Question

The air residence time in the drying chamber in seconds.

• A. 10 -- 15
• B. 5 -- 7
• C. 15 -- 20
• D. 25 -- 30

Hint:

Spray drying is extremely fast—always think in seconds, not minutes.

Answer 1

The Correct Option is B

Concept: Spray drying is a rapid drying process used in dairy industries (e.g., milk powder production). The residence time of air and particles in the drying chamber is very short to ensure quick moisture removal without thermal damage.

Step 1: Understanding spray drying.

• Liquid is atomized into fine droplets
• Hot air rapidly removes moisture
• Drying occurs almost instantaneously

Step 2: Importance of residence time.

• Must be short to avoid overheating
• Ensures product quality and nutrient retention

Step 3: Standard value.
Typical residence time: \[ 5 \text{ to } 7 \text{ seconds} \]

Step 4: Evaluating options.

• 5–7 sec → Correct industrial value
• Others → Too long, may damage product

Step 5: Conclusion.
Thus, correct answer is 5–7 seconds.