Question Water cooling effectiveness on GPU vs CPU

[Barney-]

I have both CPU and GPU under pretty much equivalent AIO liquid coolers. But when both are under heavy load, GPU core temp is way lower than CPU temp. I gather via Google this is usually the case in open loop setups too.

As the card's TDP is a fair bit higher than the CPU's TDP I would have expected it to be the other way round - any ideas why it isn't?

 

[Eximo]

The size of the GPU itself. It has much greater surface area in contact with the cooler than in your typical CPU. On Intel CPUs the cores are actually very tiny, most of the silicon is its GPU. AMD chips are also quite small, particularly the new ones.

Also GPUs are basically massively parallel processors, so the heat is spread throughout. CPUs have many specialized functions which create hotspots.

 

[rubix_1011]

There is a simple reason for this: GPU is a direct-contact with the core die, whereas CPU uses an integrated heat spreader (IHS) with thermal compound or solder as an interface material.

In short, the GPU die is directly contacting the cooling block (with a bit of thermal paste between) and therefore able to more efficiently move thermal loads into the coolant stream. CPUs have to go from the die, through thick thermal paste or solder, through the IHS, another layer of thermal paste and then to the CPU block.

GPUs will nearly always have a higher TDP rating that CPUs, but this is why GPUs often display lower overall load temps under watercooling setups than CPUs do under the same watercooling setups. It is all about thermal efficiencies gained and lost between the dies producing the thermal load and the cooler removing it.

I could probably even throw together a quick diagram if that would help.

 

[Eximo]

That too. Though even with direct die cooling CPUs still get warmer than GPUs.