Understanding radiators

hey guys ive been doing alot of reading around lately.
and ive come to radiators / heatercores.

i just need to know if im right ( by using the folowing statments

dual row are like one long tube bent over and over again with one input and one output, and the water only ever passes through the same tube.

crossflow ( or single pass?) rads are like a series of open ended tube with some kind of sump at either end with the barbs at opposite corners. and the water runs through all the tubes at the same time

cross flow are better for higher flow applications
dual row are better for lower flow rates
ive been on all morning tryign to work this out. pictures of rads without the fins would solve it in an instant for me but cant find any.
i have tried to find the answers for my sefl befor eposting by the way
Rick

R B Customs said:

cross flow are better for higher flow applications
dual row are better for lower flow rates

Click to expand...

malum in se

right!
i knew it would depend on what else was in the system but i was just checking if i had the mechanics of the rads right... just for reference if nothing else.

on the otherhand... i am on hte verge of buying a 120.2 rad to go with a silverprop cyclone SL, a DTEK White Water, and a aqua extreme 50z to throw it round the loop.

the rad unfortunatly ( ? ) will have to be an XSPC one as its all i can afford and the guy who owns part of that company lives a stones throw away from me
they make a xflow and a dual pass.
astheticly speaking the dual pass would win over the xflow honds down tbh.

but thinking about it i have a restrictive CPU block, a decent pump and a GPU block i may be better off with a dual pass anyway.
ive come to that conclusion by thinking about what you have said.

im trying desperatly to understand watercooling rather than just asking for 'the best stuff' im gettign there though
Rick

TreeNode said:

Its more like XFlow has higher flow rates while 2-pass (dual row) rads allow the water to stay in the rad longer to cool off more. But, if you consider them side by side with the same pump, an XFlow system would work better with a lower powered pump than a 2-pass rad. With a high powerful pump, a 2-pass would be better.

Click to expand...

you have to be very carefull here . you are heading the wrong direction and are about to mislead people into popular urban cooling legend

water stays in a rad the same amount of time in a closed loop weather its single or dual pass so flow is always the most important. while technically if you ONLY count a SINGLE revelution in the cycle ONLY keep in mind , THEN AND ONLY THEN is it possible for water to pick up more heat from a dual rad.
( does not include relationship between DT because its only a single cycle)

once you establish that water cooling is a closed loop and will REcycle meaning make more than 1 pass through the loop, you have just established that water will spend the same amount of time in the rad.

how this relates to efficiency is the DELTA T

you want your DT to be as efficient as possible aka as wide as possible.

that means the diference between the hot and cold basically. which will cool a hot frying pan better ? 1 liter per minute of tap water or 1 liter per minute of ice water?

ice water of coarse. so to let water stagnate inside a 2 pass rad is going to be less efficient. your ice water just warmed up and is not making any room for new ice water to come in..

if this is confusing you need to review that this is a closed loop in which the distance the water travels is always the same and the amount of water is the same. .



a race track... say you have a race track and you go 5 miles an hour around the track ( slow flow). you go around a 1 mile track in 12 minutes . its still 1 mile though.

NOW go around a race track at 60 miles per hour . you just went 1 mile in 1 minute. YOU STILL ONLY WENT 1 MILE . you did it 12x as fast ( high flow).

but you picked up more heat ( more than slow flow) because your ice water was FRESHER ( spent less time and kept the Delta T here after called Dt, WIDER). this is where spead aka flow creates efficiency.

TreeNode said:

Though, this is not even considering the flowrates through the blocks and hose length which will alter things. If you have restrictive blocks, you can't possibly get the water circulating the "right way" through an XFlow anyhow so you would go with a 2-pass to balance it out.... etc.

Click to expand...

now this is just ... i dont know.. i cant see what you are trying to demonstrate.
maybe if you re word it i can figure out what you are trying to say.

pumps are rated to work in efficncy with certain head ratings at certian speeds. so some pumps are like a slow moving wide deep river . they have more force behind them but they are not moving as fast BUT they overcome minor restriction better so that it does not slow their flow FURTHER .

high flow low head pumps are the oposite like a shallow stream that runs at much higher speeds ( or velocity if you like big words). the problem is they are reduced in speed very easily by restriction so thier speed could slow down a LOT more .

so if i have a pump that pumps 10 gallons a minute and its low power and the restriction slows its speed down to 2 gallons per minute it will not be as effective as a higher head pump that pumps max speed of 6 gallons a minute but WITH restriction only pumps 3 gallons . basically the higher head overcame the resitance more effectively to have an over all higher flow to restriction rate..( these are demonstration synthetic numbers only , not based on any particular pump)

this is where choosing your pump is important . some people over do the pump they need in either to high a flow or to high a head for thier system . its a HUGE balancing act where you haev to match your block and rad ( with Fan ) to the right pump for you.

ways to manage the balancing act .
reduce restriction through shorter tubing runs
reduce restriction through less bends in the loop ( this includes going from dua l pass to single pass)
use a pump that is suited to the systems OVERALL restriction require ment and keeps the flow near the water blocks most efficient speed( this also balances the speed vs deminished returns)
balance everything vs noise and stable OC (aka how much bleeding ears are you willing to put up with)

some hints that i dont usually give system designers but might as well.

you can eliminate tubing lenght by using VERTICALLY mounted single pass cores .
keep the pump at the BOTTOM of the loop so that the pump outlet is very close to the core bottom inlet ( this should reduce a large portion of tubing)
the cores outlet should sit just below the water block inlet so that water is still traveling in an upward movement( this bleeds the system as air travels up and with flow not against it)
from your water block you should have a VERTICALLY mounted res or air trap/tline that travels straight down to the pump inlet ( the res acts as both res air trap and tubing emoving even more tubing from the loop)
note that a good res will be tall and skinny with the water INLET slight below the fill opening BUT still higher than the OUTPUT of the water block so that air travels out of the block UPWARDS into the res where it travels to where you fill the res

it literally takes me under 1 minute to completely fill and bleed a system 100%.

your bigest problem with the design is the case. thats why i prefur tall lian li cases for this.

thorilan said:

water stays in a rad the same amount of time in a closed loop weather its single or dual pass

Click to expand...

thorilan, I've read this explanantion from you before, but wouldn't it require that there is the same length in tubing through in the single-pass and dual-pass radiators? Single pass goes from one end to the other, and dual-pass goes from one end to the other and back. Doesn't this basically mean I could fill more water in the dual-pass radiator? This would show that the length that water needs to travel in the dual-pass is more than the single-pass.

Thanks for the extended explanation for the rest, I kinda generalized the word "power" for my description of a pump, which is a no-no.

TreeNode said:

thorilan, I've read this explanantion from you before, but wouldn't it require that there is the same length in tubing through in the single-pass and dual-pass radiators? Single pass goes from one end to the other, and dual-pass goes from one end to the other and back. Doesn't this basically mean I could fill more water in the dual-pass radiator? This would show that the length that water needs to travel in the dual-pass is more than the single-pass.

Thanks for the extended explanation for the rest, I kinda generalized the word "power" for my description of a pump, which is a no-no.

Click to expand...

In a dual pass you only have half the tubes going each way. Yes the coolant travels the length of the rad twice So the coolant travels twice the speed each way so the dwell time in the rad would be the same. but the resistence is increased which lowers over all flow, as I understand it. Also if both rads have the same number of tubes and the same size endtanks both types would hold the same amount of coolant.

Aaahhh... ok Curve and Joe, that makes sense.

learning curve said:

Yes the coolant travels the length of the rad twice So the coolant travels twice the speed each way so the dwell time in the rad would be the same.

Click to expand...

Whaaaa? This isn't making sence to me, if the coolant has to travel across the rad twice then its going to be traveling twice as far, and with the same pump how is it going to be moving twice as fast?

@thorilan.. wishfull thinking on my part, but any chance of a diagram on that layout you discribed?

Ok bear with me as I try to explain as best I can. assuming 1 gpm flow into and out of a rad with a single pass and 10 tubes. Now with a dual pass with the same 10 tubes = 5 north and 5 south still the same 1 gpm, the speed of the coolant in the rad has to travel 2x as fast to exit the rad at the same 1 gpm. But this doesn't take into account the added resistance of slowing and then speeding the coolant back up in the end tanks, as well as the resistance of pushing all the flow through half as many tubes. Which tends to slow the flow rate of the entire loop.

greenmaji said:

Whaaaa? This isn't making sence to me, if the coolant has to travel across the rad twice then its going to be traveling twice as far, and with the same pump how is it going to be moving twice as fast?

Click to expand...

The actual velocity of the coolant is doubled, though the flow rate stays the same (if you ignore the slightly higher restriction of the double pass rad).

One thing that hasn't been touched on in this thread is that higher coolant velocity in the rad will produce slightly less thermal resistance between coolant and copper because there will be more turbulence to break up laminar flow. In practice, this isn't terribly important because the difference is lost in the higher thermal resistance of the air side. However, engineers I respect say that, in general, a dual row rad should be dual pass as well to avoid letting the velocity of the coolant in the tubes drop to the point where laminar flow becomes a problem.

Joe Camel said:

Click to expand...

Hmm.. you must have known that the easiest way for me to understand this was to put a pic up..Easily understandable now.

on the race track .. its 10 miles long( the whole loop) we will say and 1 mile is the rad(pit area) .

if your system flow is 20 miles an hour , in 1 hour you will have completed 2 laps of covered the rad twice or 2 miles of cooling surface. that means you spent 3 minutes per lap in the radiator x2 or a total of 6 minutes

now lets double the speed of the flow . the track distance stays the same and the pit area stays the same . only the flow changes.



if your system flow is 40 miles an hour , in 1 hour you will have completed 4 laps of covered the rad 4 times . that means you spent 1.5 minutes per lap in the radiator x4 or a total of 6 minutes

ok so now you see its still the same time in the rad no matter which speed right?

now how this relates to single and dual pass. they are the same amount of area right ? YES they are.

just imagine that a 2 pass rad is the pit area but its only 2 lanes wide and 2 miles long.
and that a single pass rad ( twice as wide) is 4 lanes wide and only 1 mile long .

thier surface area is the same right? yes. the diference is 2 parts.

1. less resistance ( hair pin turn) more of a wide lane helps maximize the DT because the longer the water sits in the rad the less heat it pics up because the DT SHRINKS as heat is picked up ( remember cold water picks up heat better than already warm water right?)

This is an interesting thread. My question is that in the real world, does using a dual pass vs using a single pass result in any measurable differences? A good pump like a DDC or D5 is going to be capable of blowing right through each with no problem. Isn't there a point where more flow/less restriction results in differences that are so small as to not really make a practical difference?

Otter said:

The actual velocity of the coolant is doubled, though the flow rate stays the same (if you ignore the slightly higher restriction of the double pass rad).

One thing that hasn't been touched on in this thread is that higher coolant velocity in the rad will produce slightly less thermal resistance between coolant and copper because there will be more turbulence to break up laminar flow. In practice, this isn't terribly important because the difference is lost in the higher thermal resistance of the air side. However, engineers I respect say that, in general, a dual row rad should be dual pass as well to avoid letting the velocity of the coolant in the tubes drop to the point where laminar flow becomes a problem.

Click to expand...

I have read that laminar flow sets in after the coolant travels about 6 inches. My idea was to build a 120.3 with 3 120mm sections like this. endtank-120mm of rad-itermedate tank-120mm of rad-itermedate tank-120mm of rad-endtank All single pass to keep the flow up and this would maximize turbulance and stop laminar flow. So what do you all think of my hairbrained concept ?

attaching my paint skills pics

now look at the heat gradient of a single pass. KEEP IN MIND THE WIDER THE DIFERENCE THE BETTER

notice that as the 2 lane ( double pass rad) reaches the end it is closer to ambient? that means the DT is not as wide or less effective . this is in conjunction with more turns creating restriction.

so you say then if single pass has more advantage why so many double pass cores out?

voigts said:

My question is that in the real world, does using a dual pass vs using a single pass result in any measurable differences? A good pump like a DDC or D5 is going to be capable of blowing right through each with no problem. Isn't there a point where more flow/less restriction results in differences that are so small as to not really make a practical difference?

Click to expand...

the main reason is that in most systems the mounting of single pass is dificult and requires longer tubing runs due to CASE size and shape. the tubing ends up adding a counter balance amount of resistance to make up for the lack of resistance in the single pass.

to counter act this you have to design your case with my designs in mind and Severly shorten your tubing runs resulting in better cooling

This is what I was triing to explain. Hope it clears it up.