1/4 inch versus 3/8 inch versus 1/2 inch
 

I know size matters to some but my question is this?
We know that hi flow (gph) is better than lo flow ...
We also know that hi velocity is better than lo velocity ...
It seems people are going to bigger tubing for fluid transfer but it seems we want to increase velocity, at least on the cooler end and push through the fluid quickly.

Should we place smaller tubing on the cooling side to speed water through and place larger tubing on the radiator side to slow fluid down??

I am sooooo confused ????

Flow is determined in part by the narrowest part of the system. This is called a bottleneck. If you introduce a bottleneck you reduce flow thoughout the system.

I understand what you're thinking but unless you have a truely massive pump, I think the loss in total flow will more then balance out the gains from the increased pressure at the block.

Widening though is much more common. Heatercores use very large diameters (5/8 ro more then 3/4) inside to slow the flow through them.

Even though there is a "bottleneck" if the pump is capable of pumping to capacity then flow should remain the same and velocity of fluid will increase... river example below.

If a wide river suddenly narrows the same "amount" of water will flow across the banks but the water will flow "faster" across the narrow banks. Am I nuts??

no you're not nuts. The bottleneck will create a pressure difference (higher before, lower after). If this does not affect the pump (it will), the water would flow at the same rate. Since it does, your flow will drop slightly depending on the pump.
If you are using very small pump (120gph area) it will cause more of a problem. Unless you have a

Also I believe the length of the bottleneck makes a difference. IE, if the bottleneck is a small fitting the flow will be reduced less than if the bottleneck is a section of hose. 'sub-bottlenecks' can hurt flow too... IE if you reduce to 3/8 and then have curvy hoses or T junctions. Such things work better with large diameter.


For the first question, high flow GPH is good, but high velocity is not as important. Hi velocity would only be required if the water was colder than ambient in the tubing and you wanted it to get to the waterblock ASAP... this is only the case if you have a REALLY REALLY hot case or are using some kind of chiller. Even so, the gain you might get with high velocity might be offset by low flow, so stick with the larger diameter whenever possible.

Also increased pressure at the block is only good because it means more flow... increased pressure would help with air (denser air absorbes more heat) but not with water (same density when in liquid state)