Question

In falling film milk evaporator, the temperature difference between milk and steam should be approximately around :

• A. 2°C
• B. 8°C
• C. 40°C
• D. 100°C

Hint:

Low \(\Delta T\) values (\(3 \text{ to } 8^{\circ}\text{C}\)) are characteristic of falling film evaporators.
This design minimizes fouling (milk stone formation) and allows the use of Multiple Effect Evaporators or Mechanical Vapor Recompression (MVR) systems.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
In a falling film evaporator, milk flows downward as a thin film on the inside of vertical tubes while heating steam condenses on the outside.
Optimizing the temperature difference (\(\Delta T\)) between the heating medium (steam/vapor) and the boiling liquid (milk) is essential for efficient heat transfer.
Detailed Explanation:
In modern dairy evaporators, the temperature difference (\(\Delta T\)) is kept as small as practically possible:
- If the temperature difference is too high (e.g., \(40^{\circ}\text{C}\) or \(100^{\circ}\text{C}\)), the heat transfer is too intense, causing the milk film to boil violently and burn onto the tube walls (fouling). This denatures proteins and disrupts heat transfer.
- If the temperature difference is too small (e.g., \(2^{\circ}\text{C}\)), the rate of heat transfer is too low, requiring an impractically large surface area.
Therefore, falling film evaporators are typically designed to operate with a temperature difference (\(\Delta T\)) of \(4^{\circ}\text{C}\) to \(9^{\circ}\text{C}\) (with \(8^{\circ}\text{C}\) being the standard optimum value).
This low temperature difference protects the milk from heat damage while maintaining efficient evaporation rates.

Step 2: Final Answer:
The temperature difference between milk and steam should be approximately 8°C.