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RE: MORE: downflow vs. cross flow, fan position

To: "'Ron Soave'" <soavero@yahoo.com>
Subject: RE: MORE: downflow vs. cross flow, fan position
From: "Haynes, Mark" <mhaynes@ball.com>
Date: Thu, 5 Aug 1999 07:01:04 -0600
Cc: "'spridgets@autox.team.net'" <spridgets@autox.team.net>
Reply-to: "Haynes, Mark" <mhaynes@ball.com>
Sender: owner-spridgets@autox.team.net
Thanks Ron, You just saved us all a 2-day seminar cost!! >:-)
Mark Haynes

> -----Original Message-----
> From: Ron Soave [SMTP:soavero@yahoo.com]
> Sent: Wednesday, August 04, 1999 8:57 PM
> To:   spridgets@autox.team.net
> Subject:      MORE: downflow vs. cross flow, fan position
> 
> Editing error - when I said there is "no difference",
> I meant for horizontal vs. vertical flow.  If you
> stayed with the whole post. there is obviously a
> difference for fan position.
> 
> 
> --- Ron Soave <soavero@yahoo.com> wrote:
> > Just got back from a 2 day conference/class on
> > automotive heat exchangers given by the SAE, with a
> > fellow named Ram Shah as the instructor (if you're a
> > Mech E, you have probably used one of his 25 books
> > in
> > school, and he works at Harrison, which does many
> > many
> > of the radiators, condensers, evaps, oil coolers for
> > all cars).  After 2 days of mind numbing equations,
> > we
> > got down to some folksy questions, and the topic
> > ofvertical vs. horizontal flow came up,as did
> > "sucking
> > vs. blowing" for cooling fans.  All things being
> > equal
> > (core size, and available airflow), there is no
> > difference.  The reason a lot of manufacturers went
> > to
> > horizontal was because of the reduction in vehicle
> > frontal height in modern cars, which require lower
> > profile radiators.  Also, if the manufacturer wants
> > to
> > increase the size of the core, a horizontal flow HX
> > allows for the same headers and collectors, the only
> > difference being longer tubes (or plates).  In a
> > downflow radiator, it is unlikely that the height
> > could be increased, so more columns of tubes would
> > be
> > required, increasing manufacturing cost.  In the
> > auto
> > industry, Shah said they start to worry if cost goes
> > up for something by more than 3 or 4 cents.  
> > 
> > For fan position, it is better to have the fan
> > behind
> > the radiator ("sucking"), with an inlet shroud
> > (important).  If the fan is in front of the heat
> > exchanger, the flow pattern across the HX surface
> > will
> > be less uniform, with the velocity pressure
> > concentration at the fan blade tip.  Additionally,
> > the
> > flow will be turbulent, (fan on or off) making the
> > pressure drop across the HX higher than for laminar
> > flow and reducing total flow (for those who care,
> > pressure drop increases with the square of velocity
> > for turbulent flow, and varies nearly linearly for
> > laminar flow).  With the fan behind the HX, the flow
> > is more laminar into the HX, and the flow field is
> > more uniform, giving much better air distribution
> > across the face of the HX.  With the fan behind the
> > HX, an inlet shroud is important, or the fan will
> > draw
> > air in locally, and not from the front of the heat
> > exchanger.
> > 
> > Still awake?  
> > Ron
> >
> > Do You Yahoo!?
> > Free instant messaging and more at
> > http://messenger.yahoo.com
> > 
> > 
> 

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