International Journal of Engineering and Technical Research (IJETR) ISSN: 2321-0869 (O) 2454-4698 (P), Volume-3, Issue-11, November 2015 54 www.erpublication.org Abstract—The simultaneous heat and mass transfer between hot air and seeds having an agar gel-based coating was studied during packed bed drying. To describe the process, a two-phase model was employed, in which the effects of bed shrinkage and non-constant physical properties were considered. The model took into account bed contraction by employing moving coordinates. Equations relating shrinkage and structural parameters of the packed bed with moisture content, required in the drying model, were developed from experimental results in thick-layer bed drying. The model verification was based on a comparison between experimental and predicted data on bed-averaged moisture content and temperature along the bed. From the experimental-theoretical analysis, the importance of shrinkage for a more accurate interpretation of heat and mass transfer phenomena in the drying of porous media composed of gel-coated seeds is corroborated. Index Terms— transport phenomena, shrinkage, drying, coating, gel-seed system. I. INTRODUCTION Research has been devoted to obtain information about polymer range that would make coating technology most effective to aggregate quality and protection to seeds and grains [1] [2]. There is also an increasing interest in agricultural sector on searching for coating systems based on aqueous suspensions containing gelling binders. Encapsulation into agar gel appears as a rather promising method. Prado et al. [3] have shown the potential of agar-based coatings for retaining micronutrients in fortified millet as well as for a better crop establishment. Agar coating does not only overcome the problems of barrier to oxygen diffusion during storage, presented by others coating materials, but also its water holding capacity enhances water uptake under germinating conditions, thus improving the crop establishment. Its gel-forming behavior, by thermal mechanism, which imparts chemical stability to coatings, has motivated investigations on the use of agar as coating system for seeds. Drying is an essential operation in seed coating, since it ensures moisture removal from the coating, promoting the gel adherence to the seed surface and preventing deterioration Manoel Marcelo do Prado, Department of Chemical Engineering, Federal University of Sergipe, São Cristóvão, Brazil, +5579991245758. Douglas Santos Andrade, Department of Chemical Engineering, Federal University of Sergipe, São Cristóvão, Brazil, +5579991280570. Dermeval José Mazzini Sartori, Department of Chemical Engineering, Federal University of São Carlos, São Carlos, Brazil, +5519999163001 due to molds infestation. Although works on drying of seeds [4]–[6] and gels [7]-[9] separately, have been extensively reported in the literature, not much knowledge is available on the drying behavior of the seed-gel system. Because of the highly deformable polymeric structure of gels, gel-coated seeds tend to be susceptible to shrinkage and to changes in physical properties during drying what alter fluid-particle interaction. Thus, beds composed by these particles offer important challenges for the analysis of simultaneous heat and mass transfer during drying. Developing a basic understanding on the drying of gel coated seeds is not only a challenge, but also an opportunity and a need. It is necessary to characterize physical changes in the seed-gel system as well as to adequate models of fixed bed dryers [10], [11] to simulate heat and mass transfer in a deformable porous media, so that the particle-fluid interaction can be understood and the drying optimized. Based on this context and in order to contribute for the integration of researches that deal with the drying of seeds and gels, the objective of this work was to analyze the drying of millet seeds coated with agar gel. The physical-mathematical modeling of simultaneous heat and mass transfer was based on mass and energy balances in fluid (air) and solid (seed-gel system) phases, taking into account the shrinkage phenomenon of the material. II. MATHEMATICAL MODELING The physical problem under consideration is illustrated in Fig. 1, in which a packed bed of gel-coated seeds is percolated by a drying fluid flowing upward. The detail of a volume element extracted from the packed bed shows that part of this element is composed of solid particulate material, whereas the remaining void space is occupied by the fluid phase. Interactions between the solid and fluid phases by heat and mass transfer occur simultaneously during drying. For a complete description of the process, the proposed two-phase model took into account the effects of bed shrinkage and moisture content on the physical properties. Other assumptions adopted included: the airflow is one-dimensional with uniform distributions of velocity, humidity and temperature in the cross section of the bed; heat losses through dryer walls are negligible; the fluid-solid heat transfer in the packed bed is predominantly convective; and heat and mass transport is one-dimensional. Analysis of the Heat and Mass Transfer during Convective Drying of a Deformable Porous Medium Composed by Gel-Coated Seeds Manoel Marcelo do Prado, Douglas Santos Andrade, Dermeval José Mazzini Sartori