temp Graph.

Tue Jan 15, 2002 7:24 am

So your inaccuracies are less eggregious than mine?

From someone who was totally and completely ignorant of the concept of a bypass around the compressor in the first place? The existence and therefore function of the bypass was, by and large, the primary focus of the thread!!! You stated in may have only been present in "large or older a/c"...

From someone who claimed to know all about enthalpy, and then couldn't define the ACM cycle as a difference in enthalpy? From someone who joined in this thread and was not astute enough to note that Temperature appears no where in the definition of enthalpy?

From someone who has insulted me repeatedly on this and other threads?

No I think not. This is your first statement to date that you were wrong about anything.

Do you want the final insult? Is that your desire? Fine. How pathetic. Take your final shot, I've proven my point.
 
FDXmech
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RE: ACM Press/Temp Graph.

Tue Jan 15, 2002 8:07 am

No offense EP, but the bypass around the ACM compressor has nothing to do with ACM startup.
You're only as good as your last departure.
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Tue Jan 15, 2002 2:26 pm

FDXMech: So is the check valve always open? No. Always closed? No.

Obviously, it's open some time, and closed some time. So as a general statement, what you've said is incorrect, b/c the check valve closes whenever the downstream pressure is greater than the upstream pressure. This pressure difference is certainly a function of whether the ACM is static or not, b/c the downstream pressure is simply compressor discharge pressure. At higher operating speeds, the check valve will seat, and as the compressor spins down, the check will reach a point where it opens, which is to say as the ACM reaches a static condition.

As I've said many times, check valves make poor throttles, so their operation is largely binary (ie open or closed).

VC10 ref'd this in the orig thread with the statement and schematic on the DC10: "note that the bypass is used anytime the ACM is static". The 727 works in the exact same fashion.

 
airplay
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RE: ACM Press/Temp Graph.

Tue Jan 15, 2002 2:36 pm

EP

I do not NEED the last word, but I will continue to answer to your attacks.

True. The definition of Enthalpy does not typically make reference to "temperature".

Funny though that enthalpy is sometimes refered to as "total heat" and sometimes even "heat content".

Why? Because when considering enthalpy in practical solutions (someday you might even do that) temperature (discharge or otherwise) is typically one of the properties of a system that is being investigated. Doing a study of the enthalpy of an air conditioning system without discussing the resultant temperatures is almost as useless as discussion enthalpy with unexperienced know-it-alls.

By the way, you really need to start presenting statements within the context they were presented. You continuously say that I was completely ignorant of the compressor by-pass valve in some systems when I clearly stated that I was merely not aware of them in the systems I am familiar with.

Wouldn't it be fair then to say you were completely ignorant of systems WITHOUT by-pass valves? And that because of your statements with respect to the tight clearances of the ACM compressor you were cleary ignorant of the construction of an ACM? And that because you dismissed and discredited anyone or any authoritve data that conflicted with your erroneous statements that you were cleary ignorant of the general accepted operational descriptions of aircraft ACMs? No....that would be jumping to conclusions.

You even called my statements idiotic and ridiculous. I never made any statement categorily dismissing the possibility of an ACM compressor bypass valve. In fact in response to VC-10's statement:

"One point you omitted was that the airflow doesn't have to go through the compressor on system start up. There is a by-pass valve that by-passes the air around to comp, then, as the turbine spins up and turns the compressor, the comp. delivery air back pressure closes the by-pass valve."

I stated:

"I'm assuming you're describing one specific type of ACM. I've never seen one that operates the way you describe. Of course that doesn't mean it doesn't exist.

This is an example of the difficulty in discussing every aspect of some complex systems. There are countless specific designs!

I guess that's what makes it interesting."

You never present that quote. Why? Because it doesn't fit your discussion style. You would much rather present statements out of context and then try to intimidate people into seeing things your way.

The internet needs fewer people like you on these forums Mr. Powr.

 
EssentialPowr
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RE: ACM Press/Temp Graph.

Tue Jan 15, 2002 2:40 pm

FDXmech:
VC10's quote 11-18 14:20:36:

"In addition I quote from my DC10 training notes:

""The compressor bypass check valve allows air to bypass the compressor and act on the turbine to spin up the ACM. As the unit spins up, compressor output pressure seats the comp by-pass vlv...etc""

So yes, the compressor bypass on the DC10, 727 and I'm sure many designs enables the ACM to spinup.

The above is not earthshattering, though; that's just the way a check valve works...
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Tue Jan 15, 2002 3:33 pm

Airplay,

Nice mouth vomit, but temperature and heat are different things. Your correlations b/t the enthalpy and temp further show your knowledge of physical things continues to be rather limited.

Your quote: "When considering enthalpy in practical solutions, temperature is one of the properties of a system being investigated." What??? That statement is just...crap. It's Idiotic and Ridiculous (at best).

Enthalpy and temperature are different things -GET it??? One IS a property of a system, another isn't. You can learn which is which, but it's clear "enthalpy" is your word of the week. Too bad you have NO IDEA what you're babbling about.

Are you telling the kid at the McDonald's window that your coffee doesn't have enough ENTHALPy in it? To it?

You have always blamed me for misinterpreting what you wrote; this is another example of your literary genius.

So, You-
Couldn't find a check valve in your OWN 727 schematic and hadn't the slightest idea how it worked when you did, (otherwise it would have been apparrent)

Had never seen an application in which the compressor bypass "started" a static ACM, and wouldn't consider the notion,

Had NO IDEA what a cycle was, not to mention enthalpy, and think that heat rotates an ACM (uh oh - it's Enthalpy again),

Make assumptions about how I FEEL about others in this Industry, and tell me I'm obsessive

Threaten to stop posting, but can't

And finally want to rehash the whole thing, b/c you jumped in on this thread and continue to prove your technical incompetence every time you hit the enter key? Just let it go.
 
FDXmech
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RE: ACM Press/Temp Graph.

Wed Jan 16, 2002 3:52 am

DC10
If this bypass valve didn't exist, the path of the bleed flow would always interface with the ACM compressor, even if the ACM was idling, due to no or low cold air demand.

In this, shall we say warm air mode, the ACM is idling at low speed due to the *turbine* being bypassed. The air bypasses the compressor due to the unnecessary drag on air flow this would produce.

This compressor bypass valve offers an alternate flow path around the ACM compressor, but not to be used by the turbine to increase ACM speed because ACM RPM is intentionally being kept low. But rather to avoid the ACM compressor from impeding flow and acting as a blockage.

I've researched the most current revisions of our DC10 and MD11 maintenance manuals and factory Garrett Airesearch manuals, absolutedly no mention of ACM startup anywhere, not even an "oh by the way" unintentional benefit.

727
As said previously, only the *727-200* incorp. the check valve between primary and secondary heat exchanger, and this due to a different mix valve design than the 727-100 (which does not incorp. the ck vlv). The function of which allows the bleedflow to bypass the ACM completely and flow thru prim. and sec. heat exchanger then to the mix valve intermediate port.

A300/310
The packs are nearly identical to the DC10 and no mention of startup found.

A330/340
I do not work these a/c but 310 engineer quoted the m/m which *did* mention startup.
You're only as good as your last departure.
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Wed Jan 16, 2002 5:05 am

FDXmech,

I am going to limit my comments to the DC10 due to the fact a schematic is readily available on the "orig" thread" that can be ref'd by all, and to keep the scope manageable.

Would you agree with the following statements?

1. That the thottle for the DC10 ACM is the Turbine bypass. By design, it modulates easily to full open, closed, or anywhere in b/t.

2. A check vlv makes a poor throttle, as it is "open" or "closed".

3. The comp bypass check vlv closes, or seats, at a specific pressure, and will remain closed until that pressure again decreases beneath a certain value.

3. In summary, the comp bypass check vlv prevents compressor choking when operating in the "warm air mode" and is open during the warm air mode.

4. For the "cold air mode", comp bypass chk vlv closes and enables what I call startup (or spinup) as the unit transitions to the "cold air mode" at its max design speed.


LEt me know-
 
FDXmech
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RE: ACM Press/Temp Graph.

Wed Jan 16, 2002 7:57 am

1. yes

2.yes

3.yes

3a. ? When you say compressor choking, I can only agree on the premise you mean air flow choking trying to pass the compressor on its way to/thru the turbine bypass valve, not the compressor itself being choked.

4. As you say, and I agree, a butterfly check valve does not modulate.

The iota the compressor develops more pressure than the comp. inlet, the c/b/v closes.
I can't see how this could be construed as an intentionally engineered system to allow spinup and avoid a comp/turbine stalemate. Perhaps *maybe* if the compressor bypass was springloaded to a degree which required a more substantial pressure differential over compressor inlet than just "as long as it's greater than comp. inlet".

So at what point do you feel the ACM should spin before the turbine overpowers the compressor?

Also, from pictures I have of the DC10 ACM rotating assembly, the pitch of the centrifugal compressor blades at its center inlet would induce compressor rotation the same direction as the turbine spins it.
You're only as good as your last departure.
 
310_engineer
Posts: 163
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RE: ACM Press/Temp Graph.

Wed Jan 16, 2002 9:15 am

WOW  Wow!
I have been out for three months and thought this discussion would be burried a long time ago, well the first topic is, but part deux started.

I have just finished reading part one and the beginning of this one. In part one almost at the end Jetfixer made me laugh. He stated that an A320 has a CBPV, if there is one Airbus that doesn't have CBPV it is the A320, guess he better used his holliday to learn to fix jets. Big grin
Jetfixer: the valve you are talking about is the pack-bypass valve which is controlled by the packcontroller, it regulates the pack disscharge temp. by adding hot air.

Talking about learning:
EP did you figure out the difference between centrifugal and axial compressors yet?  Wink/being sarcastic

The turbine By-pass (like on the DC-10) acts a little like the 320's pack by-pass. Together with the Ram Air inlet and outlet flaps of the heatexchangers, it regulates also the pack disscharge temperature. You can see on the schematic that they are all linked together. And yes you could say the turbine by-pass acts like a "throttle" for the ACM. By bypassing the air(=energy) from the turbine, the turbine has less to eat and the ACM will run on lower speed. Makes sense to me. Don't kill me if I am wrong (to be honest I don't think I am wrong)

But when you are saying that a check valve makes a poor throttle, as it is open or closed. Do you mean full open and full closed? In that case I disagree, a check valve can have intermediate positions, it depends on the differential pressure between the two sides and the time the pressures are equalled.

regards
Mike

 
EssentialPowr
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RE: ACM Press/Temp Graph.

Wed Jan 16, 2002 10:00 am

310 engineer - Uhhh, yeah... Hate to say I knew the diff b/t a centrif and an axial, but I mistyped. Did I get blasted for that or what!!! I was simply trying to show an analogy b/t axial flow, compressor blade tip clearance, and the tolerance b/t the impeller and housing of a Centrifugal compressor.

I agree w/ your A320 comparison...

But, if one looks at various throttle designs, I can't think of a single example in which a chk vlv is used as a throttle, simply b/c the nature of the valve is "open" or "closed". Throttling is a continuous process that, at the least, requires uninterrupted flow. On a simple check vlv, as soon as downstream pressure exceeds upstream pressure, the valve closes, thus enabling the ACM to extract 100% of the available enthalpy from the bleed. I'm assuming the DC10 uses a simple chk design, as a range of setpoints is not indicated on the schematic. Really, all it needs to do is close when turbine back pressure equals bleed pressure into the unit, so I don't see that it needs to have intermediate setpoints.

Further, that check vlv should seat at a low enough pressure such that is doesn't "chatter"; which would in turn decrease its reliability due to unnecessary wear. A check vlv simply isn't used in high cycle/frequency applications, as flow through it would be constantly interrupted. It's more of an off/on design, as fluid flow dynamics thru a chk are pretty ugly...But I digress.


FDXMech -

3a. I still say that the comp bypass is there simply b/c, in the "warm air mode", forcing the bleed air through a stationary or almost stationary compressor accomplishes nothing. In fact, we lose valuable enthalpy in spinning a compressor for no reason. Rotation in while freewheeling direction may be in the correct direction; in the past I argued that it couldn't be in the "wrong direction" but the consensus of the forum appears to be to the contrary. But it's much more elegant to simply bypass the compressor when it's not needed, and eliminate the variables of either spinning it in the wrong direction, or spinning it in the correct direction and simply wasting enthalpy.

I think the comp bypass chk vlv is a simple chk vlv that closes as soon as it sees pressure. That probably occurs right after the turbine bypass starts to close, as soon as that back pressure exceeds the bleed pressure. This forces more air across the turbine, which in turn rotates the compressor. This creates a low pressure into the comp inlet, so the path of least resistance is now thru the compressor. As the discharge pressure increases, the chk vlv closes.


whew-
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Wed Jan 16, 2002 10:05 am

Pls omit above para 3a, sentence 3, as it is directly from the Department of Redundancy Department, and mistyped to boot.
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Wed Jan 16, 2002 10:13 am

FDXmech

3a. I agree completely w/ your statement.
Sorry, should have said that first.

 
airplay
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RE: ACM Press/Temp Graph.

Thu Jan 17, 2002 12:17 pm

Hahahahahaha....

EP

In a few more posts you'll have flip-flopped completely.

Let me ask you this: When the ACM in your world has started and the compressor by-pass valve has closed, what continues to drives the ACM? What maintains it's rotation? If it needed the bypass to "start" then why doesn't it need it to maintain operation? Please describe the dynamic flow and how the whole thing stays running.

What happens if the compressor bypass valve is stuck open? Stuck closed? You may want to rethink just how "efficient" these things are when you answer that.

Further, isn't it funny that you are using the word "enthalpy" in a discussion about an ACM which is a device whose function is to reduce the temperature of bleed air? And you further use the words "warm" and "cold" (properties of temperature) in the same paragraphs as the word "enthalpy" even though you stated:

"Your quote: "When considering enthalpy in practical solutions, temperature is one of the properties of a system being investigated." What??? That statement is just...crap. It's Idiotic and Ridiculous (at best). "

I never said enthalpy and temperature were interchangable so STOP IMPLYING IT!

And....you did it again!!!! You took the following quote from me:

"I'm assuming you're describing one specific type of ACM. I've never seen one that operates the way you describe. Of course that doesn't mean it doesn't exist.

This is an example of the difficulty in discussing every aspect of some complex systems. There are countless specific designs!

I guess that's what makes it interesting."

And took it out of context with the following reply:

"So, You- ......Had never seen an application in which the compressor bypass "started" a static ACM, and wouldn't consider the notion,"

Do you not understand how loathsome this sort of behaviour is?

I promise to stop posting when you learn to stop quoting me (and others) out of context in an attempt to discredit. This is akin to slander and I will continue to defend my credibility even if it means exposing your ignorance.

One more question. Why are you so afraid to reveal your background? I'd seriously like to know what exactly makes you an expert on all of this. We already know you've never actually seen or held a real ACM.

Student? Armchair Enthusiast? Doctor? Lawyer? Nurse? Fill us in. It may establish some credibility.


 
EssentialPowr
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RE: ACM Press/Temp Graph.

Thu Jan 17, 2002 1:08 pm

Airplay,

Hhhmmm

Frankly, I'm fairly pleased with the results of this thread. The only things that stunk it up were a malicious conceptional error about the fundamentals of ACM cycle, and blind flailing on your part as someone who has only screamed for a pat on the back for not being able to recognize a check valve in a schematic or understand a thermodynamic cycle. Or what heat is. Or temp...

If you don't understand how the DC10 ACM works, then reread this post. I have described the turbine bypass as the throttle, and the compressor bypass as the "on/off" valve for the entire ACM, which it is. I have seen no discussion to the contrary.

I just don't get how you can't accept the fact that the ACM equation is:

Qdot in = h compressor -h turbine. As the individul that brought up the concept in the first place, and I might add does a fair amount of technical writing, I'm quite comfortable about where I've used the words "enthalpy" and "temp".

Isn't it STRANGE that IT MAKES SENSE to EVERYONE ELSE but YOU?

Further, I've told you 1,000 times that an ACM cannot convert heat to rotational energy, b/c heat can only be transferred through radiation, convection, or conduction. The enthalpy of the bleed air drives the ACM, period. Need I remind you that your ignorance of the fact that this is a cycle? If you cannot define a simple cycle, then it is follows that you ain't gonna get this thread.

What the hell does "considering enthalpy in practical solutions..." mean? Please, b/c I need a good laugh, tell me when you have considered enthalpy in ANY topic prior to this...YOU explain that ridiculous sentence - give an example, reword it -
DO NOT BLAME me for CRAP you write; You are and have been free to explain it the whole time. Otherwise, maybe you should author sentences which you can explain (that's really the key to this forum isn't it??)

And, as FDXmech astutely put it, he simplified the condition the ACM was operating in as a function of "warm air mode", or "cold air mode." The function of the ACM is to supply cold air. The principle of operation is the diff in enthalpy b/t the compressor and the turbine. Temperature is a THermodynamic PRoperty of a system. Again, seems like everyone agrees on the content..Except YOu, so you just have a vendetta...

So now you're an expert on enthalpy, when you had no idea how to define this or any other cycle? Are you kidding?

You couldn't even find the bypass on your 727 schematic!! You thought the note about the bypass was a temp limit!! To quote you, "All is not lost."

Should I ref those threads? You had NEVER EVEN SEEN a compressor bypass; otherwise you would have RECOGNIZED what IT WAS on (YOUR!!) 727 schematic!!

So, from my viewpoint, I consider you to be maliciously trying to salvage some credibility or Attaboy b/c you can't make a succint and valid point, write poorly, have a terrible attitude, and blame me for it. You want a reprieve? Try again on another topic.
 
airplay
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RE: ACM Press/Temp Graph.

Thu Jan 17, 2002 1:32 pm

EP

Simply answer the questions at the beginning of my last post.
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Thu Jan 17, 2002 2:13 pm

Read 01-16 02:00:24, para 3a.

That's half of your problem, Airplay. The answer is posted; you can't decipher it.

What's new?
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Thu Jan 17, 2002 2:14 pm

Actually, it's your Entire Problem.
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Thu Jan 17, 2002 2:26 pm

I'll spell it out for you, since I know you're confused.

01-16 02:00:24 describes how the DC10 ACM goes from idle w/ the comp bypass chk open, cold air demand starts to close the turbine bypass, which initiates flow across the turbine and also creates back pressure which closes the comp bypass chk vlv. Once closed, the ACM can now extract the max possible enthalpy from the bleed air as the ACM spins up. The comp bypass enables the ACM to be bypassed when not needed. It closes when the ACM has a cold air demand.

Got it now?

So, Airplay, why don't you "consider enthalpy in a practical solution" of some kind??

Come on, I REanswered your question...
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Thu Jan 17, 2002 2:45 pm

Forget it.

I don't want a copied sentence from
"Contemporary Physics for Housewives", Large Print Ed.
 
airplay
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RE: ACM Press/Temp Graph.

Thu Jan 17, 2002 11:57 pm

If as you say the "compressor bypass enables the ACM to be bypassed when not needed" then why is air still introduced to the turbine????

Doesn't the action of driving air through the turbine without it even passing through the compressor have an effect on the enthalpy of the air? Of course it does.

You have not described the function of the compressor bypass valve. You have described the function of the temperature control valve. Funny...the manufacturers didn't call it the "Enthalpy Control Valve"......

You ongoing problem? Breaking quotes into snippets and taking them out of context in an attempt to discredit. Your latest rather transparent example?

I stated in an earlier post:

"Funny though that enthalpy is sometimes refered to as "total heat" and sometimes even "heat content".

Why? Because when considering enthalpy in practical solutions (someday you might even do that) temperature (discharge or otherwise) is typically one of the properties of a system that is being investigated. Doing a study of the enthalpy of an air conditioning system without discussing the resultant temperatures is almost as useless as discussion enthalpy with unexperienced know-it-alls. "


But, you broke down that entire quote and stated:

"So, Airplay, why don't you "consider enthalpy in a practical solution" of some kind??"

I need a few laughs right now....so I think I'll go review your last few posts of the original ACM thread. You really screwed up there for someone who comes across as such an expert, (with no credentials)

 
airplay
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RE: ACM Press/Temp Graph.

Fri Jan 18, 2002 2:12 am

The last post was intended as a response for EssentialPwer....in case you hadn't guessed already!

 Smile
 
jetfixer
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RE: ACM Press/Temp Graph.

Sat Jan 19, 2002 12:16 pm

Airplay, Essentialpowr, sorry to butt in on your discussion but I beleive 310 Engineer needs to learn to read.

Where did I refence the A320 having a Compressor bypass valve. Here it is again for you to read.
My position is you are right about the compressor bypass valve and its use for the ACM.

A320 MM ref says additionally, "The bypass valve always maintains an air cycle machine flow to keep the air cycle machine idling during all pack operation conditions". Thought I'd add that since I don't remember it being mentioned.

I am perfectly aware of how the bypass valve ties into the system. Maybe you need to hit the books again 310 Engineer and find out what else the bypass valve does.

As others mentioned the CBPV can aid in ACM start up. I also thought people might be interested to know that the bypass valve can also effect ACM operation so I added it to my post and thats why I said "additionally", so you all wouldn't think it was the primary fuction of the valve. Since most of us are familiar with A/C packs, I didn't think I had to explain each components operation down to the smallest detail. This is a secondary benefit of the bypass valve, just like the CBPV.

Well I guess I'll return to my K Mart cash register cause I can't fix planes.  Laugh out loud
Thanks for shopping.


Jetfixer  Smokin cool


Continue on EP, Airplay.
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Wed Jan 23, 2002 2:03 pm

Airplay,

Exactly what part of my description of the compressor bypass valve on the DC10, do you not understand? I have described the function of the compressor bypass CHECK valve explicitly. It is a CHECK valve; temp mixing is controlled downstream from the ACM (but any novice can ascertain that, right?) If you don't get that, then it's obvious you don't even understand how a check valve works.

The very name describes its function. If there is no demand for cold air (as it's provided by ambient), then there is no need to spin the ACM assembly. Do you even understand what "idle" means? Look at the DC10 diagram, and trace the flow referencing "warm air" demand and "cold air" demand.

Try as you might, your paragrah "Why? Because when when considering enthalpy..."

---The WHOLE PARagraph----

is a tenth grade attempt in the useage of a concept in which you clearly have ZERO understanding. Your statement, conceptually, is BACKWARDS, but I'll leave you to figure it out. Continuing to write that ridiculous statement like it has ANY technical merit is laughable.

YOU DIDN't EVEN know the ACM operated on a cycle, REMEMBER? So now you're an expert on air conditioning/pressurization system DESIGN? That's really funny. Tell me all you know about enthalpy, but I urge you to go copy a legitimate statement, b/c that one is damn funny.

So, go reread the description I offerred. It seems as though everyone else agrees with it. Except you, b/c you just can't interpret a diagram. But that's another of your proven deficiencies...so now, not only can you not find a check valve (727), but you can't understand what it does when it's spelled out.

No wonder this forum frustrates you so much.
 
EssentialPowr
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RE: ACM Press/Temp Graph.

Wed Jan 23, 2002 2:16 pm

REf the DC10 schematic as posted by VC10 in the "original" thread.

Of the people who have participated in this thread, is there anyone that diagrees with the thread posted:

1-17 06:26:32?

Does it make sense? (The DC10 ACM was specified to limit the scope of the discussion.)

Thanks for any responses; I'll assume a lack of response indicates agreement, since there have been none prior to this. (I hate to assume what Airplay actually understands, as it's apparrently quite miniscule.)

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