restriciting flow rates

[curnow]

I read this: Restrict the flow as necessary to get the best temps
here: http://forums.overclockers.ws/vb/showthread.php?s=&postid=353340&t=7097#post353340

I have a fairly high capacity pump (1100 litres/290 gallons an hour). Should I possibly think about slowing the flow rate in my system? And, if so, where should it be slowed to improve the temps?

[The Overclocker]

water should go through the radiator slowly and through the water block fast, so there is a problem here already, put a kink in the tube infront of the radiator and see if this makes a difference

[azhari]

Originally posted by the overclocker
water should go through the radiator slowly and through the water block fast, so there is a problem here already, put a kink in the tube infront of the radiator and see if this makes a difference
Wouldn't that restrict the water flow through the whole system, including the block? Shouldn't matter where the kink is. Sounds like what needs to be done is to have small diameter flow channels in the block (which will speed up the flow through the block) and large diameter pipes in the radiator (to slow down the flow).

Anyone try this combination? What were your results?

[BillA]

flow rate is being confused with velocity

the coolant flow rate is defined by the pump capability "against" the total "restriction" of the system

the velocity at any point within the system is related to the cross-sectional area at that point

larger diameter = slower flow (not lower, just slower)

slow flow velocity through the radiator (relative to the wb flow rate) is achieved by component selection

be cool

[Stephen Castles]

i have a 300gph pump and the way mine will be set up is:

the water pump at the bottom of the case will move water up the the water block then to the radiator at the top up the case. by the time the water gets the the block it's still moving pretty fast, but once it's gotten to the radiator it's slowed down alot. This setup works well

[cld230]

Hmmm... as I see it, unless you have a reservoir in your system somewhere that is either getting really full, or really empty, your flow rate is going to be the same throughout the system. (ie. amount of water leaving the pump = amount of water going into the pump).

What you are trying to do by adjusting the flow rate through your system, is make sure that the temperature of the water coming out of the reservoir is as close as possible to ambient, while running as high of a flow through your block as possible. The flow rate through both will always be the same. Adjusting your flow rate will find a happy balance between these where your reservoir won't heat up, but you are maximizing the flow through your waterblock.

[cld230]

Originally posted by azhari

Wouldn't that restrict the water flow through the whole system, including the block? Shouldn't matter where the kink is. Sounds like what needs to be done is to have small diameter flow channels in the block (which will speed up the flow through the block) and large diameter pipes in the radiator (to slow down the flow).

Your flow rate through the system will be constant. Large pipes in the radiator MAY result in the radiator having a larger volume, so the water has more time to exchange heat. If the volume in the radiator is the same, small pipes will have more surface area. You would be comparing a huge length of small pipe to a short length of a big pipe. The small pipe will have much more flow resistance, so that could be good or bad depending on your pump, but if the flow rate is kept the same, the extra surface area is a benefit.

[Owenator]

The issue hear is flow velocity or speed versus the volumetric flow rate. GPM is a volumetric flow rate the volume of water moving around the system. TO get better heat transfer you sometimes slow down the 'speed' of the water by increasing the area of the flow channel, that's why bigger tubing can help, it slows down the speed of the fluid but the same volume i sbeing moved. I have been toying with the ideal of having two tubing sizes. 1/2" ID from the pump to the radiator, 3/8" tubing from the rad to the water block, and then 1/2" tubing from the water block back to the pump. The idea is that the flow will have less retriction until it needs to speed up to go into the water block. Also, it's important to note that the restriction to flow or flow resistance will be lower on larger tubing that smaller so the pump will have an easier time and put out more flow if you drop the flow resistance of the whole system. Just my $0.02.

O

[cld230]

Originally posted by Owenator
I have been toying with the ideal of having two tubing sizes. 1/2" ID from the pump to the radiator, 3/8" tubing from the rad to the water block, and then 1/2" tubing from the water block back to the pump. The idea is that the flow will have less retriction until it needs to speed up to go into the water block. Also, it's important to note that the restriction to flow or flow resistance will be lower on larger tubing that smaller so the pump will have an easier time and put out more flow if you drop the flow resistance of the whole system. Just my $0.02.

O


I agree with the part here that says that the larger tubing will give you less flow resistance and make life easier for your pump. I'm not sure about the whole notion of using smaller tubing to get the water to "speed up" before going into the water block. If your water block doesn't change, and the flow restriction introduced by a reducer at the water block is less than the resistance due to the length of narrower tubing, your total pressure drop through the system will be less, your flow rate will be higher, and the flow velocity through your water block (flow rate / area) will be higher.

[Owenator]

Originally posted by cld230



I agree with the part here that says that the larger tubing will give you less flow resistance and make life easier for your pump. I'm not sure about the whole notion of using smaller tubing to get the water to "speed up" before going into the water block. If your water block doesn't change, and the flow restriction introduced by a reducer at the water block is less than the resistance due to the length of narrower tubing, your total pressure drop through the system will be less, your flow rate will be higher, and the flow velocity through your water block (flow rate / area) will be higher.

You are right. I want the flowrate to increase in the entire system. I haven't calculated it but the idea is that the increased flowrate will have higher velocity in the block but the larger flow area of the large tubing will slow the water into the radiator. I was even toying with the idea of using 3/4" ID tubing in the system except for the rad to block connection. The idea is to have the water block be the largest flow resistance and hence highest flow velocity but keep the rest of the system "free flowing" with low resistance. In any case my pump still has to over come the gravity head flow resistance from the pump to the rad mounted in the top back of my case. I am estimating that the gravity head is the highest resistance at about 12" (of H2O). I may dig out my Fluid Dynamics text and do a more rigorous calc. if I have time.

O