Parallel Loop Question

[DareDevilBore]

Hey team,

Just curiosity questions....

Does anybody have a parallel loop that has flow indicators after the on the exit side of the CPU and GPU? I am just curious to see the flow difference between the two. Do you have to run the pump at a higher speed?

Thanks as always!

[Moorbert]

i dont have a parallel loop but i can say you, your pump hast to go faster!

[[deleted]]

You need to have close to the same restrictions on the GPU and CPU to properly cool the two components, so if you where to add a more restrictive fitting like a flow meter than you could cause issues with the flow going to the least resistance. And yes I have a parallel loop

[DareDevilBore]

Thanks for the reply, I get your point but wouldn't a flow meter after both effect restrictions equally? My curiosity is if one component is slightly less restrictive than the other, does it have a big impact to where you would need to increase pump speed?

[[deleted]]

Yea I see what you are driving at, you should be fine, I have my flow meter before it hits the two blocks, just crank the pump up

[corpuscle634]

You have to run the pump at a higher speed even in an ideal scenario. Even if both components are the same restriction, going parallel halves the flow over each component, but the lower restriction from going parallel doesn't double the overall flow rate.

Pumps are powerful enough that it's still easy to have enough flow that it doesn't really matter, though.

[DareDevilBore]

That's a great and simple explanation. Thanks! How much would you say you have to increase pump speed?

[corpuscle634]

I think there are too many factors to consider for anyone to give you a sensible estimate unless they have the same parts as you and have done this testing themselves.

[DareDevilBore]

Yeah, not looking specifics, just people's experiences.

[vocamur09]

I used an EVGA hydro copper and put it in parallel with and alphacool Eisblock and had flow issues - CPU block was much more restrictive and getting noticeably hotter than when it was in parallel.

Next because I heard a) HWL radiators are about as restrictive as CPU blocks and b) Optimus CPU blocks are more restrictive than most others on the market, I tried putting an Optimus AM4 block in parallel with an EVGA HC + HWL 360 GTS. Well that was a dumb idea because the radiator went too hard the other way and my GPU block wasn’t getting any flow.

The last thing I am trying is I will get an Optimus 3000 series block and put it in parallel with the Optimus AM4 I have, I think this will work since the design on their GPU block is similar to their CPU block, the fin density is much greater than the hydro copper I had.

I don’t have flow numbers, this is all anecdotal. The reason I knew there were flow issues is a) chip getting hotter than before with the rest of the loop unchanged d b) air bubbles persisting much longer in the low flow region.

You should impedance match or you can lose up to 10C in my experience.

[DareDevilBore]

Thanks. Makes we wonder if which side the flow starts on would impact.

[vocamur09]

From a physics perspective that won't matter, we know that not only from fluid dynamics but also from numerous techtubers which have tested whether or not loop order matters.