Modeling of Shrinkage During Desiccation of Extruded Durum Semolina

Alex R Griessman, Purdue University

Abstract

Extruded durum semolina pasta was dried over saturated salt solutions, and the change in both volume and moisture content were recorded for each sample. Drying temperatures were between 40 °C and 80 °C, and relative humidities were between 0.09 and 0.96. The resulting data was analyzed using multilinear regression to determine the key parameters required to predict shrinkage during drying. It was determine that both drying temperature and change in moisture content were statistically significant predictors of volume change, with drying temperature having less impact than change in moisture content. It was found that shrinkage had a quadratic relationship with both predictors. The nonlinear relationship between moisture content change and linear shrinkage is evidence of the glass transition impacting the final material dimensions. The material properties of extruded durum semolina pasta were researched in literature, and moisture sorption isotherms, effective diffusivity, and stress relaxation curves were employed to calculate deformation during drying. Shrinkage was assumed to be caused solely by capillary pressure that occurred during drying. Mass transfer was described using the advection-diffusion equation in Lagrangian coordinates, and strain was calculated using the generalized Kelvin-Voigt model for viscoelasticity. The resulting system of partial differential equations was solved numerically using finite element method, and the results were compared to experimental data for validation. The deviation from experimental results was 10% to 20% at higher equilibrium moisture contents and increased as the ambient moisture content was decreased. This error was assumed to be a result of the capillary pressure model used. If a better model were determined experimentally, it would likely improve the accuracy of the model.

Degree

M.S.

Advisors

Okos, Purdue University.

Subject Area

Food Science|Applied Mathematics|Engineering

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