OWWWWWWWWW, my head hurts after that.
Dave
Ron Soave wrote:
> --- "Wm. Severin Thompson" <wsthompson@thicko.com>
> wrote:
>
>>Ron (Grasshopper...the Unlearned One) is no doubt
>>sitting in his newly
>>purchased racecar in his garage, making vroom vroom
>>noises, with the wrong
>>stick shift in his hand...
>>
>
> Grasshoppah back from walking on rice paper without
> leaving mark...
>
> This is all from memory, so no one bitch if I leave
> out a few things. Pressure drop - the resistances
> need to be considered in series. Glen is correct that
> small fittings will control the resistance, but small
> lines + small fittings is worse than large lines +
> small fittings. To figure the difference, take
> diameter 1 and raise it to the 4th power. Take
> diameter 2, raise it to the 4th power it. Divide one
> by the other - that's your difference.
>
> Basically, the pressure drop is a defined by:
>
> DeltaP = K * q
>
> Looks a lot like V=I*R, right? and it is...
>
> q is the dynamic pressure, aka velocity pressure, aka
> "dynamic head" (easy, Flounder...). It is also .5 *
> density * velocity squared/gravity. So the velocity
> squared term dominates. What determines velocity?
>
> V=w/(density * flow area). So as the area gets
> smaller, the velocity gets higher at a given flow
> rate. The area is a function of diameter squared, and
> the q is a function of the velocity squared, hence the
> 4th power relationship above.
>
> So what is "k"? It's a resistance factor, also a
> function of geometry. For a hose, K=4fL/d, where 4f
> is the friction factor, L is the length of
> tubing/duct/etc, and d is the effective diameter of
> the duct. So as d decreases, K increases, delta P
> goes up. Again, small diameter is not good.
>
> What about 4F? f is equal to (.046)/(Re^.2). And Re
> is the Reynolds number, which is density X velocity X
> diameter divided by viscosity. Again, small diameter
> = high velocity, equals high Re, equals high f, equals
> more pressure drop.
>
> Enough of that, keep the restrictions small, the
> pressure DROP will be low.
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