Re: Rougtero Water Screw

[Benjamin Austin <jedi@ecn.purdue.edu>]

On Thu, 29 Oct 1998, Kris Ames wrote:

> > > 
> > > To fly you have to move a lot of air (very compressible stuff) at a
> > > pretty good clip. To pump water (to either move the water or, in the
> > > case of screw powered boats and subs, move the pump) is much easier
> > > since water is not compressible. Dervish powered screws are where its
> > > at :)
> > > 
> > > Using the screw pump you can change the tubing diameters to get
> > > pressure variences to force better speed than just moving water.
> > > 
> > > Using an inverted screw could be even more successful...
> > > 
> > > 						-Steve
> > 
> > 
> > unfortunately, the flow rate can't change, so the point is moot.  A
> tower 
> > from which the water can flow is the best plan.  Screwing air will
> never
> > work, but that is a fluid dynamics thing and you should ask Kris.
> > (hahaha)  We had to wait for lift from aero to fly.> 
> 
> 
> True flowrate (volume per time) will not change but the velocity at any
> point can be changes by bigger/smaller:
> 
> m'(mass flow rate) = Density * Velocity * Crossectional Area of pipe. 
> Assuming the mass flow rate is constant (it could vary if the people
> powering the screw are intermittent and lazy)  the velocity must change
> when the pipe diameter changes since density is also a constant.
> 
> As far as screwing air (unless we are not talking spider monkey's here), 
> I don't think that is possible either mainly because air is compressible
> and there fore would not enter the screw to begin with unless it was
> pressurized to do so.  If you are capable of pressurizing the air then
> their in no need to use a screw any way since you can make things flow
> due to the pressure differential.
> 

All that you would need is a fan (a very small screw) connected to a 
shaft and a method to increse the pressure/temperature on one side of it 
(ie. some firemage spell).  Gee, if the people at Pratt & Whitney only 
knew how to cast fire spells, turbines would be a lot more efficient.

BJ