PA 120.3 and MCR320 in parallel

If I put a PA 120.3 and a MCR320 in parallel, would the water flow through each one about equally? I am thinking of adding another rad to my loop and I have a MCR320 I'm not using. I know I could do 2 loops, but then I'd have to have another pump and more holes in the case (externally mounted rear radiators). So I was thinking of just adding the MCR320 to my existing loop. But then I was thinking, should it go in in series or parallel. After some searching here, it seems like parallel would be better.

And yes I'm after that elusive .1C :)

Any advise is greatly appreciated.

]Monty[

Putting them in series is better, in almost all normal circumstances.

Putting them in parallel halves the flow rate to each (at best) and will result in a far greater performance loss than merely putting them in series and dealing with the extremely minor flow-rate loss of the extra pressure drop of doing so. In general, radiators are very low pressure drop items, so putting them in series has minimal overall impact on flow rates. What's of more importance is keeping the flow rates up through the radiators, or at least above 4LPM.

When dealing with multiple radiators, the rules are these:

*) Water-flow series
*) Air-flow parallel

OK, thanks for that Cathar.

OT - Nice bike.

]Monty[

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Originally Posted by montyshaw

OT - Nice bike.

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Yours too!

Cheers. Although, it ain't pretty no more. It'll be fixed again.

Ouch Cathar.

Is that the source of your injuries right now? What happened?

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Originally Posted by Polizei

Is that the source of your injuries right now? What happened?

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I was an idiot is what happened. I took a chance on a worn front tyre at one of the world's fastest motorcycle race-tracks, that being Phillip Island.

Rounded Turn 2 at around 85mph (one of the slower corners actually), and the front wheel started to slide. Did everything "right". I know this 'cos the slide lasted a good 20m (~60'). I did everything I could to give the front tyre a chance to re-grip, and it did re-grip for small fractions of a second, but let-go again, and in the end it wasn't to be.

Low-sided the bike, but must've dug some part of me into the track, and before I knew it I had somersaulted with my right-ankle as the pivot point (ie. an 80mph one-legged somersault) which micro-fractured the Talus, and 'cos it happened so fast, after the somersault I slammed the right wrist into the track for good measure, chipping the top off the ulna, and causing multiple cross-fractures to the radius where it joins the wrist. The damage to the radius was fairly serious, with risk of the bone collapsing, so they had to plate the radius to hold it together, and did a bone-graft to put the chip off the ulna back into place.

Am near totally house-bound. Won't be able to walk for 9 more weeks. The Talus is the main weight-bearing bone in the foot, so the usual 6-weeks healing time isn't the case here. 'Cos the bone is such a structurally important bone, the doctors recommend a full 13 weeks (3 months) before it can be considered to be healed completely enough to not risk expanding the fractures through walking/running/whatever.

Wrist, at the moment, is aching. Am on pain-killers. Only have around 50% full mobility in the wirst, but it's still very inflamed and swollen and it'll get better in time as the swelling settles. Strength in wrist is about 1/50th of normal. For example, picking up a cup of coffee is about the limit of what it can do, and even that hurts. Will probably be another 5 months before the wrist gets back to a semblance of normality.

Typing is not an issue though, and I telecommute for work, so my work has been unaffected.

Cathar why are you saying series is better? Parallel has much much less pressure drop because the flow is halved between the 2 rads. Also, those "tests" you mentioned are done with a constant 10C coolant/air temp difference, which means at more flow, MORE HEAT IS ADDED TO THE WATER TO ACHIEVE THE 10C air/coolant delta. There have been a few people who tried series vs. parallel, and parallel got better temps :P
Let me guess, now I'm going to be slaughtered for challenging the god? :rolleyes:

Well, I've tested it myself, but okay.

I'll be gentle. I don't attack people for asking questions, just those who attack me or others without good reason.

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Originally Posted by serialk11r

Also, those "tests" you mentioned are done with a constant 10C coolant/air temp difference, which means at more flow, MORE HEAT IS ADDED TO THE WATER TO ACHIEVE THE 10C air/coolant delta.

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Talking about Bill's tests here eh? So if we had to add more heat to maintain a 10C coolant/air temp difference, what would have instead happened if we didn't add more heat (constant heat load)? Did the air-in temp change? If not, what changed?

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Originally Posted by serialk11r

There have been a few people who tried series vs. parallel, and parallel got better temps :P

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So I'm guessing these people used a known, measured, and fixed constant heat-load across all tests, and monitored their air-in, water-in, and water-out temperatures, and measured the delta's?

Right now for me, I don't think those tests mean ANYTHING...I'm still thinking about it. I still think more flow only slightly increases the performance of the radiator...I don't want to type up the explanation, takes too long. I'll have my mom bring some Y fittings home...I don't have any and the hardware store doesn't sell them for some damn reason, then I'll test it for myself. But definitely, parallel should give the loop overall higher flow.

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Originally Posted by serialk11r

Right now for me, I don't think those tests mean ANYTHING...I'm still thinking about it. I still think more flow only slightly increases the performance of the radiator...I don't want to type up the explanation, takes too long. I'll have my mom bring some Y fittings home...I don't have any and the hardware store doesn't sell them for some damn reason, then I'll test it for myself. But definitely, parallel should give the loop overall higher flow.

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So what you're basically saying is that you'd prefer to trust your assumptions, over those who have actually tested it.

Parallel will give the loop more flow, for sure. How much more? How much are you waving your hands and simply assuming here? Here's a calculated plot based upon established pressure drop figures:

http://www.employees.org/~slf/curves/pumps/serpar.png

In series, the radiators will have ~5.3LPM flowing through the system and each radiator.

In parallel, the radiators will have ~2.75LPM flowing through them, and ~5.5LPM flowing through the system.

There will be an extremely minor benefit at the waterblocks for moving from 5.3 to 5.5LPM, and a definite deficit at the radiators for dropping from 5.3LPM to 2.75LPM.

The two effects do counter-oppose each other to a certain degree. Which one "wins" depends on a number of factors, but for the general case with modern waterblocks, the performance loss at the radiators outweighs the minor waterblock benefits through the small flow-rate increase.

The differences are small though, I'll grant you that. They are small enough such that many people with 1C resolution on their CPU's won't notice it, but will typically range in the fractions of a degree, but in almost all circumstances should favor the in-series configuration. If people see differences larger than that, something else has changed.

The larger the radiators, the higher the initial flow-rates, and the more powerful the fans, then it is more likely that an in-liquid-parallel config will win, but once again, the differences are never large, and certainly NEVER larger than the waterblock performance differences between the disparate system flow-rates.

Thanks for the little simulation there. No I didn't say I trust my assumptions more than people who actually tested it, I think there isn't really that big of a difference in the first place, and I'm going to test it myself :P And yes, the difference isn't going to be that big but...ah well, I just think tweaking things is cool.

great explanation!! i am going to run some numbers to back that up, be right back

The water is still going through 2 radiators no matter how you do it. So how could running parallel provide less of a drop?

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Originally Posted by SDatl404

The water is still going through 2 radiators no matter how you do it. So how could running parallel provide less of a drop?

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less flowrate through the rads because the flowrate is halfed, thus less cooling perforamnce.

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Originally Posted by sick_g4m3r

less flowrate through the rads because the flowrate is halfed, thus less cooling perforamnce.

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I am talking about flow rate drop. Not overall cooling performance. Overall flow rate of the loop should be the same due to the fact you have the same level of restriction in the loop.

Running through the maths of it.

Given a 100W CPU heat load, and even when tripling the Swiftech supplied C/W's for the block, the difference between 5.3 and 5.5LPM is just 0.11C at the CPU die (in favor of 5.5LPM).

The difference in water temps, for 5.3LPM through the rads, and 2.75LPM through the rads, for 108.5W of heat load (CPU + pump heat), is actually 0.11C in favor of the series config. (Use Yate-Loons at 12v).

LOL. 0.11-0.11 = 0.00C.

There'd actually be no difference between series/parallel for the proposed config.

Running the fans faster would favor parallel by 0.01C or so, and vice-verse for slower fans.

Okay - I'm going to change my stance now and say that there'd be no discernible difference between series/parallel. Go with whatever is easiest.

Okay then. Running some more scenarios.

2 x single fan radiators => In liquid-flow-series is very marginally better (~0.1C)
2 x dual fan radiators => No preference for either
2 x triple fan radiators => In liquid-flow-parallel is very marginally better (<0.1C)

In the past I had only tested 2 x single-fan rads, which explains what I saw in my testing, which indeed was <0.2C differences in favor of flow-series.

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Originally Posted by Cathar

[injuries]

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Ouch...
Get well soon :)
I see you found some use for the extra time, making all these tests - well done :up:

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Originally Posted by Cathar

Okay then. Running some more scenarios.

2 x single fan radiators => In liquid-flow-series is very marginally better (~0.1C)
2 x dual fan radiators => No preference for either
2 x triple fan radiators => In liquid-flow-parallel is very marginally better (<0.1C)

In the past I had only tested 2 x single-fan rads, which explains what I saw in my testing, which indeed was <0.2C differences in favor of flow-series.

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even with the flow halfed to the rads its only that little difference? i was expecting 2-3C

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Originally Posted by sick_g4m3r

even with the flow halfed to the rads its only that little difference? i was expecting 2-3C

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It's because there's just so much cooling power on offer with two x dual-rads. Yeah, the radiators perform worse with less coolant flow, but because the overall C/W is so low, a 5% performance difference (which is what the difference between 2.75LPM and 5.3LPM is), doesn't equate to much of an actual temperature change because the radiators are holding the water temps to around 2C above ambient anyway. 5% of 2C is 0.1C.

At half the flow, the pressure drop is much less than 1/2 but then the rads aren't exactly the biggest restriction in a loop so...
In series the second rad gets cooler water (but only cooler by a tiny bit) which means that it will cool worse (but by a tiny bit). :P doesn't really matter.

wait, i have a question.

say i have a D5 and 2 MCR320s, a fuzion, and a mcw60.

how would one calculate the expected flow of such a system?

the pressure drops of the parts can only be found at certain flows, and when you cross them with the D5 pq curve, the flow is not the same.

so i am very confused. how do you find the flowrate given a pump and the parts?

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Originally Posted by sick_g4m3r

wait, i have a question.

say i have a D5 and 2 MCR320s, a fuzion, and a mcw60.

how would one calculate the expected flow of such a system?

the pressure drops of the parts can only be found at certain flows, and when you cross them with the D5 pq curve, the flow is not the same.

so i am very confused. how do you find the flowrate given a pump and the parts?

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Add up the pressure drop vs. flow curves...sorta hard to do but you could probably get an approximate equation for each and then add. Then as for tubing...there's theoretical pressure drops for tubes, so I'd take however many feet you're using, and add a little more on top of that because of bends. Hope that makes sense...

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Originally Posted by serialk11r

At half the flow, the pressure drop is much less than 1/2 but then the rads aren't exactly the biggest restriction in a loop so...
In series the second rad gets cooler water (but only cooler by a tiny bit) which means that it will cool worse (but by a tiny bit). :P doesn't really matter.

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Are you saying that the greater the flow the higher the resistance gets? I have a hard time choking down that water cooling pumps could push enough water for you to even reach noticable loss in flow due to radiator configuration.

Saying the other radiator gets cooler water is like saying half of a larger radiator gets cooler water. If you didn't need the water colder after it left the first one why have a second? :shrug:

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Originally Posted by serialk11r

Add up the pressure drop vs. flow curves

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how exactly does one add these up? And then after they are added up for all the parts, do you find the intersection with the PQ of the pump?