VC-10 From United Kingdom, joined Oct 1999, 3677 posts, RR: 36 Posted (11 years 5 months 3 weeks 9 hours ago) and read 3414 times:
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:-
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 From United States of America, joined Jul 2001, 2676 posts, RR: 7 Reply 1, posted (11 years 5 months 2 weeks 2 days 17 hours ago) and read 3254 times:
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?
EssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2 Reply 5, posted (11 years 5 months 1 week 4 days 17 hours ago) and read 3217 times:
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 From United States of America, joined Sep 2000, 1820 posts, RR: 2 Reply 6, posted (11 years 5 months 1 week 4 days 16 hours ago) and read 3210 times:
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 From United Kingdom, joined Oct 1999, 3677 posts, RR: 36 Reply 8, posted (11 years 5 months 1 week 4 days 11 hours ago) and read 3211 times:
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 :-
Posted 2001-11-06 21:16:31 and read 1178 times.
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". "
Airplay From , joined Dec 1969, posts, RR: Reply 10, posted (11 years 5 months 1 week 4 days 4 hours ago) and read 3194 times:
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 From United States of America, joined Sep 2000, 1820 posts, RR: 2 Reply 11, posted (11 years 5 months 1 week 3 days 22 hours ago) and read 3182 times:
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.
VC-10 From United Kingdom, joined Oct 1999, 3677 posts, RR: 36 Reply 14, posted (11 years 5 months 1 week 2 days 7 hours ago) and read 3148 times:
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.
EssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2 Reply 15, posted (11 years 5 months 1 week 1 day 19 hours ago) and read 3127 times:
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 From , joined Dec 1969, posts, RR: Reply 16, posted (11 years 5 months 1 week 1 day 6 hours ago) and read 3109 times:
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".
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 From United States of America, joined Sep 2000, 1820 posts, RR: 2 Reply 17, posted (11 years 5 months 1 week 22 hours ago) and read 3099 times:
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 From United States of America, joined Sep 2000, 1820 posts, RR: 2 Reply 18, posted (11 years 5 months 1 week 19 hours ago) and read 3100 times:
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...
EssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2 Reply 20, posted (11 years 5 months 1 week ago) and read 3078 times:
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.
EssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2 Reply 22, posted (11 years 5 months 6 days 17 hours ago) and read 3070 times:
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 From , joined Dec 1969, posts, RR: Reply 23, posted (11 years 5 months 6 days 17 hours ago) and read 3070 times:
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'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.