From Laboratory Experiments to Design of a Conveyor-Belt Dryer via Mathematical Modeling

Abstract

A conveyor-belt dryer for picrite has been modeled mathematically in this work. The necessary parameters for the system of equations were obtained from regression analysis of thin-layer drying data. The convective drying experiments were carried out at temperatures of 40, 60, 80, and 100°C and air velocities of 0.5 and 1.5 m/sec. To analyze the drying behavior, the drying curves were fitted to different semi-theoretical drying kinetics models such as those of Lewis, Page, Henderson and Pabis, Wang and Singh, and the decay models. The decay function (for second order reactions) gives better results and describes the thin layer drying curves quite well. The effective diffusivity was also determined from the integrated Fick's second law equation and correlated with temperature using an Arrhenius-type model. External heat and mass transfer coefficients were refitted to the empirical correlation using dimensionless numbers (J _h , J _D  = m · Re ⁿ ) and their new coefficients were optimized as a function of temperature. The internal mass transfer coefficient was also correlated as a function of moisture content, air temperature, and velocity.

Keywords:

• Drying kinetics
• Thin layer drying
• Characteristic drying curves
• Convective drying
• Heat and mass transfer coefficients
• Belt dryer

ACKNOWLEDGMENT

The Parchin Chemical Complex (PCC) of Iran supported this work. We wish to acknowledge the contribution of the employees of the research and development division of PCC, especially Mr. E. Nazari, for their feedback and advice.

Notes

*X _j , X _f , and X _eq are in (kg w/kg d.s.)

(1): MR = k ₁ · exp (− k ₂ · τ).

(2): MR = k ₁ · exp (− k ₂ · τ ⁿ ).

(3): MR = 1 + a · τ + b · τ².

(4): MR = exp [k ₁ · τ/(1 + k ₂ · τ)].

¹Relative deviation percentage; (calc. − exp)/exp