Abstract
An experimental and numerical study of a two-dimensional spatio-temporal variation of the temperature, moisture content, and mechanical stress during the convective drying process of unsaturated and deformable products (leather) were conducted. The bovine leather sample response under convective drying is described by a mathematical model. The leather sample was modeled by an elastic medium, and the mass, heat, and momentum transfer principles are applied. The numerical results agreed well with the corresponding experimental data. The variation of the internal temperature and moisture content was simulated for different drying conditions. A reduction by 15 °C was noted in the optimum temperature for best product quality when the drying air relative humidity was 20%. The cost to achieve a better quality product was found to be minimized due to the decrease in the optimum temperature. The presented simulation results of the elastic material could be applied to the leather, which will reduce the needed time of exposure for predetermined final water content. The damage of the sample is more likely to occur at the beginning of the drying in the time interval of 300–400 s. According to these simulations, the sample’s face, which is exposed to the drying air, has the highest stress; therefore, the sample’s face is at a high risk of cracking. It is also observed that the risk of damage to the sample corresponding to the maximum level of the stress is higher for the highest drying temperature of 60 °C. The peak of the three thicknesses of leather can be achieved for normal stresses in the interval of 60,000 to 140,000 MPa at around 10,000 s.
Highlights
The main factors affecting the drying processes are the nature and the desired functionality of the dried product, and the quantity of the removed water
The leather samples used in the present experiment were delivered by a Factory located in the Grombalia region at the Nabeul governorate in Tunisia
The observed discrepancies between the two results are mainly from the non-precise evaluation of the various parameters of the material. These discrepancies are due to the permeability and Young’s modulus which are key parameters of the simulation, the hypothesis of a medium remaining saturated, and the accuracy of the initial and boundary conditions
Summary
The main factors affecting the drying processes are the nature and the desired functionality of the dried product, and the quantity of the removed water. Hawlader [8] developed a mathematical model to simulate heat and mass transfer in products that could have shrinkage during the drying process. Other researchers studied shrinkage deformation theoretically by mathematical modeling of heat and mass transfer processes and experimentally on some fruits and vegetables. Some scientific works, dealing with the hydrothermal parameters of leather, considered that this material remains saturated over a large part of drying [27,28,29] This present work a 2D transitory model describing the physical phenomena occurring inside deformable materials during the drying process. The hydrothermal part of the model is represented by the equations of diffusion/convection of liquid water and the heat conduction/convection coupled with the solid contraction velocity to describe the effect of shrinkage. A vertical type tunnel with operating conditions controller was used as the experimental setup
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