A TEMPERATURE-DEPENDENT EQUILIBRIUM MOISTURE-CONTENT EXPRESSION FOR SKIMMED-MILK PARTICLES

An expression to determine the equilibrium moisture content (X(eq)) of skimmed milk particles as a function of temperature and relative humi dity has been developed. This expression was based on a first order te mperature rate function and mad use of 4 desorption isotherm correlati ons, evaluated at 14, 34 and 45-degrees-C, to define the temperature r ate constant. The difference between X(eq) as calculated by this expre ssion and the 45-degrees-C correlation, when applied to typical spray dryer operating temperatures would be of the order of 50% or more. Thi s is considerable and could contribute to the improper assessment of t he performance of a spray dryer. A comparison was made between the new expression and 2 recent temperature dependent correlations from the l iterature. It was found that the new expression predicted lower equili brium moisture contents than the 2 correlations, for the conditions ex pected in an operational spray dryer.