Process Viscosity Measurement: In-Line Viscometers
Continuous measurement of fluid viscosity in pipelines: Galvanic ViscoSite VL800 Viscoliner process viscometer, product blending and quality control.
What is viscosity and why is it measured?
Viscosity is a fluid's resistance to flow, in other words its consistency. The performance and processability of many products, such as oils, heavy fuels, resins, paints, food products and polymers, depend on viscosity. In a process, viscosity determines the quality of product blending, pumping and atomization conditions and the progress of a chemical reaction. Because laboratory measurements require samples to be taken at intervals, continuous in-line measurement allows consistency deviations to be noticed immediately and blending or temperature adjustments to be made automatically.
Where is viscosity measured?
- Refinery and oil production: On fuel and oil blending lines.
- Chemical and polymer processes: In reaction and blending control.
- Paint, adhesive and food production: In quality control of product consistency.
How is viscosity measured?
Process viscometers measure the fluid's resistance to the vibration or movement of a sensor element immersed in it. For example, the VL800 Viscoliner sensor is a stainless steel probe with a cylindrical tip, connected to the pipeline by a flange; as the fluid's viscosity increases, the sensor's movement is damped, and the electronics unit converts this information to a viscosity value. Because temperature strongly affects viscosity, the measurement is generally assessed together with process temperature. The result is transmitted to the process control system through a current output or communication.
For high-viscosity and fouling fluids, sensor cleaning and calibration should also be included in the maintenance plan to keep the in-line measurement stable.
Choosing a viscometer
- Viscosity range and process temperature
- Sensor material and flange connection class
- Sensor position in the line and flow conditions
- Enclosure protection class and supply voltage
Viscosity measurement with Tetra
Tetra supplies the Galvanic ViscoSite process viscometer (VL800 Viscoliner) in Türkiye. Installation, commissioning, calibration and service are provided by Tetra.
Frequently asked questions
What are the units of viscosity?
Dynamic viscosity is expressed in Pa·s or mPa·s; 1 mPa·s equals 1 cP (centipoise). Kinematic viscosity is given in mm²/s, and 1 mm²/s equals 1 cSt (centistokes). Kinematic viscosity is found by dividing dynamic viscosity by density, so density must be known to convert between the two values.
Why does temperature matter in viscosity measurement?
For most liquids, viscosity falls markedly as temperature rises; even a difference of a few degrees can change the result significantly. In-line viscometers therefore also measure process temperature, and the result is converted to a reference temperature when required. When comparing with laboratory results, check that both measurements are expressed at the same temperature.
Why might an in-line viscometer read differently from a laboratory result?
In non-Newtonian fluids, viscosity depends on shear rate; a process sensor and a laboratory instrument measure at different shear rates, so results can differ. Temperature differences, deposits on the sensor surface and flow conditions at the sensor position also create differences. Carrying out a laboratory correlation during commissioning is therefore recommended.
Why is viscosity controlled on a fuel line?
For heavy fuel to atomize properly in burners and engines, it must be at a specific viscosity. An in-line viscometer keeps viscosity at the target value by adjusting the temperature of the fuel heater. This approach helps combustion conditions stay more stable even when fuel quality changes.
Products measuring this parameter
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