Modelling of moisture migration during convective drying of pineapple slice considering non-isotropic shrinkage and vari
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ORIGINAL ARTICLE
Modelling of moisture migration during convective drying of pineapple slice considering non-isotropic shrinkage and variable transport properties Poonam Rani1 • P. P. Tripathy1
Revised: 21 January 2020 / Accepted: 2 April 2020 Ó Association of Food Scientists & Technologists (India) 2020
Abstract The present work aims to develop a 3-dimensional finite element (FE) model to analyze moisture migration during drying of pineapple ring considering moisture dependent diffusion coefficient (D) and mass transfer coefficient (hm) along with radial and longitudinal shrinkage. Pineapple rings were dried at 70 °C temperature and 0.6 m/s air velocity to study the moisture loss and shrinkage kinetics during drying. Thickness, outer radius and inner radius of hollow cylindrical pineapple slices were reduced by 79.3%, 32.2%, and 51.2%, respectively due to the occurrence of shrinkage during drying. Non-linear regression analysis showed the quadratic model to best fitted to the experimental moisture ratio data for explaining the shrinkage phenomenon in pineapple slice during drying. Shrinkage was accommodated into FE modelling using the arbitrary lagrange-eulerian method. Consideration of variable D showed better agreement with the experimental data than consideration of constant D, however constant and variable hm predicted similar results. Incorporation of shrinkage phenomena during modelling led to prediction of more accurate result showing 0.06% deviation from experimental curve, but neglecting the shrinkage resulted in a 17% deviation. Hence, model developed with consideration of shrinkage along with variable D and hm presented best fit with experimental drying curve. Developed model allowed the visualization of spatial moisture profile within the sample during drying, which would be useful for estimating the correct drying time, optimizing and designing of drying process.
& P. P. Tripathy [email protected] 1
Agricultural and Food Engineering Department, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India
Keywords Finite element model Drying Pineapple Diffusion coefficient Shrinkage Mass transfer coefficient List of symbols A Exposed surface area (m2) D Moisture diffusion coefficient (m2/s) oM=ot Slope of moisture vs. drying time curve DR Drying rate (kg/h.m2) do Outer diameter of pineapple slice (m) di Inner diameter of pineapple slice (m) l Thickness of pineapple slice (m) M Moisture content (kg water/kg dry weight) Me Equilibrium moisture content (kg water/kg dry weight) Mo Initial moisture content (kg water/kg dry weight) M1 Moisture content at the sample surface MR Moisture ratio N Number of observations R2 Coefficient of determination ri Inner radius of slice (m) ro Outer radius of slice (m) t Time (s) wb Wet basis Ws Weight of dry solid (kg) f Number of constants V Volume of pineapple ring (m3) S Shrinkage parameter Spre,I Predicted shrinkage parameter Sexp,I Experimental shrinkage parameter RMSE Root mean square error 2 v Reduced chi-square error hm Conve
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