To the List,
I have to agree with Jack, about the position of the fan, with a fully
shrouded unit, but I will take exception that most of the after market fans
available are not fully shrouded. Most of the after market fans have a
blade guard and supports and not a true shroud. The major concern should
be finding a unit that has a high CFM rating at the lowest possible
amperage. Most electric fans draw 10 amps or more, and this is quite a
drain on any good to marginal electrical system. But by shopping around you
can find units that draw as little 6.8 amps and can be mounted either as a
pusher or puller system.
As always this is JMO,
----- Original Message -----
From: Jack Brooks <brooks@belcotech.com>
To: Trevor Jordan <tjordan@vic.bigpond.net.au>
Cc: Triumph List <Triumphs@autox.team.net>
Sent: Wednesday, February 03, 1999 8:32 AM
Subject: RE: electric fans- puller vs pusher
>
>Trevor,
>
>I am in complete agreement with almost all of what you said, however the
>efficiency I was referring to was the overall radiator efficiency,
comparing
>the shrouded puller versus the pusher fan. I firmly believe that in a
>stopped or slowly moving vehicle a shrouded puller (tractor) fan will do a
>better job than a pusher.
>
>We can debate whether having a fan hub in front of the radiator will
provide
>more of an obstruction to cooling than placing it behind the radiator, due
>to turbulent vs. laminar flow through the slotted TR3A grill, but a fully
>shrouded puller is going to outperform a pusher without the moving vehicle
>air ram effect.
>
>Jack Brooks
>TS69032L
>NJ car show: http://pages.hotbot.com/family/triumph
>>At 11:57 PM +1100 3/2/99, Jack Brooks wrote:
>>
>>>Putting the fan in front of the radiator partially blocks the radiator,
>>>inhibiting the flow of air and cooling. A "puller" fan is superior in
>>>performance to a "pusher" in this respect.
>>
>>A pusher fan will block the air flowing into the radiator whereas a
tractor
>>(puller) fan will block the air coming out of the radiator. Is there
>>likely to be any great difference in efficiency? A pusher fan will
disrupt
>>the flow of air through the radiator more than a tractor, but after it
>>comes through the grill it is likely to be fairly turbulent already.
>>
>>In either case, electric fans normally windmill when travelling at any
>>significant speed and present much less obstruction to airflow than their
>>appearance would suggest.
>>
>>An argument can be made that a pusher fan increases the pressure, density,
>>and heat transfer capacity of the air flowing through the radiator. A
>>tractor fan does the opposite. But I am not sure that any of these issues
>>count for much - space for the fan and simple convenient mounting points
>>could be more important.
>>
>>>Since I am concerned about total
>>>amps used for a given amount of cooling, it makes the most sense
>>to install
>>>the most efficient configuration, especially since I am getting rid of
the
>>>mechanical fan altogether and have lots of room for a fully shrouded fan.
>>
>>The electric fan will run when the car is stationary or moving slowly. In
>>these circumstances the fan is creating the airflow not blocking it. It
>>should not run very often and unless your electrical system is marginal it
>>should cope. What the generator/alternator cannot supply will come out of
>>the battery which will be replenished when the fan stops. Fans typically
>>draw about the same current as the lighting system, so the fan should
>>create no problems during the day. You could test it with the lights and
>>fan operating together to see how the electrical system copes.
>>
>>Trevor Jordan
>>74 TR6 CF29281U
>
>
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