Water-Cooled Video Cards In a Parallel Config. HOW?

[halfblazed]

I am currently working on my water-cooling system. I am cooling my CPU and 2 GTX680's.

I have been doing some research and found that there are two ways to water-cool multiple video cards: Parallel and Series.

I fully understand series. The liquid enters the first card, goes through the block and exits into the second card via a VID connector. Simple.

However, Parallel has two VID connectors; or the cards are connected to each other twice.

I don't understand how this is possible. In my mind it seems like fluid would only be able to flow to the "slave" or bottom card and only partially flow to the "master" or top card.

I hope you can understand my explanation. If not heres a Link to a picture of what I am talking about:

http://www.overclock.net/t/847199/parallel-water-cooling-video-cards

If some one could put it into simple terms it would be greatly appreciated!

Thanks in advance!!

P.S. - Is it possible to post pictures on here?

 

[Maxx_Power]

I am currently working on my water-cooling system. I am cooling my CPU and 2 GTX680's.

I have been doing some research and found that there are two ways to water-cool multiple video cards: Parallel and Series.

I fully understand series. The liquid enters the first card, goes through the block and exits into the second card via a VID connector. Simple.

However, Parallel has two VID connectors; or the cards are connected to each other twice.

I don't understand how this is possible. In my mind it seems like fluid would only be able to flow to the "slave" or bottom card and only partially flow to the "master" or top card.

I hope you can understand my explanation. If not heres a Link to a picture of what I am talking about:

http://www.overclock.net/t/847199/parallel-water-cooling-video-cards

If some one could put it into simple terms it would be greatly appreciated!

Thanks in advance!!

P.S. - Is it possible to post pictures on here?

Here is how it works:

In Parallel, like in a circuit or so, the input is subdivided into multiple streams, all of which simultaneously go into different cooling blocks, the combined flow VOLUME is equal to the input volume, so each card gets half the volume of flow. At the input connectors of each card, the pipe is connected with a layout that looks like a Y channel (topology wise), so that the same input is given to cards 1 and 2, and since each water block poses the same flow resistance, each block gets the same flow rate.

In Series, the flow is directed to the first card, and after it completes the cycle in the first card, the output of the flow is directed to the input of the 2nd card, then out of the card to the radiator, etc...

An analogy would be, that a river diverges into 2 streams, and if the 2 streams flow over the same distance and have the same resistance to flow, then logically they should flow with the same rate, with the sum of the flow rate of both streams equal to the parent river. If one of the two streams have a significant resistance to flow, like a dam or something, then most of the water would be channeled to the other stream with less resistance (loading and load balancing). In the water cooler setup you pointed at, the 2 cards have the same water blocks (they must be, or comparable for parallel setups), thus the water flow rate in each of the card would be about the same in parallel. The volume of flow in each water block is 1/2 of the original flow before dividing into 2 streams.

 

[halfblazed]

Best answer selected by halfblazed.

 

[halfblazed]

Here is how it works:

In Parallel, like in a circuit or so, the input is subdivided into multiple streams, all of which simultaneously go into different cooling blocks, the combined flow VOLUME is equal to the input volume, so each card gets half the volume of flow. At the input connectors of each card, the pipe is connected with a layout that looks like a Y channel (topology wise), so that the same input is given to cards 1 and 2, and since each water block poses the same flow resistance, each block gets the same flow rate.

In Series, the flow is directed to the first card, and after it completes the cycle in the first card, the output of the flow is directed to the input of the 2nd card, then out of the card to the radiator, etc...

An analogy would be, that a river diverges into 2 streams, and if the 2 streams flow over the same distance and have the same resistance to flow, then logically they should flow with the same rate, with the sum of the flow rate of both streams equal to the parent river. If one of the two streams have a significant resistance to flow, like a dam or something, then most of the water would be channeled to the other stream with less resistance (loading and load balancing). In the water cooler setup you pointed at, the 2 cards have the same water blocks (they must be, or comparable for parallel setups), thus the water flow rate in each of the card would be about the same in parallel. The volume of flow in each water block is 1/2 of the original flow before dividing into 2 streams.

Thats crazy. Thank you for clearing that up for me.

I am assuming you have some experience with water-cooling (or perhaps a better understanding of physics than me at least). In your opinion, which is better for a 2 card SLI setup?

I have heard that Series is better for 2 card SLI and Parallel is better for 3 card SLI. Is there any truth to that? Something to do with Series slowing the flow rate with 3 cards...

Thanks in advance!!

 

[Maxx_Power]

Thats crazy. Thank you for clearing that up for me.

I am assuming you have some experience with water-cooling (or perhaps a better understanding of physics than me at least). In your opinion, which is better for a 2 card SLI setup?

I have heard that Series is better for 2 card SLI and Parallel is better for 3 card SLI. Is there any truth to that? Something to do with Series slowing the flow rate with 3 cards...

Thanks in advance!!

It depends on your pump (mostly). If you do your 2 cards parallel, the flow resistance of the two cards (total resistance) becomes 1/Rtotal = (1/R1 +1/R2), so if the water blocks 1 and 2 are identical, then the resistances are nearly equal (because of extra piping to card 2, there IS a SLIGHT difference, very small), then R1=R2, so Rtotal is half of flow resistance per water block. This means a net reduction in flow resistance in Parallel setups. For series setup, the pressure of the 1st card is added to the 2nd card, so the flow resistance Rtotal=R1+R2, or about twice each card.

SO, if you have a pump that has a good pump volume, go with a parallel setup, you'll make the most out of the pump, and maximize your cooling. If you have a pump with a high pumping pressure, but low volume, go with a series setup, the high pressure will help to push the water through 2 blocks.

HOWEVER, since you have a radiator in the loop, and the flow channels are typically a lot longer in the radiator, and narrower, you can assume that a lot of the flow resistance comes from the radiator loop, which gets to our next point:

As for number of cards in total, for a 3 card setup, I would imagine the flow resistance gets quite high (since it is R1+R2+R3, so if R1=R2=R3=R, then Rtotal=3R). Plus in 3 card SLI setups, you will need a large radiator, the radiator flow resistance will become even higher. This maybe too much for most small pumps, so it might be worth it to go parallel to lower the total water loop resistance (resistance of the water blocks, the radiator and the pipings), so that the pump can cope. That is one reason, the other reason is that in a 3 card setup, if you go with series, the water temperature sequentially rises after each card, so the output of the 1st card maybe 15 degrees above ambient, the 2nd card will be another 15 degrees, and by the time the water gets to the 3rd card, it is already hot, and it won't carry as much heat from the 3rd card, because the temperature differential between the fluid and the card is much lower now (heat transfer is proportional to the temperature difference). Those two reasons may make it very unappealing to run multi-card setups in series for water cooling.

For 2 card situations, since the 2nd card only sees 1 card's worth of temperature added to the cooling fluid above ambient, it may not be so bad if you can pump the fluid fast enough so that the temperature rise on the 1st card is low anyway. In 3 card or more situations, remember that in series, the resistances add, so it becomes even harder to pump the coolant fast enough across all 3 cards to try to cool off the last card.

Also, if you go with parallel in multi-card setups, the cooling of each card isn't affected by the load on the other cards, so if the game doesn't scale well, or the load balance isn't exactly 50-50 (or 33-33-33, etc) across your cards, no single card can heat up the other cards because the flow is subdivided to be independent.

That's a mouthful....