Rotameter type viscometers are used both industrially and in the pilot plant to measure the viscosity of the process fluids and continuously indicate, record or control the process. This type of viscometer is used in a closed flow system
Viscometer has been successfully used to maximize combustion efficiency by controlling the viscosity of fuel oils in marine boilers and stationery
Operating principle of viscometer:
The operating principle is similar to that of the variable area flow meter, where the viscous drag force on a float is proportional to the opening of the required orifice (between the float and the conical tube) to move the fluid through that orifice at a constant flow rate.
In a flow meter type rotameter, the forces acting on the float are affected by the flow rate, by the floating weight and the specific gravity of the liquid, and by the viscosity of the fluid being measured.
For flow metering applications, the floats are designed so that the viscous drag area is relatively small, so the float is relatively insensitive to viscosity. In the viscometer version of this design, the flow rate through the variable area meter is held constant
Construction and Working of Viscosmeter
To obtain accurate viscosity measurements with rotameter-type viscometers, the flow rate must be constant. Because this required flow control can be obtained in three different ways, there are three different designs: single float, double float and concentric float.
The simple float viscometer is a direct and continuous reading viscosity instrument. A positive displacement pump (other flow control devices can also be used) provides the constant sample flow rate through the instrument
The single float viscometer is also available as a transmitter that is used when screens or remote controls are required. In this case, the position of the float is detected by the use of an armature attached to the float extension bar with a magnetic detection device around its outer periphery.
The recommended flow rate is between 0.75 and 2.0 GPM (2.9 and 7.6 l/m).
The glass tube viscometer is rated for 450° F (232° C) temperature and for 90 PSIG (621 kPa) pressure.
