The original fan blew air away from the card but the new fan
seems to be sucking air towards the card. Is this normal?
It depends on several factors.
Width & design of the card/GPU/heatsink/fan assembly...
o Blowing air away from the heatsink may generate lower temps
---- because the airflow is not immediately recirculated
o Pulling air into the heatsink may generate lower temps
---- because the airflow path is beneficial for such
---- re location of intake & exhaust matters (and varies)
Noise of resulting heatsink/fan assembly...
o A heatsink presents a particular resistance to airflow
---- resistance rises to the square of airflow velocity
o Intake side of a fan is most susceptible to resistance
---- having the fan exhaust side near the heatsink can be quieter
o Impingement heatsinks often perform best "air blowing in"
Cost can be saved by blowing air onto a heatsink...
o Fans that intake air over a heatsink suck in heated air
---- air seen by the fan is not at case-ambient
---- air seen by the fan is instead at higher heatsink temps
o Fans that exhaust air over a heatsink suck in cooler air
---- air is drawn from the case which is at case ambient
---- case ambient is above room ambient but below heatsink temp
o Cooler air reduces the temperature of fan bearings
---- so allows cheaper fan bearings (fans) to be fitted
---- however case ambient is still around 38-40oC
Radial fans may be used on some graphics cards as they create a
different visual effect and are usually specified to overcome the
resistance of the heatsink at lowest cost. Unfortunately radial fans
have a turbulent airflow path around 70% of the fan circumference
which results in a noise akin to a vacuum cleaner. This is known as
value added sound effects, useful in games involving vacuum cleaners.
What matters is the GPU is kept within specs, and general case
ambient temps are also kept within specs - because HD, CPU-Cooler,
GPU and indeed PSU itself must be cooled by case ambient air temps.
As a rule try to get a case-ambient of <38oC, ideally around 32oC.
The most important temperature is that of your HD - since HDs are
electromechanical devices & temp is a major factor in their lifespan.
Specifically HD physics-of-failure invariably involves the word "heat".
You can design a system to use either direction of airflow.
o Usually intake of a fan in free air vs against a heatsink = lower noise
---- exceptions can occur due to particular design
o In the past it didn't matter so much as low Wattage = low CFM
---- high end cards have GPUs with high idle wattage, let alone peak
Sucking air at a card does allow longer fan life, use of cheaper fans,
or simply better cooling - although that can depend on the chassis.
Better cooling in free air can be inferior cooling when fitted.
Most OEM graphics cards fans are pretty grotty, so going backwards
on that step would be an accomplishment - probably often achieved.
Around 55% of all IT failures are due to heat, distorted by the HD
vulnerability - so if you can keep case ambient temps low, that's fine.
If the heatsink is a finely spaced affair (skived copper) then cleaning
it occasionally may help reduce temps. Many designs suffer 2 probs
o Open area under the fan to improve airflow (when heatsink is clean)
---- but in skived-copper heatsinks gaps form a matrix for dust buildup
o Air velocities are insufficient to clean skived copper heatsink gaps
---- once dust matting begins it forms a matrix for further dust buildup
---- dust soon spans the gap providing a basis for further buildup
---- since gap c/sectional area is low it greatly reduces heatsink
efficiency
Laptops with skived copper heatsinks are most vulnerables to dust matting,
fans will run faster then more often in as little as 6 months in carpetted
areas.
GPU & some CPU designs can suffer it. Dust per se is not a problem, but
dust that mats sufficiently to obstruction airflow at air entry is a
problem.
Desktop OEM heatsinks often use wider spaced fins to avoid this problem.
Filters are not a solution - clean filter resistance is often greater than
the
maximum static pressure of an axial fan which is created at zero cfm. The
solution is to simply dust-out the PC with a (clean
paintbrush.
