Question

Suspensions containing a high percentage (about 50% or greater) of small, deflocculated particles would show which of the following flow properties?

• A. Plastic flow
• B. Dilatant flow
• C. Newtonian flow
• D. Pseudoplastic flow

Answer 1

The Correct Option is B

To understand the flow properties of suspensions containing a high percentage (about 50% or greater) of small, deflocculated particles, we need to examine the characteristics of various flow types in fluid dynamics.

Suspensions can exhibit different flow behaviors depending on the concentration and nature of the particles. Let us review the flow types mentioned in the options:

• Plastic flow: This type of flow is characterized by a yield stress, meaning the fluid will only start to flow after a certain stress is applied. It is typical of systems with flocculated particles forming a network.
• Dilatant flow: In this type of flow, the viscosity of the suspension increases with increasing shear rate. It is typically observed in suspensions with high concentrations of deflocculated particles. Under shear stress, these particles become more ordered and create resistance to flow.
• Newtonian flow: This flow behavior is characterized by a constant viscosity regardless of the shear rate. It is typical for ideal fluids like water or mineral oils.
• Pseudoplastic flow: Also known as shear-thinning flow, where the viscosity decreases with an increase in shear rate. This behavior is observed in polymer solutions or slurries where entanglements decrease with shear.

Given this, the correct answer is 'Dilatant flow', as suspensions with high concentrations of small, deflocculated particles tend to show increased viscosity with increasing shear rate due to the formation and interaction of particle structures under stress.

Let's rule out the other options:

• Plastic flow: A system with deflocculated particles does not typically require a yield stress to initiate flow.
• Newtonian flow: This flow type is unlikely because the viscosity in dilatant systems is not constant.
• Pseudoplastic flow: As mentioned, pseudoplastic fluids exhibit a decrease in viscosity with increasing shear rate, which is opposite to the behavior described for dilatant flow.

Thus, for suspensions with high concentrations of small, deflocculated particles, Dilatant flow is the most appropriate characterization.