Experimental and fundamental critical analysis of diffusion model of airflow drying

• Published in: Drying technology Vol. 34; no. 15; pp. 1884 - 1899
• Main Authors: Nguyen, T. H., Lanoisellé, J.-L., Allaf, T., Allaf, K.
• Format: Journal Article
• Language: English
• Published: Philadelphia Taylor & Francis 17-11-2016; Taylor & Francis Ltd
• Subjects: Agro-material; Airflow; Carrots; Chemical Sciences; Constraining; critical airflow velocity; Diffusion; Diffusivity; Drying; Drying agents; drying kinetic model; Heat transfer; Kinetics; mass transfer; Material chemistry; Pressure drop; Raw materials; Velocity; critical airflow velocity; Agro-material; drying kinetic model; heat transfer; mass transfer
• ISSN: 0737-3937; 1532-2300
• DOI: 10.1080/07373937.2016.1155052

Scientific literature of agromaterial drying present contradictory conclusions in terms of the kinetic effect of airflow velocity. Some authors confirmed that it does not trigger any modification of drying, while some articles tried to establish empirical models of the effective diffusivity D
eff
versus the airflow velocity, what is fundamentally erroneous. By analyzing internal and external transfer phenomena, this research aimed at recognizing that once air velocity is higher than a critical airflow velocity (CAV), the internal transfers become the limiting phenomenon. CAV depends on the effective diffusivity and the product size. It was calculated in the cases of two studied raw materials (apple and carrot), differently textured by instant controlled pressure drop (DIC). Values of CAV greatly depend on diffusivity of water within the matrix. At temperature T = 40°C, they were 1 m/s for untreated carrot and 2.1 m/s for DIC-textured carrot, whose D
eff
values were 1.31 and about 3 × 10
−10
 m
2
/s, respectively. Also, at temperature T = 40°C, they were 2.1 m/s for untreated apple and 3 m/s for DIC-textured apple, whose D
eff
were 1.4 and about 10.4 × 10
−10
 m
2
/s, respectively.