What is the apparent viscosity of a fluid?
The apparent viscosity of a fluid depends on the shear rate at which it is measured. The apparent viscosity of a dilatant fluid is higher when measured at a higher shear rate (η4 is higher than η3), while the apparent viscosity of a Bingham plastic is lower (η2 is lower than η1).
How do you find the apparent viscosity of a non-Newtonian fluid?
For most non-Newtonian fluids the constitutive relation between the deviatoric stress tensor T and the applied strain rates E can be described by a time independent scalar function μ=μ(˙γ), such that T=2μ(˙γ)E.
What method can be used to determine the viscosity of fluids?
Viscosity can also be measured by applying oscillating vibrations to the sample and monitoring the damping effects of the fluid. These can be assessed by monitoring power input, the decay time of oscillations, or changes in the resonated frequency.
What are the three types of viscosity?
Types of Viscosity & When to Apply Them
- Dynamic (absolute) viscosity – the measurement of the fluid’s internal resistance to flow when force is applied.
- Kinematic viscosity – refers to the ratio of dynamic viscosity to density, or a measurement of the viscosity of a fluid in motion.
How is apparent viscosity measured?
Apparent (shear) viscosity: Apparent, or shear, viscosity refers to the relationship between viscosity and shear rate. In Newtonian fluids, this value doesn’t change, but with non-Newtonian fluids, apparent viscosity is directly affected by the shear rate. It can be calculated by dividing shear stress by shear rate.
Can apparent viscosity negative?
No viscosity cannot be negative. Viscosity is a measure of momentum diffusion which cannot become negative since it would imply a violation of second principle of thermodynamics.
How do you find the viscosity of a Newtonian fluid?
The more usual form of this relationship, called Newton’s equation , states that the resulting shear of a fluid is directly proportional to the force applied and inversely proportional to its viscosity. The similarity to Newton’s second law of motion (F = ma) should be apparent….(dynamic) viscosity.
| F | = η | dvx |
|---|---|---|
| A | dz |
Is Bingham plastic a Newtonian fluid?
For Bingham plastic fluid, the shear stress beyond the yield stress is linearly proportional to the shear rate. If the yield stress approaches zero, the Bingham plastic fluid can be approximately treated as a Newtonian fluid.
What is cup and bob viscometer?
They measure the torque required to rotate a disk or bob in a fluid at a known speed. “Cup and bob” viscometers work by defining the exact volume of a sample to be sheared within a test cell; the torque required to achieve a certain rotational speed is measured and plotted.
What are Bingham bodies?
A Bingham plastic is a viscoplastic material that behaves as a rigid body at low stresses but flows as a viscous fluid at high stress. It is named after Eugene C. It is used as a common mathematical model of mud flow in drilling engineering, and in the handling of slurries.
How is viscosity measured?
The viscosity of a liquid (see Viscosity) is measured using a viscometer, and the best viscometers are those which are able to create and control simple flow fields.
What is apparent viscosity?
Apparent viscosity (sometimes denoted η) is the shear stress applied to a fluid divided by the shear rate ( η = τ γ ˙ ). For a Newtonian fluid, the apparent viscosity is constant, and equal to the Newtonian viscosity of the fluid, but for non-Newtonian fluids, the apparent viscosity depends on the shear rate.
Can viscosity be measured without knowing the shear rate?
In the case of non-Newtonian fluids, measurement of apparent viscosity without knowledge of the shear rate is of limited value: the measurement cannot be compared to other measurements if the speed and geometry of the two instruments is not identical.
What is a single viscosity measurement at a constant speed?
A single viscosity measurement at a constant speed in a typical viscometer is a measurement of the apparent viscosity of a fluid.
Why is viscosity measurement important for rheological fluids?
Measurement of apparent viscosity for rheological fluids is extremely important for a variety of industrial processes such as transportation of slurries in mineral processing, petrochemical and chemical processing, rheocasting of metal matrix composite, etc.