Mass Transfer

Mass transfer is one of the fundamental phenomenons that occur during processing of food products or storage of agricultural products. Mass transfer mostly pertain to migration of moisture in porous food material due to an external stimulus such as convective drying, infrared heating, microwave heating, water absorption by food materials etc. Unsteady state denotes a condition where the movement of moisture occurs due to either convection or diffusion changes with time. Mass transfer can occur in the multicomponent form for different components in food materials or can occur simultaneously with heat transfer.

Liquid transfer are not only due to volumetric liquid concentration gradient but also due to temperature gradient additionally; when liquid is present in vapor form an additional transfer is also possible. Mathematical formulation of mass transfer has been attempted with number of different physical models. Unsteady state coupled transfer problems described by non linear partial differential equations, for mass transfer and heat transfer are more relevant for lower density and high moisture foods.

Mass transfer contributes to a change in mechanical conformation which in turn affects mechanical properties. Temperature induced mass transfer also affects chemical reaction such as gelatinization, enzyme kinetics, reaction kinetics etc. Coupling the physical process of heat and mass transfer with mechanical changes in relation to chemical interactions makes this study complex and necessitates several assumptions for a practical implementation.