Product Viscosity Versus Shear

Chemical and Process Engineering Resources

Feb 11 2013 06:50 PM | Steve Hall in Fluid Flow

Shear Rate in Pipeline

The shear rate at the wall of a circular pipe is calculated with:

Eq. (8)

And here are the results:

Table 4: Viscosity Results
Parameter	Test 1	Test 2
Flow rate	220 kg/min	160 kg/min
Density	1.26	1.26
Pipe diameter	47.5 mm	47.5 mm
Velocity	1.65 m/s	1.20 ft/s
Shear rate	277 sec^-1	202 sec^-1
Viscosity at 25°C	68 cP	83 cP
Corrected viscosity, 34°C	42 cP	53 cP
Compare with calculation	39 cP	47 cP

Discussion and Conclusions

After correction for shear rate and temperature, viscosity measurements from the Brookfield viscometer result in reasonably good estimates of pipeline pressure drop. It is important to ensure that the sample has reached the target temperature of 25° before recording the reading.

The limitations in this study include:

1. Pressure gauge reading accuracy due to the range of the instrument and the relatively small value being read.
2. Estimated placebo product density.
3. Unknown dependency of viscosity on the time of the applied shear stress. Further measurements with the Brookfield viscometer could be made to determine if there is a time dependency.

References

ⁱHall, S.M., Rules of Thumb for Chemical Engineers, Butterworth-Heinemann (2012)

ⁱⁱSpecific gravity determined from the pump speed (40% x 449 rpm max) and capacity (0.96 l/rev). This gives volumetric flow rate. From the measured mass flow rate, the specific gravity is calculated. Results from the two flow tests were averaged to obtain a value of 1.26.

ⁱⁱⁱBrookfield Engineering Labs, More Solutions to Sticky Problems, downloaded from http://www.brookfieldengineering.com/

^ivPoling, B.E., Prausnitz, J.M., O’Connell, J.P., Properties of Gases and Liquids, Fifth Edition, McGraw-Hill (2001).