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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]

Solar dryers are equipped with photovoltaic panels to increase energy efficiency, profitability and independency on nonrenewable energy. Also, these dryers need to be assessed from economic, environmental, and energy-exergy perspectives to determine whether the devices are cost-effective and feasible on a large scale. This study has performed energy, exergy, economic, and environmental evaluations on the newest solar dryers equipped with photovoltaic panels and photovoltaic thermal collectors. In this regard, solar dryers with hot air collectors, concentrating solar dryers, photovoltaic thermal dryers, infrared, greenhouse, and heat pump solar dryers equipped with photovoltaic panels and photovoltaic thermal collectors were investigated. Then, studied dryers were categorized. Initially, this classification was carried out regarding the dried products and subsequently, their economic-environmental and energy-exergy were compared. Despite the short drying time of infrared and heat pump solar dryers, these dryers' construction and energy costs are relatively high. Comparatively to other solar dryers, concentrating solar dryers have high energy efficiency and short drying times. [ABSTRACT FROM AUTHOR]

In the present analysis, a novel four-mode solar dryer was developed and tested for the drying of Garcinia pedunculata. The four combinations considered were indirect-mode solar dryer without storage (ID-WOS), mixed-mode solar dryer without storage (MX-WOS), indirect-mode solar dryer with storage (ID-WS), and mixed-mode solar dryer with storage (MX-WS). The feature of this dryer that sets it apart is its capability to convert the drying cabinet into various modes simply by sliding the walls of the four sides of the cabinet. The storage system is made space efficient, by filling the gravel up to the surface of the absorber plate inside the solar air collector. For ID-WOS, MX-WOS, ID-WS, and MX-WS, respectively, the drying durations were 30 h, 25 h, 28 h, and 8 h, and the drying efficiencies were 18.55%, 24.03%, 20.32%, and 29.94%. In ID-WOS, MX-WOS, ID-WS, and MX-WS, the average exergy efficiency was determined as 47.08%, 65.10%, 52.46%, and 68.07%, respectively. Environmental impact was studied for all four cases. The energy payback periods for ID-WOS, MX-WOS, ID-WS, and MX-WS were 1.47, 1.61, 1.48, and 1.62 years, respectively. The study indicated that MX-WS outperformed the other three configurations in all aspects. [ABSTRACT FROM AUTHOR]

In this research, a closed-flow solar dehydrator with a refrigeration moisture extraction system was evaluated, likewise, the dehydration temperature time was optimized by evaluating three types of heat transfer fluids. The dehydration equipment included devices to absorb thermal energy from incident sunlight, such as a trombe wall and a parabolic cylindrical collector, and a thermo bank system. In addition, the influence of three types of heat transfer fluids (water, oil and oil nanofluid + silver nanoparticles) was evaluated. This dehydration system was applied to process the Pouteria lucuma fruit. The results indicate the reduction of the dehydration time by 58.19% using nanofluid. This treatment prevents the modification of the physicochemical properties of the product and helps preserving its organoleptic properties. [ABSTRACT FROM AUTHOR]

Typical fuel-driven commercial dryers have excellent efficiency with homogeneous high-quality output, but they are beyond the access of farmers with limited agro land and financial resources. In this study, drying trials with potato slices were carried out utilizing a laboratory scale built drier coupled with an unique solar air heater. Assuming the set-up as mixed mode type solar dryer, performance of the dryer during the drying of potato slices was studied and the results were compared with that of open sun drying (OSD). The novel two pass solar air heater used in this project has aluminum turbulators arranged in staggered fashion. The absorber plate with aluminium turbulators present inside the double pass solar air heater reached a maximum temperature of 68°C. The average efficiency of the novel solar heater was about 72%. The moisture content of potato was reduced to 18.23% in 8 hours from 82.15%. The maximum thermal efficiency of the dryer was determined as 34%.The average specific energy requirement was estimated as 1.61 kWhkg−1 and the shrinkage ratio was found to be 0.2 at the end of 7 hours. [ABSTRACT FROM AUTHOR]

A research program was undertaken with the goal of developing dehumidifier solar wood dryers and wood thermal phytosanitary treatment cells. The first step of the program, was dedicated to the development of the numerical tools that would assist in the design and optimization of the dryers. These were based on an approach that combines micro (at the level of the wood board) and macro (at the level of the entire dryer and its solar heating system) modellings, and that uses typical year weather data, to perform the simulations. A finite difference numerical code was employed to predict the time evolution of the wood and air properties during the thermal phytosanitary treatment of wood. These predictions are employed as input to the TRNSYS© software to model the retained solar phytosanitary treatment installation configuration. In this system, the air leaving the treatment cell is recycled. But prior to injecting it back, it is mixed, in the right proportions, with outside air in order to adjust its humidity. The recycled air temperature is then risen to the operating value in an air-water heat exchanger fed from the storage tank of the solar water loop. The latter includes solar evacuated collectors, two pumps, a storage tank and a heat exchanger. The concept technical feasibility was prooved. The sytem optimization showed that, for a cell to be installed in Tunis, a 22 m2 evacuated tube collector and a 1.5 m3 water reservoir are needed for the treatment of 1 m3 wood stack i.e. 0.7 m3 of wood (reduced to 0.42 m3 in the winter season). A prototype of the optimized system was constructed and preliminary experimental tests are presented. [ABSTRACT FROM AUTHOR]

Solar air heaters are low-cost, simple structure, reliable, and high energy conversion efficiency devices to produce hot air for drying applications. In this study, an infrared film-assisted double pass solar air heater has been developed, manufactured, and tested for a sustainable drying process. The main contribution of this research is the supply of heat energy to continue the drying process even when solar radiation is insufficient. The experiments were carried out in three different weather conditions depending on solar radiation and grape pomace was chosen as the drying product. According to the obtained results, the average thermal efficiency of the solar air heater was determined as 76.4% for the experiment under high solar intensity, 64.1% for the experiment under medium solar intensity, and 45.63% for the experiment under low intensity. The effective moisture diffusivity values and the mass transfer coefficient were calculated in the range of 5.70 × 10−12 to 2.39 × 10−10 m2/s and 1.52 × 10−9 to 1.94 × 10−7 m/s, respectively. In the experiment that was conducted on high solar intensity, where 69% of heat energy was provided from solar energy, the product dried in 110 min. In the experiment carried out on a day when the solar radiation was insufficient, it was observed that the product dried in 220 min and the heat energy from solar energy decreased to 21% and the energy rate consumed by infrared film increased to 61%. [ABSTRACT FROM AUTHOR]

In this study, a novel modular solar dryer unit which is made up of corrugated plates and a glass glazing has been investigated. The developed dryer was integrated with a solar air heater and experimented in mixed-mode operation for crop drying in Northern Cyprus. Average drying rate and drying efficiencies for apple, banana, chili pepper, and grapes were found as 30.2, 82, 67.8, and 98 g/h and 38.1%, 43.84%, 40.03%, and 42.12%, respectively. Average temperatures across the dryer were also measured as 43°C, 47°C, 48°C, and 44°C for the same order of materials. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on a natural convection indirect mode solar dryer with phase change material (PCM) for drying of banana slices. The drying system consists of one collector with PCM and a drying chamber with two equally spaced trays. The paraffin wax was used as PCM in the dryer which release latent and sensible heat after sunset that make dryer operate effectively for the next 5 h. For the experimental investigations, 400 g of banana slices were dried from 73.2% (wb) to 20% (wb) of moisture content in 18 h (13 h day time operation + 5 h PCM) during April 2018 at Gorakhpur, Uttar Pradesh, India. Fourteen thin layer models for drying of banana slices, available in the either empirical or non-empirical form, were fitted using experimental data. A statistical analysis software, XL-stat was used to evaluate the values of constants of models and errors through non-linear regression analysis. Modified Henderson and Pabis model was found best suitable for the drying behavior of banana slices among all the models of thin-layer drying characteristics. The average drying rate for the lower tray and upper tray were 0.1316 and 0.1310 kg of water/kg of dried product/h respectively. The moisture content was reduced at a faster rate for the lower tray with moisture ratio from 100 to 28%. The maximum and average dryer efficiency were 9.88 and 2.98%, respectively, and the maximum and average collector efficiency were 85.46 and 66.32% respectively. This study showed that indirect type solar dryer with paraffin wax is suitable for drying of banana because it takes considerable time for drying and can be used for drying of other agricultural crops. [ABSTRACT FROM AUTHOR]

The technical performance and economic analysis of a developed hybrid solar-electric dryer (HSED) were investigated in this research work with respect to energy, exergy, and environmental sustainability. Experimental investigations were performed with and without load during the rainy season, in which the sunshine periods were affected by intertropical discontinuity, prompted by cold-prevalent wind interference from the Atlantic Ocean and regional water catchment. Thermal characteristics and drying efficiency of the hybrid dryer, as well as the effect of different drying temperatures (50, 60, and 70°C), air velocities (0.5, 1.0, and 1.5 ms−1), and sample thicknesses (10, 15, and 20 mm) on the overall and specific energy usage for 1,500 g batch size of fresh sliced tomato samples, were investigated. The percent energy contributions of the solar and electric heat units at varying air velocities were also determined. Results obtained indicate that the mean solar collector efficiencies during sunshine hours ranged between 24.6 and 70.3%. The total and specific energy consumption of tomato slices (Lycopersicon esculentum) varied between 5.61–120.31 kJh and 5.18–167.59 kJhg−1, respectively. Analysis of variance results show that drying air temperature, sample thickness, and velocity of air were significant at P > 0.05. The percent energy contribution by solar and electric heat units varied between 44.57–56.24% and 43.76–55.43%, respectively. Drying time and drying efficiency ranged between 130 ± 7 and 330 ± 5 min and 4.33–36.38%, respectively. The average energy efficiency of the hybrid system increased from 15.67 to 38.17%, whereas the mean exergy efficiency varied between 32.2 and 87.9%. The sustainability indicators such as ratio of waste exergy, sustainability index, and improvement potential of the HSED ranged from 0.083 to 0.158, 1.93–6.77, and 0.099–0.289 kJs−1, respectively. Optimum drying conditions for improved final quality were given. The economic analysis established that the HSED could save up to $1,490.33 per annum with a low payback period (0.72 years), thus making the dryer cost effective and economically viable. Prospects for improvement and future works were highlighted. [ABSTRACT FROM AUTHOR]

The present work evaluates the thermal performance of direct, indirect, and mixed mode passive solar dryers under no load condition in terms of efficiency and convective heat transfer coefficient between absorber plate and moving air (hc,p-a). The temperature measurements of various components of the collector and drying chamber of solar dryers were monitored at regular time intervals throughout the experimental period. Based on the energy balance equations of different parts of the dryer and experimentally observed temperatures, the hc,p-a was determined. The no load efficiency was found to be 31.40%, 27.55%, and 41.43% in direct, indirect, and mixed mode solar dryers, respectively. The efficiency was observed to be a function of temperature difference between absorber plate and air and the radiation intensity. The average values of hc,p-a was found to be 16.31, 14.92, and 23.81 W/m2°C in direct, indirect, and mixed mode solar dryers, respectively. Finite element (FE) model was developed using COMSOL Multiphysics software to study the temperature distribution of air inside the solar dryers. The lower values of statistical errors indicated a close agreement between the experimental and predicted air temperature inside the dryers. [ABSTRACT FROM AUTHOR]

Solar energy has great potential as an alternative energy source, but variations in solar radiation require the use of additional energy sources to maintain a continuous drying process. We developed a process for drying kiwifruit using a solar dryer and an energy accumulation system with paraffin wax as phase change material. The final moisture content, total polyphenols, and antioxidant capacity were evaluated and compared with freeze drying. The analyzed experimental factors were kiwi slice thickness and the use or nonuse of fuzzy logic control systems to regulate the air flow through the devices. Critical moisture content, shrinkage, solar panel, and solar energy accumulator efficiencies were calculated. In addition, five empirical models were fitted to the drying curves. The solar panel showed an efficiency between 56 and 76%. The use of the fuzzy logic control system extended the period of available energy, thus prolonging the use of the solar panel and solar energy accumulator and using only 10% of the stored energy; otherwise, without the control system, 43% of the stored energy was used. The highest drying rates were achieved for kiwifruit slices 4 mm thick, using the solar dryer with the control system. The loss of polyphenols and antioxidant capacity were minimal for kiwifruit slices of thickness 8 mm without the control system. [ABSTRACT FROM AUTHOR]

A computational fluid dynamics model was developed to simulate the corn drying process in a solar cabinet dryer. Incident solar radiation was modeled using a dual-band spectrum to simulate the absorption of shortwave radiation by corn and account for the greenhouse effect caused by glazing materials. The performance of the dryer was simulated at fair and overcast weather conditions. The model allowed visualization of temperature, humidity, and air velocity profiles in the dryer. The model was validated with experimental results, which showed an overprediction of temperature (8.5%) and humidity (21.4%). The experimental humidity profile suggests that there was stagnation in the airflow of the dryer, which was accurately predicted by the model. The model was used to simulate the dryer’s performance under overcast conditions, and the predicted moisture removal was 32% less than the simulated fair-weather case. [ABSTRACT FROM AUTHOR]

The design of so-called “ventilated tunnel solar dryers" is presented in this work under theoretical and practical aspects. These dryers consist in a tunnel with a black floor and a plastic top, ventilated with fans supplied by a photovoltaic module. Along this tunnel, the air first passes through a heating part, which is product free and where the air is heated due to greenhouse effect. It then enters the second part of the dryer, the drying part, where the products to dry are spread. A rational and general design procedure based on the solving of energy and mass balance equations is developed and followed. This procedure allows designing the ventilation system and calculating the lengths of the heating and the drying parts of a dryer according to a scope statement and to design conditions insuring an efficient and homogeneous drying. Two dryers were designed, built and operated, in the frame of two development aid programs, in Cambodia and in Uganda. The fieldwork highlighted the importance of practical building and operating aspects, reported in the present paper, and of including people of the local communities in these programs. Results of field drying experiments are shown and demonstrate the validity of the design procedure. In particular, the validity of the energy balance equations at the basis of the procedure is demonstrated. [ABSTRACT FROM AUTHOR]

Drying of agricultural food products is one of the most attractive and cost-effective applications of solar energy. The solar dryer is less reliable due to the intermittent nature of solar energy. This shortcoming can be overcome to some extent by storing solar energy. Information on sensible and latent heat storage materials and systems is spread widely in the literature. In this paper, we try to gather information about the previous and current research works in the field of thermal energy storage technology for solar air heater and dryer. The relative studies are classified on the basis of the type of storage material used in solar dryers, i.e. phase change material (PCM), rock, water, etc. Several designs of solar dryers with different heat storage materials were proposed by researchers. Recent studies focused on PCMs such as Paraffin and salt hydrate, due to their high heat storage capacity per unit volume. [ABSTRACT FROM AUTHOR]

Solar-biomass hybrid dryer systems use biomass burners as the backup source of heat to warm the air prior to charging it in the drying chamber. The flue gas produced from biomass combustion has a considerable amount of heat and is exhausted into the ambient. This article presents a new approach that uses the cogeneration (Co-Gen) technique in utilizing the flue gas exhausts from the burner. This approach enhances the circulation of warm air in the drying chamber and eliminates the need for an extraction fan. The exhaust flue is simply injected inside the chimney at the upper part to increase the natural stack effect caused by the rise in temperature and reduction in pressure. This technique is investigated experimentally; the dryer is tested with and without Co-Gen by drying red chili. The system efficiency of the biomass mode using Co-Gen is enhanced by 6%. In addition to enhanced efficiency, the main advantage of this approach is the elimination of electricity, given that the Co-Gen replaces the electrical extractor. This advantage renders the hybrid solar drying applicable in rural areas. [ABSTRACT FROM PUBLISHER]

There are many solar dryers for drying agricultural produce. This article explains the drying methodology and the thermal efficiency of the solar dryer with the bed tilted to a certain angle and oscillated at a particular frequency while drying non-parboiled paddy grains. The oscillating bed solar dryer dried 36 kg of non-parboiled paddy grains in just a day to the required level of moisture content, and the average moisture present in the dried grains was 13.56%. The average dryer thermal efficiency was 26.3%. The specific moisture extraction rate was 1.11 kg/kWh. [ABSTRACT FROM PUBLISHER]

A natural circulation solar dryer for drying products in the form of powder has been developed. It is of modular design and aperture area of one module is 3.34 m2. A new concept of moveable glazing has been introduced for ease in loading and unloading. Air entering the dryer moves in a zig-zag path as it flows over the product and under each tray before leaving from the top. There is a provision to dry the product under shade. Also, the dryer can be dismantled and stored in a room during off-season. The dryer was tested to dry Di-calcium phosphate (DCP) at Ludhiana (31°N). The average drying efficiency for a batch was found to be 54.0%. The cost of drying DCP using this solar dryer was 0.56 Rupees per kg of dried DCP as compared to 1.94 Rupees per kg of dried DCP for a wood-fueled industrial dryer. In comparison to a solar tunnel dryer for DCP drying, the initial investment per kilogram of the dried DCP, floor area per kilogram of wet DCP, and cost of drying per kilogram of dried DCP for this dryer was reduced by 7.1%, 67.2%, and 16.4% respectively. [ABSTRACT FROM PUBLISHER]

Different methods for the drying of pears, namely a solar stove, a solar dryer, and a tunnel dryer, were studied. All processes were conducted in three consecutive years to analyze if the behavior of each drying method showed evidence of a similar pattern, along with producing products similar to the traditional pears that are dried using direct sun exposure. The results showed that all methods led to a considerable reduction in drying time as compared to open-sun drying. Indeed, the drying time for the solar stove and the solar dryer showed a reduction of more than 40% while in the drying tunnel this reduction increased to more than 60%. In addition, it was also possible to conclude that the properties of the dried pears obtained by the three processes correspond to dried fruits similar to the traditional dried pears. [ABSTRACT FROM AUTHOR]

The novel low-cost band thermodynamic dryer equipped with a solar collector, a parabolic focusing collector, a heat exchanger, screw fan, and a drying cabinet with a band was designed and tested. The maximum temperature in the solar collector reached 85°C, which was 55°C above the ambient temperature. The required drying time was 4.5 h, much reduced from the traditional solar drying time of 48 h. The final moisture content of the Roselle calyx was 12% w.b., which is the recommended storage moisture content. Measurements of ambient temperature and humidity, air temperature, and relative humidity inside the dryer as well as solids moisture loss-in-weight data are employed as a means to study the performance of the dryer. Solar drying was compared with conventional sun drying and heated air drying, using the following evaluation criteria: drying time, dried Roselle color, texture, taste, and production cost. For evaluation, a model-based Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) methodology was used. After the evaluation, the proposed continuous solar dryer was found to be better than conventional drying and heated air drying due to slower drying rate and better quality of the dried Roselle. [ABSTRACT FROM AUTHOR]

A prototype of a hybrid solar dryer was developed for drying of tomato. It consists of a flat-plate concentrating collector, heat storage with auxiliary heating unit, and drying unit. It has a loading capacity of 20 kg of fresh half-cut tomato. The dryer was tested in different weather and operating conditions. The performance of the dryer was compared with an open sun-drying method. Drying performance was evaluated in terms of drying rate, color, ascorbic acid, lycopene, and total flavonoids. Tomato halves were pretreated with UV radiation, acetic acid, citric acid, ascorbic acid, sodium metabisulphite, and sodium chloride. Sodium metabisulphite (8 g L-1) was found to be effective to prevent the microbial growth at lower temperature (45°C). [ABSTRACT FROM AUTHOR]

Solar energy technologies offer a clean, renewable and domestic energy source, and are essential components of a sustainable energy future. Turkey lays in a sunny belt between 36° and 42° N latitudes and is geographically well situated with respect to solar energy potential. The objective of the present study is to investigate many aspects of solar energy applications in Turkey, giving the brief historical development and Turkey's solar energy potential and consumption. The following applications were taken into consideration: solar water heating, steam generation, solar cooker, solar drying, solar houses, and photovoltaics (PVs). In the early 1960s, solar energy was realized as an alternative energy in Turkey, while in the mid-1970s, solar thermal utilization technologies began gaining the high attention of universities, the government and, the industry, and have been developed at an increasing speed. Residential and industrial consumption of solar energy in Turkey started in 1986 and 1988, respectively. Solar energy use accounted for 129 kilo tons of oil equivalent (ktoe) in 2000 and is projected to be 431 ktoe and 828 ktoe in 2010 and 2020, respectively. Among all the above solar thermal utilization methods, the solar water heating has been, and will still have, the greatest emphasis in Turkey, reaching a total annual production capacity of 1,000,000 m². Recently, the number of the PV installations has significantly increased and Turkey's total PV installed capacity is expected to be 3 MWp in 2010. [ABSTRACT FROM AUTHOR]

The paper deals with sorption isotherms and drying kinetics of Eucalyptus globulus. The sorption isotherms have been determined using a static gravimetric method and then fitted by GAB equation at T = 30, 40, and 50°C over a range of relative humidity from 0.05 to 0.9. The drying kinetics in a solar dryer with an auxiliary heating system are determined. The results show with good reproducibility that temperature is the main factor in controlling the drying rate. The drying rate equation is determined empirically from the characteristic curve of drying. [ABSTRACT FROM AUTHOR]

Prototypes of greenhouse effect GHE solar dryer have been tested and their technical performances for drying of tropical products have been obtained. Quality of the dried products was comparable to the existing standard used in estate plantation. The latest drying experiment with fermented cocoa beans using mechanical stirrer, and with a stationary rectangular bin for coffee berries, showed that the developed drying system was capable of reducing the total specific energy to 6.2 MJ/kg and 5.2 MJ/kg water evaporated, respectively. Therefore, the results of the study suggest that the current design could now be used in helping the farmers and fishermen to produce better quality products. [ABSTRACT FROM AUTHOR]