A Comparison Of Drying Kinetics Based On The Degree Of Hydration And Moisture Ratio

The most widely used experimental parameter for modeling drying processes is the loss of sample mass, which is converted to the ratio between the water content at time t and the initial water content (moisture ratio, MR). Here we studied the drying of pineapple fruits and converted the experimental data for loss of mass to degree of hydration αH(t), which corresponds to the ratio between the water content and the sample mass. This approach allowed us to propose a thermodynamic model for the drying process. The results for the minimum local Gibbs free energy showed that for a degree of hydration of 0.1 the process was more spontaneous at 110°C and a drying time of 90min. However, the entropy of the process was maximal at 70°C and a drying time of 163min. The optimization of drying process and quality of the dried product should be better controlled throughout such this thermodynamic monitoring. The treatment of the data applying the MR approach in the structure transition model produced reasonable fitting, but with several limitations related to the thermodynamic derivation.601192198Akanbi, C.T., Adeyemi, R.S., Ojo, A., Drying characteristics and sorption isotherm of tomato slices (2006) Journal of Food Engineering, 73 (2), pp. 157-163Baini, R., Langrish, T.A.G., Choosing an appropriate drying model for intermittent and continuous drying of bananas (2007) Journal of Food Engineering, 79 (1), pp. 330-343. , (This article is of particular importance because of the comparative analysis of different methods used to characterize drying in intermittent and continuous processes.)Bispo, J.A.C., Bonafe, C.F.S., Joekes, I., Martinez, E.A., Carvalho, G.B.M., Norberto, D.R., Entropy and volume change of dissociation in tobacco mosaic virus probed by high pressure (2012) Journal of Physical Chemistry B, 166 (51), pp. 14817-14828Bispo, J.A.C., Bonafe, C.F.S., Xavier, D., Brandao, T., Rodrigues, C., Oliveira, M.G.A., Optimizing drying processes by using a structural transition model and entropy change maximization (2014) Drying Technology, 32 (8), pp. 910-918. , (This work shows that optimization of the energy expended during drying, as well as physical properties such as composition, hydration and texture, should be reached at optimal conditions by minimizing the Gibbs free energy of water release or, for entropy-driven processes, by maximizing the entropy of water release. The applicability of this approach in industrial processes could be very relevant.)Bispo, J.A.C., Silva, C.M.R., Bonafe, C.F.S., Assis, D.J., Modeling drying isotherms using a structure transition model (2013) Drying Technology, 31 (9), pp. 1008-1019. , (This work provides the first description of the use of the concept of extent of reaction to characterize drying processes based on structural transition. 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Analysis of the fluid-dynamic behavior of fluidized and vibrofluidized bed containing glycerol

The fluid-dynamic characteristics of fluidized and vibrofluidized beds of inert particles in liquids are being widely studied by researchers interested in understanding and modeling the paste drying process. In this work characteristic fluid-dynamic curves of pressure drop versus air velocity were obtained for fluidized and vibrofluidized beds with glycerol. Glycerol was used as a standard fluid to simulate a paste in the bed, and "ballotini" glass spheres were used as inert particles. The fluid-dynamic behavior as well as the quality of the fluidization regimes was analyzed through pressure drop versus air velocity curves and visual observation of the flow patterns in the beds. The results indicated that standard deviation curves are a useful tool for gaining an understanding of the fluid-dynamic behavior of a vibrofluidized bed. They allow detection of changes in the fluid-dynamic behavior which were not observed by analyzing only the pressure drop versus air velocity curves. For fluidized beds (G=0.00), it was also observed that analysis of curves of standard deviations of pressure drop may help in the estimation of more accurate values of minimum fluidization velocities