Drying & Water Content with bound & unbound water

Water Unbound & Bound

1. Drying & Water Content Dryers with their classification, various dryers Equilibrium moisture content, free, bound and unbound water

2. Drying is the process of removing moisture or water content from a substance, typically a solid material such as food, wood, or chemicals, to improve its stability, reduce its weight, or prepare it for further processing. This process is commonly used in industries such as food processing, agriculture, pharmaceuticals, and materials manufacturing. Drying is defined as a process of moisture removal due to simultaneous heat and mass transfer. Heat transfer from the surrounding environment evaporates the surface moisture. The moisture can be either transported to the surface of the product and then evaporated or evaporated internally at a liquid-vapor interface and then transported as vapor to the surface.

3. Drying and evaporation are relatively same but the main difference is that drying involves removal of small amount of water at temperature below its boiling point while evaporation involves the removal of large amount of water at its boiling point. The moisture migration into or from a product is dependent on the difference in vapor pressure between the atmosphere and the product. Capillary Diffusion Concentration difference

4. Theory of Drying Water may be present in a wet solid as bound water and as unbound water. Bound water is the minimum water held by the material that exerts an equilibrium vapor pressure less than that of pure water at the same temperature while unbound water is the amount of water held by the material that exerts an equilibrium vapor pressure equal to that of pure water at the same temperature. Two steps are needed to dry materials: 1. Heat must be supplied and 2. L iberated vapor must be removed by an air stream.