Quote:
Originally posted by bigben2k
Reynolds calculation
v=14.2 m/s
a=0.001 m
b=0.005 m
A=0.000005 m^2
P(or C)=0.031 m
d'=0.00167 by 8 channels= .0134
So Reynolds = 14.2 * .0134 / 8.9*10-4
= 107 ?
(didn't I say I needed help )
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Sorry Ben, but it's time to get yourself a decent fluids text. You are mixing "hydraulic diameter" and "characteristic dimension". A hydraulic diameter applies to calculating an equivalent diameter for a non-circular flow pathway. It's really useful when working with channels, which are typically rectangular or v-shaped (or something else comprised of straight sides). Before you try calculating and applying a Reynolds number, ya really ought to know what it represents (and why one would bother to calculate it).
Once you do that, you'll find that pressure drop across an orifice is not something that's analytically defined. There are general relationships that use coefficients dependent upon the shape of the orifice. The relationships are based on classical physics while the coefficients are the "as measured fudge factors" determined through careful lab experimentation over the years. You're really, really putting the horse ahead of the cart right now. You can run all the "calcs" you wish, but until you get the understanding behind them they are of little value.
Honestly you will be hard pressed to find existing data to determine how your intended entrance will perform with your pump (and the rest of your system). You can take pot shots at it, but the only way to be confident that you're even within +/- 20% is to build and measure. Even then, you'll only be just starting to find out what is really "best".
Find out more about orifice calcs, pressure drops, and Reynolds numbers. Rough out where you think you need to be (range of +/- 50%). Start prototyping some stuff to see where you really are.