# Bioprocess Engineering Questions and Answers – Non Newtonian Fluids

This set of Bioprocess Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Non Newtonian Fluids”.

1. Apparent viscosity for Non- Newtonian fluid is ____________
a) Constant
b) Depends on the shear stress
c) Depends on the shear rate
d) Dynamic

Explanation: Apparent viscosity (sometimes denoted η) is the shear stress applied to a fluid divided by the shear rate. 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. In such case, the ratio between shear stress and shear rate is not constant; nevertheless, this ratio for non- Newtonian fluids.

2. What is the SI unit of apparent viscosity?
a) Pascal – second
b) Pascal
c) Newton – second
d) Newton / hr

Explanation: Apparent viscosity has the SI derived unit Pa•s (Pascal-second, but the centipoise is frequently used in practice: (1 mPa•s = 1 cP).

3. In the following Equation, what does “n” represents?
τ = K $$\dot{\gamma}^n$$
a) Fluid behavior index
b) Flow behavior index
c) Fluent behavior index
d) Newtonian fluid behavior index

Explanation: Power law:
τ = K $$\dot{\gamma}^n$$
Where, τ is the shear stress, K is the consistency index, (γ) ̇is shear rate, and n is the flow behavior index. The parameters K and n characterize the rheology of power-law fluids. The flow behavior index n is dimensionless.

4. Which of the following is an example of Bingham plastic?
a) Blood
b) Starch
c) Paints
d) Toothpaste

Explanation: 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 used as a common mathematical model of mud flow in drilling engineering, and in the handling of slurries. A common example is toothpaste, which will not be extruded until a certain pressure is applied to the tube. It then is pushed out as a solid plug.

5. Which of the following represents the graph and estimate it with the correct properties?
a) Dilatant, Decreases with increasing shear rate
b) Pseudoplastic, Decreases with increasing shear rate
c) Bingham plastic, Increases with increasing shear rate
d) Casson plastic, Increases with increasing shear rate

Explanation: In a shear thinning fluid, or pseudoplastic fluid, apparent viscosity decreases with increased stress.
μa = K$$\dot{\gamma}^{n-1}$$
Where, n<1.
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6. The Thixotropic fluid characteristic is common in cell cultures.
a) True
b) False

Explanation: Thixotropic behaviour is not uncommon in cultures containing fungal mycelia or extracellular microbial polysaccharides, and appears to be related to reversible ‘structure’ effects associ – ated with the orientation of cells and macromolecules in the fluid.

7. “In Rheopectic fluid apparent viscosity decreases with time the fluid”?
a) True
b) False

Explanation: When a shear force is exerted on some fluids, the apparent viscosity either increases or decreases with duration of the force. If apparent viscosity increases with time, the fluid is said to be rheopectic; rheopectic fluids are relatively rare in occurrence. If apparent viscosity decreases with time the fluid is thixotropic.

8. The S.I unit of kinematic viscosity (v) is __________
a) m/s2
b) m2/s
c) m/s
d) ms2

Explanation: The SI unit of kinematic viscosity is m2/s. The cgs physical unit for kinematic viscosity is the stokes (St).
1 St = 1 cm2•s−1 = 10−4 m2•s−1.

9. A Static fluid can have ___________
a) Zero normal stress and non-zero shear stress
b) Non-zero normal and shear stress
c) Negative normal stress and zero shear stress
d) Positive normal stress and zero shear stress

Explanation: Fluid with zero shear stress within it is known as static fluid. When ever fluid moves it undergoes continuous deformation due to shear (caused due to viscosity of the fluid). So when the fluid is in rest no shear stress develops and only normal stress exists. So static fluid has zero shear stress.

10. Which of the following is shear thinning fluid?
a) Pseudoplastic
b) Dilatant
c) Rheopectic
d) Bingham plastic

Explanation: In rheology, shear thinning is the non-Newtonian behavior of fluids whose viscosity decreases under shear strain. It is sometimes considered synonymous for pseudoplastic behaviour, and is usually defined as excluding time-dependent effects, such as thixotropy. Shear-thinning behaviour is generally not seen in pure liquids with low molecular mass, or ideal solutions of small molecules like sucrose or sodium chloride, but is often seen in polymer solutions and molten polymers, and complex fluids and suspensions like ketchup, whipped cream, blood, paint, and nail polish.

11. When n>1, which of the fluid does it represents?
a) Pseudoplastic
b) Bingham
c) Newtonian
d) Dilatant

Explanation: When physicochemical interactions create bonds that are strong enough to resist breakage during shear, this mechanism would dominate and dilatant (shear-thickening) behavior is observed. Shear-thinning fluids are used for lubrication and paints and require less volume. Its viscosity increases as the shear rate increases.

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