A. Sadeghi - Department of Agricultural Machinery, College of Agriculture, Tarbiat Modares University, P. O. Box: ۱۴۱۱۵-۳۳۶

Application of feed pellets in animal and aquatic farming industries has grown because of both the physical and the nutritional benefits it provides. Development of feed pellets manufacturing industry is also considerable. Steam conditioning process, which plays an important role in pelleting production, includes heating feed particles, adding moisture, and mixing the mash. Pellets cooling and drying processes are also involved in heat transfer phenomena. In this study, thermal conductivity of feed pellets was determined at different temperatures ranging from ۲۵ to ۸۵°C and moisture contents of ۱۱.۸ to ۱۸.۲% wb. It was measured by the transient technique using the line heat source method assembled in a thermal conductivity probe. It turned out that decreasing moisture contents from ۱۸.۲ to ۱۱.۸% (wb) produced non-linear reduction in thermal conductivity. The average values of thermal conductivity changed from ۰.۱۵۰۹ to ۰.۲۱۴۳ W m-۱ °C-۱ at different moisture contents. Tests conducted on two pellet size categories (based on nominal diameter) revealed a significant difference in thermal conductivity between these categories. The thermal conductivities of the first category (minor than nominal dia.) appeared to be ۸.۵% higher than those of the second category (superior to nominal dia.). Average values of thermal conductivity changed from ۰.۱۵۳۸ to ۰.۲۳۳۳ W m-۱ °C-۱ for the first category and from ۰.۱۲۳۵ to ۰.۲۴۵۶ W m-۱ °C-۱ for the second category (in ۲۵°C). In addition, some empirical models were developed to express thermal properties as a function of moisture content and temperature.

Feed pellets, Line heat source method, thermal conductivity