ESTIMATION OF MOISTURE DIFFUSIVITY COEFFICIENT AND THERMAL-PROPERTIESOF ALFALFA PELLETS

Heat and mass transfer characteristics of alfalfa pellets are needed i n the optimization of coolers for freshly-made pellets and in managing storage schedules of the pellets in silos and bins. Moisture diffusiv ity and thermal properties are important parameters used to characteri ze the heat and mass transfer ability of a material. In this study, ex perimental thin-layer data on (a) moisture desorption, (b) moisture ab sorption and (c) rate of heating of alfalfa pellets were collected. By applying the inverse theory and using second order mass transfer and heat transfer equations in cylindrical coordinates, the moisture absor ption and desorption data were used to estimate the moisture diffusivi ty as a function of moisture content of the pellets while the heating rate data were used to estimate the thermal properties (thermal conduc tivity and specific heat) as a function of pellet temperature. Better estimates were obtained when moisture diffusivity of the pellets was e xponentially related to moisture content in comparison with a linear r elation between moisture diffusivity and moisture content. Moisture di ffusivity during desorption (2.40 x 10(-9) to 4.12 x 10(-9) m(2)/s) wa s about three times that of the values of diffusivity during moisture absorption (7.50 x 10(-10) to 1.26 x 10(-9) m(2)/s). A good fit to the experimental heating rate data was obtained when thermal conductivity and specific heat of the pellets were linearly related to temperature . Over a temperature range of 2 to 110 degrees C, estimated particle t hermal conductivities and specific heats of the pellets were in the ra nge of 0.04 to 0.19 W/m K and from 962 to 2114 J/kg K respectively. (C ) 1996 Silsoe Research Institute