482 Fermentation and Biochemical Engineering Handbook Salting-Salting refers to the growth on evaporator surfaces of a material having a solubility that increases with increasing temperature. It car bereduced oreliminated by keeping the evaporating liquid in close or frequent contact with a large surface area of crystallized solid Scaling-Scaling is the growth or deposition on heating surfaces of a material which is either insoluble, or has a solubility that decreases with temperature. It may also result from a chemical reaction in the evaporator oth scaling and salting liquids are usually best handled in an evaporator that does not rely upon boiling for operation Fouling--Fouling is the formation of deposits other tha an salt or sca Fouling may be due to corrosion, solid matter entering with the feed, or deposits formed on the heating medium side Corrosion-Corrosion may influence the selection of the evaporator type, since expensive materials of construction usually dictate that evapora tor designs allowing high rates of heat transfer are more cost effective Corrosion anderosion are frequently more severe in evaporators than in other types of equipment, because of the high liquid and vapor velocities, frequent presence of suspended solids, and the high concentrations encoun tereo product guality-Purity and quality of the product may require low holdup and low temperatures, and can also determine that special alloys or other materials be used in the construction of the evaporator. A low holdup or residence time requirement can eliminate certain types ofevaporators from consideration Other characteristics of the solid and liquid may need to be considered in the design of an evaporation system. Some examples are: specific heat, radioactivity, toxicity, explosion hazards, freezing point, and the ease of caning. Salting, scaling, and fouling result in steadily diminishing heat transfer rates, until the evaporator must be shut down and cleaned. while some deposits can be easily cleaned with a chemical agent, it is just as common that deposits are difficult and expensive to remove, and that time consuming mechanical cleaning methods are required 4.0 HEAT TRANSFER IN EVAPORATORS Whenever a temperature gradient exists within a system, or when two systems at different temperatures are brought into contact, energy is trans- ferred. The process by which the energy transport takes place is known as eat transfer. Because the heating surface of an evaporator represents the482 Fermentation and Biochemical Engineering Handbook Salting-Salting refers to the growth on evaporator surfaces of a material having a solubility that increases with increasing temperature. It can be reduced or eliminated by keepingthe evaporating liquid in close or frequent contact with a large surface area of crystallized solid. Scaling-Scaling is the growth or deposition on heating surfaces of a material which is either insoluble, or has a solubility that decreases with temperature. It may also result from a chemical reaction in the evaporator. Both scaling and salting liquids are usually best handled in an evaporator that does not rely upon boiling for operation. Fouling-Fouling is the formation of deposits other than salt or scale. Fouling may be due to corrosion, solid matter entering with the feed, or deposits formed on the heating medium side. Corrosion-Corrosion may influence the selection of the evaporator type, since expensive materials of construction usually dictate that evapora￾tor designs allowing high rates of heat transfer are more cost effective. Corrosion and erosion are frequently more severe in evaporators than in other types of equipment, because of the high liquid and vapor velocities, the frequent presence of suspended solids, and the high concentrations encoun￾tered. Product Quality-Purity and quality of the product may require low holdup and low temperatures, and can also determine that special alloys or other materials be used in the construction of the evaporator. A low holdup or residence time requirement can eliminate certain types of evaporators from consideration. Other characteristics of the solid and liquid may need to be considered in the design of an evaporation system. Some examples are: specific heat, radioactivity, toxicity, explosion hazards, freezing point, and the ease of cleaning. Salting, scaling, and fouling result in steadily diminishing heat transfer rates, until the evaporator must be shut down and cleaned. While some deposits can be easily cleaned with a chemical agent, it is just as common that deposits are difficult and expensive to remove, and that time￾consuming mechanical cleaning methods are required. 4.0 HEAT TRANSFER IN EVAPORATORS Whenever a temperature gradient exists within a system, or when two systems at different temperatures are brought into contact, energy is trans￾ferred. The process by which the energy transport takes place is known as heat transfer. Because the heating surface of an evaporator represents the