ABSTRACT
One of the nonthermal methods of drying and dewatering is displacement drying, where water-immiscible solvent having a higher density than water is used to displace liquid moisture from the wet material (Brandreth and Johnson, 1980; Devine, 1980). Such a displacement results from the combined action of buoyancy and surface forces when the wet material is immersed in a drying solvent. The mixture of both liquids is then separated by gravity, centrifugal forces, or evaporation and recycled to the drying system. The process depends greatly on the ability of the displacement liquid to detach water droplets from the solid surface. Since the surface tension at the water-solvent and water-solid interfaces is a key factor in water release, the process can be intensifi ed by the addition of surfaceactive agents. Advantages of displacement drying include
Reduced energy consumption compared to hot-air drying• Higher drying rates and therefore shorter drying times• Lower investment and operating costs• Capability of handling heavier water loads (up to 10% by volume) • with no loss in drying effi ciency
Additionally, this is a spot-free drying technique that leaves no trace of moisture on the material surface, which is especially important when drying fi lms, plastics, polished metals, ceramics, and so forth. So far, displacement drying has found applications in the fi elds of electronics (printed circuit boards, relays, semiconductors, TV tubes), optics (spectacle frames and lenses, fi lms, cameras), electromechanics (copiers, electric motors), and mechanics (tools, cutlery, medical instruments). According to Devine (1980), there were over 600 drying systems in operation in Europe in 1980, ranging in capacity from 40 L to several cubic meters.
