Carlos Martínez-Vera

Experimental Validation of a Mathematical Model for the Batch Drying of Corn Grains

ABSTRACT Yellow dented corn samples were dryed i n the laboratory with heated air i n a batch fluidized bed dryer at three different operation conditions. The evolution o f the temperature nnd moisture content were predicted with both, a model proposed in the literature that neglects the position dependence o f the diffusion coefficient and a modified version o f i t that takes into account the above mentioned functionality. Both models were solved by means of collocation i n finite elements. The consideration o f the diffusivity as a position function leads to better agreement with the experimental results.

TREATMENT OF POLLEN BY FLUIDIZATION

ABSTRACT This work is divided into two distinct parts: i) a study of the cleaning of pollen by encrainment with air and determination of the parameters that permit efficient levels of separation; and ii) a consideration of the drying of pollen by fluidization and an assessment of its effect on product quality. The pollen utilized consisted of fresh material, collected from traps in beehives, and characterized in terms of organic and inorganic materials. The physical properties of each of these materials, as well as their respective hydrodynamic behaviour when fuidized, were determined. Based on a statistical experiment design, it was found that superficial air velocity and pollen inventory in the dryer are major factors that affect cleaning. Results also show that the drying of pollen by fluidization is controlled by transport within the particles and, therefore, temperature was the major factor affecting drying rate and the one which determined product quality.

St-MMA-BuA terpolymerization in emulsion: II. The kinetic azeotropy and the problem of homogeneity in composition

An analysis of the kinetic azeotropy of the terpolymer from styrene(St)-methyl methacrylate(MMA)-butyl acrylate(BuA) in emulsion polymerization is effectuated. The objective is to determine the conditions for obtaining terpolymers uniform in composition. In this regard, a composition near to the unitary azeotrope is used in batch, semicontinuous and seeded emulsion polymerization processes. As expected, the monomer partition between the different phases modifies the terpolymer composition, in particular at the beginning of the semicontinuous processes. It is also observed that the unitary azeotrope in batch and semicontinuous emulsion polymerization is conserved in a large range of conversion due to the constancy of monomer concentration and radicals in the particle. In this way, a terpolymer with almost an accumulated constant composition is obtained in the seeded process. A thermodynamic analysis of the kinetic azeotropy is also made. The correspondence between the azeotropes of the binary copolymers and the values of the Flory interaction parameters of the monomers χιj is correlated. It is found that the lesser repulsion of the St-MMA pair respect to that of St-BuA provoked that the composition of the terpolymer tends to the copolymer azeotrope of St-MMA.

Prediction of Moisture Content Evolution in a Grain Batch Dryer Based on On–line Temperature Measurements

ABSTRACT The time evolution of the moisture content in a grain batch fluidized bed dryer is estimated by means of an on–line non–linear estimator (Marquardt–Levenberg algorithm). The inputs to the estimation algorithm are on–line temperature measurements and the output is the surface moisture content. The surface moisture content is used for predicting the grain moisture content through the solution of a single ordinary differential equation that combines the moisture and energy balances over the dryer. In this way the drying curves are obtained through incorporating in a very simple model easily obtainable physical information of the process.