This set of Fluid Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Types of Fluids”.

1. The relation between shear stress Z and velocity gradient of a fluid is given by where A and n are constants. If n = 1, what type of fluid will it be?

a) Newtonian fluid

b) Non-Newtonian fluid

c) Pseudoplastic

d) Bingham plastic

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Explanation: When n = 1, the relation reduces to Newton’s law of viscosity: z = A * , where A will represent the viscosity of the fluid. The fluid following this relation will be a Newtonian fluid.

2. The relation between shear stress Z and velocity gradient of a fluid is given by where A and n are constants. If n > 1, what type of fluid will it be?

a) Newtonian fluid

b) Dilatant

c) Pseudoplastic

d) Bingham plastic

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Explanation: When n ≠ 1, the relation will be treated as Power law for Non-Newtonian fluids:

. For n > 1, the rate of change of the shear stress increases with the increase in the value of velocity gradient. Such fluids are called Dilatants.

3. The relation between shear stress Z and velocity gradient of a fluid is given by where A and n are constants. If n < 1, what type of fluid will it be?

a) Newtonian fluid

b) Dilatant

c) Pseudoplastic

d) Bingham plastic

View Answer

Explanation: When n ≠ 1, the relation will be treated as Power law for Non-Newtonian fluids:

. For n < 1, the rate of change of the shear stress decreases with the increase in the value of velocity gradient. Such fluids are called Pseudoplastics.

4. The relation between shear stress Z and velocity gradient of a fluid is given by + B where A, n and B are constants. Which of the following conditions will hold for a Bingham plastic?

a) A = 0;B ≠ 0; n ≠ 1

b) A ≠ 0;B = 0; n ≠ 1

c) A = 0;B = 0; n = 1

d) A ≠ 0;B ≠ 0; n = 1

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Explanation: For Bingham Plastics, shear stress will not remain constant after an yield value of stress. Thus, A ≠ 0;B ≠ 0. After the yield value, the relation between the shear stress and velocity gradient will become linear. hus, n = 1.

5. The relation between shear stress Z and velocity gradient of a fluid is given by + B where A, n and B are constants. Which of the following conditions will hold for a Rheopectic?

a) A = 0;B ≠ 0; n > 1

b) A ≠ 0;B = 0; n < 1

c) A = 0;B = 0; n < 1

d) A ≠ 0;B ≠ 0; n > 1

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Explanation: For Rheopectics, shear stress will not remain constant after an yield value of stress. Thus, A ≠ 0; B ≠ 0. After the yield value, the rate of change of the shear stress increases with the increase in the value of velocity gradient. Thus, n > 1.

6. The relation between shear stress Z and velocity gradient of a fluid is given by + B where A, n and B are constants. Which of the following conditions will hold for a Thixotropic fluid?

a) A = 0;B ≠ 0; n > 1

b) A ≠ 0;B = 0; n > 1

c) A = 0;B = 0; n < 1

d) A ≠ 0;B ≠ 0; n < 1

View Answer

Explanation: For Thixotropics, shear stress will not remain constant after an yield value of stress. Thus, A ≠ 0;B ≠ 0. After the yield value, the rate of change of the shear stress decreases with the increase in the value of velocity gradient. Thus, n < 1.

7. The graph shows relation between shear stress Z and velocity gradient of a fluid is given by where A and n are constants. The graphs are drawn for three values of n. Which one will be the correct relationship between n_{1}, n_{2} and n_{3}?

a) n_{1} > n_{2} > n_{3}

b) n_{1} < n_{2} < n_{3}

c) n_{1} > n_{3} > n_{2}

d) n_{1} < n_{3} < n_{2}

View Answer

Explanation: The graph corresponding to n = n1 represents Pseudoplastics, for which the rate of change of the shear stress decreases with the increase in the value of velocity gradient. The graph corresponding to n = n2 represents Newtonian fluids, for which shear stress changes linearly with the change in velocity gradient. The graph corresponding to n = n3 represents Dilatents, for which the rate of change of the shear stress increases with the increase in the value of velocity gradient.

8. Which of the following is a shear-thinnning fluid?

a) Bingham plastic

b) Rheopectic

c) Dilatant

d) Pseudoplastic

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Explanation: Shear-thinning fluids are those which gets strained easily at high values of shear stresses. The relation between shear stress Z and velocity gradient of a shear-thinning fluid is given by , where A and n are constants and n < 1. This relation is followed by Pseudoplastics.

9. Which of the following is a shear-thickening fluid?

a) Bingham plastic

b) Thixotropic

c) Dilatant

d) Pseudoplastic

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Explanation: Shear-thickening fluids are those for which it gets harger to strain it at high values of shear stresses. The relation between shear stress Z and velocity gradient of a shear-thickening fluid is given by where A and n are constants and n > 1. This relation is followed by Dilatants.

10. For what value of flow behaviour index, does the consistency index has a dimension independent of time?

a) 0

b) 1

c) 2

d) 3

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Explanation: The relation between shear stress Z and velocity gradient of a fluid is given by

where A is the flow consistency index and n is the flow behaviour index.

Thus [A] will be independent of time when n = 2.

11. What will be the dimension of the flow consistency index for a fluid with a flow behaviour index of 3?

a) [M L^{-2} T].

b) [M L^{-2} T^{-1}].

c) [M L^{-1} T^{-2}].

d) [M L^{-1} T].

View Answer

Explanation: The relation between shear stress Z and velocity gradient of a fluid is given by where A is the flow consistency index and n is the flow behaviour index. Putting n = 3,

12. What will be the dimension of the flow consistency index for a fluid with a flow behaviour index of -1?

a) N/m^{2} s^{2}

b) N/m^{2} s

c) N/ms

d) N/ms^{2}

View Answer

Explanation: The relation between shear stress Z and velocity gradient of a fluid is given by where A is the flow consistency index and n is the flow behaviour index. If n = -1, A = Z * Unit of Z is N/m

^{2}and is s

^{-1}. Thus, the unit of A will be N/m

^{2}s.

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