Energetic and exergetic analysis of a convective drier: A case study of potato drying process

This research work focused on the evaluation of energy and exergy in the convective drying of potato slices. Experiments were conducted at four air temperatures (40, 50, 60 and 70 ºC) and three air velocities (0.5, 1.0 and 1.5 m/s) in a convective dryer, with circulating heated air. Freshly harvested potatoes with initial moisture content of 79.9% wet basis were used. The influence of temperature and air velocity was investigated in terms of energy and exergy (energy utilization and energy utilization ratio, exergy losses and exergy efficiency). The calculations for energy and exergy were based on the 1st and 2nd laws of thermodynamics . Results indicated that energy utilization (EU), energy utilization ratio (EUR) and exergy losses decreased along drying time, while exergy efficiency increased. The specific energy consumption (SEC) varied from 1.94×105 to 3.14×105 kJ/kg. The exergy loss varied in the range of 0.006 to 0.036 kJ/s and the maximum exergy efficiency obtained was 85.85% at 70 ºC and 0.5 m/s, while minimum exergy efficiency was 57.07% at 40 ºC and 1.5 m/s. Moreover, the values of exergetic improvement potential rate (IP) changed between 0.0016-0.0046 kJ/s and the highest value occurred for drying at 70 ºC and 1.5 m/s, whereas the lowest value was for 70 ºC and 0.5 m/s. As a result, this knowledge will allow the optimization of convective dryers, when operating for the drying of this food product or others, as well as choosing the most appropriate operating conditions that cause reduction of energy consumption, irreversibilities and losses in the industrial convective drying processes.info:eu-repo/semantics/publishedVersio

Modeling some drying characteristics of cantaloupe slices

This study investigated thin layer drying of cantaloupe slices under different drying conditions with initial moisture content about 18.53 (d.b.). Air temperature levels of 40, 50, 60 and 70°C were applied in drying of samples. Fick´s second law in diffusion was applied to compute the effective moisture diffusivity (Deff) of cantaloupe slices. Minimum and maximum values of Deff were 4.05×10-10 and 1.61×10-9 m2/s, respectively. Deff values increased as the input air temperature was increased. Activation energy values of cantaloupe slices were found between 30.43 and 36.23 kJ/mol for 40°C to 70°C, respectively. The specific energy consumption for drying cantaloupe slices was calculated at the boundary of 1.01×105 and 9.55×105 kJ/kg. Increasing in drying air temperature in different air velocities led to increase in specific energy value. Results showed that applying the temperature of 70°C is more effective for convective drying of cantaloupe slices. The aforesaid drying parameters are important to select the best operational point of a dryer and to precise design of the system

Drying kinetics of dill leaves in a convective dryer

Thin layer drying characteristics of dill leaves under fixed, semi-fluidized, and fluidized bed conditions were studied at air temperatures of 30, 40, 50, and 60°C. In order to find a suitable drying curve, 12 thin layer-drying models were fitted to the experimental data of the moisture ratio. Among the applied mathematical models, the Midilli et al. model was the best for drying behavior prediction in thin layer drying of dill leaves. To obtain the optimum network for drying of dill leaves, various numbers of multilayer feed-forward neural networks were made and tested with different numbers of hidden layers and neurons. The best neural network feed-forward back-propagation topology for the prediction of drying of dill leaves (moisture ratio and drying rate) was the 3-45-2 structure with the training algorithm trainlm and threshold functions logsig and purelin. The coefficient of determination for this topology for training, validation, and testing patterns was 0.9998, 0.9981, and 0.9990, respectively. Effective moisture diffusivity of dill leaves during the drying process in different bed types was found to be in the range from 7.10 10-12 to 1.62 10-10 m2 s-1. Also, the values of activation energy were determined to be between 75.435 and 80.118 kJ mol-1