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The article describes design of a solar dryer with a heat pump, which is used to increase heat output of the unit twice to solve the problem of using environmentally clean sources of thermal energy for fruit drying. The authors of the research have developed methodology of substantiation of the solar dryer parameters, which is applied to design and justify the optimal technological modes and parameters of the heat carrier in the unit, to describe the heat transfer characteristics of the unit operation, to assess the impact of physical environmental parameters on technological indicators of the process. The novelty described in the article is developed design of a solar dryer with a heat pump and to substantiate its constructive and technological structure. The work supplies scientifically substantiated methodic recommendations on composing and forecasting a parametric series of solar dryers for the conditions of private households and farms, and grounds their design parameters. Designed solar dryer with a heat pump affects solving environmental problems of power engineering due to substitution of the electric and thermal energy by the one obtained from solar energy, and mitigation of social problems by creating new job places needed when producing, installing and exploiting such units. The obtained results can be used for designing and improving technical aspects of fruit drying, to increase technological and energy efficiency of the process. [ABSTRACT FROM AUTHOR]

The significant production of sewage sludge by wastewater treatment plants on a global scale and the lack of correspondence between housing development and the expansion of sanitation infrastructure indicate a genuine concern regarding environmental preservation. This study addresses the crucial issue of effective sewage sludge management and its environmental impact. In the context of searching for new drying methods that optimize energy use and effectively stabilize sewage sludge, this work investigated the drying behavior of sewage sludge from treatment plants in two northern Moroccan cities using a prototype of an indirect forced convection solar dryer. The drying experiments enabled the determination of drying kinetics as well as highlighted the influence of temperature and humidity on the drying rate. The characteristic drying curve (CDC) and its mathematical expression were determined using Van Meel’s formalism. Thermal diffusivity of wastewater sludge during drying was also investigated. Using Fick’s diffusion model, diffusion coefficients ranged between 0.59 × 10-9 m²/s and 1.43 × 10-9 m²/s, demonstrating an increase in effective diffusivity with rising temperature. The Arrhenius equation provided activation energy values of 16.80 kJ/mol for Oujda samples and 19.72 kJ/mol for Nador samples, indicating the effect of temperature on effective diffusivity. A new equation based on the Midilli-Kucuk model was proposed to predict the drying behavior under untested aerothermal conditions, considering drying temperature and the initial dryness. This study offers a comprehensive analysis of the drying kinetics and effective diffusivity of sewage sludge, providing valuable insights for designing large dryers for sludge management in WWTPs. This approach presents an optimal solution for drying and stabilizing sludge, contributing to environmental preservation efforts. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate how a tracking indirect solar dryer (SD) powered by photovoltaic cells affected the drying kinetics (DK) and thermo-environmental conditions of tomato slices. In this current investigation, three air speeds (1, 1.5, and 2 m/s) are used, as well as three slice thicknesses (ST) (4, 6, and 8 mm) and two SD, one of which is integrated with fixed collector motion (FCM) and another with SD tracking collector motion (TCM). The obtained results showed that the drying time (DT) isn't significantly change with increasing air speeds from 1 to 2 m/s, this may be due to many reasons such as short DT, high temperature inside drying room, and little difference between the exanimated air speeds. When the ST is changed from 4 to 8 mm and maintaining constant air speeds, the DT for FCM and TCM rose by roughly 1.667 and 1.6 times, respectively. In addition, the drying coefficient of the TCM is higher than the FCM due to higher temperature. At 1.5 m/s air speed and 8 mm ST, the maximum values of moisture diffusivity (MD) are 7.15×10−10 and 9.30×10−10 m2/s for both FCM and TCM systems, respectively. During the study of DK, nine drying models and chose the best based on higher R2 and lower χ2 and RMSE are used. The findings of the DK analysis revealed that the modified two term II model fit the experimental data of various air speeds well when TF was dried using TCM and FCM systems at varying ST. These findings are based on recorded observations. Where the models' R2 values varied from 0.98005 to 0.99942 for FCM system and varied from 0.99386 to 0.99976 for TCM system. Regarding environmental analysis, it is found that the CO2 mitigation per lifetime is ranged between 5334.9–6795.4 tons for FCM and 6305.7–6323.3 tons for TCM. [ABSTRACT FROM AUTHOR]

The fluctuation of solar radiation throughout the day presents a significant obstacle to the widespread adoption of solar dryers for the dehydration of agricultural products, particularly those that are sensitive to high temperatures, such as basil leaf drying during the winter season. Consequently, this recent study sought to address the limitations of solar-powered dryers by implementing a hybrid drying system that harnesses both solar energy and liquid petroleum gas (LPG). Furthermore, an innovative automatic electronic unit was integrated to facilitate the circulation of air between the drying chamber and the ambient environment. Considering the solar radiation status in Egypt, an LPG hybrid solar dryer has been developed to be suitable for both sunny and cloudy weather conditions. This hybrid solar dryer (HSD) uses indirect forced convection and a controlled auxiliary heating system (LPG) to regulate both temperature and relative humidity, resulting in increased drying rates, reduced energy consumption, and the production of high-quality dried products. The HSD was tested and evaluated for drying basil leaves at three different temperatures of50, 55, and 60 °C and three air changing rates of 70, 80, and 90%, during both summer and winter sessions. The obtained results showed that drying basil at a temperature of 60 °C and an air changing rate of 90% led to a decrease in the drying time by about 35.71% and 35.56% in summer and winter, respectively, where summer drying took 135–210 min and winter drying took 145–225 min to reach equilibrium moisture content (MC). Additionally, the effective moisture diffusivity ranged from 5.25 to 9.06 × 10− 9 m2/s, where higher values of effective moisture diffusivity (EMD) were increased with increasing both drying temperatures and air change rates. Furthermore, the activation energy decreased from 16.557 to 25.182 kJ/mol to 1.945–15.366 kJ/mol for the winter and summer sessions, respectively. On the other hand, the analysis of thin-layer kinetic showed that the Modified Midilli II model has a higher coefficient of determination R2, the lowest χ2, and the lowest root mean square error (RMSE) compared to the other models of both winter and summer sessions. Finally, the LPG hybrid solar dryer can be used for drying a wide range of agricultural products, and it is more efficient for drying medicinal plants. This innovative dryer utilizes a combination of LPG and solar energy, making it efficient and environmentally friendly. [ABSTRACT FROM AUTHOR]

Osmotic processes play a crucial role in developing high-quality intermediate moisture food products. This study investigates the role of osmotic dehydration focusing on using natural sweeteners to reduce health risks from refined sugar. Jaggery and honey were used for osmosis of papaya cubes, with a Box-Behnken design to determine optimal conditions: osmosis temperature (30, 40, 50 °C), osmotic solution concentration (40, 50, 60°Brix), and osmosis time (3, 4, 5 h). Simultaneous optimization of these parameters considered responses such as water loss, solid gain, weight reduction, colour change, ascorbic acid content, lycopene content, and phenolic content. The optimized conditions were identified as 49.46 °C, 40°Brix, and 5 h for jaggery osmosed samples and 39.64 °C, 60°Brix, and 4.92 h for honey osmosed samples. Drying the osmosed samples using advanced domestic solar dryer revealed superior quality (total phenolic content and lycopene content) in jaggery osmosed papaya compared to honey osmosed papaya. The study suggests that introducing a new osmotic agent, jaggery, can enhance the nutritional value of osmosed papaya cubes. [ABSTRACT FROM AUTHOR]

This analysis investigates the widespread use of solar drying methods and designs in developing countries, particularly for agricultural products like fruits, vegetables, and bee pollen. Traditional techniques like hot air oven drying and open sun drying have drawbacks, including nutrient loss and exposure to harmful particles. Solar and thermal drying are viewed as sustainable solutions because they rely on renewable resources. The article highlights the advantages of solar drying, including waste reduction, increased productivity, and improved pricing. It is also cost-effective and energy-efficient. The review study provides an overview of different solar drying systems and technologies used in poor nations, aiming to identify the most effective and efficient designs. The focus is on comparing current models of solar dryers for optimal performance. The review underscores the importance of solar drying as a long-term, eco-friendly approach to drying food in developing countries. This review aims to evaluate how using solar-powered drying techniques can enhance food preservation, minimize waste, and enhance the quality and marketability of agricultural goods. The paper will specifically focus on examining the efficacy of these methods for drying bee pollen and pinpointing where enhancements can be made in their advancement. [ABSTRACT FROM AUTHOR]

This work assessed some properties and effects of biocoal briquettes on environmental pollution compared with utilising coal alone. A mixture of coal fines and rice husks was prepared, with cassava starch gel as a binder, before compaction in a briquetting machine and drying with a solar dryer. Samples of the coal fines, rice husk, cassava flour and briquettes were analysed for their elemental and oxide concentrations via an energy-dispersive X-ray fluorescence analyser. The heat fuels were analysed for their thermal behaviour via thermogravimetric analyser (TGA), whereas the specific surface area, pore size and pore volume were determined using a Brunner–Emmett–Teller (BET) analyser. The conversion of the tested coals to biocoal briquettes resulted in a reduction in the level of arsenic in the briquettes. Additionally, the sulphur level decreased from 1.96 to 1.11% in the Okobo-Enjema briquettes and from 1.78 to 0.90% in the Onyeama briquettes. However, the levels of manganese increased from 0.04 to 0.22% in the Okobo-Enjema briquettes and from 0.04 to 0.21% in the Onyeama briquettes. Thermogravimetric analysis at different heating rates revealed that derivative weight loss increased with increasing heating rate, from 4.4% at 10 °C/min to 5.5% at 20 °C/min. BET analysis revealed that the briquettes had larger pore diameters, volumes and specific surface areas than did the coal samples. The coal samples have greater propensity to pollute the environment as the amount of potentially hazardous elements in the samples is greater than in their biocoal briquettes. [ABSTRACT FROM AUTHOR]

Fish are one of the main sources of protein in Cambodia but they are highly perishable. This requires immediate consumption or processing for later use. In processing, fish drying is very common, but most processors practice traditional drying methods although solar dryers have been introduced, or gradually used, in Cambodia. There is a large variation in terms of drying efficiency due to large differences in solar radiation, temperature, and humidity conditions in traditional drying methods and solar dryers. However, there is limited information on the actual variation in these two systems, which should be documented in Cambodia. Using sensors to monitor micro-climatic changes inside the drying chamber will be useful to improve efficiency and performance. Therefore, the objectives of this research were to (1) design a fish dryer from locally available inputs; (2) determine changes in solar radiation over time; (3) compare relative humidity and temperatures between traditional sun-drying and the solar dryer; (4) determine the relationship among the climatic parameters; and (5) compare some physical, chemical, and biological properties of dried fish in both drying techniques with the Cambodian dried fish standards. The study was conducted in collaboration with a fish processor in the Siem Reap Province between December 2023 and January 2024 using a sensor-mounted solar dryer fabricated by the Royal University of Agriculture to dry fish and compared with traditional sun-drying. Three experiments were carried out from 8:00 to 16:00 following the common drying practices in Cambodia. In each experiment, 80–100 kg of raw giant snakehead, or 56–70 kg of prepared fish (1.04 ± 0.05 kg each fish), was prepared for drying. Data on environmental conditions were measured and analyzed. The results show that the solar dryer had higher temperatures (almost 60 °C) and lower relative humidity (about 20%) during peak hours when compared with traditional sun-drying (36.8 °C and 40%, respectively). In all cases, relative humidity decreased with rising solar radiation and temperatures. The final weight and moisture of dried fish in the solar dryer were lower than those in traditional sun-drying in eight hours. Salmonella was detected with traditional sun-drying but E. coli was not. Bacterial presence may be harmful to human health. Nevertheless, the time spent for drying in both techniques was the same, so future studies should focus on improving ventilation to remove moisture faster out of the solar dryer, which can help with faster drying and more time saving. Hybrid solar dryers should also be considered to maintain high temperatures at night, while bacteria should be counted for safety reasons. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the effects of solar drying and oven drying methods on the quality parameters of dried basil (Ocimum basilicum L.) leaves. The dried basil leaves were dehydrated at three different levels of temperature (T1, T2, and T3 = 50 °C, 55 °C, and 60 °C) using a solar tunnel dryer and an electrical oven dryer. Drying time, energy consumption, dehydration ratio, rehydration ratio, pH, and reducing sugar were observed after drying the basil leaves. The results showed that solar drying at 55 °C required the least energy (0.431 kWh) and took the shortest amount of time (110 min) to complete, whereas oven drying consumed more energy. Additionally, oven drying maintained a low pH (4.30) and reducing sugar level (2.24), extending the shelf life of the dried basil leaves, compared to solar drying. Based on energy consumption, drying time, and mineral contents, the solar drying using a solar tunnel dryer was deemed more suitable than oven drying. The best temperature for drying was determined to be 55 °C, which provided a short drying time, the least energy consumption and a statistically non-significant loss of mineral contents and dehydration ratio. Moreover, solar drying demonstrated a significantly higher speed, with a 6.7-times higher drying rate compared to oven drying, with significantly less energy consumption. [ABSTRACT FROM AUTHOR]

In this investigation, we assessed the efficacy of an indirect‐type solar drying system that utilized skewers and rack arrangements, comparing it to a conventional drying cabinet equipped with trays for dehydrating bitter gourd slices. We examined the influence of pretreatment methods and loading quantities on the solar drying process for bitter gourd slices in both configurations. The drying behavior of various combinations was scrutinized, and the physicochemical attributes of the dried bitter gourd samples, including total phenolic content, total flavonoid content, total chlorophyll content, antioxidant capacity, ascorbic acid content, and color, were analyzed. Rehydration characteristics, such as rehydration ratio, coefficient of rehydration, percent water in the rehydrated sample, and hardness of the rehydrated sample, were also determined. The bitter gourd slices achieved a final moisture content of 6.84%–8.27% wb after drying from an initial range of 88%–90% wb, within a total elapsed time of 28–55 h. The solar drying cabinet utilizing skewers exhibited enhanced efficiency, featuring reduced drying time and superior product quality compared to the tray‐equipped drying cabinet. This improved performance is ascribed to enhanced hot air circulation over the produce surface, facilitated by the uniform spacing between skewers on racks within the drying chamber. [ABSTRACT FROM AUTHOR]

The objective of this study was to develop a finite element model that explains the drying performance of a hybrid greenhouse dryer equipped with a single-pass solar air heater for drying of bitter gourd flakes. The model utilized the finite element method (FEM) to solve a set of partial differential equations (PDEs) that describe the combined heat and mass transfer process during drying. The 3-dimensional finite element model provided a visual representation of the spatial distribution of moisture within the bitter gourd sample. The mesh used in the model consisted of Lagrange triangle finite elements with small sizes and second-order geometry shapes. A time-dependent analysis was performed to capture changes in moisture content during the 5-hour of drying. The model predicted maximum crop and ground temperatures of 60.10°C and 77.20°C, respectively, with a drying efficiency of 42.91%. The relative humidity inside the drying chamber was 30.4%. The energy and exergy efficiencies were determined to be 80.09% and 53.83%, respectively. The predicted results were validated against experimental data and it was found that the hybrid greenhouse solar dryer, with moderate inside temperatures, is a suitable option for bitter gourd flakes drying while maintaining environmental sustainability. [ABSTRACT FROM AUTHOR]

Tomato fruit is a source of many important nutrients. It is difficult to store it for a long time because it contains a high percentage of moisture. The moisture content could be reduced in different ways to restrict the high growth of fungi. This study mainly aims to manufacture a simple and easy-to-use solar dryer for drying tomato fruits with solar cell-based fans. This method can be adapted to dry a wide range of Vegetables and fruits. The measured factors in this study are solar radiation, ambient temperature, relative humidity, and drying time. Solar drying is an affordable method to soothe the negative impact of post harvest losses on cultivators in Iraq. A greenhouse dryer (1 × 0.5 × 0.5 m) was constructed using glass of (τ = 0.9 for 0.4 μm < λ < 0.7 μm and τ = 0.01 for λ > 0.7 μm). Two fans are used to force an airstream with an average velocity of 0.025 m/s at the tray section. A selected quantity of tomato was washed and ground, making 1 kg of puree to check the effectiveness of the dryer. An experiment conducted on 10-11 March 2023 showed that 14 drying hours are needed to bring the paste to an acceptable quality of 0.25 brix. The efficiency of the greenhouse has not exceeded 25% on average, accompanied by an average drying rate of 60 g/hr. It was found that converting the perishable tomato crop into paste is profitable for cultivators in Iraqi conditions. Using a solar dryer is particularly profitable for local farmers by reducing crop losses, as per 1 m2 land area, a production of 6 kg of tomatoes is expected with losses of about 1 kg, and a profit of 6 thousand IQD and losses of 1 thousand IQD. A land area of 1 m2 with a dryer produces 3.6 kg of tomatoes converted into 1.008 kg tomato paste producing 15 thousand IQD without losses. [ABSTRACT FROM AUTHOR]

In the present study, the performance of a solar dryer supported by an indirect type wicked heat pipe was assessed. To transfer the heat from the solar collector to the drying chamber, a passive high thermal conductivity heat pipe was developed. At 1:30 pm, there was a 21 °C temperature difference between the drying chamber and the ambient air. The results indicated that after 12 hours of drying, the banana slices' moisture content dropped from 150 % d.b. to 11 % d.b. It is found that the average drying rates in Trays 1, 2, and 3 are the following: 0.1452, 0.1492, and 0.1613 kg water/kg dry matter/h. The effective moisture diffusivity ranged from 1×10−7 to 9.405×10−8 m2/s, whereas open sun drying had the lowest average effective moisture diffusivity of 3.87×10−07 m2/s. The estimated dryer efficiency was 26 %. Also the payback period of developed dryer was found to be 0.57 years. The developed dryer can be installed in any rural villages to dry any agricultural products. [ABSTRACT FROM AUTHOR]

As a result of increasing energy demand, seeking eco-friendly and sustainable energy resources increases the interest in renewable energy, specifically solar energy. In this study, a novel photovoltaic–thermal solar dryer system with double-pass solar air collectors and nano-enhanced absorber surface was developed, and its performance was experimentally investigated. Initially, a double-pass solar dryer (DPSD) with an absorber surface of flexible aluminum ducts coated with black matte paint was produced. Then, a double-pass solar dryer (NDPSD) consisting of flexible aluminum ducts coated with graphene and black paint was designed. These two systems were experimentally and simultaneously examined, and parameters such as energy and exergy efficiency, drying rate, and moisture ratio, which are the performance indicators of solar air collectors and the drying process, were analyzed. The sustainability parameters were also considered as a part of the analysis. The mean thermal efficiency of the solar air collectors for DPSD and NDPSD was calculated as 57.23 and 73.36%, respectively, where the airflow rates were measured as 0.024 and 0.017 kg/s. Furthermore, under the same airflow rate conditions, while the mean exergy efficiency of the collector was 27.77% for NDPSD, it was calculated as 16.64% for DPSD. Moreover, exergy efficiencies of the drying chamber varied between 27.35% and 82.20% for NDPSD and between 21.03 and 81.25% for DPSD, under the airflow rates of 0.012–0.016 kg/s conditions, respectively. [ABSTRACT FROM AUTHOR]

Tea is an important industrial crop. It is the second most popular among all the drinks. The drying operation in the tea industry fulfills the aim of enzyme inactivation and reducing the moisture content to the desired level. The energy consumption in drying operation in the tea industry is mostly in the form of thermal energy. Drying consumes a greater amount of energy than other processes in tea industries. Thermal energy needs are met mainly through fossil fuels. Renewable energy sources such as bioenergy and solar energy are also being adopted but at the minute level. Further, addressing problems such as stewing and case hardening (arises due to improper drying conditions) during drying is necessary to avoid quality loss. In this study, mass transfer modeling of drying of crush tear curl (CTC) tea particles is conducted considering natural convection around the tea particle. A finite difference method with an explicit scheme is used to solve the equations for mass transfer modeling of drying. The effect of drying air temperatures on moisture content, moisture ratio, and drying rates are computed. Drying air temperatures such as 80, 90, and 100°C have not shown effective drying. However, drying at air temperatures of 110, 120, and 130°C are recommended for drying times of 1500 s, 1200 s–1500 s, and 1200 s, respectively. Additionally, the effect of the size of the particles is studied and the lower size of tea particles is recommended for better drying characteristics. The current drying model can be used for single tray/conveyor dryers and indirect natural convection single tray solar dryer. Practical applications: The present research work demonstrates the important information for the hot air drying of CTC tea particle in single tray dryer. The drying modeling results can be used to set the proper temperature level of drying air being sent inside the dryer to avoid the under and over‐drying of tea particle and achieve the desired level of moisture content in the tea particle. Thus, the present study helps in deciding drying conditions such as drying temperature, drying duration for CTC tea particle in single tray dryer, slow speed conveyor dryer, and also in indirect natural convection single tray solar dryer. [ABSTRACT FROM AUTHOR]

The study presents the performance of a small‐scale greenhouse solar dryer (GHSD) to demonstrate hygiene and superiority over traditional methods for medicinal Adulsa and Durva leaves. The GHSD dryer lowered the initial moisture of Adulsa leaves from 73.99% (w.b.) to the final 10.63% (w.b.) under natural and forced convection in 3 and 2.5 h, respectively. Similarly, the initial moisture of Durva leaves was reduced from 67.33% (w.b.) to 11.65% (w.b.) under natural and forced convection in 2.75 and 2.5 h, respectively. Furthermore, mathematical modeling with non‐linear regression was implemented to characterize the drying of Adulsa and Durva leaves, which showed that Midilli–Kucuk and Modified Midilli were the most superior fits for reporting the drying of Adulsa leaves in GHSD and open sun drying, respectively, whereas Verma and Midilli–Kucuk models were superior fits for characterizing the drying of Durva leaves in GHSD and open sun, respectively. Furthermore, the quality of the dried Adulsa and Durva leaves was evaluated, where total phenolic content (TPC) and total flavonoid content (TFC) values were marked higher in the leaves dried by the GHSD as compared to open sun drying for both Adulsa and Durva leaves. Moreover, during antioxidant analysis, the IC50 values among the leaves dried in GHSD were recorded to be greater for the natural convection greenhouse solar dryer (NCGHSD) for both Adulsa and Durva (40.67 and 122.24 μg/mL) compared to open sun drying (101.88 and 158.20 μg/mL). A quality assessment was performed on dried Adulsa and Durva leaf samples, and they exhibited appropriateness for pharmaceutical industry drug production. Practical applications: Greenhouse solar dryer is an eco‐friendly, sustainable, clean, and hygienic way to dry herbs and medicinal plants. The greenhouse solar dryer can shorten the drying time by 50%–60% compared to natural stand in the sun (open sun drying) and improve the quality of the dried herbs, medicinal plants, and reduce the decay rate of the dried products. These leaves can be best suited for Ayurveda medicine industries for herbal powder (Churna). Being an economically advantageous greenhouse solar dryer improves the shelf life of the dried leaves, reduces their density, and lower transportation costs, leading to boost farmers' income in herbal farming and nutritional security. [ABSTRACT FROM AUTHOR]

Given the seasonal nature and high perishability of Eriobotrya japonica fruits, employing effective preservation techniques like drying is crucial to minimize economic losses and extend the fruit's availability throughout the year. This study rigorously examines the drying kinetics of Eriobotrya japonica fruits using an indirect forced convection solar dryer and highlights the technological advantages of utilizing this dryer over traditional open‐air methods, showing that controlled conditions provide improved drying rates. The research develops the equation for the characteristic drying curve. The Midilli‐Kucuk model was demonstrated to be the most appropriate for describing these kinetics under various conditions, offering a reliable method for predicting drying behavior at untested temperatures. The thermal diffusivity was determined and rises as the temperature increases. The application of the Arrhenius approach enabled the determination of an activation energy of 17.79 kJ/mol, confirming the substantial impact of temperature on the drying process. Practical applications: The global challenge of food preservation, especially for perishable fruits like Eriobotrya japonica, requires innovative and efficient solutions to minimize economic losses and ensure the year‐round availability of nutritious produce. Our research demonstrates the technological advantages of using a forced convection solar dryer over traditional methods for drying E. japonica. This system maintains a consistent air temperature, ensuring a stable energy supply, faster, and more uniform drying. A major contribution of this study is the development of the characteristic drying curve equation, which is crucial for optimizing drying parameters and designing an efficient solar dryer specifically for E. japonica. This research not only advances the understanding of the drying kinetics and thermal properties of E. japonica but also provides a foundation for the development of more efficient and sustainable drying technologies. By optimizing the drying process, this study contributes to improving the preservation and quality of loquat fruits, thereby supporting agricultural sustainability and reducing post‐harvest losses. This work is highly relevant to the broader energy community, as it showcases the potential of solar drying technologies in enhancing food preservation while promoting the use of renewable energy sources. [ABSTRACT FROM AUTHOR]

Solar dryers are a convenient option for drying fruits and vegetables, but they largely depend on climatic conditions. Climate dependency makes them vulnerable to dry products and maintain the quality of the products accurately. To mitigate this problem, an electric auxiliary heating system (AHS) was designed, constructed, and tested for a solar dryer in Bangladesh. The developed system had three parts: an auxiliary heating unit, an air duct, and hot air convection pipes. The performance testing of the AHS was done in three experimental trials. The average air velocity from the auxiliary heating unit was found to be between 3.57 and 3.80 m s−1. Trial runs showed a maximum drying temperature of 66.97°C, while the average value remained between 35.10 and 43.26°C. During the off‐sunshine hours, the AHS rose the average temperature by 1.00–12.84°C above ambient and continued the drying operation. Overall, the solar dryer with AHS saved 30%–36% sunshine hours than open sun drying, and its efficiency was estimated as 14.55%–21.9%. Regression analysis showed that the Page and Modified Page models were suitable for predicting the drying kinetics of cabbage samples. Through the results of the study, the developed AHS showed potential for significantly improving the solar drying process. It could be an effective measure for establishing a weather‐independent drying solution to reduce the postharvest losses of perishable agro‐products. Further improvements to the auxiliary heating unit, implying an Internet of Things (IoT)‐based control system will facilitate an improved and user‐convenient drying operation. Practical Applications: Postharvest losses are prevalent for perishable agricultural products (fruits and vegetables) in Bangladesh and are considered a prime reason for the inhabitants to consume a less nutritious diet than recommended. An appropriate dry chain technology that is affordable, weather‐independent, continuous, and fast in operation could be the optimal solution to this problem. Numerous types of solar hybrid dryers with different additional heating sources (electricity, biomass, LPG, etc.) have been investigated around the world. However, the extent of these research endeavors is very limited in Bangladesh. The study was thus conducted to develop a novel auxiliary heating system for a solar dryer in Bangladesh and check its technical viability. Our results indicate that an electric auxiliary heating system can be an efficient option for drying fruits and vegetables irrespective of the weather and can substantially reduce postharvest losses in Bangladesh. [ABSTRACT FROM AUTHOR]

Solar drying systems are becoming a popular alternative to traditional energy-based drying systems for agricultural products due to their effectiveness and reduced fuel consumption. Although the efficiency of solar drying systems has been thoroughly investigated, their sustainability has not been studied enough. This study aims to fill that gap by conducting a life-cycle assessment of two new solar drying systems built in Udaipur, Rajasthan, India. The environmental implications of an innovative cylindrical solar-assisted drying system and a phase-change material-based solar drying system were evaluated using cradle-to-gate life-cycle analysis. The study uses the ReCiPe 2016 endpoints (H) technique to calculate various aspects such as midpoint, endpoint, single score, normalization result, and network diagram for phase-change material-based solar drying and cylindrical solar-assisted drying. Results show that phase-change material-based solar drying has an average of 40% more impact on the environment than cylindrical solar-assisted drying, with a high impact found in human non-carcinogenic toxicity, mainly due to the production of phase-change materials. However, cylindrical solar-assisted drying system crossover phase-change material based solar drying in terms of its impact on human carcinogenic toxicity and fossil resource scarcity. The contribution to global warming of phase-change material-based solar drying is 13.7% more than that of cylindrical solar-assisted drying. The endpoint characterization indicates that phase-change material-based solar drying exceeds in terms of human health (40%) and ecosystem (37.04%), whereas cylindrical solar-assisted drying surpasses phase-change material-based solar drying in terms of impacts on resources, at 14%. The early drying in phase-change material-based solar drying makes up for its higher impact than that in cylindrical solar-assisted drying, which takes 3 hours longer to dry. This study offers guidance and methods for making the best choice of solar-powered dryers. [ABSTRACT FROM AUTHOR]

This review reports recent developments in solar greenhouse drying systems in conjunction with hybrid technological features and their designs, operations, and economic implications as well as application in agro‐food product processing. Solar energy is one of the most efficient renewable energy sources to be used as an alternative to fossil fuels. This form of energy is the finest option for space heating and electricity generation among the available renewable energy sources. Solar energy can be used directly or indirectly for dehydrating agricultural and nonagricultural products. However, the products are susceptible to natural disasters such as rain, insects, and animals in open‐air sun drying. Solar greenhouse drying systems in conjunction with hybrid technological features are one of the most recent applications used in the agro‐food processing sectors. The review shows that the quality of products dried in conservatories is superior to that of products traditionally dried under the sun. Further, higher sustainability of the solar greenhouse‐oriented hybrid drying system in terms of embodied energy, energy return time, CO2 emission, net CO2 mitigation, and carbon credit can also be observed with the strengths, weaknesses, opportunities, and threats analysis, i.e., strengths, weaknesses, opportunities, and threats of solar dryers. This shows the framework for abundant real‐world applications. [ABSTRACT FROM AUTHOR]

The first focus of this study is to investigate the design and behavior of locally built solar dryer during processing henna leaves. This was performed through the determination of the most important parameters that effect drying process. Appropriately, it was found that solar radiation has a direct effect on the collector outlet air temperature and consequently the product moisture content. Accordingly, high radiations lead having high air temperature at the drying chamber and consequently, the moisture content will decrease rapidly. Similarly, lower radiations will still lead to decrease of the moisture content, however, the drying rate will be less important than at high radiations. On the other hand, air velocity has an inverse dissipative effect of the energy and its increase leads to the decrease of the outlet temperature of the solar collector. Indeed, the highest outlet temperature from the solar collector was around 32 °C at an air velocity of 2 m/s. At 5.5 m/s, this temperature dropped to around 27 °C. The second objective of this study is to present the effect of different drying methods (i.e. forced convective solar drying and open sun drying) of Lawsonia inermis on the content of secondary metabolites (phenolic and flavonoid compounds) and compare the results with fresh henna samples. The yield of phenolic compounds was determined, and the dry crude extracts were found to be richer than the fresh sample in all of the drying modes used. The best yields are obtained with convective solar dryer and open sun drying samples (28.6 and 13.93%), respectively. The total phenolic and flavonoid contents of convective solar dryer product were 25 and 10% higher than open sun dried samples. Antioxidant tests (DPPH, ABTS, and ferric reducing power) revealed the scavenging and reducing abilities of the extract dried with the solar dryer. The values of antioxidant capacities measured by the three different methods were all consistent, appropriate, and highly correlative for assessing total antioxidant capacities. The solar dryer allows the preservation or even the increase of the antioxidant activity of the tested extracts. [ABSTRACT FROM AUTHOR]

AbstractThe objective of this study is to promote the production for small scale drying industries by reducing the drying time of agricultural products. Discrete mirrors are arranged in a parabolic fashion and used as reflectors to concentrate the incoming solar radiation. The available solar flux is doubled by using this discrete arrangement of mirrors. Optical simulations are performed using Monte Carlo Ray tracing algorithm and various effects were studied to select the best arrangement of mirrors. The concentrated type dryer has been numerically simulated and no-load testing is performed using ANSYS Fluent. Simulation is carried out for various inlet velocities from 0.1 to 1 m s−1. The concentrated setup operates between 0.4 and 1 m s−1 of velocity to obtain temperature in the range of 40–70 °C. The maximum and minimum increase in outlet temperature is 23.52% and 2.87%, and the Nusselt number enhancement is 18.94% and 4.15%, respectively. [ABSTRACT FROM AUTHOR]

Fruits and vegetables are an important part of human diet. In the present study, the thermal performance of a solar greenhouse dryer for drying Solanum lycopersicum (Tomatoes) was analyzed. The drying pattern at various locations of the drying chamber and different levels of the dryer was evaluated. The life cost analysis for drying the tomatoes in the dryer for 25 years of service was evaluated. The greenhouse solar dryer was developed with a structure base of galvanized iron pipes and a covering of a 2 mm thick polycarbonate sheet. The experiment was carried out for drying the tomatoes at various locations in the dryer using the trays and trolley system. The maximum thermal efficiency of the dryer is 26.66 % while drying out 5.8 kgs of tomatoes in one day. The economic analysis of the greenhouse solar dryer shows that the payback period of such a system can be attained in only 1.6 years which terms the dryer feasible and economically viable in the current agro-drying market. The embodied energy for the dryer was calculated at 3154.71 kWh for the system. The CO2 emission for the greenhouse solar dryer was found to be around 6.62 tonnes for a lifespan of 25 years. The net CO2 mitigation was calculated at around 41.62 tonnes which would generate an earning from 46766 INR to 62355 INR worth of carbon credits. [ABSTRACT FROM AUTHOR]

The application of solar dryer through greenhouse (GH) model as drying method for crops-based product is extremely important in industrial scale agriculture, especially in developed country. The drying model is considered environmentally friendly since it utilizes solar power as the main drying energy. However, the fundamental operational aspect of the basic GH is less discussed according to the drying mechanism of the dried product. In this work, three small-scale drying model are evaluated: open drying (OD), natural convection GH (NCGH), and forced convection GH (FCGH). The drying product is potato, which can be taken as an essential agricultural product in modern world. The OD model has the lowest mass loss rate which less than 50 % of the water from product can be evaporated. The operation of both GH is satisfactory, resulting more than 60 % moisture evaporation. The drying characteristic indicates the two-step failing rate which makes the mass loss fluctuation from the process. The highest mass loss is observed during the constant rate period around 21 % for FCGH and 18 % for NCGH. In addition, the detailed analysis on the effect of each process is discussed in this work. For example, the presence of hair-like structure and the movement of the pith of dried potato during the process. Also, a higher drying rate from NCGH and FCGH initiate the gelatinization and compartmentalization, resulting a substantial water evaporation of the product. It confirms the important correlation of the drying process and water diffusion mechanism of the dried product. The finding from this study can be taken as a vital reference for improving the operation of GH solar dryer. [ABSTRACT FROM AUTHOR]

Striving for the highest quality food product in the shortest time with the least energy expenditure is the cornerstone of the food drying process. Furthermore, the geometric properties of the product significantly influence the efficiency of the drying process. Therefore, in this study, peach slices of three different thicknesses were dried in three different dryer types. The drying of peaches was carried out using a solar energy drying system, a thermal energy storage solar dryer, and a dryer with a heat pump. The drying performances of peach slices of three different thicknesses were investigated. Moisture extraction rates (MER), specific moisture extraction rates (SMER), and specific energy consumption (SEC), which relate to the amount of removed moisture and the amount of consumed energy at the end of the drying studies, were calculated. Food analyses, such as moisture content, color, texture, and water activity were performed. Considering the amount of energy consumed, it is seen that the heat pump system consumes more energy than the solar energy system. In addition, by using the heat storage system, the drying time is shortened, and the energy consumption is reduced. A decrease in SEC values was observed with the activation of the heat storage solar dryer. [ABSTRACT FROM AUTHOR]

Drying process has been employed since ancient times to preserve agricultural products by reducing the moisture content. Solar dryer is one of the most commonly used dryers due to its availability, reliability, and environmentally friendly nature. It is practical in rural areas since solar dryer can be fabricated with a simple design. Despite its potential, designing a long-term, feasible solar dryer is challenging without a good understanding of its performance parameters, such as energy, exergy, economic, environmental (4E) aspect, and its impact on product quality. Therefore, many attempts have been dedicated to conducting these analyses. Nonetheless, the information obtained is only one-dimensional, and they do not reflect the actual behaviour of a solar dryer. This paper aims to provide a comprehensive and critical review of the additional 3E parameters, namely energoeconomic, exergoeconomic, and enviroeconomic. Moreover, the effect of solar drying on product quality parameters (Q) will be discussed. Furthermore, a new idea to perform energy, exergy, environmental, economic, energoeconomic, exergoeconomic, and enviroeconomic (7E) and quality analysis (7E + Q) is proposed and outlined to improve the operability of the solar dryer. It is envisaged that 7E + Q analysis will pave the way for more effective and efficient solar dryers. [ABSTRACT FROM AUTHOR]

Food losses and hunger around the world are majorly attributed to the lack of diverse food processing technologies and standardized methods. Solar energy is a potential solution for drying agricultural products, but traditional solar drying methods are not yet widely used. This study developed a finite element model using COMSOL Multiphysics to assess the performance of a passive greenhouse dryer for drying food products. The proposed model was used to simulate the drying of potato slices, and the results showed that the dryer was able to reduce the moisture content of the potato slices from 1 to 0.005 in 3 h. The drying efficiency was 20.52%, the relative humidity inside the drying chamber was 25.2%, and the energy and exergy efficiencies were 63.46% and 94.01%, respectively. Overall, the results of this study suggest that the passive greenhouse dryer is a suitable drying method for potato chips. The model developed in this study can be used to further optimize the design of the dryer and to evaluate its performance for other food products. [ABSTRACT FROM AUTHOR]

The paper presents the performance evaluation of a modified indirect solar dual collector dryer (MIS2CD) integrated with a thermal storage system for drying myrobalan slices. The design of the solar collector and solar collector with thermal storage was to supply uninterrupted thermal energy to the drying chamber during sunny and sunset hours. To evaluate the dryer performances, one lot (20 kg) of myrobalan was dried in the MIS2CD, and as a result, the thermal efficiency and energy supply period of MIS2CD increased by 12 ± 02% and 41 ± 1.2%, respectively. Drying characteristics of myrobalan slices in MIS2CD, TD, and OSD were studied and compared. A two-term exponential model best explains the drying kinetics of myrobalan slices dried in MIS2CD. The dried sample in MIS2CD results in lesser ΔE* values than TD and OSD methods. The highest exergy efficiency of 78.2% and lower exergy losses were recorded. The energy payback period of the MIS2CD was evaluated as 1.42 years. The CO2 emitted and CO2 reduced reduction are calculated for drying myrobalan in MIS2CD for a lifetime (20 years) of 67.85 kg and 20.65 tons, respectively. The capital cost of the solar dryer design was estimated depending on the economic considerations of the state. The drying hours were increased in MIS2CD against OSD by 59% on the annual sunny days (210 days). The sample drying period MSD and TD to reach the final moisture level of 7% was 9 h and 5 h, respectively. The total economic benefit is 22,622 INR (annually), and the 2.08 benefit–cost ratio for myrobalan dried in MIS2CD compared to TD. The MIS2CD's payback period is nearly 2.18 years, much less than the dryer's lifetime. [ABSTRACT FROM AUTHOR]

Solar drying is a renewable energy-based technique which is widely used for food preservation purpose. In this study, various drying characteristics of the solar-dried Solanum tuberosum samples of different thicknesses have been investigated at variable climate condition of Lucknow. A mathematical model has also been developed to validate experimental results to predict the drying rate, free moisture content, and other parameters. Pre-treatment of the food samples was also done before the experimental runs on the fabricated solar dryer. Global radiation has also been monitored during the study to correlate the heat transfer rate in inner and outer sides of the solar drying chamber. SEM analysis has also been done to analyze the surface morphology of solar-dried samples. All solar dried food samples have uniformly heated. There was no hot-spot condition present on the surface of the samples. The drying efficiency and payback period of the fabricated solar dryer have also been calculated as 22.9% and 1.42 years, respectively. Model data have been found in good agreement with the experimental data within a 5% error. This modified model can be used for different agro-based food materials such as carrot, kiwifruit, and yam. [ABSTRACT FROM AUTHOR]

In this article, a comparative study of different drying techniques, namely, open sun drying (OSD), desiccant drying, solar drying (SD), and solar drying with desiccant (SDWD) was done for drying potato and ginger. The thermal efficiency and air temperature differences of the solar dryer based on evacuated tube collectors were also examined. The average efficiency of the solar dryer was 29.01%. Average drying rates of OSD, desiccant drying, SD, and SDWD bed are 0.435, 0.435, 0.59, and 0.635 g/min. The moisture content of the potato was reduced from 79.6% to 32.9% by OSD, 32.6% by desiccant drying, 9.6% by SD, and 6.9% by SDWD. The moisture content of the ginger was reduced from its initial value of 82.3%–25.3% by OSD, 25% by desiccant drying, 10.1% by SD, and 3.2% by SDWD. SD assisted with a desiccant bed proved to be the best method for drying vegetables. Drying with desiccants is not feasible for drying in winter and spring seasons of the Indian climate. [ABSTRACT FROM AUTHOR]

In this paper, experimental work has been presented to study the novel design of a solar crop dryer that includes an inverted absorber perforate type collector with forced airflow. A novel design configuration was constructed and tested in the eastern Algeria climate (El Oued city) for drying potatoes. We aimed to present a test of the thermal performance of the novel dryer and use only clean energy sources for evaluating the drying efficiency. Under real climatic conditions, the experimental test indicated that the average air temperature of the drying chamber is 50 °C, and the time required for drying potatoes starting at the initial moisture content (MC) of 84.17% until the final MC of 12.5% is 6h. The highest specific moisture extraction rate value was obtained as 1.074 g water/kWh. The drying efficiencies ranged from 20.37% to 34.01%, whereas the exergy efficiency ranged from 58.48% to 93.22%. The payback period was estimated as 1.39 years. The proposed novel dryer will dry potatoes free of cost for almost its entire life period, and about $13.92 can be saved. Compared with electric oven drying, the novel one has the following advantages: the cost of electricity saving and avoiding penalty tax for CO2 emission were $11.69 and $2.235, respectively. [ABSTRACT FROM AUTHOR]

Groundnut pods contain a higher amount of moisture i.e., 40% - 50% (wet basis) at the time of harvesting which causes fungal infestation and drying play an important role to achieve a safe moisture content. The objective of the present study was to examine the effect of drying temperature on the drying behavior and acceptability of models of drying to prophesy the drying pattern of the groundnut pods. Forced air circulation hybrid convective cum solar dryer and sun drying method was used to dry the groundnut pods from initial moisture of 124.97%±1.34% (dry basis) to a moisture content of 8.75%±0.35% (dry basis). Five mathematical models were used to forecast the drying kinetics and furthermore, moisture diffusivity was determined. The different physico-chemical parameters viz., moisture content, free fatty acids, oil content, protein, ash and colour value were ascertained before and after drying of the pods. It was observed that the drying time was less for the mechanical drying method and the best-suited model for thin layer drying of groundnut pods was the logarithmic model. The higher value of R² (0.984) and lower values of SSE (0.0015) and RMSE (0.0391) was achieved in the page model for the open sun drying method. The value of effective moisture diffusivity was highest (7.1517 x 10-10 m²s-1) for a 70°C mechanical dryer. The quality parameters like oil, protein, and free fatty acids were increased after the drying process irrespective of dying temperature and method, but the increment was more pronounced at 70°C. [ABSTRACT FROM AUTHOR]

The world's population is projected to increase, impacting a 60% rise in food production demand by 2050, including the demand for maize. Currently, maize production is estimated to reach 1510 million tons in 2023, necessitating suitable methods for preserving maize kernels to maintain quality and reduce post‐harvest agricultural losses. Although drying methods present a viable solution to address this issue, the majority of farmers in Indonesia still use conventional drying methods, such as open sun drying, which has several drawbacks. Hence, solar drying systems aim to overcome these limitations by harnessing renewable, clean, sustainable, and eco‐friendly energy to support the sustainable development goals (SDGs). This research comprehensively reviews the progress of solar drying technology, providing insights into its working principles, innovative designs, and operational modes across various types of solar dryers. The 4E + Q analysis provides information regarding the performance of solar drying systems, including energy analysis to determine the quantity of energy utilized and exergy analysis to demonstrate irreversibility in thermodynamic processes. Additionally, this analysis highlights environmental impacts such as CO2 emissions and mitigation efforts, while considering economic aspects through lifecycle assessment and payback period methods. The quality assessment of dried maize kernels according to the standards set by the Indonesian National Standard (SNI) is conducted, including proximate analysis, aflatoxin levels, color measurements, and internal cracking analysis. Practical applications: Drying technology is essential for the food preservation process, enabling the maintenance of product quality and extending storage life by reducing the moisture content to eliminate the activities of microbial agents. The application of solar drying technology harnesses solar radiation as the primary energy source, making it well‐suited for crops like paddy, maize, cassava, etc. The development of solar dryers continues through modifications and the addition of auxiliary systems to achieve more efficient, economical, and sustainable technologies. The hope is that in the future, these technologies can be adopted by farmers on an industrial scale due to low operational costs, ease of operation, and controllable operating conditions. The methodological approach is necessary to evaluate the performance of solar dryers and the quality of dried products through a 4E + Q analysis, it provides information on energy consumption, exergy flow, economic considerations, environmental aspects, and quality assessments against national quality standards (SNI). [ABSTRACT FROM AUTHOR]

This research addresses the improvement of the performance of a solar dryer equipped with a PVT unit by integrating a heat exchanger into the drying system. The results indicated that introducing a heat exchanger into the drying process had a positive impact on enhancing and raising the drying temperature by harnessing the amount of free energy dissipated after the drying operation. The absorbed energy ranged from 30 J/s to 275 J/s from the hot air emitted throughout the drying process during the day, depending on the drying temperature. This paper also discusses the influence of the drying room design on the thermal balance within the room. Consequently, four different designs for the drying room were developed and studied with the COMSOL software. The findings revealed that the design-4, which optimally places two air inlets (one at the bottom and one at the top) on one side, whereas the opposing side has a centralized air outlet, utilizing a fan to ensure effective air circulation, is the best solution in terms of thermal balance and distribution of the drying air inside the drying chamber. [ABSTRACT FROM AUTHOR]

Fruits and vegetables are nutritious and good in minerals, vitamins, and fib. Most fresh fruits and vegetables contain a minimum of 70% of moisture content which causes the formation of bacteria, fungi, and viruses to affect and cause the items to rot. But dried fruits contain only less than 20% of moisture content. So drying the fruits and vegetables helps to preserve the items for longer use without causing them to rot. Dried fruits have a great source of antioxidants and help in health benefits like improving blood flow, and reducing the effects of many diseases. Compared to fresh fruits, dried fruits are good in nutrition and have less weight for packaging and transportation usage. For drying materials, various types of solar dryers are used. Natural or open sun drying methods comparatively consume more than 12 h to dry material, whereas, direct and indirect drying methods would enhance the efficiency and dry the products quicker than open drying. For the consideration of quality drying and to increase efficiency, various modifications of solar dryers are designed and fabricated. In this review, we discussed the most appropriate developments in the drying of food items, required phase change materials (PCMs), performance, and environmental analysis of SD, and also reported the various designs of the solar drying techniques. [ABSTRACT FROM AUTHOR]

Red pepper is a valuable ingredient known for its abundance of vitamins and antioxidants. But, it usually needs to be dried for longer preservation. Hence, this research is aimed at examining the drying kinetics and quality attributes of dried red peppers utilizing various solar drying methods, in comparison with traditional open sun drying (OSD) and industrial laboratory thin layer dryers (LTLD). Analysis parameters employed include determining moisture content, measuring color properties, evaluating antioxidant capacity, analyzing capsaicinoid content, and assessing microbial presence. The drying process took place in a sunny environment with fluctuations in temperature and relative humidity as evidence of the dynamic conditions experienced within the solar dryers. It was observed that the logarithmic model was the most accurate in predicting moisture ratio over time, estimating a drying time of 25 hours to achieve 10% moisture content. The result demonstrated that direct solar dryers (DSD), indirect solar dryers (ISD), and mix mode solar dryers (MMSD) methods showed moderate changes in color parameters, with average Δ L ∗ , Δ a ∗ , and Δ b ∗ values of -5.08, -23.71, and -13.62, respectively. The average overall color difference (Δ E) for these methods was 27.96. In addition, after comparing it to the LTLD method, which showed the highest content of phenolic compounds at 47.89%, MMSD displayed a slightly lower content of 44.71%. Similarly, MMSD exhibited higher levels of DPPH radical scavenging activity and ferric reducing power, measuring at 44.22% and 1163.75 μmol Fe2+/L, respectively. The capsaicin content remained relatively consistent across all drying methods, with MMSD, DSD, and LTLD demonstrating similar levels of approximately 31 mg/g. Although MMSD had slightly higher mold and yeast counts compared to LTLD, ISD, and DSD, it remained lower than OSD (less than 0.56 log 10 cfu / g ). Furthermore, MMSD showed a lower total microbial count in comparison to other drying methods. These findings suggest that MMSD shows promise as a drying technique for preserving the phenolic compounds and antioxidant activity of the dried product. [ABSTRACT FROM AUTHOR]