Vertically-mounted radiator -- ports on top or bottom?

[mneblett]

I did the search thing, but didn't find an answer for the following:

 

I'm putting together an i6600K rig, with quiet operation being a priority.  It's not intended to be an uber-azaming gaming rig, just a fast machine for office productivity, home recreation, and occasional photo/graphics work.  Case is a Fractal Design R5.  

 

I would normally be putting on a large air-cooler with a slow fan (e.g., Noctura D15), but I'm not really thrilled with the idea of having that much weight hanging cantilevered off the motherboard (Asus Z170-A).  So I'm considering the water cooling option for the first time -- cpu only, AIO for simplicity/convenience.  

 

I'm looking at rear/vertical-mounting a Cooler Master Nepton 140XL in the R5 case, operating at low fans speeds.  Primary reasons:  for my workload I don't believe I'll need a 280+ radiator to keep the 6600K thermally "safe"; the 140XL's thermal performance appears to be at least as good under load as a D14/D15; and using a rear-mounted radiator means I can keep the sound-damping panels on the top of the R5 in place to help limit emitted noise.  

 

I am also considering replacing the 140XL's supplied fans with Noctura NF A14 FLX's to further reduce fan noise. 

 

Two questions:

 

1.  Comments on my plans?

 

2.  In various video reviews, I've seen the radiator mounted with the inlet/outlet at the bottom of the radiator in some cases, and at the top in others.  Is there a good reason to do one or the other?  

 

Assuming there's no obvious motherboard component interference that has to be avoided, the engineer in me says the bottom location would be better, as it would theoretically encourage natural circulation in the event of a pump failure (hot fluid rises, cool sinks, and the resulting differential pressure might promote natural cooling flow to/from the cpu block) -- but I'm also thinking that is at best a theoretical advantage as: (i) the system would shutdown on lose of pump rpm anyways, and (ii) there only a 0.00000001% chance that this would ever be issue, i.e., I should ignore the potential for natural circulation if there is a good reason to put the inlet/outlet on top.

 

Thoughts/suggestions/advice?

 

Thanks!

Mark

[DippyG96]

ports on top, makes it so much easier to bleed the thing

[Necrodead]

ports on top, makes it so much easier to bleed the thing

 

Thats true, but with an AIO you want to get the air out of the pump, and since there is no res you actually want the air in the rad for quiet operation, meaning ports on the bottom is best, but it probably won't even matter anyways, there is little difference.

[DippyG96]

Thats true, but with an AIO you want to get the air out of the pump, and since there is no res you actually want the air in the rad for quiet operation, meaning ports on the bottom is best, but it probably won't even matter anyways, there is little difference.

i did a tldr, yeah for an AIO you want bottom ports

[mneblett]

Thanks, folks -- and wow on the quick responses! 

[Dango]

Port on the top, make easier to the pump.

[mneblett]

Port on the top, make easier to the pump.

??  Either way the pump sees a static pressure head equal to the difference in height from the coolant at the top of the radiator to the height of the pump.  Am I missing something here?

[Benji_w]

Thanks, folks -- and wow on the quick responses! 

 

Orientation doesn't matter if you've got a strong pump, if you're using a weak pump then ports at the top will help push out air. In all honesty I've never had an issue with trapped air as I just tipped my case with a EK DCP 2.2 pump with ports at the bottom of my 120mm rad. I'm sure people will disagree but in the year and a bit of watercooling I've no issue with trapped air.

[Exotath]

How do you guys feel about a horizontal tube res inline with a D5 pump? I know as long as the water level remains above the inlet it will operate fine but I seem to get a lot of flack for this in terms of bleeding the system. Which should be easy as long as I have a fill and drain port well above the res in the loop imo.

[Benji_w]

How do you guys feel about a horizontal tube res inline with a D5 pump? I know as long as the water level remains above the inlet it will operate fine but I seem to get a lot of flack for this in terms of bleeding the system. Which should be easy as long as I have a fill and drain port well above the res in the loop imo.

 

If the coolant level is making sure the pump doesn't run dry then go for it, if it makes the rig look good then epic! Personally I'd fill it with the case tipped slightly so I could put more coolant in before refills.

[Exotath]

If the coolant level is making sure the pump doesn't run dry then go for it, if it makes the rig look good then epic! Personally I'd fill it with the case tipped slightly so I could put more coolant in before refills.

 

Those are my thoughts as well. Thank you for the reply.

[ThomasD]

Port on the top, make easier to the pump.

Being a closed loop either way the physics is the same - the pump still has to push the water column all the way to the top (head height is head height.)

[Benji_w]

Being a closed loop either way the physics is the same - the pump still has to push the water column all the way to the top (head height is head height.)

 

Pretty much this, as long as the pump doesn't run dry it will be fine.