b.m.benz at prodigy.net
Wed Dec 5 10:36:42 EST 2001
Scott, this additional reply was prompted by Brett's 12/4 expo on "Shadetree
Thermodynamics" (i.e. where the sun don't shine), and in spite of our
esteemed listmaster's thinly vailed threats of censure for excessive
bandwith useage. (We should maybe revert back to Q's like, Was that your
puce 200 that I saw roll over on Route 69? Pity!)
My point of this additional reply is that IMO the participants to this
thread have been hung up on the advantages of minimumizing pressure loss
across the IC to the point of total exclusion of any charge temperature
considerations. Scott, at least you understand that charge temperature
reduction is the ONLY justification for intercooling. Apparently, others do
not, and thus may be misled by the fanatic few.
Every decision in life involves a trade off of some kind. If all you want
is one maximum quick pop, forget intercooling and get much more B4B, ala the
first '70s turbo systems. (The ultimate short tube IC is a zero tube length
IC, but with lots of tubes, right Brett?) IMO, Audi is reverting back
toward this extreme by designing cars for short burst performance, relying
primarily on the transient, heat sinking capabilities of the forced
induction system, rather than on the steady state cooling capabilities of a
good intercooler design. (Don't knock Macs, trucks nor computers. Both use
the best of ICs.) What sells in volume is what the customer can use on the
street. That statement pretty much holds for most aftermarket upgrades
Scott, your flow/PD calks are well and good, but are only a part of the
story if you do not consider the heat transfer characteristics of what you
are proposing. Good heat transfer from the fluid to the tube requires
turbulant air flow, and therefore high velocity, exaggurated by the
straightening vane effect of the fins within the tubes. If one reduces the
flow velocity by the addition of excessive parallel tubes to the point of
laminar flow within the tubes, the surface heat transfer coefficient goes to
hell, with a big drop off in cooling efficiency. You have your low pressure
drop IC, but with poor cooling capability. Not an optimum solution when the
goal is maximum heat removal. The same thing holds for the cold side of the
IC, thus I agree with you, that frontal area, fronting directly into ram
air, is all important, but for this additional reason.
As for trade offs, they are personal, mine being different than yours.
Cost always is a high priority with me. I enjoy doing things well on the
cheap. In my 3Bing the 7A project, maximumizing HP is not a goal. I am
trying only to duplicate my NAIII chiped 200Q-20V engine performance in the
90Q-20V on the cheap, under $3K. The space constraints of the 90's front
end and B4B were the driving forces leading me to the series 5K IC design.
I expect to have a 20VT with the lowest charge temperature around.
> From: QSHIPQ at aol.com
> Date: Tue, 4 Dec 2001 06:23:31 EST
> To: b.m.benz at prodigy.net, mlped at qwest.net
> Cc: 200q20v at audifans.com, s-car-list at yahoogroups.com
> Subject: Re: [200q20v] intercoolers
> [ Picked text/plain from multipart/alternative ]
> Mike make be simplistic (ask Hap), but he's right on in terms of design and
> execution. If you look at the "big dog" IC designs, you will see that short
> and more, beats long an less (ok insert jokes here;). Bernie, for more on
> this, you can go to a variety of books, Try page 59 and 60 in Corky Bell's
> book for starters. Longer tubes = greater pressure loss across the IC = bad.
> That said, I calculated the flows a while ago for the 5kt and the S4t, and
> found that two of them will work really well in parallel, the S4t a bit
> better, but the 5kt hard to beat in terms of B4B. If I can find those calcs,
> I'll post em up. But MP's summary is spot on, IMO, audi specs darn good IC's
> for a given (small) size. The problem with really efficient IC's is that
> they have very narrow working ranges before PD raises it's ugly head.
> Doubling them up is a great idea, so is going double pass with really high
> flow IC's.
> Frontal area is key, the more the better, the shorter the cores, better
> still. Stock IC's from Audi tho, are for short bursts as MP proposes, that
> can be easily confirmed with the Davtron, even the "Big ass" turbos heat soak
> the stock IC quickly (<30seconds).
> HTH, thoroughly enjoying the reads guys!
> In a message dated 12/3/01 9:59:01 PM Central Standard Time,
> b.m.benz at prodigy.net writes:
>>> Your examples are too simplistic and unrealistic to make a reasonable
>>> comment thereon, so I won't.
> Pederson writes:
>> Well all I can offer is the thought that just because a tube is
>> shorter doesn't necessarily mean it can't be as effective a heat
>> transfer sink as a longer tube SO LONG AS, or maybe a better term be
>> IF the charge air moving through it has, among other things (i.e. the
>> "turbulators" effects & functions) been slowed in its passage.
>> i.e. If you have two systems, one a single ten foot tube vs. the
>> other, ten one foot tubes, same volume or flow of air, isn't the air
>> in the ten one foot tubes going to be moving @ 1/10th the speed of the
>> single column of air in the one 10 foot tube? Therefore, volume for
>> volume, the air in both systems will be spending the same total amount
>> of "tube time" Yes? But the initial "highest" heat delta may be
>> better distributed over the first 2" or 3" of the 10 short tube
>> system, than the equivalent 36" of the single tube system?
>>> First, remember that our cars are not designed as race cars
>>> or Pikes Peak performers. IMO, They are designing cars for
>>> short burst performance,.... snips
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