Turbo vs. Supercharger. (long, technical, blabla)

[flaatr at yahoo.com (Euroroc II)]

Uhhhh.....
Right,
Exactly!
That's what I meant...
I think?
Thanks for clearing that up for me Allyn. I can finally sleep at night!

-Raffi (still looking for his calculator and copy of Halliday & Resnick to 
confirm Allyn's calculations)


At 05:55 PM 7/7/2003 -0400, you wrote:
>Raffi,
>ok, both you and Neal are correct...
>
>however... (here we go)...
>
>- the temperature rise from compressing the air far outweighs the heating
>caused by conduction heat transfer from the turbine impeller.
>
>lest take a "perfect" increase in pressure:
>if you start at 25c (77f), and boost to 1 bar (15 psi), the resulting
>temperature is 90c (194f)
>if you take into account an (optimistic) turbine compressor efficiency of
>70%, that resulting temperature jumps to 117c (242f). yes, your air
>temperature has jumped by 92c (165f), and is now pretty damned hot.
>
>while examining these numbers, it is important to note that the compressor
>efficiency value takes into account conduction heat transfer (from the hot
>compressor turbine to the cool air stream), as well as the heat build-up due
>to pure work-related inefficiencies (due to air-blade friction, etc). that
>70% value caused us another 27c (48f) jump in temperature. assuming half of
>that temperature jump was due to the conduction heat transfer, our hot
>turbine has only caused us a 13c (24f) temperature jump. comparing that to
>the original 65c (117f) jump, you can see just how small that effect really
>is compared to all of the other energy you are dumping into that intake air
>stream.
>
>- also of note, the supposed "cold pump" of a supercharger will quickly get
>heated. not to turbo temperatures mind you, but it wont exactly be sitting
>at ambient either. even with an externally compressing supercharger, it is
>still doing work on the air, and this will still cause energy (heat) to be
>absorbed by the supercharger itself, heating it.
>
>- on the flip side (back to the turbo), cool air rapidly flying by a turbine
>impeller blade will quickly cool that blade. the turbine impeller may be hot
>at idle, but it quickly 'cools as it spools' (nice catch phrase, eh? heheh).
>even with a 900f exhaust blade, the heat simply cant transfer across the
>narrow coupling shaft as fast as the cooler intake air can strip heat from
>the intake blading.
>
>phew!
>ok, enough geek-dom for today.
>
>jeesh, you'd think i was doing calcs for the twin or something... <g> :)
>
>hth
>Al
>
>Allyn Malventano, ETC(SS), USN
>87 Rieger Scirocco GTO 2.0 16v (daily driver, 190k, rocco #6)
>86 Kamei Twin 16V Turbo Scirocco GTX (30% complete, rocco #7)
>86.5 Occo 16v Trailer (rocco #8)
>87 Jetta 8v Wolfsburg 2dr (wifes daily, 285k)
>
>
>----- Original Message -----
>From: "Euroroc II" <flaatr@yahoo.com>
>To: "Neal Tovsen" <nealtovsen@yahoo.com>; "Dave Ewing"
><MK1Scirocco16v@comcast.net>; <scirocco-l@scirocco.org>
>Sent: Monday, July 07, 2003 5:31 PM
>Subject: Re: Turbo vs. Supercharger.
>
>
> > That is not correct... you can not say that having an air pump bolted
> > directly to an exhaust manifold is not going to directly contribute to the
> > air warming. It will.
> >
> > Compressing the air will cause it to get hotter, yes I agree but there is
>a
> > difference between compressing air in a cold pump or a really, really,
> > really, hot pump.
> >
> > -Raffi
> >
> >
> > At 02:19 PM 7/7/2003 -0700, Neal Tovsen wrote:
> > >The heat in the intake of a turbo car has nothing to
> > >do with being near the exhaust. Any time you compress
> > >air, it heats up. Thus, superchargers create heat too.
> > >
> > >Neal
> > >'77 G60
> > >(now with air-to-water intercooled goodness!)
> > >
> > >
> > >--- Dave Ewing <MK1Scirocco16v@comcast.net> wrote:
> > > > I'm just curious here and coming into this
> > > > conversation late (thanks AT&T
> > > > for selling out to Comcast!!) but how the heck does
> > > > the air in a
> > > > supercharger get to the temps of that in a turbo
> > > > charger when the air in a
> > > > supercharger goes from atmosphere to charger to
> > > > intake?  The front of the
> > > > motor is not even close to the same temp as the back
> > > > of the motor either.
> > > > Try changing an exhaust manifold after you drove the
> > > > car compared to
> > > > changing an alternator.  I'm just curious as I don't
> > > > know much about
> > > > superchargers but after working on cars for 20
> > > > years, I understand
> > > > temperatures!
> > > >
> > > > Dave
> > > >
> > > >
> > > > _______________________________________________
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