100% this, the ultimate performance of a cooling solution is how fast you can move heat into the working fluid and how fast the radiator can move it out of the working fluid.
AIOs confer no particularly special advantage in either. The fact that the working fluid is water means nothing, heatpipes actually use water internally too. The difference is that heatpipes are actually evaporating the water so they can actually more more heat energy (due to enthalpy of evaporation) than AIOs.
AIOs actually tend to be louder for a given amount of cooling due to cheaper, louder fans and crappy noisy pumps. Custom loops don't really suffer that but they also cost 10x as much. They mitigate a lot of the downsides like pump noise by throwing expensive, high quality components at it. That's fine as far as it goes, but AIOs themselves are not an automatic win.
A large air cooler (eg Noctua NH-D15) is going to perform very similarly to a 240/280mm with identical fans (Noctua) at the same RPMs/noise levels. The difference is that most AIOs ship with very cheap fans that are just designed to spin fast and be loud, but that cools quite effectively. You can punch up the fans on a big air cooler and push a lot more heat through them. They just are optimized for silent performance out of the box.
Furthermore, most situations are currently limited by the IHS. AMD once pushed 500W through a 120mm radiator on their 295x2 card (OC'd), and temps would stay under 60C while doing it. The radiator size is not as big an impact as most people expect, moving heat out of the loop is not the bottleneck, it's how fast you can move heat into the loop that matters. GPUs do that very efficiently (bare die, dual chip on the 295x2). 5 GHz 14nm chips push an incredible amount of wattage, 7nm chips are so tiny that they result in very high thermal density, making both of them fairly prone to IHS thermal limitations. Colloquially: the heat just can't move out of the die into the IHS fast enough. The surface of the IHS is actually fairly cool, the liquid inside an AIO is barely above room temperature, but the heat just is not moving into the loop very well.
There is a resulting thing where people splurge on high-end gear, say a 280mm, and see high temps and tell themselves "wow, good thing I bought a 280mm, a 120mm would have been way hotter!". And no, not really, the amount of radiator fins isn't the limitation, it's how fast you can move heat into the loop. If you put a probe inside the reservoir to actually see the temperature of the fluid, it would barely be different between a 120mm and a 280mm.
And in fact the temperatures would probably be barely different than if you bought a NH-D15, or a Scythe Fuma, or other large multi-tower cooler. At the end of the day the working fluid doesn't matter, it's all fins and airflow.
I always thought the value of an AIO was in packaging. Sure, I can buy a huge case that has vast amounts of open space and configurable venting. Or I can jam everything into a smaller case, install an AIO, and ensure I’ve got reasonable airflow for the heat exchanger.
Yeah that's generally the main benefit. AIOs let you build in smaller cases without too much hassle. (Although when you go down to really tiny small form factor cases often you have to use super low profile air coolers again because there's no room for the AIO radiator)
> the ultimate performance of a cooling solution is how fast you can move heat into the working fluid and how fast the radiator can move it out of the working fluid.
Really, it’s all to do with how fast the heat can be permanently ejected from the system, almost always as heated air.
Analogised to a storage array, metal heat sinks and water reservoirs are a high performance write cache. Brilliant for bursty loads but once the cache is filled they don’t improve sustained performance.
There was a Linus Tech Tips video where they water cooled via just running water from a tap through the system and then dumping it back in the sink - no radiator or fans involved. The performance was of course fantastic, but the amount of water you use running a tap constantly is pretty astronomical so it's not actually practical.
The other problem is the mineral fallout in the water. A month or so later they had destroyed their waterblocks.
What you really want is a closed-loop heat exchanger, where the components only touch distilled water, and it gets pumped to a bathtub somewhere with a heat exchanger that pushes the heat out.
> how fast you can move heat into the working fluid and how fast the radiator can move it out of the working fluid.
Nitpick: "working fluid" here implies that cooling has to involve a liquid. But there are solid-state (e.g. peltier) CPU coolers, which of course have no "working fluid." They suck, but they exist!
(I think the suckiness of the existing peltier CPU coolers might be due to their small size, though. If you gave one of them as much solid-state thermal mass to work with as a water-cooling setup has fluid thermal mass, it might be rather efficient, for the same reason a chest freezer is efficient.)
In principle, yeah, but peltiers (a) suck at moving non-trivial amounts of heat, and (b) add a huge amount of heat of their own. Like, ballpark 10x the amount of heat you're moving.
You could move like 5W and you might have to dissipate 50W of heat total. Peltiers can't realistically move 100W and you don't want to cool 1000W.
Helpfully, Linus Tech Tips has walked through this particular experiment for you already ;)
AIOs confer no particularly special advantage in either. The fact that the working fluid is water means nothing, heatpipes actually use water internally too. The difference is that heatpipes are actually evaporating the water so they can actually more more heat energy (due to enthalpy of evaporation) than AIOs.
AIOs actually tend to be louder for a given amount of cooling due to cheaper, louder fans and crappy noisy pumps. Custom loops don't really suffer that but they also cost 10x as much. They mitigate a lot of the downsides like pump noise by throwing expensive, high quality components at it. That's fine as far as it goes, but AIOs themselves are not an automatic win.
A large air cooler (eg Noctua NH-D15) is going to perform very similarly to a 240/280mm with identical fans (Noctua) at the same RPMs/noise levels. The difference is that most AIOs ship with very cheap fans that are just designed to spin fast and be loud, but that cools quite effectively. You can punch up the fans on a big air cooler and push a lot more heat through them. They just are optimized for silent performance out of the box.
Furthermore, most situations are currently limited by the IHS. AMD once pushed 500W through a 120mm radiator on their 295x2 card (OC'd), and temps would stay under 60C while doing it. The radiator size is not as big an impact as most people expect, moving heat out of the loop is not the bottleneck, it's how fast you can move heat into the loop that matters. GPUs do that very efficiently (bare die, dual chip on the 295x2). 5 GHz 14nm chips push an incredible amount of wattage, 7nm chips are so tiny that they result in very high thermal density, making both of them fairly prone to IHS thermal limitations. Colloquially: the heat just can't move out of the die into the IHS fast enough. The surface of the IHS is actually fairly cool, the liquid inside an AIO is barely above room temperature, but the heat just is not moving into the loop very well.
There is a resulting thing where people splurge on high-end gear, say a 280mm, and see high temps and tell themselves "wow, good thing I bought a 280mm, a 120mm would have been way hotter!". And no, not really, the amount of radiator fins isn't the limitation, it's how fast you can move heat into the loop. If you put a probe inside the reservoir to actually see the temperature of the fluid, it would barely be different between a 120mm and a 280mm.
And in fact the temperatures would probably be barely different than if you bought a NH-D15, or a Scythe Fuma, or other large multi-tower cooler. At the end of the day the working fluid doesn't matter, it's all fins and airflow.