Question

An example of dilatent fluid is ______

• A. non-colloidal solution
• B. rubber latex
• C. quick sand
• D. Sewage emulsion

Hint:

Remember these common industrial examples:
Pseudoplastic: Paper pulp, rubber latex, blood, paints.
Dilatant: Quicksand, starch-water suspensions, concentrated clay slurries.
Bingham Plastic: Sewage sludge, toothpaste, drilling muds.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks us to identify an example of a dilatant fluid from the provided choices.
This is a standard classification question in rheology and fluid mechanics.

Step 2: Key Formula or Approach:
Non-Newtonian fluids do not follow Newton's law of viscosity. Their behaviour is modeled by the power-law (Ostwald-de Waele) equation:
\[ \tau = K \cdot \left(\frac{du}{dy}\right)^n \]
where \( n \) is the flow behavior index:
- For Newtonian fluids, \( n = 1 \).
- For Pseudoplastic (shear-thinning) fluids, \( n \lt 1 \).
- For Dilatant (shear-thickening) fluids, \( n \gt 1 \).

Step 3: Detailed Explanation:

• Dilatant Fluids: These fluids display an increase in apparent viscosity with an increase in shear rate (shear-thickening).
When shear force is applied, the closely packed particles inside are displaced, causing the suspension to expand or "dilate."
The liquid solvent is no longer sufficient to fill the increased voids, increasing solid-to-solid friction and resistance to flow.

• Quick Sand: Quicksand is a classic example of a dilatant mixture.
When undisturbed, it behaves like a liquid, but applying sudden shear or pressure (like walking on it) causes it to instantly stiffen and act as a solid.
Other examples include starch suspensions in water (oobleck) and concentrated wet sand.

• Other Fluid Types:
Rubber latex is pseudoplastic (shear-thinning), where viscosity decreases with increasing shear rate.
Sewage emulsion is often classified as a pseudoplastic or Bingham plastic fluid.


Step 4: Final Answer:
Quick sand is a classic example of a dilatant fluid.