Depending of the product you want to heat, either for food processing or industrial purpose, most of the liquids are heated thanks to heat exchange technology. Basically, the thermal energy is transferred from a heat transfer fluid, usually water or steam, to the product through an exchange surface who separate the fluids and avoid any change in their physicochemical properties.
The heat exchange always occurs by convection: the larger the exchange surface, the more efficient the exchange, except for the microwave heating which directly heat the product. Discover the most common heat transfer methods below.
A plate exchanger is constituted of independent stainless steel plates in which circulate the heated product and the heat transfer liquid. The plates are assembled and compressed against each other in a support called a frame. It is an handy equipment as you can easily clean it by removing all the plates. The footprint is small compared to the treatment flow.
However, it is an equipment that can not process products with pieces. In addition, its clogging gets dirty very quickly with too viscous products. It is therefore especially suitable for non-viscous and homogeneous liquids.
A spiral exchanger is made of two stainless steel channels wounded together in which the heated product and the heat transfer liquid circulate at counter-current. The footprint is usually small for this type of equipment.
This equipment makes the treatment of a slightly viscous products possible. But the heat transfer coefficient is low which limits its use for important and fast temperature increases.
Tubular exchanger have have different operating configurations : single or multi-tubes. The principle is to have one or more tubes placed in a larger one where the heat transfer fluid circulates. The heat transfer is carried out by conduction from the outside to the center of the product. On an annular exchanger, the heat transfer fluid circulates in two pipes, one central and the other outside. The product is transported between the two which allows it to be heated more efficiently.
This system presents some advantages such as linear temperature rise and good temperature control. But the footprint is important and it’s not adapted to very viscous products.
Scraped surface exchanger
A scraped surface exchanger is made of 2 elements. On the external part the heat transfer fluid transmit its thermal energy to the product. On the inside, the tube where the product goes through is equipped with rotative blades that continuously scrape the internal transfer surface. The blades prevent the product from settling and burning, and it increase turbulence for optimized heat exchange.
The scraped surface exchanger is one of the only system adapted to viscous and pasty products. But it has a high cost of investment and operation.
Inline heater by microwave
Unlike previous solutions where heat is transferred by conduction from the outside to the product through its surface, microwaves heat the entire product mass directly and homogeneously, without the use of a heat transfer fluid. The heat generation is almost instantaneous and allows for a perfectly controlled thermal process.
Inline microwave heating is adapted for liquid or pasty products, with or without pieces (for example, jam). The direct thermal transfer from microwave energy to the product allow an excellent energy efficiency.
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