Mathematical Modeling of Mass and Heat Transfer in a Dehumidifying Plastic Dryer

Abstract

The dehumidification of plastic resins is an essential process aimed at mitigating the adverse effects of excessive or insufficient moisture content during thermal processing operations such as molding and extrusion. The extent to which moisture compromises the structural integrity and performance of the final product is contingent upon the specific characteristics of the polymer and its end-use application. Nevertheless, inadequate or incomplete drying of the raw material invariably introduces defects either during fabrication or in subsequent service conditions. In this study, a theoretical framework is developed to analyze the coupled heat and mass transfer phenomena occurring within a dehumidifying dryer operating under steady-state conditions. The model considers a drying bed partially occupied by a porous desiccant medium, with a closed-form analytical solution derived based on the interplay between the geometric configuration of the flow channel, the physicochemical properties of the desiccant, and the interphase mass transfer dynamics within the porous matrix. Additionally, the investigation encompasses the evaluation of moisture-loss behavior and the influence of airflow characteristics within the drying hopper—parameters deemed critical to the drying kinetics. The analysis underscores the necessity of maintaining a sufficiently high and uniform airflow to ensure that plastic pellets attain and sustain the target drying temperature for the requisite residence time, thereby facilitating effective moisture extraction and enhancing overall process reliability.