Pressure drop in tubing?

[Cronos]

I am thinking about external radiator module, with possibly 3x PA120.3 (already have 2) and one big AC fan, ~36x36cm, with shroud. Fan will be well isolated, so that entire module can be mounted in the open window or even outside.

The tubing should be at least 2m long one direction, 4m total. Tubing will be Tygon Antimicrobial, 1/2" ID.

I have calculated pressure drop for the flow ~ 1gpm, and for laminar case it should be very low, on the order of 0.1 PSI.
( Very helpful link here: http://hyperphysics.phy-astr.gsu.edu...ppois.html#poi )

However, if we estimate Reynolds number http://hyperphysics.phy-astr.gsu.edu...turb.html#turb ,
it is well above critical value 2000 ( by the way, that means all typical WC setups have turbulent flow) .

Therefore, the pressure drop cannot be estimated from simple Poiseuille's Law and should be much higher.

The question is, how much higher? 1 or 2 Psi is good enough, however 10psi is not acceptable. Anybody have any information concerning real pressure drop in the tubing that long?

[Chas_The_Man]

1 - 2 PSI / 10' of tubing for 1 - 2 GPM flow is the rule of thumb. So, its not a lot. Just buy some tubing and test it in a bucket. The curvature of the tubing will have more effect than the length. Ie, snaking across the floor and then up and out a window... well, that will be a lot worse than 10' of tubing straight horizontal. 3 Rads is the way to go for an external box I think. 2 for the CPU and 1 for the GPU / GPU's. With three, I don’t think you need Thermochills. I have 2 but I just bought Swiftechs to replace them in my external box design. Im going to save the Thermochills for another project. I'm using 3 pumps too. 2 for the CPU loop in series and one for the GPU loop. After running my Zalman on the QX6700 with about 12 feet of 3/8 tube, I find worries about flow restriction in tubing somewhat overblown.