How many computers in an overkill loop?

[Rusty Proto]

I'm trying to decide if I want to run a 12U enclosed computer cabinet with an external rad system, and while I have a good idea how I want to build the exhaust end of the loop, I have no doubt that it would be able to handle 3KW of heat no problem, which is the most that I expect to be able to run to it electrically, and well over double my absolute max likely load, assuming I start doing some out there stuff. With that in mind, if I built three or four rack mount computers to pull off of this loop, and was able to run each one full tilt, would I be able to do a single series loop for design simplicity or would I be more likely to need a pump that will blow something or will I run out of headroom before my fluid gets to thermally saturated to cool my equipment well, and thus would do better putting them in parallel via a header? I'm avoiding air cooling these computers mostly because they'll be in an enclosed cabinet that I'm betting will bake a decent gaming rig, though it otherwise makes sense for mounting where I want it. (It will be visible as furniture.) while being able to move the exhaust part of the loop to somewhere out of sight and preferably cooler.

[thrasher_565]

so pumps can push so much head pressure witch is how hi it will go vertical. i beleave d5 is about 3 meteors. but you can add more...

how may cpus and gpus? what are they?

 

if there run 100% probably going to need more cooling

pcbs need some cooling too

 

im going to guess 360 for cpu and 360 for gpu each pc.

but depends on fans and how fast and loud they are run the faster save on rads but adds nose and power...

 

 

[Rusty Proto]

For the rad, right now, I'm designing for a 16 inch square by 3 inch deep radiator with a 120 watt automotive radiator fan with an RV domestic water pump being the main circulating pump, so I figure that would be overkill, right? I'm intending to still use regular fans in the case itself and a 120V 120mm enclosure fan cooling the boards, RAM, disks, etc, but since the enclosure has mostly solid sides, I'm probably going to need to liquid cool the CPU and GPU, probably something like a Radeon 7900 XT, and Ryzen 5800 X3D or similar for each system. While I am starting with one machine right now, I am also trying to think about future expansion. Either way, I'm wanting to pull the bulk of my heat of all the machines out and drop it outside the rack with the rad.

[AnonymousGuy]

I have 4 computers on 1 loop.  You need a manifold to put them in parallel.  If you put them in series you're going to need ridiculous pressure in the loop to be able to drive flowrate and then you're dealing with shit like tubing blowing off barbs and liquid being forced past o rings.

 

The other guy's suggestion of 720 rad per system is beyond stupid overkill.  If you have decent airflow through a rad you can get away with 240 per system.

 

Flow rate 101 the pump has a fixed curve of flow rate vs. pressure.  Your loop is also a particular pressure needed to achieve a flowrate. :

 

 

So if you have a highly restrictive loop, the loop looks like the red line.  If it's less restrictive it's the green line.   Where the lines intersect the pump is what your pressure and flowrate will actually be in the loop.  So example with a PMP-600 @ 24V: highly restrictive (red) will be 10mmH2O pressure and 4LPM of flowrate.  Green will be 7mmH20 pressure and 10 LPM of flowrate.  

 

But the flowrate is for the entire loop.  If you put 10 identical systems in parallel, each branch will have the same pressure but 1/10th of the total system flowrate.   Your next question is going to be "how much flowrate do I need per branch?" .  Anything above 100lph is sufficient.  You'll find people saying 1gpm which is 220lph...that's overkill for PC heat loads.

 

(I haven't tried putting a pump in each branch of a parallel loop.  For sure you never want to put pumps in parallel in front of a loop, but I think if you put 1 pump in each branch the flowrates would add together before + after the manifolds)