IMAGE 3: The viscosity of a product will also influence other equipment choices, such as positive displacement pumps. This arrangement increases both heat transfer and energy efficiency and minimizes potential fouling of the product. These consist of three or four concentric tubes, with the product flowing through the annular space between the tubes and the service fluid flowing through the inner and outer tubes to ensure even heating and cooling. In a double-tube heat exchanger, one large tube carries the product, so there is less chance of blockage and fouling by the pieces and particles contained in the food product.įor high viscosity products such as thick sauces, honey and syrups, an annular-space heat exchanger is preferable. Where products contain pieces or particulates, such as fruit and vegetable dices, then a double-tube heat exchanger is recommended. These feature multiple tubes carrying the product within a large vessel, which contains the service fluid. Products with low or medium viscosities-such as milk, thin sauces, soups and creams, fruit and vegetable juices and purees-can usually be efficiently processed in multitube corrugated heat exchangers. This helps increase operational life while reducing maintenance costs. In addition, corrugated tube heat exchangers can have a lower pumping requirement than smooth tubular heat exchangers due to their compact nature, which results in a lower pressure drop. The corrugated design also minimizes fouling in the heat exchanger, which increases the thermal efficiency and prolongs operational periods between cleaning. Corrugated tube heat exchangers are available in various configurations, so delicate materials such as cream can be processed without damage.
Such issues can be addressed with the correct type of heat exchanger and careful system design. IMAGE 2: For the most challenging products, a scraped-surface heat exchanger may be required. Another challenge is presented by certain fat-free products that become more or less viscous with temperature, and so they may be more fluid on the cooling side of the heat exchanger than the heating side. If subjected to too much pressure, certain sauces may shear, resulting in failure to meet the end specification-such as pizza sauce not staying on the pizza during the manufacturing process. Newtonian and non-Newtonian fluids behave differently under different temperature and pressure regimens, and this can affect the handling necessary during processing. Many types of food and drink products fall into this category, including those that are particularly viscous (such as syrups and thick sauces), contain particles or pieces (such as fruit and vegetable mixtures), or are non-Newtonian fluids (such as custard). More complex materials usually need more specialized heat exchange equipment, such as corrugated tube or scraped-surface heat exchangers. (Images courtesy of HRS Heat Exchangers)įor example, the simplest thin Newtonian fluids such as water and milk may be successfully processed with simple plate heat exchangers. IMAGE 1: Annular-space heat exchangers are often chosen for viscous food products.
0 kommentar(er)
