Watercooling Experts Wanted

[jreffy]

but theres no extra surface area compared to a single pass with the same number of tubes.

yes, there is. Think of the water molecules path through the radiator. The water molecule experiences contact with more of the surface in a double-pass than a single-pass. Granted this happens FASTER, but during turbulent flow, the heat is exchanged rather quickly.

I don't think the radiators are large enough for gravity to become a problem. It's fighting gravity for a few inches, not a few feet.

you know what... if single pass radiators arent as good... they've been done wrong somehow. everything is telling me that single pass is a good dea. it just makes more sense to go through a radiator once and once only, and in one direction only. it makes physical sense, it makes thermal sense, it makes practical sense. something's wrong here.

What makes more sense is to get exposed to as much surface area as you can, which is what double-pass does. The water just moves faster in double-pass in order to cover that extra area in the same amount of time. The heat exchange happens so quickly that the speed of the water passing through the radiator does not effect the efficiency of the exchange.

[Slug Toy]

that still doesnt make sense about the surface area.

using your example... a 32 pipe single pass versus and 16 a 16 pipe double pass. they are both going through 32 pipes in total. its not like there is any sort of magic going on in a double pass that increases surface area. no matter how you look at it, 32 pipes is 32 pipes, and it will always have the same amount of area unless you start changing the pipe size... but we're doing a comparison here so that isnt the case.

if i have to, ill break out the math to prove this. dont make me do that.

[jreffy]

that still doesnt make sense about the surface area.

using your example... a 32 pipe single pass versus and 16 a 16 pipe double pass. they are both going through 32 pipes in total. its not like there is any sort of magic going on in a double pass that increases surface area. no matter how you look at it, 32 pipes is 32 pipes, and it will always have the same amount of area unless you start changing the pipe size... but we're doing a comparison here so that isnt the case.

if i have to, ill break out the math to prove this. dont make me do that.

Yes, they have the same surface area when you look at it from the outside. You're thinking about the total surface area of the radiator. Yes they are equal, the radiators take up the same amount of space. However, you are cooling the water molecules, so you have to think about the surface area that the individual molecules are exposed to! Follow the PATH OF THE INDIVIDUAL WATER MOLECULES!!! Think of how one water molecule goes through a single-pass radiator compared to a double-pass radiator.

Single Pass; It enters the inlet, goes down a tube, exits the radiator

Double Pass; It enters the inlet, goes down a tube, turns around and goes down a SECOND tube, exits the radiator.


The water molecule in a double-pass rad travels the lenght of TWO TUBES before exiting, in a single-pass the molecules only are exposed to the length of one tube. That's TWICE the exposure to surface area.


A double-pass radiator takes the same amount of water, but passes it through the radiator TWICE. that's DOUBLE the area that the single-pass fluid is exposed to. Yes, both radiators have the same surface area, but in a double-pass you are cramming all the molecules into 16 tubes. The molecule travels the length of the tube, then travel the length of the tube AGAIN. That's TWICE the exposure! You're just cramming more fluid into the tubes, hence why the flowrate in double-pass is higher, and you need a more powerful pump to make it happen.

[Slug Toy]

ok i sort of see where you're going now. half the pipes but twice the length.

now here's whats got my head hurting. are the flow rates the same? is it better to have one amount of fluid being cooled for a given time, or twice the amount being cooled for half the time? this is where the math would come in because you have to take into account... oh boy does that mean some complex figuring.

things just still arent sitting right in my head. i dont know why. i guess i have to prove or disprove myself now... or else im going to be eternally tormented.

[Indybird]

I don't mean to interrupt your thinking, but I already got the list I need from you guys, ahh...whatever
thanks

[jreffy]

ok i sort of see where you're going now. half the pipes but twice the length.

That's exactly right! Haha, it's ok, I've actually been remembering a lot of my fluid dynamics from this. I'm enjoying it a lot, I love figuring stuff out and helping people learn, anyway, on with the mental exercises!!

now here's whats got my head hurting. are the flow rates the same?

Get the time thing out of your head for now, think of it purely in terms of fluid flowrates and the amount of water passing through the tubes and radiator.

Ok. You're thinking in the right direction. The flowrate at the inlet and the outlet are equal. Because think, the entire system has to be moving at the same speed all the time, you can't have one section moving faster than the other, EXCEPT...INSIDE the radiator. If you measure the flow at the inlet and outlet of the rad, they are equal, but what about inside the tubes?

In the double-pass radiator, in order to have equal flowrates at the inlet and outlet, but only pass through half the number of tubes, the fluid accelerates inside the tubes! Think about it.

Draw 2 lines about a mile apart on a 4 lane freeway, and an 8 lane freeway. Cars represent water molecules. You need the same amount of cars to pass through this zone in an equal amount of time.

Since the 4 lane freeway is half the size of the 8 lane freeway, the cars need to travel TWICE as fast on the 4 lane freeway to get the same number of cars through that zone. Follow? Here's a simple equation.

8(tubes)*1(speed)= 8 (flowrate)
4(tubes)*2(speed)= 8 (flowrate)

Equal flowrates at the inlet and outlet, but different speeds inside the tubes!

It's the same way in the double-pass radiator. The speed of the fluid inside the tubes is twice that of the fluid inside the single-pass. This is what causes the larger pressure drop in double-pass radiators, and why you need a more powerful pump.

is it better to have one amount of fluid being cooled for a given time, or twice the amount being cooled for half the time? this is where the math would come in because you have to take into account... oh boy does that mean some complex figuring.

Actually, both fluids spend an equal amount of time inside the radiator, but inside the double-pass radiator, the fluid is exposed to more tube (remember twice the tube length?). We know that they spend an equal amount of time inside the radiator because the flowrates at the inlet and outlet are equal. However, because the double-pass radiator is essentially a longer "track", the fluid travels FASTER in the double-pass, but is inside the radiator for the same amount of time.

So in theory if you made a TRIPLE-PASS radiator, it would do an even more thorough job of cooling the fluid, however it would require MORE power in order to push the fluid even FASTER through the tubes. The reason you don't see many triple-pass rads is because there isn't much of an improvement in a triple-pass over a double-pass that would make it worth getting the extra powerful pump.

[Slug Toy]

ok now you're making me contradict myself. i dont know if i like that... because now i have to go back and check what i said and then decide what is more true.

i wonder if what i said about speed actually holds up in a real world situation. i was drawing upon my physics theory stuff for that one.

actually, i wonder if there is any turbulence in that sort of system. i would imagine that a radiator is just a bunch of tubes, nothing special. theres no real turbulence in tubes like that, especially smooth metal ones. in fact, there probably wouldnt be much turbulence in a lot of waterblocks out there either.

great. now im not even sure im real anymore. see what you've done to me? probably not a good idea to be thinking this hard at 1 in the morning.

[Silenced_Coyote]

Isn't there turbulance in the Swiftech Storm CPU waterblock?

Must be rough Slug_Toy thinking about this at 1 AM. Because I know my head is hurting just reading what you two have to say.

[jreffy]

ok now you're making me contradict myself. i dont know if i like that... because now i have to go back and check what i said and then decide what is more true.

i wonder if what i said about speed actually holds up in a real world situation. i was drawing upon my physics theory stuff for that one.

actually, i wonder if there is any turbulence in that sort of system. i would imagine that a radiator is just a bunch of tubes, nothing special. theres no real turbulence in tubes like that, especially smooth metal ones. in fact, there probably wouldnt be much turbulence in a lot of waterblocks out there either.

great. now im not even sure im real anymore. see what you've done to me? probably not a good idea to be thinking this hard at 1 in the morning.

Actually, remember how the double-pass radiator has a higher velocity? The reason why the increased velocity in the tubes is a good thing, is because it causes turbulent flow. In the world of cooling, you WANT turbulent flow. It makes sure that all the water molecules are mixed up and exposed to the aluminum so they give up their heat.

And yes, pretty much ALL waterblocks will be turbulent flow, usually through the use of small nozzles where the fluid enters the actual block. I saw a picture of either the Storm or the TDX somewhere and you could see the nozzles clearly.

[Silenced_Coyote]

Here is the little nozzles on the Storm.

Here are the wells that the nozzles shoot into.