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I want to remake my gpu's cooler cause the original fans have a terrible bearing sound on low rpm and no amount of software solution helped.

Anyway, I want to use 3x nf-a9x14 pwm 92mm fans as its fits the heat sink the best. But, as I have researched cooling designs, there are 2 ideas and not sure which one to refine:

all models are in scale, I've measured the gpu.

  1. use as little material as possible, so most of the heat sink is exposed. I need to make an 8mm tall "funnel" under the fans since there are various metal bits and pieces sticking out of it. (and i really don't want to file them down).

the design: https://i.imgur.com/FeV3tuX.png https://i.imgur.com/g4mDfPQ.png

The main issue here, what is not covered by the "funnel" wont get any active airflow, however, most cpu coolers basically follow this design (Tho fans are more closely attached), any thoughts?

  1. Re create the original shroud more or less, and hang the fans 8mm above the heat sink. This basically what the original design does, (original fans are also 6mm above the heat sink) but I'm not sure if i lose some efficiency by not directing the air from the fans. However, it also allows the air to reach the heat sink more evenly, but more covered as well.

the design: https://i.imgur.com/4BKfEdv.png https://i.imgur.com/agLY0Ax.png

Do i need to worry about smoothing out the underside of the shroud? does the 8mm gap going to cause any issues? Am i over thinking this? Is there any obvious issue I'm overlooking?

I've tried to take inspiration from asus noctua gpu which really seems just strapped 2 fans right against the heatsink. While noctua's own cooler using the same fan also right on top of the heatsink: https://caseking.hu/uploads/images/products/NHL/NHL9I.jpg However most gpu coolers have a bit of gap, and so are some water cooler radiators too.

Nah
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Yes, you are over thinking it. Either of those designs would work well. The distance of the fan to the heat sink is not critical, just as long as the all the air is directed through it which both designs appear to do. You may gain a tiny amount (ball park estimate of 5% to 10%) of cooling with your version 2 that spreads the air over the whole heat sink.

Other things you should consider:

  1. While your version 2 might be more efficient, version 1 is more reliable. If one fan were to under-perform or fail it would suffer much higher penalties than the same setup with individual ducts. Maybe not an issue if the software will throttle the chip and report the issue before damage.
  2. What does the other side of the heat sink look like. Is there sufficient space for the air leaving the heat sink to leave that area without a large pressure drop.
  3. Heat sink design is pretty involved when you are optimizing. Fin thickness affects the rate heat is conducted, spacing between affects pressure drop and consequently flow based on your fan curve, flow velocity affects your Reynolds number and consequently the boundary layer thickness and transfer of that heat to the air, and many more dependent variables. What I'm saying is, go overkill on airflow and heat sink size and don't feel bad if you come up short of a professional solution.
ericnutsch
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If aesthetics aren't an issue, GPU cooling can be best accomplished thru cool flow from the beginning. Keep GPU and CPU as far away as possible. Otherwise fans doing nothing and sharing thermal heat.

Another strategy better cooling you may consider and this is kinda ghetto or low brow. Is feed colder air into the system before the fans blow anything. Is to get a miniature air condition system and a funnel tube to siphon the cold air directly to the computer. Lowering surrounding ambient temperature of air, eases flow rate. More so, have a similar tube for the air exhaust to be disposed enter image description here

LazyReader
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