Push Or Pull Muffin Fans (?)

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.

"That's what I meant to say"

Hi Mex,

imo wrong choice.

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

MEXICOWANDERER wrote:


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

I've decided!

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

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.

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

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.

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'.

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

Mex,

Sucking works better.

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.