Mismatched fans for push/pull?

[GearingMass]

Can you mismatch fans models on a radiator in push/pull or will that screw up the air flow?
I've got a Corsair H90 and I was thinking about attaching the 140mm case fan from the Haf 932 onto the radiator in addition to the Corsair fan that came with the H90 in push/pull config. Is this a big no-no or is it acceptable practice?

 

[Johan45]

It'll work, maybe not ideal. I would put the stronger one in the push position

 

[GearingMass]

I would put the stronger one in the push position

Good advice.
Would it be better to just stick to the included one, or would there be some benefit to adding the mismatched one (even if not ideal)?

 

[EarthDog]

Better to stick to one fan performance wise? Clearly no. More fans = more air flow = better cooling on the radiator. If you actually meant to use the other fan instead of the included one, that would depend on its performance characteristics.. Does it have more airflow? Static pressure? What about its noise levels?

Does your current setup not work as well as you feel it should? Are you looking for every degree C possible?

 

[GearingMass]

Does your current setup not work as well as you feel it should? Are you looking for every degree C possible?

It's the initial build, so I've yet to see the thermals, but I suspect it will be just fine either way.
Am I trying to squeeze every last drop out? No, but I've got the extra 140mm, so if it's acceptable, why not add it. I'll just need to find some longer screws at the hardware store.

If you actually meant to use the other fan instead of the included one

I meant whether or not to use the extra case fan in addition to the included one.

 

[EarthDog]

I covered both scenarios and figured that out from your recent reply.... all good.

 

[GearingMass]

I appreciate the input

 

[Daddyjaxx]

Would it not be feasible that eventually, the stronger fans could cause the weaker ones to burn out?

 

[EarthDog]

If the mismatch was big enough and the RPM/pull of the other fan spins it past what its rated for.. Don't crank both at the same time with huge imbalance in speeds.

 

[GearingMass]

Would it not be feasible that eventually, the stronger fans could cause the weaker ones to burn out?

I would be inclined to agree. The included H90 fan is 94cfm @1500rpm, and the case fan i'm referring to is 60cfm @1200rpm.
If the weaker fan (in pull) is not able to move as much air as the stronger fan (in push), couldn't the weaker fan act as a blockage to airflow through the radiator?

 

[Robert17]

Actually the stronger fan, A, pushing the weaker fan, B, would result in some energy dissipation from A to B and increase the rotational velocity of B as well. It may have the added effect of reducing the wattage draw for B as it's PWM controller adjusts to compensate for the fans RPM reading.

 

[GearingMass]

Well now that's very interesting.

 

[bob4933]

Ignoring darcys law, bernoulis principle, and losses and only applying affinity laws>

Fan A will slow down, fan B will speed up to meet at equilibrium. More amps on fan A, less on fan B. They would meet around 1 1350 rpm each.

Fan A would be working harder, so would like die "sooner". What is sooner? No idea. Fan B is spinning faster than its design so the bearing can go bad sooner. Again, no idea on a time frame


Basically, two fan A will net the best cooling.

Fan A + fan B will be the next best, but with reduced life span

fan B alone would be the lowest, but if it's working properly.
. ?

Up to you really. Obviously all of this is best case scenario. You have friction, tip leakage, escape losses... etc that will reduce these ideas, but not significantly so.

 

[bob4933]

Actually the stronger fan, A, pushing the weaker fan, B, would result in some energy dissipation from A to B and increase the rotational velocity of B as well. It may have the added effect of reducing the wattage draw for B as it's PWM controller adjusts to compensate for the fans RPM reading.

Newtons third law still applies... reduced workload on B is simply transfered to A.

 

[GearingMass]

Hmm. I'll most likely stick with the included fan, but we'll see what the temps are like.

 

[Robert17]

Newtons third law still applies... reduced workload on B is simply transfered to A.

Actually, no. The workload on A remains the same as there is nothing telling it to do anything differently. The work load hasn't been increased, just transferred partially to B as the remaining force, after passing through the rad, is partially dissipated into the case either peripherally or by missing the B fan blades; the remaining force is imparted unto the blades. If anything, the air may pick up energy from the rad's fins from the hotter fluids, transferring partially unto fan B's blades and housing, the rest being carried out of the case more directly.

 

[Shell]

Fans in series are extremely inefficient, if you need pressure... blowers are the only option.

With mismatched fans, you want the powerful one pushing in as it has the presure to fight the resistance from the fins, and the weaker pulling, so the weaker isn't pulling vacuum as much... I think.

Essentially you'll get as much flow as if the weaker one has nearly no obstruction.

 

[bob4933]

Actually, no. The workload on A remains the same as there is nothing telling it to do anything differently. The work load hasn't been increased, just transferred partially to B as the remaining force, after passing through the rad, is partially dissipated into the case either peripherally or by missing the B fan blades; the remaining force is imparted unto the blades. If anything, the air may pick up energy from the rad's fins from the hotter fluids, transferring partially unto fan B's blades and housing, the rest being carried out of the case more directly.

Do me a favor. Go plug your vacuum cleaner in and block the suction (resistance) and hold it there. Keep holding it. Nothings telling it to work harder. What happens to your vacuum? Keep it up a little more. When the bang happens, you will understand my point. (Dramatic example... but a poignant one)

Workload on A will rise to meet changes in resistance. A fan blowing on its own will have lower amperage then a fan blowing through a radiator or into another fan moving slower. Fan A and B will meet at some point in the middle, most likely a little less then the middle. B will have more force pushing it, reducing its amperage, A will work harder, raising its amperage.

If you'd like, we can go into tip leakage, cavitation due to differential pressures, and you can explain why bernoulli's law is somehow not applicable any more (venturi effect from the differential pressures between the fans) into more detail?

As far as the turbine effect you're describing would be so microcosmically small, it would have almost no effect beyond friction losses.


edit: there is no such thing as a free lunch -.-

 

[RnRollie]

where it all boils down to is this:
IF fan A is the more powerfull/faster "push" fan
AND
IF fan B is the weaker/slower "pull" fan
THEN
as long as max speed of fan B is more as the half of max speed of fan A, then you're ok

Assuming they both have more or less the same curves, where the only major difference is the max speed.
Otherwise the fan wiht the higher static pressure has to do the pushing.


thus:
fan A MAX RPM 2000 & fan B MAX RPM 1200 = OK
fan A MAX RPM 2000 & fan B MAX RPM 800 = NOT OK

keeping them closer together is better of course... if the difference is big enough fan B might turn into a dynamo.. probably not good for the fan or the fanheader/circuit of the MB

There are of course A LOT more things at play; for example:
What if fan A is a 25mm thick 3--blade with low SP while fan B a 38mm 7-blade?
What if fans are closely matched, but fan A turns clockwise, while fan B turns anticlockwise (a papst & a delta ), etc, etc , etc

You can get submerged & overwhelmed on the subject for days, weeks, months on end


Also consider this baby, it are actually TWO fans:
https://db.sanyodenki.co.jp/product_db_e/coolingfan/dcfan/dc_fan_detail.php?master_id=2606
bolt THAT one to a radiator

or this one
https://db.sanyodenki.co.jp/product_db_e/coolingfan/dcfan/dc_fan_detail.php?master_id=3113
bolt it to your case, and its the only case fan you'll ever need




.

 

[GTXJackBauer]

Most higher end Corsair AIO cooler models come with their premium fans. Just have the fans that came with the unit and should be good to go.