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ABSTRACT
Two-dimensional analysis of heat and mass transfer during drying of a square cylinder (SC) for confined flow with a strong blockage ratio (β = 0.8) was performed using the alternating direction implicit (ADI)-based software. The influence of Reynolds number (Re = 10–50) and moisture diffusivity number (D = 1 × 10−5 − 1 × 10−8 m2/s) on the heat and mass transfer mechanisms was investigated. The convective heat transfer coefficients on SC surfaces were obtained using a commercial software package. The moisture content distributions inside a SC under transient conditions were calculated using the ADI method. The calculations showed that a higher Reynolds number enhances the overall mean Nusselt number and heat transfer coefficient value. The largest mean Nusselt number and heat transfer coefficient values were obtained at the front face of the SC, which makes the greatest contribution to the overall mean Nusselt number and heat transfer coefficient values for all surfaces of the SC. The effect of Reynolds number on the overall drying time was also investigated. Low Reynolds number and moisture diffusivity values lead to an increase in the overall drying time (Δtod). For Re = 10, the Δtod values are 502.19 → 220288 s and for Re = 50, the Δtod values are 126.14 → 70353.21 s for a moisture diffusivity range of D = 1 × 10−5 − 1 × 10−8 m2/s. Δtod-Re = 10/Δtod-Re = 50 ratios are 3.98–3.89 and 3.13 for a moisture diffusivity range of D = 1 × 10−5 − 1 × 10−8 m2/s. Δtod-D2/Δtod-D1 is 7.47 for Re = 10, and Δtod-D3/Δtod-D2 is 7.63 for Re = 50, whereas Δtod-D3/Δtod-D1 is 438.66 for Re = 10, and Δtod-D3/Δtod-D1 is 557.74 for Re = 50. Additionally, iso-moisture contours of SC were presented and relations for Nusselt number and mass transfer coefficient values were derived.
Nomenclature
| A | = | area (m2) |
| B | = | edge of square cylinder (m) |
| D | = | moisture diffusivity (m2/s) |
| hθ | = | heat transfer coefficient (W/m2K) |
| hm | = | mass transfer coefficient (m/s) |
| H | = | channel height (m) |
| M | = | moisture content (kg/kg) |
| k | = | thermal conductivity of fluid (W/m·K) |
| Le | = | Lewis number |
| P | = | static pressure (Pa) |
| Pr | = | Prandtl number |
| R | = | gas constant (J/kg·K) |
| Re | = | Reynolds number |
| t | = | time (s) |
| T | = | temperature (K) |
| u | = | streamwise velocity (m/s) |
| v | = | spanwise velocity (m/s) |
| U | = | core velocity (m/s) |
| x | = | stream wise distance (m) |
| y | = | spanwise distance (m) |
| α | = | thermal diffusivity (m2/s) |
| β | = | blockage ratio |
| ϕ | = | dimensionless moisture |
| χ | = | dimensionless location on surface |
| λ | = | under-relaxation parameter |
| µ | = | dynamic viscosity (Pa·s) |
| ρ | = | density (kg/m3) |
| Subscripts | = | |
| ∞ | = | inlet |
| bf | = | back face |
| B | = | edge of square cylinder |
| c, s | = | centerline, surface |
| ch, th | = | channel, throat |
| cr | = | critical |
| ff | = | front face |
| tf | = | top face |
Nomenclature
| A | = | area (m2) |
| B | = | edge of square cylinder (m) |
| D | = | moisture diffusivity (m2/s) |
| hθ | = | heat transfer coefficient (W/m2K) |
| hm | = | mass transfer coefficient (m/s) |
| H | = | channel height (m) |
| M | = | moisture content (kg/kg) |
| k | = | thermal conductivity of fluid (W/m·K) |
| Le | = | Lewis number |
| P | = | static pressure (Pa) |
| Pr | = | Prandtl number |
| R | = | gas constant (J/kg·K) |
| Re | = | Reynolds number |
| t | = | time (s) |
| T | = | temperature (K) |
| u | = | streamwise velocity (m/s) |
| v | = | spanwise velocity (m/s) |
| U | = | core velocity (m/s) |
| x | = | stream wise distance (m) |
| y | = | spanwise distance (m) |
| α | = | thermal diffusivity (m2/s) |
| β | = | blockage ratio |
| ϕ | = | dimensionless moisture |
| χ | = | dimensionless location on surface |
| λ | = | under-relaxation parameter |
| µ | = | dynamic viscosity (Pa·s) |
| ρ | = | density (kg/m3) |
| Subscripts | = | |
| ∞ | = | inlet |
| bf | = | back face |
| B | = | edge of square cylinder |
| c, s | = | centerline, surface |
| ch, th | = | channel, throat |
| cr | = | critical |
| ff | = | front face |
| tf | = | top face |
Acknowledgments
The author would like to acknowledge the Scientific Research Projects Department of Uludag University for supporting this research under the project number KUAP(MH) 2014/15. The author would also like to acknowledge the American Journal Experts for editing the manuscript.