# Modeling of the Drying Process of Apple Pomace
###### Abstract
There are numerous works describing the process of convective drying of apples and evaluating the quality of dried material. However, the works do not describe the process of drying apple pomace. Drying is one of the most energy-consuming processes in the processing industry. High consumption of energy is connected with the emission of large amounts of substances harmful to the natural environment [16]. It means that improvements contributing to the reduction in the technological process duration are both profitable to the production plant and the natural environment. Generally, shortening the time biological material is exposed to a high temperature has a positive effect on quality. As pomace is a valuable source of fiber, pectin, polyphenols and anti-oxidants as well as vitamins--a shorter drying time means higher retention of these elements in the dried material. Yet, both a too short and too long drying times may have adverse effects on the product [17; 18]. Despite the essence of kinetics, modeling of drying of pomace is necessary to understand the mechanism of heat and mass transfer, and is a prerequisite for the mathematical description of the whole process. Such a model plays a significant role in the optimization and control of working conditions. Technological solutions in the industry are based on simple mathematical models, which also describe the course of the process of drying very well [19]. Therefore, they are used to control this process. On the other hand, complex mathematical models describe phenomena and scientifically explain the process of drying. Mathematical modeling of dehydration process is an inherent part of modeling, develop ment and optimization of drying equipment [20]. It essentially involves detailed research on the kinetics of drying, which describes the impact of the process variables on moisture transfer. Correctly specified mathematical models may be used to select drying parameters, assessment of kinetics of drying and optimization of drying conditions [21]. Appropriate construction of drying equipment requires knowledge of drying characteristics of the material subjected to drying as well as drying kinetics [22]. It requires emphasizing that a higher temperature results in higher driving force of heat exchange. It also accelerates the process of drying as higher temperature increases the pressure of vapor. When choosing appropriate processing technology, optimization of the process parameters needs to be considered whenever possible so as to reduce the time needed to complete the process [23, 24]. Mathematical modeling facilitates this part of modeling, and enables the course to be predicted. It allows for the application of experimental results obtained in the laboratory in industry. Modeling and simulation are also indispensable for designing industrial drying plants, drying equipment as well as choosing appropriate drying conditions. Modeling of the process of drying pomace is more difficult due to the fact that apple pomace is highly heterogeneous as it contains flesh, pip integuments, pips, pedicles of different shapes, sizes and proportions. Empirical process may be presented by means of one or more models. Kinetic models for drying agricultural products are models of water content and temperature changes. These models contain physical variables, knowledge of which is required for their analysis [25]. In the process of the convective drying of solid bodies, conducted in the dominant external conditions of heat and mass exchange, an important factor is the surface of the body, through which the exchange occurs. The process is determined by the conditions of transport of water molecules from the surface of the body being dried through the adjacent gas layer. The process of convective drying of such materials is almost invariably accompanied by the shrinkage phenomenon [26]. The occurrence of shrinkage in biological material subjected to drying is most frequently the result of a significant loss of water [27].