Heat transfer plays a considerable role in the food processing industry. It helps enhance the nutritional, safety, and sensory aspects of a product. Also, subprocesses like freezing, sterilization, and preservation rely on efficient heat transfer to ensure the consistent quality of the final product.
This article will explore heat transfer in the food industry, including how it’s done and some of its challenges.
Role of heat exchangers in food processing
Heat exchangers are used for heat transfer in lots of food processes, whether it’s making chocolate, meatballs, ice cream, or processing UHT-treated milk. However, the type used varies depending on the physical attributes of the product, like viscosity, thermal diffusivity, thermal conductivity, viscosity, and specific heat.
The product’s shape may also affect the type of heat exchanger used. For instance, irregular raw material sizes require a complex heat exchanger design. Such designs allow the processes to achieve efficient heat transfer for consistent and high-quality results each time.
Here’s a look at the most common types of heat exchangers used in the food processing industry.
Tubular heat exchanger
The tubular heat exchanger’s design is the simplest of the lot. It’s essentially a double-walled pipe through which two fluids pass; one through the center tube and the other through the annulus between the two tubes. Some even have three walls and direct the processed fluid through an intermediate passage while the heating and cooling fluids pass through other annular spaces. That way, the processed fluid is surrounded on either side. Tubular heaters are not common in the food processing industry despite being relatively affordable.
Vats also feature a double-walled tank in a relatively simple design. The annular space in the exchanger contains heating fluid. An agitator may also be provided for product movement over the heat transfer surfaces. These exchangers are commonly used for batch pasteurization.
Plate heat exchanger
These are pretty common in the food industry. They consist of thin plates stacked together to provide a large heat transfer surface area within a small volume. They offer low capital costs and are easy to clean and maintain, which is why they are the most popular heat exchangers in the industry.
Scraped surface heat exchanger
These are specialized for processing highly viscous fluids with a high lumping risk. They typically consist of a double-walled pipe exchanger with a central rotating shaft that removes any excess buildup of material from the pipe’s inner wall, thus, reducing fouling of the fluid.
Heat transfer fluids
The efficiency of heat transfer also depends on the heat transfer liquid. Hence, choosing the correct fluid is crucial to the process.
Heat transfer fluids used in food processing are certified as NST HT-1 food grade. This shows that they can meet the operational requirements for incidental food contact. In addition, they can be high-flash food-grade heat transfer fluids, i.e., the operating temperature must be below the flashpoint of the fluid. Usually, the operating range lies between 15 and 340 degrees celsius.
They could also be food-grade low-temperature fluids with operating ranges of between -40 and 232 degrees celsius. These usually have a minimum odor and lower varnishing tendencies.
Note: It’s crucial to select a heat transfer fluid engineered to resist solid formations, provide high-temperature stability, and prevent system fouling.
Challenges of heat transfer in food processing
Heat transfer in food processing faces several challenges. These include steady and unsteady heat transfer occurring in different subprocesses. In addition, heating materials with irregular shapes and physical properties that vary during the cycle are also a problem.
Heat transfer when heating vegetable oils has problems of its own. There is always the risk of scorching the oil or causing the formation of fatty acids. This is avoided by;
- Using a circulation heater with an automated temperature control system.
- Using an electric immersion heater with steel sheath material and low power density. This will also maintain the oil within the ideal viscosity range.
However, fouling is arguably the biggest challenge facing heat transfer in food processing.
What is fouling?
Fouling in heat transfer is when unwanted material deposits form on the heat transfer surfaces, creating an insulation layer that reduces the effectiveness of the heat transfer process. Ultimately, this will adversely affect the pressure drop and flow performance. Fouling commonly occurs due to scaling caused by silicates, calcium carbonate, and calcium sulfate. However, it can also occur due to incrustation, sedimentation, and biological growth.
Heating elements for your food processing plant
Rama Corporation is a leading manufacturer of industrial heating elements for the food processing industry. Whether you’re looking for premade options or custom solutions, we will work with you to find the best exchanger for your needs.