Drying of Solids

At the end of drying of solids or the purpose of the end product is solid form. In spite of the solid which is primarily in solution, the trouble of producing this solid in dry form is classed under this heading. Final moisture contents of dry solids are commonly less than 10% and in several happenings, less than 1%. The method of the drying solids is considerably uncomplicated in principle.

Evaporation period and drying stage

Generally, drying is performed with heated gases in the case of a wet solid to dry as though the water were present alone without any solid, and hence evaporation proceeds as it would from a so-called free water surface as water standing in an open pan. The period or stage of drying during this initial phase, so that it is usually referred to as the constant rate period since evaporation happens at a regular rate and is independent of the solid present. The presence of any dissolved salts will make the evaporation rate to be less than that of pure water. However, this lower rate can still be regular during the initial stages of drying of solids.

Fundamental concept

A basic concept of drying relies upon expertise of the drives governing the flow of liquids within solids. Attempts have been made to improve a common principle of drying on the basis that liquid by a diffusion process. Nevertheless, this is not the fact in most cases. In reality, only a less number of types of solids do true diffusion of liquids happen. In most cases, the internal flow mechanism results from a blend of forces that may consist capillarity, internal pressure gradients caused by shrinkage, a vapor-liquid flow sequence caused by temperature gradients, diffusion and osmosis. Due to the complexities of the internal flow mechanism, it has not been possible to evolve a generalized theory of drying applicable to all materials.

Drying of materials and product quality

Drying of solids in certain cases like wood, ceramics and soap has a remarkable fathom of the internal mechanism obtained that allows control of product standard. Surveys of drying of solids have been made from the so-called external viewpoint, wherein the effects of the external drying medium like air velocity, humidity, temperature and wet material shape and subdivision are studied with respect to their influence on the drying rate. The consequences of those surveys are commonly presented as drying rate curves and the natures of these curves are used to interpret the drying mechanism.

Questions:

• What is drying of solids?
• State the significance of drying of solids?