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Old 12-18-2008, 03:38 AM   #21 (permalink)
trebuchet03
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Join Date: Dec 2007
Location: Bay Area
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The Miata - '01 Mazda MX-5 Miata
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Quote:
Originally Posted by fud2468 View Post
When doing a partial grille block, wouldn't it make sense to duct air directly from the grille opening to the radiator? Otherwise it would seem there's too much chance for turbulence enroute. A duct might allow a smaller opening in the grille to get the same amount of cooling effect.
Of course there'd still be turbulence for air passing through the radiator and into the engine compartment, but that's unavoidable.
Ray Mac
I did a quick scan of the thread and didn't see this addressed.

The worst possible thing you can do, from a heat transfer perspective, is to have laminar flow through a heat exchanger (such as a radiator). You want nice, slow, turbulent flow passing through that radiator.

why?
Turbulence increases heat transfer coefficients

Going to borrow this image


Diffuser slows down flow - due to increasing cross section.... Length and lower velocity should help the fluid go turbulent faster... Tapering diffuser behind radiator should increase velocity to be reintroduced with external flow.

Turbulence is your friend - everyone give your turbulence a hug, we've been bashing it too much

Quote:
* The bumper splits the airflow to the radiator
* The nose to radiator distance is FAR shorter than needed for Korff's Ideal Radiator Duct
* No clean exit for airflow from the radiator
* Fans and fan shrouds restrict and "dirty" the airflow after the radiator (but ARE necessary for additional airflow, like when you are travelling at low speeds after cruising on the highway for a length of time)
1. Yep
2. Totally
3. Not at all - there's other bits in the engine bay to cause problems too (hoses, et. al.)
4. It's not in front of me, but I do recall Hucho's book talking about fan shrouds (as in the Jetta model) being a compromise. All air entering the grille should pass through the radiator and never travel around. The actual car has foam sealant between the plastic shroud and radiator Plus, shrouding a fan increases it's efficiency


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If you're looking for aero gains in the cooling department.... I don't think you'll find what you're looking for - for anything short of a redesign. Keep in mind that the maximum aero gains will be less than the gains from completely blocking off your front grille(s). A function of limits, unfortunately.

If you can measure.... Attempt to measure the gains from blocking the grille. Then, decide if your time/money is worth gains less than what you measured. I'm willing to bet that your time/money are not worth it and better spent elsewhere for higher gains (*cough* - complete block; with adjustable slots for the worried - *cough*)

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