Heat and Mass Transfer

, Volume 55, Issue 12, pp 3721–3732 | Cite as

Impact of different geometric shapes on drying kinetics and textural characteristics of apples at temperatures above 100 °C

  • Nasim Kian-Pour
  • Sukru KaratasEmail author
Original Article


The aim of this research was to determine the impact of samples size and shapes on drying kinetics, transport phenomena and textural characteristics of apples during drying. Three different geometric plate shape samples including squares, circles, and triangles, at temperatures of 110 °C, 115 °C and 120 °C, respectively, were dried at a constant air velocity of 1.75 m/s, and a nonlinear regression analysis was applied to fit the results to six dehydration models. The statistical analysis indicated that the Midilli & Kucuk model was the ideal model. Fick’s second law of diffusion was applied for computation of effective diffusivities, which varied from 1.93 × 10−9 to 2.85 × 10−9 m2/s, while the activation energy varied from 20.41 to 36.51 kJ/kg.mol. Additionally, the drag forces, heat and mass transfer coefficients varied from 4.202 to 5.005 N, 60.312 to 71.763 (W/m2 K) and 0.0497 to 0.0594 (m/s), respectively. The results reveal that triangular shapes could have the potential to improve the air drying of apples at an industrial extent.


a, b, c, k, n

Drying parameters


Total surface area (m2)


Circle shape sample


Friction drag coefficient (dimensionless)


Specific heat (J/kg K)


Specific heat of apple (J/kg K)


Arrhenius factor (m2/s)


Mass diffusivity of air-water vapour mixture (m2/s)


Effective moisture diffusivity (m2/s)


Drying rate (kg water/kg dry solid. min)


Activation energy (kJ/mol)


Drag force (N)


Friction drag force (N)


Heat transfer coefficient (W/m2 K)


Convective mass transfer coefficient (m/s)




Thermal conductivity of apple (W/m K)


Air thermal conductivity (W/m K)


Characteristic length of the sample (m)


Lewis number (dimensionless)


Initial moisture content (kg water/kg dry solid)


Equilibrium moisture content (kg water/kg dry solid)


Moisture ratio (dimensionless)

\( \overline{\boldsymbol{M}\ } \)

Average moisture content (kg water/kg dry solid)


Moisture content at time t (kg water/kg dry solid)

Mt + ∆t

Moisture content at time t + ∆t (kg water/kg dry solid)


Predicted moisture ratio (dimensionless)


Experimental moisture ratio (dimensionless)


Moisture content-wet base (%)


Number of observation


Nusselt number (dimensionless)


Positive integer


Prandtl number (dimensionless)


Universal gas constant (kJ/kmol. K)


Coefficient of determination


Reynolds number (dimensionless)


Root mean square error


Square shape sample


Schmidt number (dimensionless)


Sherwood number (dimensionless)


Absolute temperature (K)


Triangle shape sample


Drying time (min)


Interval time between two weight measurements (min)


Air free-stream velocity (m/s)


Half thickness of slab (m)


Reduced chi-square


Number of constant


Thermal diffusivity (m2/s)


Kinematic viscosity (m2/s)


Fluid viscosity (kg/m.s)


Fluid density (kg/m3)



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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Department of Food EngineeringIstanbul Aydin UniversityIstanbulTurkey

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