Step 1: Define a non-contact (indirect) heat exchanger. In this type, a physical barrier, typically a metal wall, separates the heating/cooling medium (e.g., steam, hot water) from the food product. Heat transfer occurs through conduction and convection across this barrier.
Step 2: Evaluate the following options.
Steam infusion: High-pressure steam is directly injected into the liquid food, condensing and transferring latent heat. This is a direct contact method.
Scraped surface: The food product flows through a jacketed cylinder where rotating blades continuously scrape the product from the heat transfer surface. The heating/cooling medium is within the jacket, separated from the food, making this non-contact.
Shell and tube: One fluid flows through tubes, while the other flows around them within a sealed shell. The tube wall acts as the barrier, making this non-contact.
Tubular: The product flows through a tube surrounded by the heating/cooling medium (or vice versa). The tube wall is the barrier, making this non-contact.
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In conclusion, steam infusion is a direct contact method, not a non-contact heat exchanger.