Question

In spray dryer, the process of forming droplets fine enough to dry quickly, but not so fine to escape with the outlet air after having been dried is known as :

• A. Droplet size distribution
• B. Atomization
• C. Change in state
• D. Vacuole formation

Hint:

Good atomization maximizes the surface-area-to-volume ratio of the liquid, allowing almost instant evaporation (within \(0.5\) to \(2\) seconds) inside the spray drying chamber.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The core step in spray drying is dispersing the liquid feed into the hot air stream as a cloud of fine droplets.
This process must be carefully controlled to produce droplets of the right size.

Step 2: Detailed Explanation:
The process of dispersing a bulk liquid into fine droplets is called Atomization.
It is achieved using rotary disc atomizers or pressure nozzles.
Atomization must be carefully optimized:
- The droplets must be small enough to create a large surface area, allowing them to dry within seconds as they fall through the chamber.
- However, if the droplets are too small (under \(10\ \mu\text{m}\)), they form an extremely fine dust when dry.
- This fine dust can easily bypass the cyclones and escape with the exhaust air, leading to product loss and environmental pollution.
Therefore, proper atomization is designed to produce a controlled droplet size range (typically \(50\) to \(150\ \mu\text{m}\)) that dries quickly and can be easily recovered by the cyclones.

Step 3: Final Answer:
The process of forming these droplets is known as Atomization.