Study of the Drying Kinetics of Lemon grass

Experimental investigation of an indirect solar dryer with PCM-integrated solar collector as a thermal energy storage medium

An indirect-type forced convection solar dryer implementing a phase-changing material (PCM) as the energy-storing medium was designed, fabricated, and investigated in this study. The effects of changing the mass flow rate on the valuable energy and thermal efficiencies were studied. The experimental results showed that the instantaneous and daily efficiencies of the indirect solar dryer (ISD) increased with the initial increase in mass flow rate, beyond which the change is not prominent both with and without using the PCM. The system consisted of a solar energy accumulator (solar air collector with a PCM cavity), a drying compartment, and a blower. The charging and discharging characteristics of the thermal energy storage unit were evaluated experimentally. It was found that after using PCM, drying air temperature was higher than ambient air temperature by 9-12 ℃ after sunset for 4 h. Using PCM accelerated the process by which Cymbopogon citratus was effectively dried between 42 and 59 °C of drying air. Energy and exergy analysis of the drying process was performed. The daily energy efficiency of the solar energy accumulator reached 35.8%, while the daily exergy efficiency reached 13.84%. The exergy efficiency of the drying chamber was in the range of 47-97%. A free energy source, a large reduction in drying time, a higher drying capacity, a decrease in mass losses, and improved product quality all contributed to the proposed solar dryer's high potential.

Harmonizing Drying Time, Layer Thickness, and Drier Zones for Drying Kinetics: Quality and Safety of Solar Tunnel-Dried Wet-Processed Parchment Coffee (Coffea arabica L.)

Tunnel solar dryer is the recently used drying method for better quality and safety of parchment coffee. However, the higher variation of drying temperature and RH along the long tunnel solar dryer results in a heterogeneous environment in the tunnel, which could make parchment coffee dried at different times or with different moisture contents. This study is aimed at investigating the effect of solar tunnel dryer zones at different zones of the dryer, divided into three zones from the inlet to the exit side of the drier and drying layer thicknesses on the drying time, drying kinetics, physicochemical, sensory, and fungal growth loads of parchment coffee. Furthermore, seven mathematical models were evaluated to select the best-fitting model for a specific zone to predict drying time. Results showed that dryer zones significantly (p < 0.05) interacted with layer thickness for most of the measured parameters except titratable acidity and sensory properties. The dryer zone, coupled with the reduction in drying layer thickness, caused an increase in effective diffusivity and moisture removal rate and reduced drying time. The drying time to reach constant moisture content varied from 14 to 17 hours. Overall raw bean, cup, and total quality varied from 36.3 to 37, 48 to 51, and 84.3 to 87.3%, respectively. Values for physicochemical parameters ranged from 5.3 to 6.9 (pH), 2.1 to 2.6% (titratable acidity), 2.3 to 4.3°Brix TSS, 10.9 to 15.2% (ether extract), 39.2 to 53.5GAE/g (total phenolic content), and 38.5 to 59.2 (DPPH scavenging capacity). The fungal infection percentage at the end of drying varied from 4 to 93.3%, which could be associated with potential mycotoxin formation if recommended conditions were not maintained. In general, for better quality, similar drying times, and a lesser fungal load, it is recommended to use 4, 5, and 6 cm layer thickness in zones one, two, and three, respectively. The drying kinetics of parchment coffee in different dryer zones with different drying layer thicknesses showed variation. Zone one at 2 and 4 cm layer thicknesses is best described by the Verma model. Four- and six-centimetre layer thicknesses in zones 2 and 3 are best described by the modified Midilli model.

Improved Agricultural Products Drying Through a Novel Double Collector Solar Device

Backyard agricultural systems are frequently used for food production in rural tropical regions all over the world. The implementation of these systems has been used as a strategy to increase food security, to preserve the phyto and zoo diversity and to provide an alternative income for poorer rural families. Nevertheless, the absence of appropriate preservation mechanisms and nonrenewable energies can lead to significant production losses that could be prevented by the implementation of solar drying devices. The objective of this project was to design, build and validate a double collector solar device for improved drying performance. To evaluate the double collector solar device, four backyard products frequently used in the Mexico Southwest regional diet were used: carrots, chayote squash, tomatoes, and oyster mushrooms. The results showed that the solar device achieved drying efficiencies between 22.8 and 37.9% by reaching moisture values below the 12.30% threshold, which according to the international standards is considered as “Low Moisture Food”. The evaluation of the double collector solar drier is demonstrated to be an easy-to-apply and environmentally friendly method for food preservation in tropical rural regions by taking advantage of domestic renewable energy resources.

Model for Thin Layer Drying of Lemongrass (Cymbopogon citratus) by Hot Air

Lemongrass is a plant that contains aromatic compounds (myrcene and limonene), powerful deodorants, and antimicrobial compounds (citral and geraniol). Identifying a suitable drying model for the material is crucial for establishing an initial step for the development of dried products. Convection drying is a commonly used drying method that could extend the shelf life of the product. In this study, a suitable kinetic model for the drying process was determined by fitting moisture data corresponding to four different temperature levels: 50, 55, 60 and 65 °C. In addition, the effect of drying temperature on the moisture removal rate, the effective diffusion coefficient and activation energy were also estimated. The results showed that time for moisture removal increases proportionally with the air-drying temperature, and that the Weibull model is the most suitable model for describing the drying process. The effective diffusion coefficient ranges from 7.64 × 10−11 m2/s to 1.48 × 10−10 m2/s and the activation energy was 38.34 kJ/mol. The activation energy for lemongrass evaporation is relatively high, suggesting that more energy is needed to separate moisture from the material by drying.

Thin-layer drying behavior of West Indian lemongrass (Cymbopogan citratus) leaves

The objectives of this study were to investigate the effect of temperature (40, 50, 60, and 70°C), and air velocity (0.5, 1, and 2 m/s) on the drying behavior of West Indian lemongrass (Cymbopogan citratus) leaves. Drying was carried out in a computer-controlled tray dryer. Overall, the effect of temperature was seen to be more important than that of air velocity, but the air velocity did have an effect on drying rates at the start of the drying process at 50-70°C. Drying rate constants, diffusivity values, and activation energy were determined. Twenty-two empirical and semiempirical thin-layer models were tested, and although model fit varied, the Midilli model could be applied to all data with reasonable prediction of MR values.