Test: Types of Fluids - Mechanical Engineering MCQ

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 as it is a linear relation. The equation given is of a straight line.

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

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.

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.

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. Thus, n = 1.

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.

Explanation: For Thixotropics,their viscosity is time dependent and decreases as time goes on.

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.

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.

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.

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/m² and  is s^-1. Thus, the unit of A will be N/m² s.