Shouldn't fans be distant from radiators?

Q

Quartz-1

Supreme [H]ardness
Joined
May 20, 2011
Messages
4,257
In all the pictures [H]ers have posted, fans are mounted on the radiator itself. This puzzles me: doesn't this create a huge dead spot in the radiator, the size of the fan's spindle? So therefore shouldn't fans be mounted away from the radiator to maximise the cooling?

For instance, if you have a Corsair H80 and a case with three fan mountings - top at back, rear CPU, and front bottom. instead of mounting the radiator and fan on the rear CPU blowing in or out, wouldn't it make more sense to close off the rear CPU mounting and mount the radiator in the top one and the fan at the front bottom blowing in? Or mount the radiator at the top and the fan at the rear CPU and create a duct to the top fan? Sure you're getting the same volume of air, but you're increasing the cooling area of the radiator.
 
The air would be a bit more evenly spread, but the airflow would greatly diminish.

Imagine placing a fan, stand one foot in front of it -> you can barely feel any air blowing, though close up you feel a lot of airflow.

So basically the airflow diminishes greatly with distance, which is why you want your fans to be as close as possible to the radiator.
 
You are correct. The best option is to mount a shroud onto the radiator and the fans onto it. Just make sure the shroud is air tight.
 
You would have pressure drop over the length of ducting as well. You could extend it to the point where there's not enough pressure to push air through the radiator. The distances you're talking about are small, but there would still be an effect.
 
Redleader said:
You are correct. The best option is to mount a shroud onto the radiator and the fans onto it. Just make sure the shroud is air tight.
Click to expand...

Depends on the fans. Some like AP15s do not benefit from shrouds.
 
Skripka said:
With fans like AP15s, simple push yields better results than any shrouded fan configuration even shrouded push/pull.


http://martinsliquidlab.org/2012/01/15/radiator-shroud-testing-v2/3/
Click to expand...

It's radiator dependent, that's what his findings were.

Low fin density radiators will not benefit from a shroud, while higher fin density radiators will.

It actually makes sense for push to be better. The airflow of the intake of a fan is pretty much laminar, while the exhaust is fairly turbulent.

For heat transfer, you want highly turbulent air flow.
 
Last edited:
Quartz-1 said:
In all the pictures [H]ers have posted, fans are mounted on the radiator itself. This puzzles me: doesn't this create a huge dead spot in the radiator, the size of the fan's spindle? So therefore shouldn't fans be mounted away from the radiator to maximise the cooling?

For instance, if you have a Corsair H80 and a case with three fan mountings - top at back, rear CPU, and front bottom. instead of mounting the radiator and fan on the rear CPU blowing in or out, wouldn't it make more sense to close off the rear CPU mounting and mount the radiator in the top one and the fan at the front bottom blowing in? Or mount the radiator at the top and the fan at the rear CPU and create a duct to the top fan? Sure you're getting the same volume of air, but you're increasing the cooling area of the radiator.
Click to expand...

Everybody is more or less in agreement with you about the dead spot (though some fan makers attempt to address this issue). As has been mentioned there are shrouds that can help by spacing and then concentrating airflow. However, the farther the fan is from the radiator the less force the air has to push through, which is worsened with high fins per inch coolers.

Moreover, there is the issue of space. Think how many cases barely have room for a 30-40mm rad with push+pull fans, let alone a 60 or 80mm rad. Adding an extra 10-25mm per side of a radiator with a shroud is just not going to be feasible for many users. In most situations a thicker rad of the same design is going to provide better cooling potential even with lost air out the sides and a dead spot then a thinner rad with shrouds.
 
Teenyman45 said:
However, the farther the fan is from the radiator the less force the air has to push through, which is worsened with high fins per inch coolers.
Click to expand...

Is this really an issue? If you put the radiator at thetop, air will naturally rise through it - hot air rises, after all. So the job of the fans becomes to supply fresh air to replace the rising air, creating a little positive air pressure, right? Have any tests been done?
 
You need way more flow than natural convection can provide. That's what the fans are for. If you wanted to, you could run a top-mounted radiator as an intake and although the natural convection is in the opposite direction, as long as you have adequate exhaust from the case, the effect is negligible.
 
Quartz-1 said:
Is this really an issue? If you put the radiator at thetop, air will naturally rise through it - hot air rises, after all. So the job of the fans becomes to supply fresh air to replace the rising air, creating a little positive air pressure, right? Have any tests been done?
Click to expand...

Hot air may rise, but you're talking about a very small environment (small change in height and thus negligible pressure difference) with air forcefully being pushed around.

Natural convection in a computer case is almost non existent.
 
You must log in or register to reply here.
Back
Top