I knew I saved this for a reason. See? Smiths pays
$1100 for an SAE class for me, and I pass on that info
to you:
--- Ron Soave <soavero@yahoo.com> wrote:
> Date: Wed, 4 Aug 1999 19:52:19 -0700 (PDT)
> From: Ron Soave <soavero@yahoo.com>
> Subject: downflow vs. cross flow, fan position
> To: spridgets@autox.team.net
> Reply-to: Ron Soave <soavero@yahoo.com>
>
> 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
>
>
=====
Ron Soave
The optimist says the glass is half full.
The pessimist says the glass is half empty.
The engineer says the glass is twice as big as it needs to be.
The British car owner says it's leaking.
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