craig1410
|
| posted on 16/1/16 at 01:17 AM |
|
|
I've yet to see a CPU fan attached to the front of a car doing xxx MPH so I think I'll settle for the opinion of the two specialists
mentioned above as well as my own intuition until data to the contrary comes to light. 
|
|
|
|
|
02GF74
|
| posted on 16/1/16 at 01:52 AM |
|
|
One of your specialist made an incorrect statement so what else has he got wrong? Is he quoting the same stuff everyone else is quoting with no data
to back it up?
Look at spal fan data. The flow and current for straight blade fans of same diameter is the same for pull and push.
Note curved blade pull fan gives better flow for same current and size to the above.
Therefore i reject the statement that pull is better than pull since there is no indication it is comparing like with like, in fact the data implies
there is no difference unless a fan with optimised blades is used, which i suspect spal refer to.
You dont like my cpu data as it is against what you believe but is it a matter of scale or are the other factors involved that make the data not
appliicable to this discussion? I dont know and until i see data im sticking with push for reasons given earlier and the physics backs me up.
|
|
|
02GF74
|
| posted on 16/1/16 at 02:06 AM |
|
|
quote:
Originally posted by craig1410
I've yet to see a CPU fan attached to the front of a car doing xxx MPH
But you must have, the car fan is a cpu fan but bigger and im not discussing efficiency when car is moving because if the radiator is correctly sized,
the fan plays no part. People on here have used cpu fans for oil coolers.... but is data for a small fan applicable when scaled up? I expect the
airflow to be different but weve all seen scale models in wind tunnels so the airflow cant be all that different.
I'm not having a go at anyone or want to argue, but simply don't accept random quotes from "experts" that defy the laws of
physics.
Here are those laws:
1. When a gas is compressed, its pressure increases.
2. For a gas to flow there must be a pressure difference.
3. A car radiator, despite its name, transfers heat by convection.
4. The amount of heat transafered out of a radiator increases as the amount of air flowing though it increases.
5. A puller fan, cannot pull more than 1 atm of air whereas a pusher fan can. In other words, the pressure of air flowing through the radiator is
less for a puller than a pusher.
6. When a gas is compressed, e.g. air its pressure increases.
So for a pusher and puller fan of the same flow in free air, when presented with a resistence to flow e.g. a radiator,
the air flowing through the radiator will be at a higher pressure for a pusher see 1. 2. 5.
The higher pressure means there is more air going through the radiator, so more heat is transferred see 3. 4. so it is more efficient.
As pointed out the air will be at a higher temperature but that does not affect the overall result.
You experience this when driving.
If the car is idling when stationary, the temperature rises as there is no air flow
through the radiator.
When moving at a snail pace, the temperature will rise but not as fast.
When moving at speed, the temperature is constant due to the thermostat. That is because more air is being pushed through the radiator even though it
may get slightly hotter due to being compressed.
So to conclude, more heat is moved from the radiator as more air flows through it and it is a pusher fan that can flow more air than a puller hence is
more efficient.
Anyways, im leaving it at that as without any test data neither of us are going to agree.
[Edited on 16/1/16 by 02GF74]
|
|
|
gregs
|
| posted on 16/1/16 at 08:30 AM |
|
|
FWIW - don't exclude a raid to the breakers.... I've got a Proton pull fan on mine (on a civic VTEC rad!) mounted direct to the rad.
It's not the slimest (prob about 75mm) but comes with a free square cowl and flows a significant volume when it kicks in.. total investment for
fan and rad... £15.
Greg
[Edited on 16/1/16 by gregs]
|
|
|
CosKev3
|
| posted on 16/1/16 at 10:26 AM |
|
|
Where's the yawning smiley 
Dropped off nicely reading that.......
|
|
|
CosKev3
|
| posted on 16/1/16 at 03:04 PM |
|
|
quote:
Originally posted by 02GF74
Look at spal fan data. The flow and current for straight blade fans of same diameter is the same for pull and push.
Yeah but surely that's just the fan running on its own during a test without being fitted to a radiator?
|
|
|
snowy2
|
| posted on 16/1/16 at 03:39 PM |
|
|
one of the universities has done the research and there is no difference between push fan or pull fan. the shadow they cause is the same either side
of the radiator.....go for what fits and dont worry about it.
sometimes you are the pigeon, most of the time the statue.
|
|
|
snowy2
|
| posted on 16/1/16 at 03:44 PM |
|
|
ducting is very important....if the air can find a way round the radiator it will do......also a radiator stuck out in the air flow getting clean
"Laminar" air will NOT cool as well as a Radiator getting turbulent air....weird but true.
sometimes you are the pigeon, most of the time the statue.
|
|
|
craig1410
|
| posted on 16/1/16 at 04:31 PM |
|
|
quote:
Originally posted by snowy2
one of the universities has done the research and there is no difference between push fan or pull fan. the shadow they cause is the same either side
of the radiator.....go for what fits and dont worry about it.
It'd be very interesting to see that study if you know which university did it. Otherwise I'm afraid we're no farther forward in
separating myth from reality.
I'll repeat what I said last night and recommend that everyone ensures they have more than enough cooling capacity and seal between
nosecone and radiator to ensure the airflow can't bypass the radiator core. If you do that then you don't need to worry about any minor
differences between push vs pull and can go with the one you find most convenient to install or aesthetically more pleasing.
If anyone is looking for donors at the scrapyard then you'll find puller fans much more common. Whether this is because car manufacturers
believe this is more efficient or if they are also deluded I will leave up to the reader.
|
|
|
renetom
|
| posted on 16/1/16 at 05:03 PM |
|
|
fan
Hi
We used a polo rad & a polo fan which cost £6 on ebay
is reversible easy to mount & was perfect for our car
with yamaha R1.
good luck
René
|
|
|
02GF74
|
| posted on 16/1/16 at 05:45 PM |
|
|
quote:
Originally posted by craig1410
If anyone is looking for donors at the scrapyard then you'll find puller fans much more common. Whether this is because car manufacturers
believe this is more efficient or if they are also deluded I will leave up to the reader.
well didn't take for the insults to start but I'll ignore that. 
The reason you find more puller fans fitted to cars is because the fan sits in a cowl. Cowling makes a huge difference and works better when
the car is driven by being behind the radiator. I have never disputed any of that but will continue to disagree that a pull fan is more efficient
better at removing heat than push fan. The example you cite above has nothing to do with efficiency of pull vs pull but efficiency of cowl siting.
I have listed the physics and my reasoning already, please tell me which part you don't agree with.
Lets make it really simple and say you have a fan that moves the same amount of air in both directions and mount it on the mouth of a sealed jar.
Wire it up so is acts as a puller so it sucks air out of the jar. The air inside the jar will be a less than 1 atmosphere.
Wire it up so it pushes air in and the pressure inside the jar will be above 1 atmosphere.
Now mount it to a radiator so the jar in effect is the radiator matrix, the pressure will follow the same pattern.
Higher pressure = more air molecules = more heat transfer; therefore pusher is more efficient (the effect of any change in temperature is minimal as
the fans are not very good compressors). Show me at which point I am deluded.
In summary, if there is a cowl, the cowl and fan sit behind the radiator and fan is a puller.
If it is just a fan and it moves same amount of air in both directions, then it sits as close as possible and in front of the radiator.
This ofcourse assumes there is a choice where to mount the fan.
[Edited on 16/1/16 by 02GF74]
|
|
|
craig1410
|
| posted on 16/1/16 at 06:03 PM |
|
|
Just to be clear, I was suggesting perhaps I am deluded along with the car manufacturers so no need to take offense!
To avoid CosKev3 nodding off I'll keep my response short. No jars required either...
You agree a puller in a cowling is best and we've already said a cowling is recommended so sounds like a puller in a cowling is best. Job done!
[Edited on 16/1/2016 by craig1410]
|
|
|
snowy2
|
| posted on 16/1/16 at 06:08 PM |
|
|
bmw mercedes citroen use pusher fans ford vw audi use puller fans....it really doesn't make any difference....
sometimes you are the pigeon, most of the time the statue.
|
|
|
craig1410
|
| posted on 16/1/16 at 06:10 PM |
|
|
quote:
Originally posted by snowy2
bmw mercedes citroen use pusher fans ford vw audi use puller fans....it really doesn't make any difference....
Well my BMW E61 uses a puller. Can't comment on the others and wouldn't want to generalise.
|
|
|
