Originally Posted by TK421
How is it possible that he runs the GPU waterblock in parallel? Won't one of the card receive less flow because of water physics?
Don't quote "water physics" if you don't understand "water physics".
Water flows from a point of high water pressure to a point of low water pressure. The flow rate is higher when the pressure differential is higher. This is true of any fluid (i.e. air) and is also true for electricity (replace "pressure" with "voltage" and "flow rate" with "current").
The pump (battery) is the source of pressure (voltage) and each waterblock (light bulb) is a restriction in the loop (circuit) which eventually brings the pressure (voltage) to zero when you reach the reservoir (ground). Tubing (wiring) offers almost zero resistance so any two points connected by only tubing (wiring) are at the same pressure (voltage). This is true at the entrance or exit to both blocks (light bulbs). If the blocks (bulbs) are the same, then the flow (current) through either will be the same.
Now, if you have two in parallel and they're identical, the flow will be split in half exactly, which shouldn't be an issue if your flow is sufficient to begin with. Less intuitively, the overall restriction added to your loop is LESS if the GPU's are in parallel versus in series. This is where fluids and electricity are different: The restriction offered by a block is a function of how fast the water is moving. When there are two blocks in parallel, the flow is split so the water's speed is cut in half. The viscous friction is non-linear so cutting the speed in half drops the friction factor by 1/4.
What is surprising then is that your flow rate is higher if your GPU's are in parallel so you actually get a bit more than "half". The GPU's are still in series with the rest of your loop though, so the impact is small.
4-way GPU's are usually in semi-parallel with 2 pairs of parallel GPU's in series with each other because 1/4 flow rate is probably a bad thing unless you have two pumps or a completely separate GPU loop.
(Source: two fluid dynamics courses and one Hydraulics course in a Mechanical Engineering Program)Edited by YawMawn - 4/17/15 at 12:09pm