order to determine the water effective diffusion coefficient the following assumptions considerations were takeninto account: the main mass transfer mechanism was of diffusional nature, the external resistance to mass transfernegligible compared with internal resistance, the initialmoisture content was uniform throughout the sample, thediffusion coefficient is constant and not a function of moisture concentration (Crank, 1975).The solution of Fick’s second law of diffusion from a flatplate results in the following equation for the transfer ofwater (Crank, 1975):MR ¼ X t X eX 0 X e¼8 2pnX¼1n¼01ð2n þ 1Þ2 exp ð2n þ 1Þ2p2Det" # L2 ð1Þwhere MR is the moisture ratio, Xt is the moisture contentat any time t, Xe and X0 are equilibrium and initial moisture contents; De is the water effective diffusion coefficientand L is the half-thickness of the slices for drying fromboth top and bottom sides and t is the drying time. As applied to convective drying of solids, this solution is validonly for the falling rate period when internal moisture diffusion controls the dehydration rate.
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