Jump to content



Chemical and Process Engineering Resources

Product Viscosity Versus Shear

Feb 11 2013 06:50 PM | Steve Hall in Fluid Flow ***-- Share this topic:
| More

Viscosity Measurements

Pseudoplastic compounds follow a power curve, with viscosity decreasing with shear rate. Viscosity measurements were performed with a Brookfield Viscometer, Model LVDV-II+. Using the #31 spindle and Sample Adapter 13R cup, shear rate is determined by multiplying the rotational speed by 0.34iii. This gives the following raw data for the placebo product made for the tests:

Table 3: Viscosity Measurements

RPM

Viscosity (cP)

Torque (%)

Shear Rate, sec-1

0.5

8338

13.9

0.17

1.0

5159

17.2

0.34

1.5

3919

19.6

0.51

3.0

2449

24.6

1.02

6.0

1540

30.8

2.04

12.0

977.3

39.1

4.08

20.0

706.3

47.1

6.8

30.0

551.9

55.2

10.2

45.0

435.2

65.3

15.3

60.0

370.4

74.1

20.4

100.0

283.7

94.6

34

150.0

EEEE

EEEE

 

Measurements made at 25°C

Here are the data charted in Excel with the trend line and trend line equation superimposed:

figure-1
Figure 1: Graph of Viscosity Data with Trend Line

The power law equation for apparent viscosity is:

μa = K γn-1 Eq. (6)

K = flow consistency index, Pa-sn = flow behavior index, dimensionless

Viscosity is in units Pa-s. Since our data is in cP (=mPa-s), the values of K and n are 2.53 and 0.356.

The viscometer’s measurement range is limited, but extrapolation is acceptable with decreased accuracy.

Using the trend line equation, the viscosity at any shear rate is estimated. But this is for a temperature of 25°C. Since data at only one temperature is given, the Lewis and Squires temperature correlation is used to estimate the viscosity at the actual flowing condition.

figure-2
Figure 2: Lewis and Squires Temperature Correlation

The equation for this chart isiv:

eq-7 Eq. (7)





Fluid Flow Articles



6 Comments

Very good read.  I currently am working with a client in the ~400 to ~600 cP viscosity range.  This analysis will be very helpful.

 

Mark

Photo
tarang.suthar
Apr 05 2013 11:29 AM

Please give me the Viscosity calculation in Excel sheet with various Ointment and other Viscous Material

Thank you, can you also include the schmatic diagram of the set up.

Is this excellent article available as a pdf download?

Photo
Chris Haslego
Sep 11 2014 01:28 PM

Is this excellent article available as a pdf download?

Sent it to you via PM.

Photo
techno_titan
Oct 27 2014 12:17 AM

Very interesting article. May I use this as a case study for teaching my fluid dynamics class?