Heat and mass transport analysis of the drying of freshwater fishes by a forced convective air‐dryer

Drying kinetics and thermodynamic analysis; enhancing quinoa (Chenopodium quinoa Willd.) quality profile via pre-treatments assisted germination and processing

Pre-treatments assisted germination is an efficient technique to enhance the nutritional profile of Quinoa (Chenopodium quinoa Willd.). The present study investigated the impact of pre-treatments assisted germination of quinoa nutritional, anti-nutritional, and structural properties. Quinoa grains JQ-778 were subjected to various pre-treatments including soaking, ultrasound at 28 kHz &40 kHz (US 28 kHz, US 40 kHz) for 30 min followed by germination over 96-hour at 25 °C in a Biochemical-Incubator, 12/12 h dark and light dried at temperatures 50 °C, 60 °C, 70 °C, and combined temperatures (70 °C, 60 °C, 50 °C). Among evaluated models, page and logarithmic showed the best fit, presenting the highest, R2 ≥ 0.9991, X2 ≤ 0.0013, RMSE ≤ 0.0022, and RSS ≤ 0.0201. Moisture diffusion varied from 3.74 × 10-9 to 8.36 × 10-9, with R2 0.9272 to 0.9837, and energy activation from 18.25 to 28.41 kJ/mol with R2 0.9533-0.9896. US 40 kHz significantly lowered drying time without affecting germinated quinoa grains bioactive components or other qualitative factors. Ultrasonic pre-treatment at 40 kHz and drying at 60 °C yielded the highest antioxidant potency composite index of 98.78 %. The contentof phytic acid and tannin dropped by 66.66 to 82.99 % and 31.48 to 41.60 %, respectively (p < 0.05). Each treatment significantly altered quinoa's quality attributes. Principal Component Analysis revealed significant correlations between analyses, explaining 80.37 % variability. The intensity of functional groups decreased in the infrared spectra, although the transmission of signals was greater in pretreated samples than in control. Scanning electron microscopy analysis showed extensive fragmentation and surface erosion of quinoa grains after ultrasound treatment. Our data suggests that ultrasound-treated quinoa grains may enhance their nutritional value, making them a suggested source of high-protein grains, bioactive components, with distinct structural properties.

Numerical simulation and study on heat and mass transfer in a hybrid ultrasound/convective dryer

Susceptibility of airborne ultrasonic power to augment heat and mass transfer during hot air dehydration of peppermint leaves was investigated in the present study. To predict the moisture removal curves, a unique non-equilibrium mathematical model was developed. For the samples dried at temperatures of 40‒70 °C and the power intensities of 0‒104 kW m-3, the diffusion of moisture inside the leaves and coefficients for of mass and heat transfer varied from 0.601 × 10-4 to 5.937 × 10-4 s-1, 4.693 × 10-4 to 7.975 × 10-4 m s-1 and 49.2 to 78.1 W m-2 K-1, respectively. In general, at the process temperatures up to 60 °C, all the studied transfer parameters were augmented in the presence of ultrasonic power.

Drying characteristics of a Japanese dry-cured ham model: Effect of temperature and humidity

The drying characteristics of a Japanese dry-cured ham model containing uniformly distributed brine were investigated. A higher effective moisture diffusivity was obtained at a lower relative humidity (RH) level. The activation energy of effective moisture diffusivity at 40 and 70% RH increased with decreasing moisture content, and was almost constant in the late stage of drying. Therefore, the moisture likely diffused without a large difference in the moisture distribution in the sample. In contrast, under low (10%) RH, the activation energy drastically increased with decreasing moisture content in the initial stage of drying. From the results of magnetic resonance imaging, the moisture content on the surface was drastically decreased; the surface was dried and hardened temporarily (i.e., case hardening) by the fast transfer of moisture. In the middle to late stages of drying, the activation energy gradually decreased to the similar values as at 40 and 70% RH in the late stage of drying. From the results of magnetic resonance imaging analysis after drying, the moisture distribution near the surface no longer exhibited a sharp difference in moisture concentration. The partly dried state of the surface could be alleviated by the transfer of moisture from the inside of the sample. Comparing the energy consumption for drying up to 175% dry basis, the drying condition of 35°C and 40% RH was the most efficient.

Drying Characteristics of a Combined Drying System of Low-Pressure Superheated Steam and Heat Pump

The present study aimed at investigating the use of a drying system combining the concept of low-pressure superheated steam drying and heat pump drying for fish. The effects of various drying medium pressures on the temperature field, airflow field, drying time, equipment performance as well as the power consumption of the drying process were investigated and discussed. Four comparative tests with different initial pressures were carried out according to a specified drying process by the combined drying system. The results showed that when the vacuum was high, the temperature field and airflow field in the drying chamber were more uniform. Due to the poor heat transfer performance of the drying medium at high vacuum, the drying time increased with a decrease in initial pressure. It was also found that with the decrease in drying medium pressure, the power consumption of the heat pump and the axial fans was reduced, while the power consumption of the electric heater went up. Overall, the total power consumption is directly proportional to the drying medium pressure.

Mathematical Modelling of Conveyor-Belt Dryers with Tangential Flow for Food Drying up to Final Moisture Content below the Critical Value

This work presents the mathematical modeling of the conveyor-belt dryer with tangential flow operating in co-current, which has the advantage of improving the preservation of the organoleptic and nutritional qualities of the dried food. On the one hand, it is a more cumbersome dryer than the perforated cross flow belt dryer but, on the other hand, it has a low air temperature in the final section where the product has a low moisture content and, therefore, it is more heat sensitive. The results of the mathematical modeling allowed a series of guidelines to be developed for a rational design of the conveyor-belt dryer with tangential flow for the specific case of the moisture content of the final product XF lower than the critical one XC (XF < XC). In fact, this work follows a precedent in which a mathematical model was developed through the differentiation of the drying rate equation along the dryer belt with the hypothesis that the final moisture content XF of the product was higher than the critical one XC. The relationships between the extensive quantities (air flow rate and product flow rate), the intensive quantities (temperatures, moisture content and enthalpies) and the dimensional ones (length and width of the belt) were then obtained. Finally, based on these relationships, the rules for an optimized design for XF < XC were obtained.