
Model 35 Viscometer Instruction Manual
208878
Revision N, February 2013
32
η
=
γ
τ
Equation 7-7
where
τ
is the shear stress, dynes/cm
2
τ
is also calculated as k
1
k
2
θ
γ
is the shear rate, sec
-1
γ
is also calculated as k
3
N
η
is the viscosity, Poise
Table 7-4 Constants for Viscosity Calculations
Constant
Rotor-Bob Combinations
R1 B1
R2 B1
R3 B1
R1 B2
R1 B3
R1 B4
Overall Instrument Constant, K
Standard F1 Torsion Spring
η
= Kf
θ
/N
300
94.18
1355
2672
7620
15,200
Shear Rate Constant k
3
,
(sec
-1
per rpm)
1.7023
5.4225
0.377
0.377
0.268
0.268
Shear Stress Constant for
Effective Bob Surface k
2
,
(cm
-3
)
0.01323
0.01323
0.01323
0.0261
0.0529
0.106
Table 7-5 Conversion Factors
Symbol
Unit
Conversion Factor
SI Units
Shear Stress
τ
Pa
(Newton/m
2
)
1 Pa = 10 dynes/cm
2
Shear Rate
γ
s
-1
1 s
-1
(no change)
Viscosity
ƞ
Pa
⋅
s
mPa
⋅
s
1 Pa
⋅
s = 10 poise
1 mPa
⋅
s = 1 cP
Oilfield Units (R1-B1-F1)
Shear Stress
τ
dynes/cm
2
1
•
Fann = 5.11 dynes/cm
2
Shear Stress
τ
lb/100 ft
2
1
•
Fann = 1.065 lb/100 ft
2
Shear Stress
(approx.)
τ
lb/100 ft
2
1
•
Fann = 1 lb/100 ft
2
Shear Rate
γ
1/sec
1/sec = 1.7023 N
Viscosity
µ
cP
µ = (5.11
θ
/ 1.70N) x 100= 300 x (
θ
/ N)
Effective Viscosity
µ
e
cP
µ
e
= 300 x (
θ
/ N)