SLOW SPEED GTs
Now that I’ve had a chance to look at high speed GTs, it’s time to slow speed down a bit and take another look. I chose to dial votage down to 7.00V target which is about 1055-1060 RPM per my crystalfontz. In addition, I wired in an RPM monitor so I could log RPM accurate and get a nice average RPM in the end.
Test 10 GT15s @ 7V (1060RPM) PUSH + PULL
Since I already had the bench set up for push/pull, I continued with that setup and simply dialed the fans down after removing the one shroud.
The lower fan speed while retaining the same heat load raised the delta as you would expect. Now running a 12.2C delta with push/pull, but also notice that the air efficiency has gone up. This all makes sense because the air velocity and flow rate is lower, the air itself has more time to heat up. This chart also includes the logged RPM of the fan using the second or right axis to show consistency there.
Test 10 GT15s @ 7V (1060RPM) PUSH
Push only loose a touch of RPM at 7V compared to push/pull, but still pretty close. Air Flow however drops a fair amount to about 29 CFM producing a delta in the 13s. Note that air efficiency has now gone up to 67% due to the lower air flow.
Test 10 GT15s @ 7V (1060RPM) PUSH + 25mm Fan Shroud
Wish I could say things change for shrouds with slower speeds, but…
I got about the same result as with shrouds. I just don’t thing GT’s gain much of anything with shrouds no matter what speed.
Test 11 GT15s @ 7V (1060RPM) PULL
Moving on to the pull condition, I wanted to see if things would change for the GTs when slowing speeds down to see if pull would do better than push.
And nope…push is still better than pull even down at 1000RPM by quite a bit actually.
One last shroud test in pull and I’m done with the GTs. At high speed the shroud helped a tiny bit in pull, we’ll see if we get something similar at slow speeds.
Test 11 GT15s @ 7V (1060RPM) PULL + 25mm Shroud
Just like the high speed test, the 25mm shroud helped a wee tiny bit in pull, but very very little and much less than just using the fan in push.
CONCLUSION SLOW SPEED GTs
Slow speed results painted the same picture as high speed. Very minor shroud gains in pull condition, but push alone is better than pull plus shroud. No gain at all with shroud in push condition and push plus pull doing the best over all.
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Hello Martin, great work, great site, congrats!
Did you get to test push-pull on a 120mm thick 38mm rad? Linus and Tim Logan assure us it does help to reduce temps.
No, it could but considering I got gains on the RS120 slim/low density and none at all on the mcr120qp slim/low density, I don’t think you can assume any generalities. Likely depends on the exact radiator brand/type and perhaps the fan type too as it could adjust restriction enough to shift the curve to a hump in the fan curve etc. Very specific results is what I found so I would shy away from assuming more.
Very thoroughly done, Martin. I’m really glad you’re back to testing! I’m new to watercooling and I remember reading your previous conclusions about fan shrouds as I searched the net- I was set on getting shrouds. I appreciate this update.
Doesn’t it make sense that you see better results using a shroud on the XSPC than on the MCR since the FPI is very low on the XSPC at “sub 8 fpi” vs 20 fpi for the MCR?
I would think that with the denser fin configuration; the further away you move the fan the harder it will be to penetrate the dense fin structure. Which would minimize befits obtained from decreasing the deadspot of the fans center.
But on the less dense radiator you can realize the benefits more-so from decreasing the deadpsot since the loss of penetration into the fin structure is lessened.
I would like to see how a 10mm shroud performs ? I guess is that you would have better performance.
Not sure. The XSPC rad was the RS model that I tested with which is pretty close in density to the MCRqp. Anyones best guess, too variable.
Oh, sorry. I was thinking the RX model which is “Sub 8fpi”
hi martin thanks for another gret review with real numbers and real thoughts behind this.
I have a question about push pull: you allways do the push pull tests with the sames fans and speed conditions, for both push and pull fan.
I have a loop with 3 noctua nf p12 pushing fans and i have scythe karma low noise fans but low rpm too (500 rpm) that i don’t use becasue they are not enough powerfull by themselves.
i was wondering if i add the scythe fans in pull with my noctua in push, do you think i should ahve some gain nor not at all or so ridiculous that it’s not worth installing it ???
and my radiator is a swiftech mcr320 QP as you showed that radiator is important also.
thanks
I would assume there is more of a sound benefit than a cooling benefit when it comes to a shroud.
as you dont have blades rushing within a few mm of radiator fins.
I have an idea but I don’t have the know age or equipment to test.
I was wondering what the delta would be in a push pull setup on a 240mm radiator using 4x 120 SP vs 2x 120 SP push fans and 2x 140 mm A pull fans.
Thank you
Not sure and no longer have the time to test either. Generally push plus pull or two pumps in series provides about a 30% flow gain. If you had an average 10c water to air delta, that would equal about 3C. Of coarse the delta is the bigger unknown. I have built high performance water systems than run no more than 2-3 degree deltas. I have also seen AIO kits push 20C. The gain is flow so degree gain is proportional to the unknown delta.
So no shroud will require less electricity to reach the same rpm as with shroud……interesting!
I’d love to see if this results in higher or lower air flow with/without shround given the same rpm.