engleski

Validation of new mathematical model for approximation of drying kinetics data

New mathematical model for description of drying kinetics for the whole drying time (constant rate and falling rate periods) is proposed. A model is in fact modification of the widely used Page model (exponential, two parameter). The idea for that specific modification arises from the similarity between Page model and statistical mathematical model (Weibull) used for description of particle size distribution, RRSB-function. Even though, many authors claimed that this are purely statistical functions, which parameters do not have physical meaning, results obtained from drying kinetics data shows that one model parameter, tk, has the physical meaning. Parameter tk, corresponds to the time at which diffusion (at the beginning of the first or second falling rate period) as the governing mechanism for moisture movement through the inner material structure starts. The applicability of model was tested on drying kinetics data of various types (structure, origin, shape) of materials dried in a convective, microwave or vacuum drier. Materials dried in a convective drier are: thin clay slab and small spheres of Al-Ni catalyst. Two different pharmaceutical powders (hydrochlorotiazide and chlorpropamide), two types of paperboard, wet blue cutting and tanned leather and three types of wood are dried in a microwave oven. Chlorpropamide is also dried in a tunnel and vacuum drier. Drying kinetics of all investigated materials and drying methods can be successfully correlated with modified Page model, in a chosen range of hot air temperature, pressure and microwave heating intensity. Since the material structure determines the mechanism of moisture transfer, pore size distribution of some tested materials are also determined. Obtained results confirm physical meaning of the model parameter tk.

drying kinetics; mathematical model

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