fann 35A - Additional Viscosity Calculation Formulas

Model 35 Viscometer Instruction Manual
208878 Revision N, February 2013 31
7.4 Additional Viscosity Calculations
The viscosity can also be computed using the following equations. Conversion
factors are listed in Table 7-5.
η = Kf
θ
N
Equation 7-5
where
K is the overall instrument constant in (dyne-sec/cm
2
) (rpm/degree deflection)
f is the torsion spring factor
θ is the Fann viscometer reading
N is the rate of revolution of the outer cylinder
η is the viscosity in cP
For Equation 7-5, choose the correct K value (overall instrument
constant) that matches the rotor-bob combination in Table 7-4.
Choose the f constant that matches the torsion spring assembly
in Table 7-3.
For Equation 7-5, choose the correct K value (overall instrument
constant) that matches the rotor-bob combination in Table 7-4.
Choose the f constant that matches the torsion spring assembly
in Table 7-3.
η =
k
1
k
2
k
3
(100)
θ
N
Equation 7-6
where
k
1
is the torsion constant, dyne-cm/degree deflection
k
2
is the shear stress constant for the effective bob surface, cm
3
k
3
is the shear rate constant, sec
-1
per rpm
100 is the conversion factor, 1 poise = 100 cP
θ is the Fann viscometer reading
N is the rate of revolution of the outer cylinder
η is the viscosity, cP