Mathematical Modelling and Determination of Mass Transfer Characteristics of Celeriac Slices under Vacuum Drying

Abstract

IntroductionDrying is an essential unit operation in a variety of industries e.g., food, pharmaceutical, chemical, plastic, timber and paper. The industries use drying equipments to eliminate moisture from the products for one or several of the reasons such as easy handling, safe preservation and longer storage, reduction in cost of transportation, desired quality, usage diversity and improved economical value [1]. Depending on the specific product attributes required, different industry sectors require different types of drying technology. Improper drying may lead to quality deterioration of product, high energy consumption, high process duration, unseasonable charges, etc. Hence, drying of high value and heat sensitive products such as food, pharmaceuticals and biological products demands special attention [2].Most dryers can be classified as direct dryers and vacuum dryers. In direct dryers, hot air at atmospheric pressure is used to supply the heat to evaporate water or other solvents from the product whereas, vacuum dryers use a reduced-pressure atmosphere to surround the product. In comparison with conventional atmospheric dryers, vacuum dryers have some unique advantages e.g., higher drying rate, lower drying temperature, higher energy efficiency and oxygen deficient processing environment [3]. Some researchers have applied vacuum dryers to dry various food materials and investigated dehydration kinetic and quality attributes of dried products [4][5][6][7].To predict drying behaviour of materials being dried, design new dryers, and control the process, mathematical modelling is widely used to simulate the drying process. The main proposed mathematical models used to describe the drying behaviour of agricultural materials are categorised as theoretical, semitheoretical and empirical models. Theoretical models are built based on the understanding the fundamental phenomena and mechanisms involved during drying process whereas the two other models are built by fitting model parameters to experimental data using multiple linear regressions. Theoretical simulations can give an explanation for phenomena occurring during the process but, they are more difficult and require substantial amount of computing time. The empirical models are derived from a direct correlation between moisture content and drying