Continuous and Intermittent Drying (Tempering) of Oblate Spheroidal Bodies: Modeling and Simulation

Abstract

In this work, modeling of continuous and intermittent drying of oblate spheroidal bodies is presented. The model considers the liquid diffusion as the only process of mass transfer inside the body, constant diffusion coefficient and equilibrium conditions at the surface of the solid. The diffusion equation is described in the oblate spheroidal coordinates system and it was discretized using the finite-volume method. Formulation was applied to predict drying of lentil grains. Several cases of intermittent drying for lentils were simulated: using a same time of tempering (time of rest), beginning in different drying time and for two or more drying passes (time steps) along the process. For a same useful time of the dryer, it was observed that the intermittent drying always increases the efficiency of the process. Another outstanding result is the improvement of the final quality of the product due to the absence of large moisture content gradients inside of the product during the drying process after tempering.

Comparison between continuous and intermittent drying of whole bananas using empirical and diffusion models to describe the processes

“…However, an empirical equation does not makes it possible to explain this aspect. According to Silva et al (2012) and several authors, such as Carmo et al (2012) and Yang et al (2013), the quality of a dried product depends on several factors and, among them, the internal stresses produced by the distribution of moisture (and temperature) within the product during the transient process. Thus, information on the moisture distribution within the infinite cylinder that represents the banana is important because it permits a subsequent analysis of internal stresses during the drying process.…”

Conventional and intermittent drying modeling of agricultural products: A review

“…During the heating of the grain with hot air, the material and its respective moisture content are heated at predetermined time intervals, and during the tempering time, the migration of moisture contained within the grain to the surface occurs, promoting a uniformity of moisture throughout the grain (Do Carmo et al, 2012).…”

“…The employability of high temperatures causes degradation of the grain, reduction of antioxidant compounds, and loss of germination power. However, low temperatures lead to longer times in the drying process until the desired moisture is obtained, resulting in high operating costs (Do Carmo et al, 2012; Pereira et al, 2015). In this context, drying models have been validated based on experimental data and they have been used in optimization studies aiming to obtain the best operational conditions to maximize material quality preservation and to minimize heat consumption.…”

Modeling and simulation of intermittent drying of high moisture foods

“…This consideration is reasonable when tempering times are used between the stages, since this procedure provides redistribution of the water content in the solid during the holding time. Therefore, a moisture profile of the initial stage could be used to calculate the ideal tempering time required for the moisture to become homogeneous [13].…”