Dear Friends,
I just feel it is time to toss in my two pence [that's öre over here]
worth of knowledge into this thread...
Some of You have been talking about the instance that a radiator
is too small for its purpose and that adding an electric (shrouded
or unshrouded) fan will not solve the problems with a hot engine on
a hot day.
Well, I must disagree, friends. I think, no I know it should do...
I'm working in a part of the industry some of You might disagree
with, where we've got lots of different heat exchangers and where
we dump around 70% of our energy input into the sea and put the
remaining 30% to use... So I imagine You all do understand that we
do whatever possible to better those figures... ;-)
> [No it's not the military... But I doo think the figures could
> well be them... I leave that part of business to our beloved TCS
> President, Lt Sewe Lindberg.]
Sometimes we run into the problem that it is not possible to change
the physical dimensions of a heat exchanger, but we do need to have
it transfer more energy "from one side of the wall to the other"...
Well what do we do then? We increase the flow of the colder media
through the exchanger per time unit. Simple... And the principle is
the same irrespective of what the media is; a liquid or a gas...
[So far no one has invented a solid media heat exchanger... ;-) ]
It costs us more energy in pumping effort but it does what we intended
to do: increase the exchange of heat in a given exchanger design...
The same principle is fact when it comes to an undersized auto
radiator... If it is to transfer more heat away from the engine
cooling system one needs to increase the amount of air passing
through the radiator per time unit. The standard engine driven
fan is a fixed part of this calculation, since it only does what
it is designed to do; pull a given amount of air through the
radiator per revolution, and the amount of revolutions per given
time unit is relative to the engine revolutions [and the exchange
factor given by the pulley diameters if it is not driven directly
off the crankpulley]. At idle or in slow speed traffic the fan pulls
less air than what is needed if the engine goes hot.
What can be done in such a case [Assuming a change to a bigger or
more efficient radiator is out of the question.] is to increase the
airflow. A good way is to fit an electric, thermostat operated,
additional fan. A puller is to prefer [it disrupts the airflow ahead
of the radiator less] but a pusher is OK [if a puller is impossible
to fit together with the ordinary engine driven fan] since the
difference is only some 10 - 30% efficiency. The extra fan will help
the ordinary one [given that the fans don't work over the same area
of the radiator] to increase airflow _per time unit_ when it cuts in.
And the given radiator will dissipate more heat energy into the air-
stream, cooling the engine more...
On the question of removing the ordinary fan and only use an electric
one we are leaving my professional familiaritys with this, but there
must be some good and simple reason most modern cars have electric
fans instead of engine driven ones. Remember, an electric motor and
the rest of the setup is much more expensive to the manufacturer than
a simple fan bolted to a pulley...
So I guess the motoring industry have already answered our question,
which is best/most effective etc. No question about it, it is the
electric one since for one it doesn't work when it is not needed and
do work when it is needed. The exact contrary to the engine driven
mechanical fan who flows lots of air [when the vehicle are at speed]
when it is not needed and nearly no air at all [during an idling
standstill] when it is needed the most... ;-(
The mechanical one also increases the mass that needs to be accelerated
when revving up the engine...
[My Spit is going to get a puller when it goes out of hibernation,
and (sadly) the original [option aluminium] one will have to go to
give room for it.]
Your Odd one...
What part of the industry, You ask?
A nuclear power plant... 1206MW generator... Boiling water reactor...
--
Odd Hedberg
Pomonagatan 4
S-74236 Östhammar International liaison secretary,
Sweden Triumph Club of Sweden
'70 Spitfire Mk3 FD82497LO Signal Red
E-mail: odd@triumphclub.se / odd.hedberg@bigfoot.com
Club URL: http://www2.passagen.se/triumph/
Home Telephone: Int+ 46-1731 7131
Geographical Position: N 60deg15min E 18deg23min
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