Question

Turbulence in the flow of milk in between plates is mainly achieved by

• A. Excessive flow rate
• B. Corrugations in plate
• C. Too narrow gap between plates
• D. Increase in milk density

Hint:

The pressed corrugations (chevrons) in heat exchanger plates serve a dual purpose:
- They act as static mixers to induce high turbulence at low flow rates.
- They provide mechanical support and rigidity, allowing the thin plates to withstand high pressure differentials.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
In plate heat exchangers (PHE) used for milk pasteurization, achieving turbulent flow is essential to maximize the convective heat transfer coefficient.
Turbulent flow mixes the fluid layers, reducing the boundary layer thickness and increasing heat transfer efficiency.

Step 2: Detailed Explanation:
Let us analyze how turbulence is induced in plate heat exchangers:
- While increasing the flow rate can induce turbulence (by increasing the Reynolds number), operating at excessive flow rates is impractical due to high pumping costs and increased pressure drop.
- Changing fluid density or reducing the plate gap also have limited practical effectiveness.
- In commercial plate heat exchangers, the stainless steel plates are pressed with complex patterns of corrugations (such as chevron or herringbone patterns).
- As milk flows through the narrow channels between these plates, the corrugations continuously disrupt the boundary layer and force the fluid to change direction rapidly.
- This induces intense localized turbulence at relatively low flow rates (low Reynolds numbers).
- This corrugation design maximizes heat transfer efficiency while maintaining manageable pumping pressures.
Therefore, turbulence is mainly achieved by the corrugations in the plates.

Step 3: Final Answer:
Turbulence in plate heat exchangers is achieved by the corrugations in the plates. Hence, the correct option is (B).