ABSTRACT
Intermittent drying generally refers to batch drying operations, wherein the operating conditions are altered during the course of removal of internal moisture to match the drying kinetics and allowable maximum product temperature so as to obtain enhanced thermal efficiency and higher product quality. The operating conditions include drying medium flow rate, temperature and humidity, as well as operating pressure. Different modes of heat input (e.g. convection, conduction, radiation, volumetric heating) may also be applied sequentially or concurrently as a function of time to match the drying kinetic characteristics of the product being dried. The objective of intermittency is to allow time for the internal moisture to migrate to the exposed surface before thermal energy is applied so that the moisture can be evaporated more efficiently without overheating the product. This chapter provides an outline of the basic principle of intermittency, different types of intermittency, as demonstrated by selected published works, which focus on the effectiveness of the intermittency concept for higher thermal efficiency and product quality enhancement. On the negative side, the overall time may be increased marginally although it is compensated by overall reduction in energy. The concept of intermittency can also be applied to continuous drying for which heat input is varied spatially.
