Solar Dryer Research Articles

Influence of a double-stage solar tunnel dryer on the preservation of quality characteristics and the Modelling of colour variations in red chili peppers

In this work, the influence of two-stage solar tunnel drying on the preservation of quality attributes of both chili pepper varieties, Mareko Fana (MF) and Bako Local (BL), was studied. Both varieties were dried in different drying modalities, i.e. solar tunnel and open sun drying. The quality attributes were evaluated during the drying process using FTIR and spectrophotometry techniques. Different colour evolution models were implemented and a suitable model was selected. The results showed that after drying of the Mareko Fana chili variety, the lightness retention was found in the range of 81 %–89 %, the redness retention between 25 % and 42 % and the yellowness retention between 14 % and 38 %. For the Bako Local variety, the values were in the range of 78 %–82 %, 42 %–60 % and 36 %–55 %, respectively. The first order model gave a higher correlation coefficient (R2 > 0.96), which indicated the suitability of the model for predicting the color variation for both varieties. The volatile aromatic compounds in the chili peppers were greatly lost during open sun drying, while solar tunnel drying maintained these compounds for both varieties. However, during the solar tunnel drying process, a significant amount of alkyl halides or alkyl-chlorides were lost. The amount of dihydrocapsaicin and capsaicin from the chili peppers ranged from 10,172 μg/kg to 16,313 μg/kg and 16,676 μg/kg to 27,189 μg/kg for both dihydrocapsaicin and capsaicin, respectively. In tunnel, open-air, and uncontrolled open-air solar drying, the MF chili variety lost copsaicinoid content by 3.4 %, 14.8 %, and 38.3 %, respectively; in the BL variety, comparable losses were 1.8 %, 4.4 %, and 13.6 %. A minimum loss of ascorbic acids was recorded during solar tunnel drying. The results showed that well-designed double stage solar tunnel dryers are important for effective drying processes that preserve quality attributes of the chili pepper.

Assessment of an indirect solar dryer for small-scale resin production: Energy, exergy, economic (3E), and sustainability analysis

This study evaluates an innovative domestic indirect solar dryer (ISD) for drying grapes (Vitis Vinifera L.), focusing on energy, exergy, economic, and sustainability performance. Two trials with crop loads of 15% (Trial-1) and 33% (Trial-2) were conducted. Trial-2 exhibited higher energy efficiencies in the solar collector (SC) and drying chamber (DC) compared to Trial-1, with efficiencies of 61.4% and 58.5% for SC, and a 13% increase in DC efficiency. The daily average exergy efficiencies for SC and DC ranged from 11%–13% and 54%–58%, respectively. Trial-2 also showed a 113% higher life cycle savings, a 54.4% decrease in payback period, and a 23% lower waste exergy ratio compared to Trial-1. Pre-treatment of grapes resulted in superior dried product quality. The study highlights the ISD’s potential as an economically and environmentally sustainable solution for small-scale agricultural ventures, providing insights for renewable energy sectors

An interoperable ontology for CPS-enabled Polyhouse Solar Dryer: A case study of the AgroESP project

Polyhouse is a commonly used conventional method for solar drying of food products. These Polyhouse Solar Driers (PSDs) are characterized by their enclosed structure and translucent covering, providing a controlled environment conducive to efficient food drying. Smart polyhouses, equipped with a Cyber-Physical System (CPS), further enhance this process by optimizing environmental conditions and enabling real-time monitoring. In smart PSDs, the data are obtained from diverse sources with different specifications in accuracy, resolution, and range. This multifaceted nature of the information obtained from various sources significantly compounds the complexity of the system. This complexity of data from diverse sources within smart polyhouses necessitates a standardized knowledge representation. Ontologies serve this purpose by establishing a common vocabulary and structure for data integration, promoting semantic interoperability and effective communication among diverse systems. This paper proposes a novel unified ontology designed to model complex polyhouse CPSs, aiming to address semantic interoperability issues and streamline data integration across various domains. The proposed polyhouse ontology attempts to reuse the concepts defined in existing ontologies rather defining new concepts for efficient knowledge sharing and enhanced understanding of polyhouse operations. The practical applicability of the polyhouse ontology has been verified with competency questions and through field deployment in a CPS enabled smart Polyhouse Solar Dryer.

Low-cost solar dryer dehydrates silver banana with a prediction of diffusion approximation model

Solar dryers made from recycled materials offer a cost-effective solution for promoting the widespread adoption of this technology and reducing food production costs. In this study, a low-cost solar dryer was constructed using repurposed materials, employing indirect exposure, and its performance was evaluated through a kinetic study on banana slice drying (Musa spp.). Drying was carried out until equilibrium moisture, reaching constant mass. The drying air's temperature and relative humidity (RH, %) were monitored. Fourteen empirical models were used to fit the experimental data. The banana slices took approximately 300 min to dry, with final moisture of 1.8%. The mean operational conditions during natural drying were 59.08±9.16 °C and RH = 39±4%. The diffusion Approximation model fitted the drying curve better, as it presented the lowest reduced Chi-square (χ2 = 2.9×10-5) and a high coefficient of determination (R2 = 0.9998). The effective diffusion coefficient (Def = 5.4×10-9 m2/s, R2 = 0.9935) was determined. Thus, the solar dryer demonstrated efficient performance in the banana drying process, requiring minimal design effort. Furthermore, despite the limitations in controlling the drying conditions, most of the mathematical models successfully predicted the drying process due to the dryer's ability to maintain the continuity of the drying curve, suggesting potential viability for this low-cost dryer.

Development of Solar Dryer Combined with Infrared Radiation for Phlai (Zingiber Montanum (J. Koenig) Link ex A. Dietr.) Drying

Development of Solar Dryer Combined with Infrared Radiation for Phlai (Zingiber Montanum (J. Koenig) Link ex A. Dietr.) Drying

Effect of Oven and Solar Portable Dryer Drying Methods In Terms Of the Antioxidant Activity of Moringa Oleifera Leaves

Drying is a method that is widely used because this method is very simple and cheap. Drying techniques using conventional methods are the most widely used methods in drying food ingredients. Moringa leaves (Moringa oleifera) are a food ingredient widely used as a natural dye and contains many antioxidant components. Antioxidant components such as flavonoids, polyphenols, lycopene, and ß-carotene. In this research, the drying process was carried out by comparing two conventional drying methods by an oven and a portable solar dryer. The research method was carried out using a sample preparation process for the drying process of Moringa leaves, followed by an analysis of antioxidant activity using the DPPH method. From the results of research that has been carried out, antioxidant activity was found to be 5.22% in drying using the oven method and 14.02% in drying using the solar portable dryer method. The conclusion from the research that has been carried out is that the drying method will significantly influence the antioxidant activity of Moringa leaves. Apart from that, temperature conditions and the length of the drying process will also influence antioxidant activity.

Sustainable solar drying: Recent advances in materials, innovative designs, mathematical modeling, and energy storage solutions

The utilization of solar drying technologies has gained increasing importance in the context of sustainable and energy-efficient processes. This exploration delves into current trends in solar drying, specifically focusing on materials, designs, and their integration with energy storage solutions. Within the materials domain, we examine solar collectors, absorbers, and the impactful role of phase change materials (PCMs) in augmenting drying efficiency. Innovative designs and configurations are discussed, offering insights into advanced solar drying systems. Furthermore, the integration of energy storage technologies is highlighted, critical role of energy management in solar drying applications is emphasized. The assessment encompasses performance and efficiency enhancements, including mathematical modeling and the optimization of heat transfer processes. Challenges and potential future directions in solar drying are explored, along with the promising areas for ongoing research. The object is to provide a comprehensive perspective on the recent advancements in solar drying, offering valuable insights for sustainable practices and future developments.

Assessing mathematical models for the intermittent drying of cocoa (Theobroma cacao L.) beans

Fine flavor cocoa quality is significantly impacted by its postharvest drying process which can be enhanced through mathematical modeling. The objective of this study was to carry out the mathematical modeling of cocoa bean drying kinetics for a greenhouse dryer and considering intermittent drying. In this study, a natural convection solar greenhouse dryer was used to dry cocoa beans with negligible losses to an acceptable moisture content (6.6%) and cotyledon pH (5.25). Models based on Fick’s second law of diffusion, Newton’s model, and Hii, Law and Cloke’s model were developed considering (i) the entire drying period, and (ii) intermittent drying for Fick’s and Newton’s. Effective diffusivities and drying constants increased up to 1.01 ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} 10–11 m2/s and 0.0165 1/h respectively during drying. Newton’s model slightly outperformed Fick’s model, and the models considering intermittency showed slight improvement over the models for the entire drying period. Considering intermittency when modeling cocoa drying may be useful since a better fit to experimental data resulted, and variation of effective diffusivity and the drying constant was observed over the drying period.

Hybrid solar drying of sludge from kraft pulp mills

Abstract Sludge generated from kraft pulp mill wastewater treatment plants (WWTPs) is typically non-inert solid waste and is commonly disposed of in landfills. In this study, a novel approach for repurposing WWTP sludge from a kraft pulp mill in Brazil for energy generation was assessed. With the global cellulose market projected to reach $ 61 billion by 2033, there is a growing need for sustainable energy solutions and disposal of associated industrial byproducts. This study investigated the performance of a hybrid active solar dryer for reducing the moisture content of sludge to enhance the feasibility of sludge burning in a biomass boiler. Through rigorous experimentation and design of experiments (DOE) planning, optimal parameters for the hybrid dryer were determined, specifically, a volumetric airflow rate of 1.1 m/s and an entrance temperature of approximately 51 °C. This innovative approach not only addresses the environmental concerns associated with sludge disposal, but also contributes to the broader goal of advancing sustainable technologies in the midst of global energy challenges.

Energy Analysis and Economy Performance of a Hybrid Solar Dryer for Drying Coffee

This work studies the effect of the drying temperature on the profile of the water content, drying rate, drying efficiency, economic performance, and the quality of Robusta and Arabica coffee beans using the hybrid solar dryer. The drying instrument with the help of LPG heating is used in this research with a specified temperature of 40 ℃, 50 ℃, and 60 ℃. The research is conducted on a sunny day for 1 day for each temperature and coffee beans. The temperature profile shows that the lowest water content in the study is 60 ℃. The drying rate for both 50 ℃ and 60 ℃ are similar and the highest average efficiency of the instrument is at 50 ℃ for both Robusta and Arabica beans. The dominant peak in GCMS analysis result of coffee samples was caffeine with a total area percentage of 30.89%, the description of the coffee bean structure using SEM test resulted in a hole size of 5-10 µm, the obtained fat content was 1.6%, the obtained protein content 17.3%. A hybrid solar dryer is an environmentally friendly solution that enables faster coffee drying, with a payback period of 1.5 years for both coffee bean types.

Experimental study of solar drying kinetics and evaluation of activation energy of Eriobotrya japonica fruits

AbstractGiven 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 applicationsThe 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.

Drying kinetics (mathematical modeling) and quality evaluation of herbal leaves (Adulsa and Durva) dried in small‐scale greenhouse solar dryer (GHSD): Experimental investigation and comparative analysis

AbstractThe 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 applicationsGreenhouse 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.

Physical Characterization of Solar Thermal Energy Storage (TES) Materials for Solar Dryers: Case of Volcanic Stone (Pozzolan) in Chad

Physical Characterization of Solar Thermal Energy Storage (TES) Materials for Solar Dryers: Case of Volcanic Stone (Pozzolan) in Chad

Experimental investigation of indirect solar dryer integrated with wicked heat pipe

Experimental investigation of indirect solar dryer integrated with wicked heat pipe

Development of an auxiliary heating system for a solar dryer in Bangladesh

AbstractSolar 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 ApplicationsPostharvest 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.

Review Paper on Diffierent Types of Solar Dryer

Abstract: One of the most appealing and economical uses of solar energy is drying agricultural goods. With differing degrees of technical performance, a multitude of solar dryer types have been devised and developed across the globe. In general, solar dryers come in four different varieties: (1) direct solar dryers, (2) indirect solar dryers, (3) mixed-mode dryers, and (4) hybrid solar dryers. The product being dried, as well as technical and financial concerns, are reviewed in this paper together with other solar dryer kinds. Technically speaking, integrated storage, high efficiency, compact collector design, and long-life drying systems are the main focuses in the development of solar-assisted drying systems for vegetables. There exist alternative systems to air-based solar collectors. By using a water-to-air heat exchanger, water-based collectors are another option. A water-to-air heat exchanger can be used to push hot air used for drying agricultural products to pass through it. As part of the solar drying system, the hot water tank stores heat

Comparative Performance Evaluation of Active Greenhouse Solar Dryer with and without Reflective Floor Material

Comparative Performance Evaluation of Active Greenhouse Solar Dryer with and without Reflective Floor Material

Dehydration of Onion Slices for Food Processing Application Using Internet of Things-Based Smart Solar Drying System

Abstract Indian onion producers experience significant economic losses as a result of the unpredictable fluctuations in onion prices during the harvesting and postharvest stages. To address these difficulties and increase farmers' earnings, the transformation of onions into value-added goods such as onion paste, onion powder, onion sauce, and onion oil has emerged as a possible option. The objective of this project is to create a smart solar drying system based on Internet of Things (IoT) technique specifically designed for the dehydration of recently harvested red onions. In April 2023, a series of five experimental tests were carried out, examining the effects of different onion slice thicknesses ranging from 2 mm to 4 mm, with intervals of 0.5 mm. Each trial consisted of running the dryer for a duration of 9 h, specifically from 9:00 a.m. to 6:00 p.m., throughout the daylight hours for three consecutive days. The experiment involved evaluating different drying characteristics, such as moisture content on dry and wet bases, shrinkage ratio, and thermal efficiency. The drying time required to achieve a 10% moisture level (w.b.) was reduced by 30.19%, 16.98%, 11.32%, and 3.77% when comparing a 4-mm slice thickness to thinner alternatives of 2 mm, 2.5 mm, 3 mm, and 3.5 mm, respectively. The dryer had a superior thermal efficiency of 27.89% when the thickness was 2 mm, in contrast to 19.50% when the thickness was 4 mm. Significantly, onions that were dehydrated from slices measuring 2 mm and 2.5 mm in thickness showed exceptional suitability for the production of powdered onion.

Development and Performance Assessment of Sensor-Mounted Solar Dryer for Micro-Climatic Modeling and Optimization of Dried Fish Quality in Cambodia

Development and Performance Assessment of Sensor-Mounted Solar Dryer for Micro-Climatic Modeling and Optimization of Dried Fish Quality in Cambodia

Uncovering quality changes of shrimp (Penaeus vannamei) during solar drying and its relationship with protein-related properties

This study explored the intrinsic relationship between the quality traits and protein-related property changes during the solar drying of shrimps (Penaeus vannamei). During drying, the shrimp exhibited a gradual decline in L*a*b* values and a notable increase in the hardness and chewiness. Proteins were degraded and oxidized. Especially, the trichloroacetic acid-soluble peptide and carbonyl contents increased, whereas the total sulfhydryl content decreased. The proportions of different types of intramolecular bonds were significantly changed. The ionic and hydrogen bonds greatly decreased to 10.72% and 9.05% and the hydrophobic and disulfide bonds notably increased to 19.38% and 28.19%, indicating the changes in the spatial structure of the protein and its denaturation during the drying process. The Pearson's correlation analysis showed that protein degradation and denaturation greatly affected the textural properties and protein oxidation caused color changes. The result of this work provides a theoretical support for improving the quality of shrimp products.