Question

In a food processing plant, heating and cooling of foods are conducted in equipment called heat exchangers. Which among the following is NOT a type of non contact heat exchanger?

• A. Steam infusion
• B. Scraped surface
• C. Shell and tube
• D. Tubular

Hint:

"Non-contact" means there's a wall between the food and the thing heating it. "Steam infusion" and "steam injection" mean shooting steam directly into the food - this is direct contact heating.

Answer 1

The Correct Option is A

Step 1: Define a non-contact (or indirect) heat exchanger. In a non-contact heat exchanger, the heating/cooling medium (e.g., steam, hot water) is separated from the food product by a physical barrier (usually a metal wall). Heat is transferred by conduction and convection across this barrier.
Step 2: Evaluate the options.

Steam infusion: In this method, high-pressure steam is injected directly into the liquid food product. The steam condenses, transferring its latent heat directly to the food. This is a direct contact method.
Scraped surface: The product flows through a jacketed cylinder, and rotating blades continuously scrape the product off the heat transfer surface. The heating/cooling medium is in the jacket, separated from the food. This is non-contact.
Shell and tube: One fluid flows through a set of tubes, and the other fluid flows over these tubes within a sealed shell. The tube wall is the barrier. This is non-contact.
Tubular: The product flows through a tube, which is surrounded by the heating/cooling medium (or vice versa). The tube wall is the barrier. This is non-contact. \end{itemize} Therefore, steam infusion is the direct contact method and not a non-contact heat exchanger.