(from Nexxos thread regarding PQ)
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Originally Posted by Cathar
To do it properly you really need to measure it.
For a "ballpark" though. Classic flow mechanics tells us that the level of flow resistance is proportional to the flow rate squared (P = Q ^ 2). This doesn't take into account turbulence and boundary layer conditions though.
For a fairly decent ballpark equation to extrapolate from OC.com's results I've personally found that P = Q ^ 1.85 offers a pretty decent approximation across the typical range of flow rates seen in water-cooling. P = pressure. Q = flow. Not as ideal as having real data, but when given a single pressure/flow point like OC.com I personally found it to give a fairly close ballpark curve.
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Re the P=Q^1.85 fit, I think there is a better way.
I assume you are familiar with the idea of a "k-factor", I stumbled across it recently when exploring the flow measurement problem.
Your PQ
curves are not behaving, shouldn't one be able to generate a constant which, even allowing for transitions between flow regimes and boundary conditions, is relatively flat across flowrate?. I am getting this with measured data, (see attachment) it is constant enough that I would propose that every block has a "K-factor", a constant encompassing restrictivity described by the equation: K=Q/sqrt(dP) or P=(Q/K)^2, essentially the flow rate squared relationship. It's probably your curve fit that I am seeing, it is not generating a constant. If it is real, that's very interesting, there's probably a way to extract a Reynolds number curve from it.
Sorry if I am being disruptive, I have not been following this closely but I thought the K-factor thing might be relevant. It for sure is another way to generate a PQ curve from a single data point...
