Push Or Pull Muffin Fans (?)

[MEXICOWANDERER]

Lesson time for Mex.

Is there a difference? Some more suitable for case exhausting than others? Push air in? Pull air out? I take advantage of natural convection effect but if some fans are more efficient than others I wish to learn about them...

Thank you....

[JaxDad]

Parasitic losses in (in this case) air increase exponentially. They also decrease exponentially.

In a high velocity wind tunnel it makes a difference, in a little cooling fan, I think you’d be hard-pressed to measure the difference.

[MEXICOWANDERER]

"That's what I meant to say"

[pianotuna]

Hi Mex,

imo wrong choice.

https://www.quora.com/Why-is-sucking-air-through-a-wind-tunnel-more-efficient-than-blowing-air-throu...

MEXICOWANDERER wrote:


Have to step lightly around fan performance descriptors here...

I've decided!

It's going to, er...push...air

[westend]

I just wouldn't trust "her", Mex. I don't like those eyes...

I've always thought that pushing air into an enclosure works the best.

[MEXICOWANDERER]

Well shoot! It's made in Japan!

Have to step lightly around fan performance descriptors here...

I've decided!

It's going to, er...push...air

[Gdetrailer]

BFL13 wrote:

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.

Standard "RV" fans found in ceiling vents and range hoods are run of the mill low cost brush type motors which can be reversed via wiring. Easy to spot those since the motor sticks way out from the fan blades.

"Muffin" fans name comes from the flat axial motor design which computer fans use and the motor does not stick out of the fan case.

Many years ago, I used to have a handful of used original 120V Muffin fans from Mainframes, they really had the brand name of Muffin on them. Eventually sold them at a Hamfest. They worked great but too noisy for me.

The Muffin name is one of those things now days that a brand name is used to generically identify a type of design.

I changed out my RV vent fan with a nice 4" computer case fan, very quiet, uses much less energy and moves much more air.

I would also agree with a few of the comments, find larger fans which run at lower RPMS, something like 2800-3400 RPM can be rather quiet.. 4500-6000 RPMs fans are loud and will get real annoying real fast.

Most decent computer fans you can lookup the manufacturers model numbers and get the CFM, RPM, DB specs.

Some may even list static pressures it can operate in..

Static pressure IS what the OP is really needing since that determines how well the fan can push or pull air with restrictions.

HERE is a PDF from Sunon which has a lot of good info plus specs on their fans.

[landyacht318]

My compressor fridge came with a 120mm condenser, and a cheesy airflow 120mm fan attached to it, pulling air through the condenser, which looks like a car radiator.

This cheapo sleeve bearing airflow fan was louder than the compressor, and it drew 0.12 amps.

I removed this fan, and replaced it with a Noctua NF-F12 fan. 0.05 amps, and mounted it to push air into condenser instead, but a quick test revealed it did not like to bemounted in a pulling orientation, as it was loud and did not seem to move much air.

Pushing and installed in the cabinet enclosure designed for fridge, the Fan could no longer be heard.

Compressor duty cycle was reduced also, from ~5:30 on to ~4:45 on, a reduction in compresor run time of about 45 seconds each time it cycled on, which is a significant improvement.



5 years after tis modification to the compressor fridge's ventilation, the NF-F12 got relocated to exhaust the fridge and electrical cabinets together, running 24/7, and the new Noctua A12x15 installed on condenser, effectively a push pull scenario. I did not time duty cycles after this change, but the fridge peformance has always been impressive.

My one 92MM Delta fan used as an interior directional air circulation fan has a filter on it, but instead of one layer of material close to the fan, I made a filter sock extending 6 inches behind the fan with 4 inch deck screws keeping it from getting sucked inward into impeller. When filter gets loaded it can suck the sides of the filter inward, but airflow does not seem to be impacted all that much.

Noctua's latst fan, the A12x25 is designed for both good static pressure rating and good airflow. The tips of fan blade are 0.5MM from the case. I eagerly await the arrival of the 3000 rpm industrial model, which I have no idea if it is actually in the works.

If I were seeking to cool a hard working powersupply and noise and amp draw was not a factor, A Delta 120MM fan 252 cfm fan on the lid pushing in would be the call.

I consider my RSP-500-15 to be working pretty hard, and Noise is a primary consideration. I added a Noctua 60Mm fan pushing in, and a Noctua 80Mm fan sucking out, in addition to the very high rpm 40MM provided fan suckin out.

I have a thermistor on an internal heatsink.

I tried reversing the flow of the 60 and 80Mm fans, and then both pushing and then both pulling. The one internal heatsink read coolest with the 60mm pushing and the 80mm pulling, but the heatsink was also directly under the 60mm pusher.

The loud 40Mm meanwell fan only comes on aver 32 amps output, and the 80Mm exhaust puller fan next to it seems to have its airflow reduced by 2/3 when it does come on.

My run times above 32 amps are limited. Without the Noctua fans added to case lid, the 40Mm fan would cycle on and off at just 6 amps of load, and was loud enough to be intolerable.

I could likely improve results further, but see no need as there is little doubt the power supply runs much cooler than required to remain happy, and I have also vastly increased the heatsinking on the casing opposite the transistors. These certainly get warm at max output, and I 'could' attach 60MM fans to them. But max output rarely lasts more than 30 minutes and the internal heatsink's thermocouple has yet to exceed 125f.

Any test results of a push pull sceanrio on a power supply will depend on the fans themselves, and where they are located. If I were to only add one fan to a powersupply, it would be a static pressure fan pushing in on the opposite side of the internal fans that suck out, and I would not go batcrap crazy with the rpms of chosen fan.

Its great to have a powerful high rpm fan, provided one can throttle it back when max airflow/pressure is not required.

Throttling can be done with a pwm on the power leads, or on the blue wire of a 4 wire PWM fan, or by voltage on the power leads.

I've used all three methods and the 4 wire PWM fan with the blue wire fed a pwm signal is my favorite method, using Noctua industrial fans and their speed controller.

But the high rpm Delta fans are powerful monsters and it is occassionally good to let Godzilla loose, but instead of shootng fire he shoots ice which likely makes 'him' a 'her'.

[MrWizard]

I've worked on lots of cnc machinery control cabinets
Blowing in is better than sucking out

The cabinets usually had both types fans
the bottom, with high static pressure blowing in,
and fans at the top of the cabinet door or sides sucking out, and filters on the bottom input fans of any machine not in a clean room environment

[pianotuna]

Mex,

Sucking works better.

[ctilsie242]

One thing I like adding if possible on the intake side is some type of filter, provided one remembers to change/clean it every so often. This also does a good job at ensuring bugs don't get sucked in.

[Chris_Bryant]

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

[Gjac]

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.

[RayJayco]

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

[landyacht318]

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&...

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.