Estimation of water diffusivity parameters on grape dynamic drying

Inês N. Ramos, João M.R. Miranda, Teresa R.S. Brandão, Cristina L.M. Silva*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

42 Citations (Scopus)


A computer program was developed, aiming at estimating water diffusivity parameters in a dynamic drying process with grapes, assessing the predictability of corresponding non-isothermal drying curves. It numerically solves Fick's second law for a sphere, by explicit finite differences, in a shrinking system, with anisotropic properties and changing boundary conditions. Experiments were performed in a pilot convective dryer, with simulated air conditions observed in a solar dryer, for modelling the process. The equivalent radius of grapes decreased 30% until the end of the process, stressing the need to include shrinkage in mass and heat transfer models. It was observed that macroscopic shrinkage reflects cellular shrinkage, if plotted versus the normalised water content. Diffusivity values ranged between 1 × 10-16 and 1 × 10-10 m2/s. The developed methodology yields very good prediction of dynamic drying curves.

Original languageEnglish
Pages (from-to)519-525
Number of pages7
JournalJournal of Food Engineering
Issue number4
Publication statusPublished - Apr 2010


  • Dynamic convective drying
  • Grapes
  • Numerical modelling
  • Water diffusivity


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