The Comparison of Two Models of Convective Drying of Shrinking Materials Using Apple Tissue as an Example

Abstract

Modeling of drying of capillary-porous materials is a mathematically complex problem. It takes into consideration simultaneous heat and mass transfer inside the material with physicochemical properties changing during the drying process. Modeling of the process mentioned above consists of describing the heat and mass transfer balances by means of differential equations. Moisture diffusion coefficient as a function of moisture content and temperature of the material is a crucial parameter that controls the process. An additional problem occurs when moving boundary of the shrinking material is taken into account. In the present work, the identification of diffusion coefficient as a function of moisture content and temperature on the basis of two different models is shown. The two models include the Pakowski model (defined in the stationary coordinates) and the Kechaou model (defined in moving coordinates). Experimental data necessary to verify the models were obtained on the basis of series of tests for different boundary conditions performed on an apple tissue. During the drying process, samples of apple undergo significant volumetric shrinkage. In this article, the comparison of the two models describing the convective drying process of shrinking material is presented together with the comparison of the identified moisture diffusion coefficient.

Mathematical modeling of intermittent and convective drying of rice and coffee using the reaction engineering approach (REA)

“…Complex optimization procedures need to be conducted subsequently to represent the dependence of diffusivity on moisture content and/or temperature (Azzouz et al, 2002;Pakowski and Adamski, 2007;Mariani et al, 2008;Vaquiro et al, 2009;Ramos et al, 2010;Silva et al, 2010;Ruiz-Lopez et al, 2011). Pakowski and Adamski (2007) and Ruiz-Lopez et al (2011) showed that various mathematical expressions of diffusivity need to be attempted to yield the most appropriate diffusivity function. It can be observed that the experimental data is required by both diffusion approach and the REA in order to generate the parameters but the REA requires more efficient procedures than the diffusion based approach to generate the drying parameters.…”

“…The models may not be practical for applications in industries where quick and accurate decisionmaking is necessary. In particular, the diffusivity needs to be estimated as a function of temperature and water content (Azzouz et al, 2002;Ruiz-Lopez and Garcia-Alvarado, 2007;Pakowski and Adamski, 2007;Mariani et al, 2008;Vaquiro et al, 2009;Ramos et al, 2010;Silva et al, 2010). In addition, Crank's effective liquid-diffusion based model implemented by several researchers (Steffe and Singh, 1982;Cihan and Ece, 2001;Ramesh, 2003;Iguaz et al, 2003) offers simplicity of mathematical modeling and computation so that diffusivity can be simply determined (but rather roughly) by taking slope of reduced moisture content versus time.…”

Drying model for cylindrical pasta shapes using desorption isotherms

“…(1), the diffusion of moisture in cylindrical-shaped pasta can be expressed as (Pakowski & Adamski, 2006) …”

Quality Aspects of Fruit and Vegetables Dried Convectively with Osmotic Pretreatment

“…Osmotic dehydration (OD) as a pretreatment process before proper drying enables moisture removal from vegetables and fruits up to 50%. Besides, the application of osmotic pretreatment considerably reduces chemical, physical and biological adverse changes which occur during long lasting convective drying, called hot air drying (Kowalska and Lenart, 2001;Pakowski and Adamski, 2007;Piasecka et al, 2012;Witrowa-Rajchert and Rząca, 2009). …”