DRYING MODEL FOR SKIM MILK IN A VERTICAL COCURRENT SPRAY DRYER

Abstract

In this thesis, a mathematical model has been developed for analysis, design and simulation of a vertical co-current spray dryer. The model considers several important features of drying as described below. > Drop/particle size ranges from 80 to 100 pm. > Particle shrinks as a shrinking balloon in the constant rate zone, and after attaining critical moisture content the diameter of particle remains constant. > Dependence of physical properties and other constitutive parameters on temperature. > Porosity of particles. In the model, drying medium is assumed to be saturated on the surface of the particle, intraparticle thermal gradients being small are neglected, and nozzle zone and any thermal degradation are not considered. The model comprises a set of non-linear coupled ordinary differential equations. These are solved by mathematical equation solver MATLAB 7.0. Model has been validated with the data available in the literature. Spray drying of skim milk is taken as the system for the purpose of analysis and simulation. An empirical correlation has been developed for the decrease in drying rate after the attainment of critical moisture content. This correlation is based on the data available in the literature, and it facilitates numerical simulation process. Detailed results of numerical simulation has been presented. iii