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The drying process in agriculture is energy-intensive and traditionally relies on fossil fuels, which are becoming less reliable and more expensive. This study designed and simulated a hybrid solar hot plate dryer system using the computer to reduce reliance on fossil fuels. The system's main components are a flat plate collector, photovoltaic panels, and a wind turbine. This system was simulated in three cities of Iran, including Bushehr, Kerman, and Shahrekord, from May 22 to October 23. Results showed that Bushehr had the best wind turbine performance, producing 1.35 × 109 W annually. Shahrekord was ideal for solar energy, reaching solar radiation levels of about 4540 kJ/m2hr in September and generating 6660 W of solar-heated water. Finally, by comparing the yearly yield, it was concluded that Bushehr had a higher yield than the other two cities due to its geographical location, which was 0.301. The results of this research indicated that Iran, with its sunny days and wind energy potential, will be a very suitable place for installing and operating the hot plate solar dryer system. Future studies should look at longer-term simulations, use real-time data, and consider cost-benefit analyses to improve system efficiency and applicability. [ABSTRACT FROM AUTHOR]

The drying kinetics and physical and chemical characteristics of Leucaena esculenta seed drying using a forced convection solar dryer are described. The drying kinetics behavior is examined for three experiments under climate conditions of three different winter days in central Mexico, observing significant effects related to the reported pH levels of the seeds with values of 6.34, 5.98, 5.97, 5.82, and 6.07. The airflow measurements inside the drying chamber were observed, including the geometric dimensions, color, appearance, weight, and moisture loss, and the effective diffusivity coefficient D e f f of Leucaena esculenta with values between 1.23 × 10−7 and 8.09 × 10−9  m 2 s . Solar drying, with the technology used in this study, is a viable alternative to give added value to Leucaena esculenta. This study can be the basis for developing alternatives to preserve seeds for animal and human consumption. [ABSTRACT FROM AUTHOR]

The aim of the current research is to dry apples using a solar dryer with a desiccant cycle in two modes: direct radiation -convection and indirect radiation -convection. Two types of drying methods, direct and indirect with desiccant and without desiccant, moisture content, and drying in open air were used. Pre - prepared apple slices (flavored with cinnamon) were placed on a specific -sized mesh, the initial weight of the samples was measured, and they were placed inside the solar dryer with a desiccant cycle in two modes: direct radiation -convection and indirect radiation -convection. During the drying process, the evaporation rate, texture, wrinkling, water reabsorption, vitamin C retention, color changes, and sensory characteristics at different treatment levels (30% sucrose and without sucrose, 0.5%, 1%, and 2% cinnamon) were examined. Additionally, several samples were dried as controls without cinnamon flavoring using the solar dryer. Data analysis was conducted using a completely randomized factorial design and the statistical software SPSS version 26. The results of the study showed that in both direct and indirect methods, with and without desiccant, the moisture removal rate in samples without sucrose was higher compared to samples with sucrose and cinnamon. Comparing control samples in both methods with and without desiccant moisture showed that the evaporation rate of samples with desiccant moisture was significantly higher. Furthermore, in samples with sucrose, the evaporation rate was lower in the desiccant method, and in direct sunlight drying, the drying rate was significantly lower compared to solar dryer drying. The results of evaporation rates in the indirect drying method also indicated that similar to the direct method, the evaporation rate of samples with cinnamon treatment and without sucrose was higher than that of samples with sucrose and controls. Tissue analysis results also indicated that the highest firmness was observed in the direct method without desiccant for samples without sucrose, with no significant difference in means. Cinnamon also increased the firmness in samples without desiccant moisture in the indirect drying method, and samples with sucrose had less wrinkling, with an increase in cinnamon concentration leading to more wrinkling, with the highest increase observed in the direct method without desiccant at 2% cinnamon and in the direct method with desiccant at 1% cinnamon concentration. The water reabsorption rate in both direct and indirect drying methods showed that samples with sucrose had better water reabsorption conditions, and the vitamin C degradation rate indicated that the use of sucrose improved vitamin C retention. Color change analysis also showed that samples with sucrose had more favorable conditions in both methods. Therefore, the results related to sensory evaluation characteristics indicated that samples with sucrose and different cinnamon concentrations received the highest sensory evaluation scores. Hence, it can be stated that samples dried with osmotic solution and sucrose generally had better acceptability in terms of physical appearance, color, taste, and flavor . [ABSTRACT FROM AUTHOR]

Evacuated tube solar collector (ETSC) has gained significant attention due to its high thermal efficiency and ability to harness solar energy more effectively as compared to flat plate solar collector. The present review analyzed the in-depth mechanism of analytical modeling of ETSC, different factors influencing the performance, and applications in drying of Agri-commodities. Evacuated tubes with and without heat pipes are used for air heating purposes. ETSC with tracking and non-tracking, selective coating techniques, and for reducing heat loss during drying operations are reported. The system performance is greatly influenced by the ETSC design, absorber coating, heat transfer fluid, mass flow rate of working fluid, inclination or tilt angle, collector size, and distance between tubes. Moreover, Computational fluid dynamic (CFD) simulations of the various ETSC-based drying systems were compiled to investigate their flow patterns, heat transfer characteristics, and overall system performance. This literature inherently provides the way for the development of evacuated tube-based innovative and sustainable solar dryers in small and industrial scale. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive review of the most significant and recent technologies that have been integrated with solar dryers, demonstrating a notable enhancement in the performance of solar dryers. The majority of review articles in this field that have been published have concentrated on the application of solar drying for food preservation in agricultural industries. Numerous researchers have found gaps at the component level and suggested different modifications to solar thermal collectors to enhance drying efficiency. Various technologies that have been created and put into use have effectively and efficiently optimized the energy requirements. Nevertheless, there are not many studies that concentrate on the possible integration strategies in different industries where drying is a crucial step in the production process. This study presents a comprehensive overview of the key drying processes used in different industries to provide readers a sense of the current status of existing technologies and the on-going research being done in the topic of sun drying. To develop innovative drying systems for large-scale enterprises that can be used to other industrial settings, it has been suggested that solar drying be integrated with the current drying techniques. This paper discusses how solar energy is used in the food sector, with a focus on solar air heaters and how they are integrated into solar drying processes. This will help industries and researchers make the drying process compatible with solar energy. This study also offers an alternative viewpoint by examining and contrasting solar dryers based on the many designs that are employed, as well as strategies to increase the solar dryer's efficiency, shorten its drying time, and improve its overall performance. Additionally, this study shows how various solar drying methods such as using gravel, sand, paraffin wax, etc. affect the rate at which moisture is removed based on sensible and latent heating. [ABSTRACT FROM AUTHOR]

A drying technique utilizing solar energy on shredded apples as raw material for apple infusion has a reduced emission risk while also producing high-quality drying products.This study aimed to determine the optimum semi-theoretical mathematical model for drying shredded apples after blanching and non-blanching treatments utilizing three simple mathematical models: Newton, Henderson, Pabis, and Page. The results showed that blanched shredded apples dried using the Convective Solar Drying (CSD) method had the highest rate of decrease in the moisture ratio compared to those dried in the open sun drying (OSD). The three semi-theoretical models examined can be used to forecast the rate of decline in the water content ratio of dry shaved apples in all treatment combinations, as demonstrated by a value of R2 more than 0.9. Based on a comparison of the validity of each semi-theoretical model utilized, Page's model is the best model for characterizing the drying kinetics of shredded apples for both blanching CSD, non-blanching CSD, blanching OSD, and non-blanching OSD drying. The information acquired will be important in selecting an appropriate apple pretreatment handle and drying model for shredded apples.

Cardamom, also known as the "Queen of Spices," is the world's oldest recognized spice with a high market value for its dried final product. In this work, the drying kinetics of small cardamom (cv. Njallani) has been studied using a solar and a heat pump dryer. Before drying, the produce was pre-treated in sodium carbonate (Na2CO3) at 1%, 2%, and 3%. The treated small cardamom samples are dried as a single and double layer at 40, 45, and 50 °C. The maximum temperature observed inside the solar dryer is 80 °C, resulting in a faster drying rate than the heat pump dryer but poor quality and greenness ((a*) − 0.8 to − 3.25) even after being pre-treated with Na2CO3. The heat pump dryer showed a constant and falling rate drying period at all the temperatures, with the highest drying rate at 50 °C. It required at least 12 h to dry the cardamom samples from 455.5 to 10.2% moisture content as a single layer. The temperature and the bed thickness have the maximum influence on the water activity of dried cardamom (0.54–0.64). A higher greenness value and essential oil percentage are obtained from the small cardamom dried in the heat pump dryer at 45 °C.The COP and SMER are found best at 50 °C. Four different models are used to predict the moisture ratio curve of the dried cardamom, with the quadratic model having the highest R2 value. [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]

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 dryers are solar thermal devices which increase the drying temperature and aid in moisture removal from the load, leading to faster drying of the agri-product as compared to the open sun drying. Conversion of grapes to raisins can be effectively achieved through solar dryers, and efforts are ongoing to improve the efficiency and further reduce the drying time. Usually in order to reduce the drying time for the conversion of grapes to raisins several pre-treatment methods with the use of chemicals are employed. In the present work pre-treatment in the form of blanching of grapes is adopted without the use of any chemicals to study the effect on the drying time in the solar dryer. The experimental results have been compared with the study of conversion of grapes to raisins with the same solar dryer without blanching. It is found that pre-treatment in the form of blanching resulted in a reduction in drying time to almost half. Experimental observations for the temperature profile studies relating to ambient temperature, air temperature inside the dryer, base plate temperature and solar radiation are presented in the form of graphs and calculations have been carried out for the estimation of drying rate and efficiency.

In this study, a solar dryer incorporating a flat plate heat exchanger to recover heat from exhaust air was investigated to explore the usability of different types of collectors in the system. Their usability was further evaluated through economic and environmental analyses. Moreover, the thermodynamic performance of the solar dryers was evaluated under two weather conditions in Nepal. Apple drying experiments were conducted for 8 h from 09:00 to 17:00 from February to April 2023 on solar dryers and with open sun drying (OSD) in Dhulikhel, Nepal. The results showed that the low emissivity (low-e) coated aluminum collector was more efficient in terms of collector efficiency and drying rate than collectors with flat or v-corrugated GI absorbers. The average collector efficiency and drying rate were found to be 89 % and 107 g/(h × m2) using the low-e coated aluminum collectors, while the values were 50 % and 84 g/(h × m2) for the GI sheet collector. The results indicated a slight improvement in the performance of v-corrugated collectors, with values of 53 % and 89 g/(h × m2). The drying rate for OSD was found to be 78 g/(h × m2), which was lower than for the dryers with all collectors used in this study. In terms of economic analysis, the dryer equipped with the low-e coated collector was found to be superior, with a payback time of 1.61 years compared to the dryers with flat or v-corrugated GI collectors. Reducing the thermal losses due to radiation by using the low-e coated absorber was shown to be more important than increasing the absorber area using v-corrugated GI sheets.

In line with the aim of drying food products of high quality in the shortest time and with the least energy consumption, 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. SMER, MER, and SEC values, 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, 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.

Traditional open sun drying methods face issues such as weather dependence, contamination risk, inconsistent drying rates, and nutrient loss. This study investigates a novel photovoltaic (PV)-integrated solar dryer designed to improve seaweed drying efficiency by effectively removing moisture content. Addressing the needs of Malaysian seaweed growers for a reliable and efficient drying method, this research compares conventional open sun drying with solar drying by evaluating key parameters such as moisture removal rate, drying rate, and dryer efficiency. Using a sample size of 100 grams, experimental results demonstrated that moisture loss was higher with solar drying, resulting in significantly lower final weights for Sargassum polycystum (43.8 g) and Cystoseira barbata (40.1 g) compared to open sun drying (55.81 g and 52.9 g, respectively). The drying rate for seaweed in the solar dryer was also higher, with Sargassum polycystum at 7.03 g/hr and Cystoseira barbata at 7.5 g/hr, compared to 5.52 g/hr and 5.89 g/hr for open sun drying. Additionally, the drying efficiency of the solar dryer outperformed open sun drying, with Sargassum polycystum achieving 9.52 % and Cystoseira barbata 10.13 %, compared to 7.4 % and 7.9 %, respectively, for open sun drying. Economic analysis revealed an estimated annual profit of USD 2270, indicating the economic viability of the proposed system. The findings suggest that the PV-integrated solar dryer offers a promising alternative to traditional drying methods, providing enhanced efficiency and economic benefits for seaweed farmers.

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]

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]

The world population is more than 8 billion and about 20-25 percent people does not have enough food to eat. It has been estimated that world as a whole more than 30-50 percent vegetables, fruits etc. are lost before it reaches to the consumers. To overcoming spoiling problems of vegetables and fruit; various preserving methods are used and renewable sources are best for this purpose by which we can save energy for preservation and keeping the product in their natural flavor by drying it. Drying is one of the oldest methods of preserving food. The solar drying system utilizes solar energy to heat air and to dry any food substance. It brings about a substantial reduction in weight, volume, minimizing packing, storage, and transportation costs, and enables storability of the product under ambient temperatures. This paper present the Construction of Continuous solar dryer which can be used for drying various fruits and vegetables products in rural areas under hygienic conditions. The Continues solar dryer was constructed consisting of a solar collector cum drying chamber. The overall dimension of the continues solar dryer is 1830x300x620mm and the drying chamber was painted black to absorb maximum solar radiations. The glass was covered, it permits the solar radiation into the system but resists flow of heat energy out of system and product were moving continually from inlet to outlet through chain conveyors. This chain conveyors was connected to the Rollers and the roller was connected to belt pully to reduction motor and VFD to control the chain conveyor from inlet to outlet to dry the product at required moisture content. [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]

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]

This study was aimed to investigate an air-flow distributer of a solar dryer. This study was contained two factors: First, the air outlet throttle (three angles, 30°, 60°, and 90°). Second, the design of the air inlet with three levels (new design (I2), without (I1), and half-opening air inlet gate of the new design (I3)). The results show significant effects on these parameters, where the highest efficiency (51.7%) was obtained at (I1) and (30°) angles. While the temperature changes between the inlet and outlet had a significant effect on the pressure difference, the pressure difference increased, reaching (1.65 Pa). Also, the drying rate was affected by the temperature and the amount of air entering the dryer. The highest drying rate gave (0.165 kg/h) when used the air discharge angle (30°) with the (I3), where this increased the temperatures of the air in the dryer reduced the air entering. [ABSTRACT FROM AUTHOR]

The assessment and enhancement of any drying system for optimal drying processes relies on critical parameters, namely moisture diffusivity and activation energy. In this study, medicinally beneficial kohlrabi of 40‐mm diameter and 6‐mm thickness samples were dried under three different drying methods, namely open sun drying (OSD), natural air‐circulation mode (NACM) single slope direct solar dryer (SSDSD), and forced air‐circulation mode (FACM) SSDSD. The experimental results showed that the drying chamber operating temperature and air velocity played significant roles in the moisture diffusion process and activation energy required to dry the kohlrabi sample. The FACM exhibited the highest average moisture diffusivity values at 7.29 × 10−10 m2/s, surpassing both NACM (5.65 × 10−10 m2/s) and OSD (3.28 × 10−10 m2/s). The activation energy needed for the drying process was the lowest in FACM at 27.44 kJ/mol, followed by NACM at 31.37 kJ/mol and OSD at 35.29 kJ/mol. This is due to the uniform temperature distribution and high airflow rate in the case of FACM. Additionally, 10 thin‐layer models were tested for all three experimental conditions. The statistical analysis showed that for OSD and NACM, the Midilli et al. model, and for FACM, the Page model was best suited for representing drying kinetics with lowest χ2 and root mean square error and highest R2 values. Furthermore, the energy and exergy assessment guaranteed an evaluation of the solar drying system's efficiency. Practical applications: This research provides valuable insights into optimizing solar drying methods for kohlrabi preservation. Understanding how temperature and air velocity influence moisture diffusivity and activation energy allows practitioners to enhance drying efficiency. Forced air‐circulation mode (FACM) single slope direct solar dryer (SSDSD) emerges superior, with higher moisture diffusivity and lower activation energy. The study also identifies appropriate drying kinetics models for each method, aiding the accurate prediction of drying behavior. Emphasizing efficiency, the research highlights FACM's superior thermal efficiency and natural air‐circulation mode's higher exergetic efficiency. These insights empower practitioners to make informed decisions, potentially improving agricultural product preservation, reducing energy consumption, and promoting sustainability. Moreover, the research's findings hold significant implications for industrial food processing and preservation applications, suggesting the direct implementation of optimized solar drying techniques in large‐scale settings for kohlrabi and similar agricultural products. [ABSTRACT FROM AUTHOR]

The paper proposes a solar collector with sensible heat storage materials for crop drying applications. The materials used were pebbles and gravels. The experiments were conducted under the meteorological conditions of Ujire, Karnataka, India. The bed thickness of pebbles and sand was 20 cm, and air velocity for pebbles and sand as absorbers was 4 m/s and 2 m/s. The experiments were started at 9 o'clock and stopped at 17 o'clock; for every one-hour interval, readings were recorded. Experimental and theoretical heat transfer analyses were carried out and the results were discussed with the help of characteristic curves. The collector with pebbles as absorber showed better performance than the collector with sand as absorber. This is due to surface roughness and higher Reynold's number. The maximum theoretical and experimental values of temperature resulted for pebbles were 344 K and 321 K, and for sand 334 K and 322 K, respectively. The average theoretical efficiency obtained with pebbles as absorber was 39%, and for sand 28.5%. The average value experimental efficiency with pebble as absorber was 25%, and for sand 11%. The developed collector system with pebbles and sand as absorber provides moderate temperature heat and is best suited for drying of crops. [ABSTRACT FROM AUTHOR]

In this study, a novel adaptive solar dryer with a coating of polymer-dispersed liquid crystals (PDLC) was designed, built, and characterized to evaluate its optical properties and thermal performance by modulating the transmission of solar radiation toward the drying chamber. PDLC films can electrically switch between opaque and transparent states, making them ideal for controlling solar radiation. Unlike conventional direct dryers, the proposed solar drying system takes advantage of direct solar radiation, known for its rapid drying process, while minimizing the impact on product properties. The results show that the PDLC coating exhibited a significant difference in transmittance between the “on” and “off” states under ambient conditions. At 400 nm, the transmittance varied by 20 %, increasing to 30 % at 450 nm. The solar dryer with dynamic control of solar irradiance constantly maintained a temperature range of 52.19 °C–57 °C. Lower relative humidity values were achieved compared to the uncontrolled solar dryer, resulting in a uniform irradiance distribution within the drying cabinet. The solar dryer with dynamic control of solar irradiance (acrylic and PDLC film) presents a total thermal resistance (0.02817 mK/W) exhibiting better heat permanence inside the drying cabinet compared to polycarbonate (one of the materials most used for drying systems). The system's thermal efficiency ensures reliable operation regardless of weather conditions, efficiently capturing and converting solar energy into heat.

Aloe Barbadensis Miller, commonly known as Aloe vera, has been widely used in different applications, such as medicinal treatments and cosmetic products. However, its transportation and handling present challenges due to oxidation and property loss caused by direct environmental exposure. A strategy to mitigate these effects is dehydration, where different industrial-scale methods such as freeze-drying, spraying, refractory windows, and convective drying can be applied. Despite their effectiveness, those dehydration techniques are both energetically and economically costly. Solar drying technology offers a cost-effective, lower-energy alternative addressing sustainability, socioeconomic, scientific progress, and integrated sustainable development challenges. Nevertheless, solar drying through direct sunlight exposure has been minimally explored for drying high-water-content products like Aloe vera, potentially due to the inherent challenges of drying under uncontrolled environmental conditions. In response, this paper introduces a methodology for pre-treating and pre-drying Aloe vera gel using a low-cost solar dryer prototype, achieving up to 50% water activity reduction in experimental tests under uncontrolled conditions in Colombia, South America. The proposed prototype features a drying cabinet with energy autonomy and forced convection. The experimental evaluation compares the quality of pre-dried Aloe vera gel with freeze-dried samples, demonstrating comparable attributes under favorable environmental conditions. The results demonstrate the feasibility of pre-drying Aloe vera gel within 13 to 48 h, with a maximum drying rate of 0.38 g/min. During this process, water activity decreased from an initial value of 0.975 to a final value ranging between 0.472 and 0.748. Furthermore, the quality of the dehydrated gel was assessed through color analysis, comparing it with a freeze-dried sample. Subsequent color analysis of the freeze-dried samples revealed minor changes in product quality compared to those dried using the proposed solar drying method. These results demonstrate the effectiveness of the proposed solar dryer in pre-dehydrating Aloe vera gel, yielding characteristics similar to those achieved through conventional methods. [ABSTRACT FROM AUTHOR]

Uneven drying is the key drawback of a conventional multi-tray dryer. Therefore, an improved active solar dryer with and without integrated sensible heat storage (SHS) was proposed. A unique feature of this dryer is its movable walls from the sides of the dryer to transform it to an indirect or mixed-mode as and when necessary. Garcinia Pedunculata (GP) is a local seasonal medicinal fruit in Northeast India. Drying kinetics of GP, the dryer performance and economic analysis of dryer were evaluated in the indirect solar dryer without SHS (Exp. I), mixed-mode solar dryer without SHS (Exp. II), indirect solar dryer with SHS (Exp. III), mixed-mode solar dryer with SHS (Exp. IV), and open sun drying (OSD). The dryer's average efficiencies were 18.12%, 22.37%, 21.74%, and 24.46% for Exp. I, Exp. II, Exp. III, and Exp. IV, respectively. The moisture content of GP was reduced to 12.09% in wet basis (w.b.) from 87.99% (w.b.). The overall drying time for Exp. I, Exp. II, OSD, Exp. III and Exp. IV were 31, 26, 53, 28, and 10 h, respectively. From the eleven drying models, the Two-Term model was the best-fitted model for Exp. I, Exp. II, OSD and Exp. III, and Midilli and Kucuk model was for Exp. IV. The final product's fragrance and colour are better for Exp. IV. Developing this dryer for Exp. I, Exp. II, Exp. III and Exp. IV, the price required was around 25,000, 27,000, 26,000, and 28,000 INR (1 US$ = 74.57 INR), respectively, while the economic payback periods are 1.6 years, 0.9 year, 1.4 years, and 0.59 year, respectively. [ABSTRACT FROM AUTHOR]

Open sun drying is the predominant process used for food preservation by smallholder and subsistence farmers (SHSFs), and their families, globally constituting about 2 billion people on about 475 million farms. The major problems with this process are the slow, unreliable speed of completion, rain-caused loss of vital food sources, risks from mycotoxin accumulation, environmental contamination, and loss of nutritional quality. SHSFs represent the poorest and least educated human demographic, whose survival is largely ignored by Governments, untouched by international aid programs, and with limited access to basic utilities. Solar drying systems can greatly improve the preservation of safe and nutritious food, but current systems deployed put this technology beyond the reach of the demographic which needs it most. Here, our objective was to develop the technology for the simplest low-cost drying system, which would minimize all risk factors, particularly eliminate mycotoxin accumulation, and which could be practically deployed by SHSFs. [ABSTRACT FROM AUTHOR]

Drying is one of the crucial processes in agricultural production, especially in grain processing. The drying process can improve grain quality and affect the grain content. However, maintaining the temperature is a challenge in the drying process. Because it can influence the drying performance and produce a low-efficiency reduction of water content, in this study, the hybrid drying system is proposed to improve the performance of the forced convection dryer system. The proposed system used a proportional integral and derivative (PID) control system to obtain the optimal temperature. The proposed system was compared with natural drying and forced convection methods. The experimental result showed that the proposed system performed excellently for three performance evaluations. The average temperature was obtained as the highest of the other methods, with 54.68 °C and 54.55 °C for coffee and cocoa beans. The water content can be reduced by an average of 27.38% and 42.67% for coffee and cocoa beans. Then, the proposed system also had the highest reduction efficiency of water content than the other methods, with 62.71% and 36.94% reductions for coffee and cocoa beans, respectively. The results indicate that the proposed hybrid system performs better than the other methods. [ABSTRACT FROM AUTHOR]

The present work presents the effective application of waste heat rejected from window air conditioning (AC) in a waste heat dryer (WHD) for drying plantain banana slices. The comparison between drying with the waste heat dryer coupled with an AC unit (ACWHD) and a natural convective indirect solar dryer (SD) reveals significant differences in drying kinetics, supply air conditions, and thermodynamic performance. The drying kinetics of banana slices obtained with ACWHD and SD were validated by revisiting the concepts of dryer performance index (DPI) and generalized drying curve. The temperature of the hot air supplied to the drying chamber in ACWHD was 48 °C while the relative humidity of the supply air was below 30 %. The thermodynamic performance assessment revealed that the exergetic efficiency was about 45 % and 16 % for ACWHD and SD respectively. The results of exergy based sustainable index and environment impact factor indicated the potential application of the waste heat of residual air from AC units for drying applications. Thus, the results of the present study imply that this novel idea has appreciable potential for commercialization with large-scale central air conditioning units in commercial complexes and industries where the magnitude of heat rejection will be multi-fold.

Drying assumes a pivotal role in the preservation of high-moisture products over extended durations. Despite the widespread utilization of solar dryers owing to their energy-efficient nature, they are often plagued by prolonged drying durations, subsequently impacting the quantity of dried products. This investigation endeavors to introduce an innovative technique aimed at augmenting the efficacy of solar drying processes. Specifically, the study integrates forced convection solar drying with electrohydrodynamic (EHD) drying. The experimentation entails the drying of pineapple slices conducted between December 2023 and January 2024 in Nakorn Pathom, Thailand. The pineapple slices, featuring a ring-shaped geometry, are subjected to varying corona voltages ranging from 7 to 10 kV. The findings reveal a direct correlation between the corona voltage and the diffusion coefficient of the pineapple slices, wherein an escalation in corona voltage leads to an elevation in the diffusion coefficient, consequently resulting in a reduction of moisture ratio during the drying process. Consequently, the novel drying approach exhibits superior efficiency compared to traditional solar drying techniques, particularly as corona voltages increase. Moreover, the study employs Buckingham-Pi terms to predict the fluctuations in the diffusion coefficient, yielding a diffusion coefficient function with an R2 value of 0.996. Subsequently, a novel kinetics model for the drying process is proposed, boasting an average R2 value of 0.98. This model is envisioned to serve as a vital tool for enhancing and advancing forced convection solar-EHD dryers in forthcoming industrial applications.

This research presents the prediction of temperatures in the chamber of a solar dryer using artificial neural networks (ANN). The dryer is a forced-flow type and indirect. Climatic conditions, temperatures, airflow, and geometric parameters were considered to build the ANN model. The model was a feed-forward network trained using a backpropagation algorithm and Levenberg–Marquardt optimization. The configuration of the optimal neural network to carry out the verification and validation processes was nine neurons in the input layer, one in the output layer, and two hidden layers of thirteen and twelve neurons each (9-13-12-1). The percentage error of the predictive model was below 1%. The predictive model has been successfully tested, achieving a predictor with good capabilities. This consistency is reflected in the relative error between the predicted and experimental temperatures. The error is below 0.25% for the model’s verification and validation. Moreover, this model could be the basis for developing a powerful real-time operation optimization tool and the optimal design for indirect solar dryers to reduce cost and time in food-drying processes.

Novel thermal characteristics of drying banana slices in an indirect dryer are presented for four different experimental drying conditions in the forced convection mode. The novel characteristics include measuring the airflow velocity in the drying chamber, measuring the thermal profiles in different trays comprehensively and measuring the relative humidity under different conditions. Two tests are carried for 16 h in two consecutive days (8 h per day for each test). The first test is on acloudy day followed by a sunny day, while the second test is carried out on two consecutive sunny days. Tests 3 and 4 are 24 h tests with high (0.23 m/s) and low (0.11 m/s) average drying chamber airflow velocities under good solar radiation conditions. The maximum temperatures obtained in the collector and the drying chamber are around 80 and 48 °C, respectively, for the 16 h tests. Significantly lower collector and drying chamber temperatures are obtained due to cloudy conditions. Maximum collector temperatures are around 84 and 95 °C for the high and low average airflow chamber velocities for the 24 h tests. The corresponding maximum temperatures in the drying chamber are around 50 °C for the 24 tests. The final moisture ratios are 0.26 (cloudy and sunny days) and 0.20 (two sunny days), respectively, for the 16 h tests. These final moisture ratios are lower than those obtained for the 24 h tests which are 0.32 and 0.28, respectively. Increasing the drying chamber airflow velocity results in faster moisture removal during sunshine hours for the 24 h tests. For tests 1, 2, 3 and 4, the maximum average collector efficiencies during the sunshine period are around 60, 80, 40 and 10 %, respectively. The average drying efficiencies for the total solar drying period for tests 1,2,3 and 4 on day 1 are 6.9, 6.9, 5.5 and 5.7 % respectively. These values are comparable, suggesting that the average collector powers, airflow velocities and efficiencies have a very small effect on the average solar drying efficiency for the whole drying period. The quality of the bananas slices mainly in terms of the colour and shape is also compared with previous studies and commercially available products. A reasonably acceptable quality product is obtained.

Drying is the process of moisture removal which is applied to many foodstuffs including fruits and vegetables for preservation and storage purposes. Since solar energy is one type of environmentally friendly renewable energy, open-type solar dryers, natural convective type solar dryers and greenhouse type solar dryers were designed and fabricated in this study for the preservation of fruits and vegetables. A comparative study among various solar drying methods was performed to study the drying performance by maintaining the quality and texture of the dried foodstuffs. Factors such as solar radiation, ambient temperature, moisture in the air, materials used for glazing, inclination, etc., were considered during the fabrication of the solar dryer so that a better estimate of the performance of the solar dryer could be obtained. The lowest drying rate was observed when convective drying was used as an indirect mode of heating. The maximum drying rate observed in open drying was 0.088 kg/kgh, whereas in convective drying under the same conditions, it was 0.03 kg/kgh, which was almost 65% less. This in turn also resulted in the dried samples displaying a better texture and better color. The shrinkage effect on the samples was less pronounced for those samples in the convective dryer than it was for those in the open and greenhouse dryers, as the method uses indirect drying. Comparing convective and greenhouse drying, more shrinkage and a greater browning effect were observed for the open drying method. Out of three types of solar dryers, the greenhouse dryer was selected to study thermal performance because of its better drying rate. DHT11 sensors controlled through Arduino programming were employed in this study to record the temperature and moisture at various locations in the greenhouse dryer setup. The range of energy efficiency of the greenhouse solar dryer was estimated to be from around 15% to 25% on average. This might be due to a greater extent of energy losses. No significant difference was observed in the energy efficiency with respect to the samples used for drying. [ABSTRACT FROM AUTHOR]

The preservation of perishable foods through their transformation is always a major challenge for producers. Several methods are applied for this purpose, and progresses are recorded by improving these processes or by finding new means. In our work, the method of dehydration and natural drying of tomatoes using a natural dryer with indirect solar energy with air circulation by extractor is used to describe and then predict the process of obtaining the finished product in the form of tiny dried fragments or powder. This is the novelty of this research, which uses the unconventional design of experiments. This consists of finding a mathematical model based on the interaction of 3 parameters that interact with each other, namely the trays temperature, the drying speed and the relative humidity in the solar dryer. The interference of the values of one of these 3 parameters on the 2 other parameters acts directly on the result of the drying process. The matrix treatment of the data of several carried out experiments in the resolution of 13 equations gives us the required responses and permits us to draw the graphs, the contours and the responses surfaces that access us to a more detailed analysis. [ABSTRACT FROM AUTHOR]