Experimental and Numerical Study for Convective Drying of Deformable Rubber Sheet

Abstract

Natural rubber is one of the major exporting products of Thailand. A few number of research has been carried out on the operating parameters to ensure fast drying of this product. Investigations on the shrinkage of rubber sheets occurring during the drying process have not been conducted so far. Optimization of the operating parameters for the fast drying of rubber is presented in this work. Experimental work was set to vary the velocity, temperature, and relative humidity from 1.5 to 4.0 m/s, 60 to 70°C and 40 to 60% (ideal) respectively. Computational Fluid Dynamics (CFD) approach using the finite element method was used to study the 2D conjugate shrinkage behavior of the rubber sheet thickness under the convective drying condition. An isotropic, linear elastic model was assumed. The Arbitrary Lagrangian-Eulerian (ALE) method was used to solve the two-dimensional problem in accounting for the shrinkage effect. The inference from the experimental studies showed that drying at temperature of 65°C at 2.5 m/s was optimal for best rubber sheet quality as higher temperature affected the rubber sheets quality. Lastly, drying at the lowest possible relative humidity reduces the drying time, equilibrium moisture content and water activity. The optimal operating conditions from the experiment is 65°C, 2.5 m/s for the temperature and velocity. The rubber sheet moisture content was reduced to 0.4% db within 38 hours of drying. The shrinkage percentage was estimated to be 9.1%. The agreement between experimental and simulation results are acceptable in terms of statistical parameters. The formulated predictive model can be used as a quality index evaluation for rubber sheet and for drying process optimization. Water activity can also be used in locating regions that could be prone to microbial spoilage. The drying time was reduced in comparison to the traditional drying of rubber sheets.