Viscosity and temperature are interdependent. Correlating viscosity data between the process and the laboratory can be difficult, especially when the process temperature fluctuates and the lab viscosity measurements are taken at a fixed temperature. More often than not, periodic lab viscosity measurements are not adequate for process control as process changes can result in drift and the result is that the actual viscosity od the end-product and end up significantly different from the lab projection.
The answer to this problem is TCV or Temperature Compensated Viscosity.
TCV provides an accurate calculation of viscosity at a specific reference temperature which differs from actual process conditions. This function assumes a linear relationship between temperature and the double logarithm of viscosity and is based on ASTM Method D341. Once enabled, TCV is highly accurate for Newtonian hydrocarbons and yields a reliable approximation for most other Newtonian and non-Newtonian fluids.
The ViscoPro2100 viscometer incorporates a TCV feature and it can be enabled through the Web User Interface (UI). The following article provides you with the necessary information to enable and set-up the Temperature Compensated Viscosity feature on your viscometer so that you can adequately correlate the process viscosity and laboratory viscosity and provide uniform product to your customers.
The reference temperature is the temperature at which it is desired that the viscosity be calculated at. For maximum accuracy, it is recommended that this be set within two degrees of actual process conditions.
For every fluid, the relationship between viscosity and temperature will be somewhat different and this correlation is described using the coefficient TCC (Temperature Compensation Coefficient). To calculate TCC for a given fluid, the viscosity of the fluid should be known at two different temperatures. For maximum accuracy, these two temperatures be 20°C apart and that they bracket the actual process temperature at +/-10C. The parameter TCC is given by:
where the fluid has viscosity η1 (cP) at temperature ϴ1 (°C) and viscosity n2 (cP) at temperature ϴ2 (°C).
As an example, if the expected operating temperature is +40°C, it would be appropriate to use viscosity values measured at both 35 and 45°C to calculate TCC. Suppose the viscosity of the fluid is 209.5 cP at 35°C and 117.8 cP at 45°C. The TCC parameter is determined as:
This calculated 3.547 TCC value can now be entered along with the desired 40C reference temperature using the ViscoPro2100 Web UI under Configure..Calculations..TCV. TCV values will now be logged and can also be shown directly on the ViscoPro2100 viscometer display in the Configure..System..Display menu.
Contact sales@cambridgeviscosity.com with any questions.
