Viscometer
Viscosity is a measure of resistance to flow for a liquid. Higher viscosity means a stronger resistance to flow. Determining intrinsic viscosity and kinematic viscosity is a fundamental requirement to properly carry out many industrial and manufacturing processes, including food preparation. Rotary rheometers, viscometers or viscosimeters are used to measure fluid or other properties of materials such as their viscosity. Viscometers are known to use a variety of configurations to measure rheological properties of a fluid. In measurement and automation technology, the viscosity of a fluid flowing in a pipe, particularly of a liquid, is frequently determined by means of meters which, using a vibratory transducer and meter electronics connected thereto, induce internal friction forces in the fluid and derive therefrom a measurement signal representative of the respective viscosity. Vibratory viscometers generally employ a transducer which has an immersible portion which is vibrated with a small amplitude. Fluid viscosity/density/viscoelasticity can be determined from the frequency and/or amplitude changes in the vibration and/or the power required to sustain the vibration when the immersible portion of the transducer is immersed in a fluid. Rotational vibratory viscometers generally comprise a transducer having a tip immersible in a fluid the viscosity of which is to be determined, an electromagnetic drive coil for causing the tip to rotationally oscillate with a very small angular amplitude, a feedback control circuit for maintaining the angular amplitude of oscillation of the tip at a predetermined constant value irrespective of the viscosity of the fluid, and a circuit for determining the power supplied to the drive coil. A capillary viscometer is commonly used because of its inherent features such as simplicity, accuracy, similarity to process flows like extrusion dies, no free surface, etc. In capillary viscometers, liquid is made to flow through a capillary tube under a known pressure difference and the measured rate of flow is used to calculate the viscosity. The capillary viscometer, though inexpensive and simple to use, is mostly limited to Newtonian liquids due to the fact that the velocity in the tube and, therefore, the shear rate is constant. In the cone and plate viscometer, liquid is sheared between an inverted rotating cone and a stationary flat plate and the torque required to turn the cone at a known angular velocity determines the viscosity. While comparatively expensive, the cone and plate viscometer allows analysis of all aspects of rheological behavior.
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