Modeling of the Seedless Grape Drying Process using the Generalized Differential Quadrature Method

Abstract

Mathematical modeling of the grape drying process is important in understanding the transport phenomena involved in the production and processing of dried grapes. Drying models proposed in the literature have simplifying assumptions, and thus ignore important phenomena such as shrinkage and changes in transport properties which occur during the drying process. Consequently, a mathematical model is developed for the seedless grape drying process, which considers the effects neglected in previous models. Since an analytic solution to this nonlinear model is impossible, the generalized differential quadrature method is used to solve the models' equations. The model is validated with experimental data obtained from a laboratory scale convective tray dryer operating at 50-70°C and an air velocity of 1.5 m/s. Model predictions are in close agreement with experimental data due to the inclusion in the model of shrinkage and variation in moisture diffusivity. Model results can serve as a framework to improve the performance of existing and novel dryers, and also in the design of process simulators for dryers.

Diffusion models for the description of seedless grape drying using analytical and numerical solutions

“…In order to increase the drying rate, commonly a pretreatment is accomplished before drying. Several pretreatment techniques involving the use of chemical additives are described in the literature [2][3][4][5][6]. However, the demand for natural foods, without adding chemicals, is increasing in many parts of the world.…”

“…However, the demand for natural foods, without adding chemicals, is increasing in many parts of the world. Therefore, alternatives to chemical additives are used as pretreatment for the production of raisins, for instance: abrasion method [7] and dipping in hot water [6,8].…”

Description of Seedless Grape Drying and Determination of Drying Rate

“…Experimental data obtained by Esmaiili et al (2007) for the drying of seedless sultana grapes (Vitis vinifera L.) with hot air are explored in the present paper. In order to increase the skin's permeability to moisture, a pretreatment was applied.…”

“…To increase the drying rate, a pretreatment is usually accomplished. According to Silva et al (2012a), several pretreatment techniques involving the use of chemical additives are described in the literature (Pangavhane et al, 1999;Doymaz and Pala, 2002;Doymaz, 2006;Esmaiili et al, 2007). However, several authors observe that the demand for natural foods is increasing in many parts of the world.…”

“…Thus, alternatives to chemical additives are used as pretreatment for the production of raisins, such as abrasion (Di Matteo et al, 2000) and dipping in hot water (Esmaiili et al, 2007;Ramos et al, 2010). For example, Esmaiili et al (2007) studied drying of seedless grapes submitted to two types of pretreatments, as is described in the following. The grapes were dipped in an alkaline emulsion of ethyl oleate (EO) and also in hot water (HW) before drying.…”