Resumo

SANTACRUZ-VAZQUEZ, V. et al. Effects of air-drying on the shrinkage, surface temperatures and structural features of apples slabs by means of fractal analysis. Rev. Mex. Ing. Quím [online]. 2008, vol.7, n.1, pp.55-63. ISSN 1665-2738.

Shrinkage-deformation phenomenon of apple slabs during convective drying was studied, aiming to analyse its causes. Apple slabs were dehydrated in an experimental drying tunnel using a factorial design 4². Independent variables were airflow (1, 2, 3 and 4 m/s) and drying air temperature (50, 60, 10 and 80 °C). Relative shrinkage (A/Ao) was evaluated during drying as the ratio of the projected (top view) area of slab at any time during the process (A) to the initial area (Ao) of the same slab. In five punctual measuring zones on the surface of the slab, surface temperatures (ST) and moisture contents (MC) were evaluated. ST and MC were different for each measuring zone, causing irregular dehydration. Fractal analysis was used to evaluate the non-linear (A/Ao) observed pattern and ST distribution. Fractal dimensions for (A/Ao) ratios (FD_A) and ST (FD_ST) were 1.08-1.30 and 1.12-1.54 respectively. Temperatures of 60° and 10°C, and airflows of 2 and 3 m/s caused the highest irregularity of shrinkage and highest FDA and FDST values. Scanning electron microscopy images for measuring zone were captured and fractal dimension of texture of images were obtained (FD_SDBC) it was observed that nonlinear shrinkage was related to irregular microstructure given by FD_SDBC.

Palavras-chave : shrinkage-deformation; power law; fractal dimension.