Through all the info Ive seen over the years relating to Stans "cell" no one has mentioned the surface area of the plates of 'their' designs or reasoning behind it.
The earliest info I read , Stan had a central pipe of 5 in, x 1/2 in, dia with an outside pipe of
4 in, x 3/4 in, dia .
If you calculate the surface area of the 5 in, pipe it is equal to the inside area of the 4 in, pipe.
length ;5 in,=127mm
diameter ;1/2 in,=12.7mm
circumference =2 x pi x radius =39.898mm
Area = length x circumference ; 127mm x 39.898mm = 5067mm
The pipe thickness is 1/16 in, and the gap is also 1/16 in, = 1.5875mm
From that calculation you can find the predicted capacitance using area ,distance between plates and the so called permittivity of water .
The calculated capacitance for the SS pipes is by standard formula
C = er x e0 x A / d
er = relative permittivity , this case = 80.37 or 80 or 78.54 ,depending on source of info
e0 = permittivity of free space = 8.854^-12 , (thats .000000000008854)
A = Area ,in metres , this case = .005067 metres
d =distance between plates = .0015875 metres ( 1/16 inch )
answer 80.37 = 2.27 nf
80 = 2.26 nf
78.54 = 2.22 nf
If you change pipe dia or length you have to recalculate ,remembering the outside pipes wall thickness is subtracted from its dia ,its the inside dia your after to find its inside area.
Theres a difference between using square plates and using pipes as plates
a square has 4 sides and 2 surfaces
a pipe has 2 sides and 2 surfaces
The stainless pipe is seam welded so the 2 sides are brought tegether leaving the top and bottom
as the only 2 'sides'
Maybe this helps where there is no leakage of the E field ,only at the top and bottom ??
(A toroid coil contains its mag field by having no air gap in its core as opposed to a solenoid core having the field escape at the ends)
one way to calculate the length of the outside pipe is to start with the surface area of the centre
pipe and divide that by the internal circumference of the outside pipe.
In the case of a 3/4 inch pipe, you subtract the wall thickness of 1/16 inch.
3/4 inch = 19.05mm - 3.175mm = 15.875mm internal diameter
15.875mm x pi = 49.87mm circumference
Area 5067 / 49.87mm = 101.6mm length , which is bang on 4 inch