Influence of product geometry and process variables on drying energy demand of vegetables: An experimental study

摘要

The changing aspects of energy and its high demand during convective drying of food products prompted this present study, which aims at investigating the impact of product geometric shapes and process parameters on the energy demand of vegetables during convective drying. It considered three distinctive shapes (sphere, S-g; cylinder, C-g; and slab, R-g) of vegetables (cucumber, garden egg, and white carrot) at constant sample volume, dried in a laboratory convective dryer. The Box-Behnken Design tool was used to design the experiment and explored the effects of material geometries at varying drying conditions (air temperature: 50, 60, and 70 degrees C; air velocity: 1.0, 1.5, and 2.0 ms(-1)) on the total and specific drying energy demand, drying efficiency, percent product shrinkage, and drying time of the fresh vegetables. Results obtained revealed that the spherical-shaped samples exhibited high moisture diffusion and gross reduction in drying time (120 min), thus greater potential for energy and drying system improvement. The values of the effective moisture diffusion, D-e (0.72 x 10(-10) = D-e = 2.13 x 10(-9) m(2)s(-1)) increased with drying temperature, and the maximum D-e-value was obtained for the S-g-carrot sample. The percent product shrinkage ranged between 78.66-94.73% for the C-g-garden egg and S-g-cucumber samples, respectively. The specific energy demand of the fresh cucumber, eggplant, and white carrot samples varied significantly (p .005) with sample geometry. The maximum specific energy demand (16.38 +/- 0.41 MJ/kgH(2)O, respectively) was obtained for the cylindrical shaped samples, whereas the minimum specific energy demand of 9.06 +/- 0.24 MJ/kgH(2)O was yielded by the spherical shaped samples. The mean energy and drying efficiencies of the system ranged from 3.25 to 12.26% and 7.22 to 28.24%, respectively; whilst drying time ranged between 470 and 840 min. At the optimum process variables of 69.85 degrees C, 1.22 ms(-1), 0.999 geometric shape, and -0.9977 crop sample, the specific energy demand, drying time, drying efficiency, and percent shrinkage were found to be 14.21 +/- 0.84 MJkg(-1), 820 +/- 9.00 min, 22.76 +/- 0.74%, and 92.104 +/- 1.00%, respectively. Prospects for future application and recommendations for further studies were suggested.Practical Applications Despite the merits of artificial dryers, the food processing industry is still confronted with tremendous challenges of high energy demand and low process efficiency associated with the drying of food products, especially fruits and vegetables. Product physical attributes and drying conditions among other factors generally contribute to huge drying energy consumption, which affects the dried quality of the end product. The results of this study are of significant benefit to the food processing industries, as they may be applied in the design of efficient industrial crop dryers and optimized process guide for prolonged shelf life of processed food products, and enhanced process efficiency.