Convective drying of a moist porous object under the effects of a rotating cylinder in a channel

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Convective drying of a moist porous object under the effects of a rotating cylinder in a channel Fatih Selimefendigil1 · Seda Özcan Çoban1 · Hakan F. Öztop2 Received: 9 September 2019 / Accepted: 1 December 2019 © Akadémiai Kiadó, Budapest, Hungary 2019

Abstract Numerical study of evaporation in porous medium during convective drying process was examined, and heat and mass transfer of liquid water and water vapor through porous media was investigated by using the Galerkin weighted residual finite element method. The porous moist object has a rectangular shape and is assumed to represent a food sample. Two-dimensional laminar flow of dry hot air was used in the channel with a rotating circular cylinder. Different locations and angular rotational speed of the rotating cylinder were considered to control the convective heat transfer and mass transportation. The radius of rotating cylinder and velocity of drying air were also varied with five different values. Results showed that rotational angular speed and drying air velocity had significant effect on heat transfer and mass transport phenomenon for the porous moist object. Keywords  Convective drying · Heat and mass transfer · Porous matrix · CFD List of symbols cp Specific isobaric heat capacity (kJ kg−1 K−1) c Concentration D Diffusivity ­(m2 s−1) h Convective heat transfer coefficient (W m−2 K−1) Hevap Heat of evaporation (J mol−1) ⃗I Identity vector k Thermal conductivity (W m−1 K−1) L, l Length (mm) M Molar mass (kg mol−1) mevap Mass of evaporation (mol m−3 s−1) n Mass flux (kg m−2 s−1) P, p Pressure (Pa) R Universal gas constant (J mol−1 K−1) Revap Evaporation rate (kg m−3 s−1) r Radius (mm) s Surface area ­(m2) S Saturation T Temperature (K) t Time (min) q Heat flux (kJ m−2 s−1) * Fatih Selimefendigil [email protected] 1



Department of Mechanical Engineering, Celal Bayar University, Manisa, Turkey



Department of Mechanical Engineering, Technology Faculty, Fırat University, Elazig, Turkey

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u⃗ Velocity vector V Volume ­(m3) x  x coordinate (mm) y  y coordinate (mm) Greek letters ρ Density (kg m−3) ε Porosity κ Permeability μ Dynamic viscosity τ Tortuosity Subscripts a Air c Capillary eff Effective evap Evaporation g Gas l Liquid ma Moist air p Pressure r Relative s Solid sat Saturation v Vapor w Water

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Introduction Heat and moisture transport from porous materials such as foods, bricks and biological membranes is a very common issue to investigate in the literature. Particularly, there is a wide range of foods that the transport mechanism had been investigated for the drying [1–9], heating [10–14], frying [15–19] and other food heat and moisture transport processes [20–26] and currently, it is a topic of interest. Drying processes are one of the main applications for long-life storage of fresh foods because of large water removal from products. Convective drying is one of the most preferred applications in food drying industries because it is the simplest and most economical technique a