Suck or Blow ?????????

Well I asked the Question and here is the Answer

From Nick Adams @ Demon Power Products

Some racers are not sure whether to suck or blow.

One day they will find out if they are lucky which is best for them.

However regarding fans , blowing is the only effective way. The reason is that the impellor collects air from a 180 degree sphere and blast it as a jet onto the hot target. If you fit a skirt around the fan body the blast is even more effective.

Now if you were to try and suck the hot air from the target it would have to occupy the 180 degree sphere or cold air would also be pulled in, say from the sides which would have no cooling effect. But if the fan had skirts enclosing the hot target then the air flow would remove the heat .

Also the cooling effect is directly proportional to the surface area that the moving air passes over, so fitting a multi finned heatsink should help the cooling. But beware that sometimes the heatsinks are a poor fit with air gaps between the motor and heatsink and also the airflow can be turbulent and less effective.

I recommend the biggest fan possible as the air moved by the fan blades increases greatly for just a small diameter increase. So use at least a 30mm and up to 50mm square is possible.

Note that fans vary considerably and the airflow of the cheap ones is almost useless

Get a high rpm fan say 5 to 6 volt and run at the 7.2 volt. Also the deeper they are the more effective the blades, so look for a 8 to 10mm deep case, which will also be stronger.

Expect to pay up to £15 for a real high performance fan.

The one I use is 50mm square, 10mm deep, weighs 20gm, 5volt. Airfow rated at 10.2 cu ft/min (or 17.34 cu m /min) Anyone want to work out the litres per sec? I think it is about 4.75.

Anyway that is a good airflow, and keeps my LRP 10.5 brushless from meltdown.

So suck or blow, you decide.

Nick

_________________
Sponsored By Demon Products , SMG Shell Art & My Pocket

Numb Nuts Tri Club 2007 /2008 Pro Stock Champion

.