On Thu, 25 Oct 2018 21:09:51 +0100, Rod Speed wrote:



"Gym Sulkinson Fork" wrote in message
news
On Thu, 25 Oct 2018 17:31:23 +0100, Rod Speed
wrote:



"Gym Sulkinson Fork" wrote in message
news On Thu, 25 Oct 2018 17:09:56 +0100, Rod Speed
wrote:



"Gym Sulkinson Fork" wrote in message
news On Thu, 25 Oct 2018 16:25:20 +0100, Rod Speed

wrote:

Gym Sulkinson Fork wrote

Why are these fitted instead of just a stationary vent like you see
on
caravans?

They act like a pump.

http://www.flettner.co.uk/van-roof-vents/

I don't see the point in using the wind to power a vent, when the
air
was
already moving.

It isnt from the place you want to move it from.

Surely that's like fitting a generator to your bicycle to power a
motor
to
make you go faster?

Nope, more like using a wind generator to generate
electricity and using the electricity to drive a fan, but
without the losses involved with the electricity
generation and the electrical fan.

But the point is to move air into or out of (shouldn't matter which,
air
still goes through the van) where the vent is.

It does actually, particularly when getting it to
remove the hot air in the roof space in summer.

but if you let the wind blow it in, then it goes out where it's
currently
coming in.

Yes, but is going against the natural flow of the hot air
coming out of the roofspace, so doesn't work as well.

Think of electrically powered exhaust fans.

The work much getter moving the air out of the roofspace
than moving outside air into the the roofspace.

Makes no difference how that fan is powered,
still works better to move the hot air in the
roofspace in the way it wants to go by convection.

I tend to do that when designing desktop computers,

I only bother with the cpu fan, but don't run mine with covers on.

It has been said (but I've never tested it) that you get better cooling of at least some of the components with the cover on. Hard disks for example I can believe it with. Or indeed anything that doesn't have its own fan.

but mainly because of where the hot chips are and what needs the most
cooling. I have intake fans front bottom cooling the disks,

I don't bother cooling mine but I use the lower speed ones
that only get warm to the touch when the room is over 30C
before I turn the air cooler on.

Never buy the high speed WD drives. I once had a 6 disk array of 1TB WD Caviar blacks. They did have some cooling, although not a fan blowing directly onto them, and every single one failed over 2 years. Must have cost WD a fortune. They were uncomfortable to touch for more than a few seconds.

then across the graphics card,

I'm not into gaming so mine don't even have a fan.

I also use graphics cards for scientific research and bitcoin mining (used to for that last one - it's not profitable).

The only game I ever play is Freecell Pro and it isnt
exactly demanding of the video card.

You're odd.

then over the CPU then out the top back and/or top.