Liquid Controls SP3850 - Manual (Page 49)

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SP3850 Flow Computer
7.4 Computation of Viscosity Coef. A and B
The flow computer solves an equation which computes the viscosity as a
function of temperature. Two parameters must be entered for this
calculation to be performed. These are the setup parameters Viscosity
Coef. A and Viscosity Coef. B. A table listing these values for common
fluids is available in Appendix A.
Alternately, if your intended fluid is not listed, the Viscosity Coef. A and B
can be derived from two known temperature/viscosity pairs. Begin by
obtaining this information for you intended fluid. Convert these known
points to units of Degrees F and centipoise (cP)
The information is now in a suitable form to compute the Viscosity Coef. A
and Viscosity Coef. B using the following equation based on the fluid state.
For a liquid, A and B are computed as follows:
(T1 + 459.67) • (T2 + 459.67) • ln [ cP1/cP2]
B = ——————————————————————
(T2 + 459.67) - (T1 + 459.67)
cP1
A = ———————————
exp [ B / ( T1 + 459.67) ]
cP • Density of Water at 4 °C
NOTE: cS = ——————————————
Density of Fluid at Flowing Conditions
For a gas, A and B are computed as follows:
In [cP2 / cP1]
B = ————————————————
In (T2 + 459.67) / (T1 + 459.67)
cP1
A = ———————————
( T1 + 459.67) B
cP • Density of Water at 4 °C
NOTE: cS = ——————————————
Density of Fluid at Flowing Conditions
Computation of
Viscosity
Coef. A & B