Equilibrium moisture content and latent heat of vaporization of grapes

Drying process is a heat and mass transfer phenomenon where water migrates from the interior of the drying product on to the surface from where it evaporates. The equilibrium moisture content is used to determine whether a product will gain or lose moisture under a given set of temperature and relative humidity conditions. The grapes are in equilibrium with their surrounding conditions of temperature and relative humidity when the vapor pressures or the surrounding air are in equal with the vapor pressures corresponding to the saturation temperatures of water inside the grapes. In the present study, two empirical equations for equilibrium moisture content and latent heat of vaporization of grapes are presented. A test rig has been designed and constructed to obtain the available experimental data used to fit the empirical equations. These two formulae are very important to evaluate the drying rate of the grapes at a particular condition and also to calculate the correct values of latent heat of grapes as a function of equilibrium moisture content.