Coating  [ Return towards  Applications  ]

Let's present a quick overview of the thermal phenomenon during the coating process. Coating is a surface heat transfer phenomenon where the global surface of the product has to be considered, and is a transitory phenomenon. To get an understanding of this, observe what is going on when you immerse a frozen product in a liquid for a very short time. The product is considered to be "wet"; the quantity of "wetting" liquid depends on product parameters (surface, shape, temperature) and on liquid parameters (viscosity and temperature, composition, superficial tension ...).

The liquid/solid thermal exchange has a very high heat transfer coefficient (4,200 KJ/h.m².°C). After a period of time, determined by the parameters above, a temperature equilibrium is reached. This requires an equal enthalpy variation between the "cold" product and the "hot" liquid. To maintain quality and a maximum temperature of -18°C , the product needs to be cooled very rapidly. In an industrial context, products are not coated one by one. To avoid binding between products, they need to be moved constantly and to be given a large amount of refrigeration in a very short period of time. This is the origin of the coating in tumblers using liquid nitrogen.