This research work is concerned in the exergy analysis of the continuous-convection drying of onion. The influence of temperature and air velocity was studied in terms of exergy parameters. The energy and exergy balances were carried out taking into account the onion drying chamber. Its behavior was analyzed based on exergy efficiency, exergy loss rate, exergetic improvement potential rate, and sustainability index. The exergy loss rates increase with the temperature and air velocity augmentation. Exergy loss rate is influenced by the drying air temperatures and velocities because the overall heat transfer coefficient varies with these operation conditions. On the other hand, the exergy efficiency increases with the air velocity augmentation. This behavior is due to the energy utilization was improved because the most amount of supplied energy was utilized for the moisture evaporation. However, the exergy efficiency decreases with the temperature augmentation due to the free moisture being lower, then, the moisture begins diffusing from the internal structure to the surface. The exergetic improvement potential rate values show that the exergy efficiency of onion drying process can be ameliorated. The sustainability index of the drying chamber varied from 1.9 to 5.1. To reduce the process environmental impact, the parameters must be modified in order to ameliorate the exergy efficiency of the process.

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This research work is concerned in the exergy analysis of the continuous-convection drying of onion. The influence of temperature and air flow rate was studied in terms of exergy parameters. The energy and exergy balances were carried out taking into account the onion drying chamber. Its behaviour was analysed based on exergy efficiency, exergy loss rate, exergetic improvement potential rate and sustainability index.The exergy loss rates increase with the temperature and air flow rate augmentation.Exergy loss rate is augmented at higher drying air temperatures and flow rates because the overall heat transfer coefficient increase. On the other hand, the exergy efficiency increases with the air flow rate augmentation. This behavior is due to the energy utilization was improved because the most amount of supplied energy was utilized for the moisture evaporation. However, the exergy efficiency decreases with the temperature augmentation due to the free moisture is less, then, the moisture begins diffusing from the internal structure to the surface. The exergetic improvement potential rate values show that the onion drying process presents a high potential to improve the exergy efficiency. The sustainability index of the drying chamber varied from 1.9 to 5.1. To reduce the environmental impact of the process, the parameters must be modified in order to ameliorate the exergy efficiency of the process.

Dried fruit consumption is increasing due to its nutritional and healthy properties. Apples are an important source of essential nutritional compounds such as antioxidants, vitamins, minerals, and fibers. In this work, the kinetics of drying and rehydration of green apple slices peeled and unpeeled (Granny Smith cv) were studied. The apple slices were dried at 50, 60, and 70 ºC, and after that, rehydrated at ambient (Ta) and boiling temperature (Tb). The drying kinetics were adjusted with the Dincer and Dost model, giving a good fit (R2 > 0.98). Effective diffusivity (Deff) and the convective mass transfer coefficient (hm) were also determined, both coefficients increase with drying temperature, being 1.25×10-9 m2.s-1 and 9.53×10-7 m2.s-1 the highest values obtained for the peeled apple slices respectively. Subsequently, Peleg and Weibull models were adjusted to the rehydration experimental data obtaining a good fit (R2 > 0.99). Deff values increase significantly with rehydration temperature but take similar values between peeled and unpeeled samples. Equivalent diameter, pH, acidity, soluble solids, and moisture content were determined to compare the fresh apple slices with those after dehydration and post rehydration process. The apple slices rehydrated at boiling temperature better preserved the characteristics of fresh samples due to the short immersion times in water, no significant differences were observed between peeled and unpeeled apples. According to the obtained results, it is convenient to dry the apple slices unpeeled at 70 °C and rehydrate them at Tb.