Solved: Relation between nozzle size, length and extrusion force (pressure)

I remember seeing a formular somewhere (here? Hydraraptor?) that showed the dependency between
nozzle diameter, length and the required extrusion force.

I seem to remember that' it's a fourth power law
on the diameter, and it has even had a name ('somebody's law'), but I can't find it anymore - my google
foo seems to be lacking today.

Does anybody have the formula or a link for me?

Thanks!

So long,
Tyberius Prime

Edited 1 time(s). Last edit at 12/12/2012 12:44PM by tprime.

Obviously, thirty seconds after posting this, I find nopheads description at [hydraraptor.blogspot.de]

I was once taught a infrared heat loss equation and told that it was one of few natural equations with a fourth-order variable. I never saw any others until now.... and WOW. I never thought that this was fourth order! For sure, I've noticed that going from .5 mm to 1 mm nozzle felt close to r^4 more easy to push filament through by hand (2^4 = 16 times easier). This concerns me for the .15 mm diameter I've been planning to try soon : /

Bending stiffness is proportional to the 4th order of the radius - hence why 10mm rods are much stiffer than 8mm.

Within stars you can get some silly size power approximations of exponents. The helium flash in a star has a reaction rate proportional to the 40th power of temperature! (according to xkcd)

Not relevant but quite interesting!

Edited 1 time(s). Last edit at 12/14/2012 04:03AM by konwiddak.