Push Or Pull Muffin Fans (?)

I've always been an exhaust proponent, but landyaght's post makes sense.

A "fan in the can" moves more laminar flow air than just a fan by itself. The closer the fan blades are to the ID of the can the more efficient it will be. Cooling fans for avionic equipment on Air Craft use these types of fans as well as exhaust fans to remove gas fumes on boats in the bilge. Tail rotors on some of the newer helicopters use this also because it is more efficient than just a rotor blades by itself.

With computer fans, the smaller they are, the more noise they make in order to move air. Larger is typically better as they move more air at less rpms meaning much quieter.

I don't know your situation, however I have used adapters successfully in some situations to increase flow while decreasing noise, albeit only as a last resort.

This is an example of 80mm or 92mm to 120mm:
Fan adapter


With that said there is basically 2 types of computer fans, air flow and static pressure, with static pressure fans used when you are blowing through a radiator/heat sink (or even a screen or filter as dust is enemy to all things electronic) and an air flow fan when there is minimal obstruction. Static pressure fans have a more focused flow.

In the reviews that I have read, the static pressure fans blowing through a radiator or heat sink, were typically 1-2 degrees cooler.


As far as which is better, positive or negative air pressure, usually positive air pressure is better. (Positive pressure is more intake than exhaust).
I found a link that can explain why better than I can as I don't like typing:
Positive or Negative air pressure

I agree with Landy, that it is better to push air through obstructions than pulling. However with screens or filters, you really don't have much choice.
Again, filtering out dust is very important unless you plan on cleaning the inside often as dust is an insulator, thus lowering the cooling effects.

I typically design computers with positive air pressure. YMMV

My experience with many different computer fans says if there is to be resistance to airflow, better that resistance be in front of the fan, rather than behind it.

The blades trying to scavenge air through resistance makes them much less effective, and louder.

High static pressure rating is achieved most effectively, by increased rpm.

Since you enjoy Dual ball bearing fans, Delta makes some top quality fans some of which can turn at obscene rpms.

I have a delta PFB0912uhe, a 92 MM fan, on a voltage bucker which shaves a volt off the top. Still so powerful that loss is of no concern, and i can reduce fan speed to silent via a 10K ohm remote pot.

They have very powerful 80Mm fans too.

http://www.delta.com.tw/product/cp/dcfans/download/pdf/PFB/PFB80x80x38mm.pdf

138CFM and 51MM H20 and 9000 rpm 65DB

https://www.amazon.com/Delta-23-8038-01-Ball-Bearing-Cooling/dp/B009I0CG64/ref=sr_1_2?s=electronics&ie=UTF8&qid=1527039721&sr=1-2&keywords=PFB0812DHE

That Somnabeech is a air moving machine.

The blades in front of the impeller concentrate the airflow.

My 92MM fan column of air spreads only to 10 inches diameter at 3 feet.

Gdetrailer wrote:

BFL13 wrote:
It depends on the location of the vents. If there is a lower "in" and a higher "out" then you pull in at the bottom and push out at the top. If the unit is horizontal with a vent at each end, you have a choice which is push and which is pull as long as they aren't the
same :)

OK if the question is for horizontal and you have one fan for one end, do you suck or blow? Then I am not sure. My converters are like that, but I need to check what they do.

The ones I have worked with are easy to mount the other way around, but reversing the wires as mentioned earlier is also a way.

Hmm.. COMPUTER CASE TYPE DC "muffin" fans are not "reversible" via the wiring. Do so at your own risk :E

Computer case type muffin fans are BRUSHLESS MOTORS AND ARE ELECTRONICALLY DRIVEN. The drivers are not designed to have the polarity reversed and will go up in smoke.

Now if you are talking BRUSH type DC motors, then yes you can reverse by changing polarity.. However brush type DC motors are much less efficient and put out tons of RFI noise from brush arcs.

OK thanks for the correction. I mounted mine the other way around and left the wiring as is. I got the reverse wiring idea from up-thread (wrong!) I know my RV ceiling vent fans run backwards it you swap the wires--in fact one is supposed to push or pull--you can choose by its switch.

I think the cheaper fans that only list CFM work best a 'pull' air thru the device

for a good 'push' the air in fan, the fans with specs of high static pressure work best

when working with pairs one in and one out
matched pairs work well

this is all 'observation' experience
from years of working on machinery control cabinets

Specifically I am trying to determine Delta T pressure inside and outside the chamber. The higher the differential the better (obviously). The chamber is 1-1/2' x 1-1/4' x 2-1/2' tall. The emitting thermal element will be mounted on the deck inside. I am considering an 80 mm circulating fan. The emitter has an integral fan.

I used push-pull fans on the Hyperwatt power supply and even the toroids remained very near to ambient exterior at 56 amperes continuous. A highly modified Megawatt.

The current exercise is on a 130 ampere Meanwell RSP-1500-15

BFL13 wrote:
It depends on the location of the vents. If there is a lower "in" and a higher "out" then you pull in at the bottom and push out at the top. If the unit is horizontal with a vent at each end, you have a choice which is push and which is pull as long as they aren't the
same :)

OK if the question is for horizontal and you have one fan for one end, do you suck or blow? Then I am not sure. My converters are like that, but I need to check what they do.

The ones I have worked with are easy to mount the other way around, but reversing the wires as mentioned earlier is also a way.

Hmm.. COMPUTER CASE TYPE DC "muffin" fans are not "reversible" via the wiring. Do so at your own risk :E

Computer case type muffin fans are BRUSHLESS MOTORS AND ARE ELECTRONICALLY DRIVEN. The drivers are not designed to have the polarity reversed and will go up in smoke.

Now if you are talking BRUSH type DC motors, then yes you can reverse by changing polarity.. However brush type DC motors are much less efficient and put out tons of RFI noise from brush arcs.

It depends on the location of the vents. If there is a lower "in" and a higher "out" then you pull in at the bottom and push out at the top. If the unit is horizontal with a vent at each end, you have a choice which is push and which is pull as long as they aren't the
same :)

OK if the question is for horizontal and you have one fan for one end, do you suck or blow? Then I am not sure. My converters are like that, but I need to check what they do.

The ones I have worked with are easy to mount the other way around, but reversing the wires as mentioned earlier is also a way.

I've been ventilating the crawl space under our house with a solar panel driving 4 muffin fans - 2 pushing and 2 pulling - for 5 years now. They are cheap little workhorses.

Dave