The drying process has been experimentally studied and analyzed to simulate and design a
drier. As drying is a process of removing moisture to a safe level, the equilibrium moisture
content is defined as the moisture content in equilibrium with the relative humidity of the
environment. The equilibrium moisture content is divided into, static and dynamic. While
the static is used for food storage process, dynamic is used for drying process. The drying
process is experimentally obtained and presented as moisture content on x-axis and rate of
drying on y-axis. A deep bed of food grains is assumed to be composed of thin layers
normal to the hot air flow direction. The equations for thin layer were written initially, using
empirical, theoretical and semitheoretical equations. The conditions of the grain and air,
change with position and time during drying of a deep bed of grains. Logarithmic and
partial differential equation models to simulate the deep bed dry modeling are dealt in
detail (Murthy, 2009).
In a different direction, the first and second law of thermodynamics (Torres-Reyes et al., 2002)
have been used to develop the design methods for a particular application. Semi-empirical
formulae are developed to calculate the rise in air temperature as it passes through the heater.
NTU (number of transfer units) has been defined analogous to the heat exchangers, as a part of
design. Using entropy balance the maximum temperature reached by solar collector is written
and then Entropy Generation Number is developed to find the entropy generated during
thermal conversion of solar energy. Finally, the drying temperature is established as a function
of the maximum limit of temperature the material might support.