MIL-HDBK-1004/10
EQUATION:
R
=
0.012 P log (D/d)/L
(13)
where
R
=
anode-to-electrolyte resistance (ohms)
P
=
water resistivity (ohms-cm)
L
=
length of a single anode (feet) (backfill is not used)
D/d
=
ratio of anode diameter (d) to tank diameter (D)
(same units for each)
The anodes are usually arranged in a circular array in the tank bowl. The
optimum diameter of this array can be determined by the following formula:
EQUATION:
DN/2(B + N)
(14)
r
=
where
r
=
radius of anode array (feet)
D
=
tank diameter (feet)
N
=
number of anodes
If four or more anodes are used in a circular array, the following modified
Shepard formula should be used to calculate the resistance of the array:
EQUATION:
R
=
0.012 P log (D/a)/L
(15)
where
a
=
factor for equivalent diameter from table below,
multiplied by the optimum diameter of the anode circle
(calculated previously)
Number of
Factor for
Anodes
Equivalent
in Circle
Diameter
4
0.08
6
0.11
8
0.18
10
0.28
12
0.43
14
0.70
P
=
water resistivity (ohms-cm)
L
=
length of a single anode (feet)
D
=
tank diameter (feet)
Field Measurement. Calculations, as previously discussed, can give
6.2.1.5
good approximations of anode-to-electrolyte resistance under actual
conditions. While these calculations can be effectively used for system
design, if the environment is well known, the actual anode-to-electrolyte
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