•Construction and instrumentation of an earthen-based prototype building.•In-situ study of drying kinetics in cob and light earth layers constituting a hybrid walling system.•In-situ study of ...vertical shrinkage in cob and light earth layers constituting a hybrid walling system.•Correlation between water content and shrinkage in the cob and light earth layers.
Present work focuses on the study of drying and shrinkage kinetics in cob and light earth layers constituting a hybrid walling system. In-situ measurements were performed on the walls of a CobBauge prototype building under construction in Saint-André-de-Bohon (France). To do so, an adapted monitoring system has been designed and implemented. Thus, volumetric water content sensors and dial indicators were immersed and placed in different positions in different walls of the building. Drying kinetic and shrinkage rate in both layers have been measured. Results show that drying and shrinking processes follow an exponential decay in both structural and thermal layers. Correlations between water content and materials shrinkage have been found and discussed. This study will contribute to the optimization of earth construction times in general, and in particular, form-stripping times.
The drying process of green pellet is the intermediate link of direct reduction in rotary hearth furnace, which can reduce energy consumption, prevent green pellet from bursting during drying and ...reduce pulverization rate. In this study, the effects on the drying rate of raw metallurgical dusts pellet at a hot air flow rate of 1 m/s and drying temperatures of 211°C, 254°C, 282°C and 314°C was investigated to clarify the drying characteristics of the green pellet. The results show that there were accelerated drying stage, constant drying stage and deceleration drying stage in the drying process of green pellet. The drying temperature had a significant effect on the dehydration rate during the drying process. The effective diffusion coefficient increased with the increase of drying temperature, and the activation energy of the whole drying process was 10.4 kJ/mol. Then the drying fitting models of Page (III), Lewis, Wang and Singh, and Weibull are used to describe the drying kinetics of green pellet. The fitting results show that the green pellet drying process is consistent with the Page (III) and Weibull models. Finally, the Weibull model was selected to compare the experimental values with the fitted values and the results indicate that the fitting model can well describe the actual drying process.
Lemon balm (Melissa officinalis L.) has been recognized for multiple health benefits due to bioactive compounds. Dehydration is usually the most widely used method to preserve and concentrate these ...elements. However, it can also affect and totally or partially degrade the quality of the product under incorrect processing conditions. This research aimed to evaluate the effect of drying parameters on Melissa’s physicochemical, microbiological, and sensory properties. In total, four treatments were analyzed according to the experimental design (T1: 25 °C and 1.5 m s-1, T2: 25 °C and 3.0 m s-1, T3: 45 °C and 1.5 m s-1, and T4: 45 °C and 3.0 m s-1). Drying kinetics were determined using a vertical airflow dryer and a continuous weighing system. The results were compared with fresh leaves. The findings obtained show that increasing temperature and varying drying speed reduces moisture content and aw but increases enzymatic activity and essential oil content. In the drying process, temperature has a greater effect in the initial stages of the process, while drying speed on the internal structure of the raw material. By optimizing the drying conditions, it is possible to reduce the drying time by 44%. Page’s model showed excellent ability to predict drying kinetics under various drying conditions (RMSE <0.04 and R2>0.98). In terms of color, lightness decreased because of temperature, while a* and b* values were affected by non-enzymatic browning. Treatment T4 was the product with the highest acceptability. The findings obtained provide a theoretical basis to optimize the lemon balm drying process. Drying Melissa at 45 °C and 3.0 m s-1 can improve the quality and composition of the final product.
Thermal digestion has emerged as a novel technique for the rapid treatment of solid organic waste (SOW). Dehydration mechanism and fate of nutrients during the thermal digestion of the SOW were ...explored. A series of experiments were carried out in a specially designed laboratory-scale dehydrator to determine its drying kinetics. The statistical analysis revealed that the diffusion model predicted the dehydration profile most accurately than other models. The effective moisture diffusivity coefficient depended on the temperature and varied from 2.81 × 10−08 m2/s to 8.68 × 10−08 m2/s at the tested temperature range. The activation energy required for complete dehydration was found to be 26.56 kJ/mol. The artificial neural network (ANN) model was found highly efficient (R2 - 0.983) in predicting the total drying time required for attaining equilibrium moisture content. The total N decreased from 2.2% to 1.81% due to evaporation of ammonical nitrogen, while the availability of P and K was increased from 0.38% to 0.43% and 1.47% to 1.75%, respectively when the temperature was increased from 110 °C to 170 °C. The thermal dehydration technique was found effective in digesting the organics and improving the bioavailability of the nutrients, which favours for its re-utilization in agriculture.
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•Diffusion model predicted the drying profile more accurately than other models.•The activation energy for drying the SOW was found to be 26.56 kJ/mol.•Digestion at 150 °C consumed minimal energy and prevented loss of nutrients.•ANN model precisely predicted the drying time required for complete dehydration.•Thermal digestion improved the bioavailability of the nutrients.
► Effects of air velocity and temperature on drying kinetics and quality attributes of apples were study. ► Dehydration rates increased as air conditions were increased due to high moisture ...diffusivities values. ► Rehydration rate, colour and antioxidant activity decreased at high process temperature. ► Increase in firmness during drying could be explained based on glass transition temperature. ► Microstructure analysis showed that cell disruption occurred at high air temperature and velocity.
The aim of this work was to study the effect of temperature and air velocity on the drying kinetics and quality attributes of apple (var. Granny Smith) slices during drying. Experiments were conducted at 40, 60 and 80°C, as well as at air velocities of 0.5, 1.0 and 1.5ms−1. Effective moisture diffusivity increased with temperature and air velocity, reaching a value of 15.30×10−9m2s−1 at maximum temperature and air velocity under study. The rehydration ratio changed with varying both air velocity and temperature indicating tissue damage due to processing. The colour difference, ΔE, showed the best results at 80°C. The DPPH-radical scavenging activity at 40°C and 0.5ms−1 showed the highest antioxidant activity, closest to that of the fresh sample. Although ΔE decreased with temperature, antioxidant activity barely varied and even increased at high air velocities, revealing an antioxidant capacity of the browning products. The total phenolics decreased with temperature, but at high air velocity retardation of thermal degradation was observed. Firmness was also determined and explained using glass transition concept and microstructure analysis.
•Ultrasound-assisted vacuum drying was proposed to dehydrate fruit juices.•A comparative study on the ultrasound-assisted vacuum drying of hawthorn fruit juices.•Ultrasound-assisted vacuum drying at ...higher intensity contributed to a better quality.•Ultrasound-assisted vacuum drying improved the drying efficiency and product quality.
In this study, ultrasound-assisted vacuum drying (UAVD) was employed as a new approach to improve the efficiency and produce dried hawthorn fruit juice powders with acceptable quality. To achieve these goals, the effects of ultrasound intensity (at four levels of 15.29, 20.38, 22.93 and 24.46 kW/m2) were evaluated. The results showed that UAVD significantly shortened the drying time (P < 0.05), and with the increasing ultrasound intensity, the drying rate increased and the drying time decreased. Based on statistical tests, the Page model was found to fit well to the drying kinetics. After drying, a decline in quality of fresh juices was observed. As compared with vacuum drying individually, UAVD significantly reduced the colour degradation, and increased the retention of the total flavonoids content, five flavonoid compounds contents and antioxidant activity. It was shown that UAVD at the higher ultrasound intensity varied from of 20.38 to 24.46 kW/m2 contributed to a better quality in the dried juice powders. Overall, this study demonstrates that UAVD is a promising technique for improving the drying efficiency and quality retention of hawthorn fruit juices.
•The medium scale greenhouse solar dryer allows local industries to dry handmade papers at a faster rate.•Energy and economic analyses have been carried out to ascertain the feasibility of the ...proposed system.•Drying behavior of handmade papers has been evaluated with the help of ten mathematical models.•The developed GHSD's experimental results are promising and scaled up version of such system can be installed in industries.
In the presented experimental study, a medium-sized industrial greenhouse solar dryer (MSGSD) of floor area 1.82 x 1.52 m2 was developed using low-cost, locally available materials and tested in the winter season (November- December 2022) for eco-friendly handmade paper drying. The handmade papers having initial moisture content of 60 % (w.b.) were dried to a moisture content of 8–10 % (w.b.), and time taken to dry these papers varied from 3 to 8.5 h depending upon the paper type (off-white or coloured), paper thickness (100–200 GSM) and number of papers (75–150) dried inside the dryer. However, drying in the open sun and shade took 4 to 10 h and 19 to 29 h, respectively, to achieve a moisture content of 8–10 % (w. b.). The instantaneous thermal loss efficiency factor of the developed dryer was calculated for forced and natural convection modes of operation and found to be in the range of 13.1 % − 23.5 %. Ten theoretical models were investigated for characterizing the drying process, out of which the Midilli-Kucuk model was observed to be the best fit with experimental data. The economic analysis revealed a payback period of 0.61 years.
•Performance analysis of novel hybrid greenhouse dryer attached with evacuated tube collector.•New model for predicting the moisture ratio of crop drying inside the solar dryers.•Evaluation of ...convective and evaporative heat transfer coefficients for three cases.•Drying behavior analysis of tomato, ginger and bottle gourd for three cases.
The objective of the paper is to carry out the heat transfer analysis of novel designed hybrid active greenhouse solar dryer (HAGSD) attached with water-in-tube type evacuated collector. The experimentation is carried out to investigate the performance of dryer with and without evacuated tube collector (ETC) under active mode. Three high moisture seasonal crops namely tomato, ginger and bottle gourd have been dried inside the dryer for the two cases and also in open sun drying. Also the drying kinetic of crops has been fitted with ten drying rate models given by researchers. A new drying rate model is also obtained which gives a very close fit with experimental drying rate. The average values of convective heat transfer coefficients for dryer with ETC are 153%, 3.8% and 305.4% higher than the dryer without ETC for tomato, ginger and bottle gourd respectively. The drying time in case of dryer with ETC for tomato, ginger and bottle gourd is 9, 12 and 6 h respectively less than the dryer without ETC. The overall efficiency of the dryer for the three crops varies between 14.22 and 27.99% for dryer with ETC, while for dryer without ETC, it varies between 9.63 and 24.88%.
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