TAILIEUCHUNG - Mass Transfer in Chemical Engineering Processes Part 8

Tham khảo tài liệu 'mass transfer in chemical engineering processes part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Mass Transfer Enhancement by Means of Electroporation 165 Fig. 8. Dependence of diffusion coefficients of PEF-treated samples on drying temperature and on the specific PEF energy. a Dependence on temperature of diffusion coefficients during drying of untreated freeze-thawed and PEF treated potatoes. PEF treatment conditions were E kV cm and tPEF 500 ms. Drying was carried at variable temperature in a drying cabinet with an air flow rate of 6 m3 h Lebovka et al. 2007b . b Dependence on the specific applied energy of PEF treatment of diffusion coefficients during drying of bell peppers. PEF treatment conditions were E 1-2 kV cm and tPEF 4-32 ms. Drying was carried at 60 C in a fluidized bed with air velocity of 1 m s Ade-Omowaye et al. 2003 . inducing a significant decrease in the activation energy Ea which translates in smaller dependence of Deff on extraction temperature. Fig. 9a reports the activation energies of intact PEF-treated and thermally-treated apple slices estimated from the data of sugar concentration in the extraction medium through Eq. 13 and 14. Apple samples treated by PEF E kV cm and tPEF s exhibited an intermediate activation energy Ea 20 kJ mole which was significantly lower than for intact samples Ea 28 kJ mole and measurably higher than for samples that were previously subjected to a thermal treatment at 75 C for 2 min Ea 13 kJ mole . Moreover PEF treatment also induced an increase of the Deff value in comparison to untreated tissue for all the different temperatures tested Jemai and Vorobiev 2002 . For example at 20 C Deff estimated from PEF-treated samples m2 s was much closer to the Deff value of denatured samples m2 s than to the Deff of intact tissue m2 s . In addition at 75 C the Deff value of PEF-treated samples was m2 s-1 compared with m2 s for thermally denatured 166 Mass Transfer in Chemical Engineering Processes samples indicating that the electrical treatment had a .

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