Influence of shrinkage during natural rubber sheet drying: Numerical modeling of heat and mass transfer

We developed a theoretical model for the transport phenomena affected by shrinkage in rubber sheet drying. The conjugate approach involving the simultaneous transfer of momentum, heat and mass in the drying chamber and rubber sheet was investigated by computational fluid dynamics. An isotropic, linear elastic model was assumed, and the shrinkage was correlated with the moisture content evolution in the rubber sheet. The Arbitrary Lagrangian-Eulerian (ALE) method was used to solve the two-dimensional problem accounting for shrinkage. The shrinkage across the rubber sheet thickness was estimated at 9.1% and the moisture content was reduced from 0.4 to 0.05 kg-water/kg-dried sheet at an average holding relative humidity of 60% within 46 h. Simulations and experiments showed good agreement (R2 values for moisture content and shrinkage were 0.9809 and 0.9991, while RMSE were 0.0196 and 0.0091). The derived model can be used as a quality index evaluation for rubber sheet and for drying process optimization. Water activity can also identify regions that may be prone to microbial spoilage. The drying time was lower than for traditional sun drying of air dried sheets (as high as 152 h) or drying in a natural flow chamber (72 h).