ABSTRACT
Various intermittent drying operations have recently increasingly been used at laboratory, pilot, and industrial scales. They all aim to improve product quality and/or process performance by reducing energy consumption. Intermittent drying is a drying operation with several periods of varying external dehydration conditions with different drying rates. In intermittent drying, air¤ow temperature, velocity and/or humidity, heat input, pressure, and/or other external drying parameters (such as microwave (MW) or RF) are applied in a discontinuous manner to suit the drying kinetics and quality requirements of the material. The idea is often to introduce tempering periods to even out the internal moisture content and temperature elds. The quality of the nal dried product can also be enhanced along with process performance. In each tempering period, moisture gets redistributed inside the material. This produces several desired effects. Quality is enhanced by avoiding or reducing overheating or overdrying of the surface layer. Quality degradation can be due to surface cracking, breakage, or crusting, and under certain conditions even scorching of the material. The drying rate can also increase as the material surface gets rewetted to that higher heat/mass transfer can occur at the exposed surface of the material.
