not directly EFI related, but close

[George M. Dailey]

Gentlemen, a question came up on another list about which routing (paralell
or series) is better for cooling an engine (fuel injected ofcourse)equiped
with dual radiators. Since there are several megawatts of brain power right
here, it thought I'd ask.
Keep in mind all factors that are involved. 

Thanks in advance, and feel free to mail dircetly to me if you fell this is
not DIY-EFI enough <gmd at tecinfo.com>.

GMD

>Date: Sat, 18 Jan 1997 10:09:46
>To: KitCar at bolis.com
>From: "George M. Dailey" <gmd at tecinfo.com>
>Subject: Re: lowering radiator
>Cc: IMD1 at msn.com
>
>Ah, a challanger! Clik clank... that cool sound of a 9mm auto being
loaded... Most (all) technical books I have read say the opposite. If series
cooling is superior, why aren't the factory radiators designed that way
instead of running all the flues in paralell?  We do agree that the higher
the delta T (temperature differential between the coolant and ambient air),
the more heat transferd, right?  We also agree that by using the paralell
routing we will decrease the total system fluid resistance, right? With any
pump (engine cooling or boiler feed pump), decreasing the fluid resistance
that it pumps into, will increase the flow. When you place the rads in
series you will increase the total system resistance. There will be a
pressure differential accross each rad and the whole system. This will be
greater than the the paralell arrangement.  All of these delta Ps will
reduce the total flow through the system. With less water being pumped
through the system, total cooling can only be reduced. Notice that I have
not given any numbers. The reason is simple. There are too many varaibles
like pump curves, ambient temp, coolant temp, coolant pressure, and fluid
viscosity to take into consideration. But, given two identical radiators,
the paralell routing will offer higher heat exchanging potential. Of course,
if one rad is allready capable of doing the job, an additional unit in
series will only cool it that much more. Keep in mind that if the coolant
leaving the first rad is equal to the air temp, there can be no additional
cooling.
 
A cloged rad will hurt you more in series than in paralell. Since the full
flow of the cooling system must go through each rad in series, one cloged
rad will seriously reduce the total system flow through both rads. You are
right about the balance cooling thing...to an extent. But you will not get
it with the series set up either. 
 
I'm not a Mech. Engineer. Just a person who does plentey ME design projects.
 
Good luck to person who asked about the rad problem. If you need additional
justification in making the right decesion, let me know.
>
>GMD
>
>
>At 12:22 AM 1/18/97 -0500, you wrote:
>>
>>
>>On Fri, 17 Jan 1997, George M. Dailey wrote:
>>
>>> I reccommend running the rads in paralell. Tee the inlets and outlets. You
>>> will get higher heat transfer with the largest temperature differential
>>> (coolant to air). Running the rads in series will make one of them have a
>>> lower temp diff (coolant to air). This will lessen the maximum heat
>>> dissapation available.
>>> 
>>
>>Nope.  Two half rads in series is the same thing as one big one, which
>>works just fine.  With 'em in parallel, you must haave almost exactly the
>>same flow in each to equalize cooling.  Hard to achieve in practice.  The
>>car will overheat.
>>
>>John
>>
>>
>>
>