TAILIEUCHUNG - Heat and Mass Transfer Modeling and Simulation Part 9

Tham khảo tài liệu 'heat and mass transfer modeling and simulation part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Some Problems Related to Mathematical Modelling of Mass Transfer Exemplified of Convection Drying of Biological Materials 151 D D0exp EJf 1 T 1 j 34 Mulet et al. 1989a b expressed the water diffusion coefficient by the following empirical formula D a exp b T 1 j 35 The water diffusion coefficient as a function of moisture content and dried material temperature was described by Mulet et al. 1989a b D exp a b T 1 cM and Parti Dugmanics 1990 D _ -b A a exp I. Tữkĩĩ cM 36 37 Dincer and Dost 1996 developed and verified analytical techniques to characterise the mass transfer during the drying of geometrically infinite slab infinite cylinder sphere and irregularly by use of a shape factor shaped objects. Drying process parameters namely drying coefficient S and lag factor G M t -Me Mc - Me Gexp -St 38 were introduced based on an analogy between cooling and drying profiles both of which exhibit an exponential form with time. The moisture diffusivity D was computed using D Pl 39 The coefficient gi was determined by evaluating the root of the corresponding characteristic equation Dincer et al. 2000 for slab shapes b1 2013G3 - - 40 for cylindrical shapes b1 - - 41 for spherical shapes b1 - - 42 Babalis Belessiotis 2004 used the following method of calculation of effective moisture diffusivity. If following assumptions are accepted in Eq. 31 152 Heat and Mass Transfer - Modeling and Simulation i. the external mass transfer resistance is negligible but the internal mass transfer resistance is large Bw x ii. the first term of infinite series is taken into account successive terms are small enough to be neglected its simplified form can be expressed as follows M t -Me Mc Me -yexp X -X Dt A R2 J 43 6 Logarithmic simplification of Eq. 43 leads to a linear form ln M t -Me Mc - Me 44 By plotting the measured data plotted in a logarithmic scale

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