A Comprehensive Review of Design and Technological Advancements across Various Types of Solar Dryers

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

Optimizing Solar Drying: A Critical Review of Shapes, Orientation, and Future Prospects for Hybrid Solar Dryers

This comprehensive review focuses on the performance of solar dryers, with a specific emphasis on their structural shape and orientation. Researchers have extensively examined these design parameters, often employing Computational Fluid Dynamics (CFD) to assess thermal attributes and predict temperature distribution, airflow patterns, and temperature profiles within the structures. Geographical location significantly influences solar dryer shape preferences, with the parabolic shape finding favor in tropical regions for its superior solar radiation capture and storm resistance, while even-span and Quonset shapes are popular elsewhere. Solar dryer orientation is another crucial factor, with east-west alignment consistently proving optimal due to its ability to maximize year-round solar radiation absorption and, consequently, enhance drying efficiency. Economic considerations, however, fall beyond the scope of this review, which predominantly focuses on thermal aspects. This investigation reveals diverse global preferences for solar dryer shapes and orientation, highlighting the necessity of considering geographical factors in design choices. While CFD and shape/orientation dynamics have provided valuable insights, there remains room for future research to expand into transient state simulations under various conditions, contributing to a more comprehensive understanding of solar dryer performance. Such insights promise to promote sustainable and efficient drying processes, benefitting agricultural and drying applications across the globe.

Sustainability assessment of solar drying systems:a comparative life-cycle analysis of phase-change material-based vs.cylindrical solar dryers

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

Experimental Study and Thermal Modelling of Cocoa Shell Convective Drying in an Indirect Solar Dryer

The concern of the present work is the convective drying of empty cocoa shells in an indirect solar dryer. Some drying experiments, using one sample, were carried out. During the experiments, the sample is introduced in the drying chamber. Then at steady time intervals, the sample is withdrawn from the drying chamber, for a rapid weighing. After each weighing, the sample is reintroduced in the dryer. At each time interval, the ambient temperature of the drying chamber and its relative humidity γ are measured by a thermo-hygrometer. From the experimental data, a theoretical determination of the moisture evaporated from the product was performed and a good agreement was found between the theoretical and experimental values, confirmed by the value of the RMSE. Those calculations used the constants in the Nusselt number found in literature. Then those constants were evaluated again, to get new values more suitable with the experimental data. The dimensionless numbers of Nusselt, Grashof and Prandtl were calculated. That allowed the calculation of the average value of the Nusselt number. The average convective heat transfer coefficient was determined.

Some construction parameters of unglazed perforated solar dryers for medicinal plants

Erecting solar dryers for medicinal plants require the best design option to suit such plants.Investigations were carried out on some design parameters of the unglazed perforated solar dryers under the prevailing weather conditions of Ismailia,Egypt.Effects of different parameters on the heat exchange effectiveness were investigated.Parameters considered in this study including hole(perforation)diameters,dimensions apart,material being used and its thickness all were investigated to reveal the effects of suitable suction velocity,prevailing wind speed and its direction under the simulated incident solar radiation of the investigation site.Based on the obtained results for heat exchange effectiveness under controllable conditions,solar drier was built and investigated outdoors under the prevailing weather conditions of the investigation site.Holes diameter of 3 mm for all the investigated plates and under the different conditions resulted the highest obtained heat exchange effectiveness.Diamond shape for Holes distribution with dimensions of 29 mm×29 mm apart gave higher heat exchange effectiveness above the commonly used distribution(square shape).Temperature increase above ambient per unit of incident radiation was found as(0.0162±0.0007)℃m^(2)/W,when the best designed performance was investigated in the open environment.Using that perforated surface as an absorber in constructed dryer to dry Rosemary(Rosmarinus officinalis L.),reduced the moisture content from 65%(wet basis)to 38.1%on eight hours on the first drying day of the 18th April,2010 while the reduction in moisture content of the sample dried in the shade area was from 65%(wet basis)to 42.2%under the same prevailing weather conditions at the same time.

Analysis and survey of the application of solar dryers in eastern Nigeria

A survey on the use of solar dryers for drying purposes was carried out in some communities in eastern Nigeria.The objective of the study was to ascertain the extent uses of solar dryers by local farmers and the rural populace.The survey method included oral interview and questionnaire administration.The results of the study revealed that the practical use of solar dryers is absent domestically and industrially.However,great enthusiasm was shown by the farmers in the use of solar crop dryers if their performance is satisfactory with respect to quality and quantity of products dried at a given time interval.Most farmers rejected the idea of establishing communally maintained and operated systems but preferred commercialized systems where payments are made per unit quantity of products dried.The study therefore recommends the development of affordable solar crop dryers with auxiliary heat sources to mitigate the effects of daily and seasonal fluctuation in solar radiation in order to cope with the demands of a profit oriented commercial drying system.Such a system holds a lot of promises for entrepreneurs.

Drying rates of some fruits and vegetables with passive solar dryers

Two passive solar dryers were designed and constructed with available local materials.The passive solar dryers which were direct and indirect types were tested with pepper(Capsicum annum L.),okro(Abelmoschus esculentus L.)and vegetables(Amaranthus hybridus L.)in order to evaluate the drying rate of these produces.The moisture content of 78.9%(w.b.)for 180 g freshly harvested peppers was reduced to 24.0%(w.b.).The drying rate in the direct passive solar dryer was found to be higher than the indirect passive solar dryer.The initial moisture content of 92%(w.b.)for 1000 g okro was reduced to 20%(w.b.).The drying rate in the direct passive solar dryer was also found to be higher than in the indirect passive solar dryer.The initial moisture content of 90%(w.b.)for 400 g vegetable was reduced to 20%(w.b.).The drying rate with the direct passive solar dryer was found to be higher than that with indirect passive solar dryer.During the course of drying,after each crop was kept inside the drying system,the temperature of the drying was monitored at an-hour interval;the moisture content was also monitored at a three-hour interval until there was no more change in the weight of the crop.The crops dried faster with the direct passive solar dryer than with the indirect passive solar dryer.As a result of the highest temperature attained in the direct passive solar dryer,the rate of moisture removal was the highest in this dryer.

Drying of Fish Sardines in Oman Using Solar Tunnel Dryers

This paper deals with the design, construction and performance evaluation procedure of a solar tunnel dryer in drying fish. A 12 meter long and 2 meter width half-circled tunnel was designed and constructed to dry about 50-100 kg of freshly harvested fishes per batch. The half of the tunnel base was used as the flat plate air heating solar collector and the remaining half as a dryer. The drying air was forced from the collector region （north side） to the drying region （south side） of the half circled tunnel where the product is to be dried. The drying temperature could be easily raised by some 5-30 ℃ above the ambient temperature inside the tunnel at an air velocity of approximately 0.2 m/sec. The test was conducted with 51.5 kg freshly harvested sardines （hall-load） with initial moisture content of 66.5% （wet-basis） to analyze the performance of the dryer. The fishes were dried to a final average moisture content of 15.5% （wet-basis） within three days （30 hours）. It was possible to reach the moisture content level for safe storage within less than three days （30 hrs） with solar tunnel dryer and 7 days in open air natural sun drying. The improvement in the quality of fishes in terms of color, brightness, flavor, and taste and food value was distinctly recognized.

Experimental Study of a Modified Icaro Solar Dryer: The Case of Coffee Drying

Food losses in the developing country are thought to be 50% of the fruits and vegetables grown and 25% of harvested food grain. Food preservation can reduce wastage of a harvest surplus, allow storage for food shortages, and in some cases facilitate export to high-value markets. Drying is one of the oldest methods of food preservation. Drying makes produce lighter, smaller, and less likely to spoil and helps to minimize the moisture content in coffee beans as high moisture content during storage is certain to ruin the taste and appearance of coffee. This work presents the results of an experimental study of forced convection drying of coffee cherries in a modified Icaro solar dryer. The study aims to validate the numerical models developed for further research. The experimental tests envisaged also aim to determine the mass loss curves of the product by fixing or calculating its initial mass (1 kg), its initial water content (70%), the ambient temperature, the drying airflow (0.02 m3.s-1 to 0.09 m3.s-1) and the exchange coefficients. The influence of these aerothermal parameters on the drying time of a most commercialized coffee variety (Robusta) was studied. Finally, the results revealed an increase in the efficiency of the heat transfer air and a reduction in the water content of the coffee cherry from 70% to 9.87%, after 30.2 hours.

Experimentation of a Forced Convection Solar Dryer for Drying Sweet Potatoes at the Higher Institute of Technology of Mamou-Guinea

This study was carried out at the Mamou Higher Institute of Technology during the period from March 10 to April 15, 2022, with the aim of designing and testing a solar dryer with forced convection by drying potatoes. The dryer was designed using local materials. Its main geometric parameters are: 1) height of the drying chamber (90 cm), 2) length of the drying chamber (50 cm), 3) width of the drying chamber (43 cm), 4) surface of the racks (0.1806 m2), 5) surface of the heat accumulator (0.2537 m2). The experiment focused on the vacuum test of the dryer for two days and that of the drying of the sweet potato for three days from 8:30 a.m. to 5:30 p.m. The average vacuum test temperature values of the three environments are respectively accumulator (43°C), dryer chamber (41°C) and ambient environment (34°C). Four kilograms (4 kg) of boiled sweet potato were dried. The average temperatures in the accumulator and in the drying chamber during the three days of drying are respectively 33°C and 39°C. The final mass of the dried product is 1.2 kg, with a quantity of water extracted of 2 liters or 63% of the initial mass of the product. The average drying rate is 0.074 kg/h. The drying kinetics showed a decreasing rate in the absence of the heating period and the constant rate period.

Effect of Drying Air Velocity on Drying Kinetics of Tomato Slices in a Forced-Convective Solar Tunnel Dryer

The objective of this work is to analyse the extent to which a change in the drying air velocity may affect the drying kinetics of tomato in a forced-convective solar tunnel dryer. 2 m?s?1 (V1) and 3 m?s?1 (V2) air speeds were applied in similar drying air temperature and humidity conditions. Main drying constants calculated included the drying rate, the drying time and the effective water diffusivity based on the derivative form of the Fick’s second law of diffusion. Henderson and Pabis Model and Page Model were used to describe the drying kinetics of tomato. We found that solar drying of tomato occurred in both constant and falling-rate phases. The Page Model appeared to give a better description of tomato drying in a forced-convective solar tunnel dryer. At t = 800 min, the drying rate was approximately 0.0023 kg of water/kg dry matter when drying air velocity was at 2 m/s. At the same moment, the drying rate was higher than 0.0032 kg of water/kg dry matter when the drying air velocity was 3 m/s. As per the effective water diffusivity, its values changed from 2.918E?09 m2?s?1 to 3.921E?09 m2?s?1 when drying air velocity was at 2 and 3 m?s?1 respectively, which is equivalent to a 25% increase. The experimentations were conducted in Niamey, on the 1st and 5th of January 2019 for V2 and V1 respectively. For both two experiments, the starting time was 9:30 local time.

Multiple Phase Change Materials for Performance Enhancement of a Solar Dryer with Double Pass Collector

The fluctuation in drying temperature influences the food products’quality and drying time significantly during the drying process using an indirect solar dryer.One of the effective methods to reduce these variations in the temperature is based on thermal storage materials to control the drying temperature.An experimental investigation is presented in this study to evaluate the performance of an indirect solar dryer with air double pass using multiple phase change materials(PCM)as thermal storage materials.Two PCMs with different melting points are used to store the available heat energy during peak sunshine periods and reduce the drying temperature fluctuations.Drying tests on a food product sample are conducted in three cases,the first was without PCMs using natural convection.The second and third cases are based on forced convection with and without using multiple PCMs under Baghdad city conditions.The results showed that;approximately a steady temperature of hot drying air was obtained during relatively low ambient temperatures when the dryer was incorporated with multiple PCMs.The drying time of the product sample for the natural,forced convection without PCMs and forced with PCMs was 87,72 and 47 h,respectively.The higher performance of the dryer was for the forced convection with PCMs.The reduction percentage in drying time was about 17.2%and 46%for the forced convection without and with PCMs respectively compared with natural convection.The average drying rate for the natural,forced without PCMs and forced convection with PCMs was 0.0093,0.0135 and 0.0172 kg/h,respectively.The enhancement in thermal efficiency of the solar collector and drying chamber with multiple PCMs was 43%and 25.5%,respectively,compared with a typical solar dryer.

Experimental Performance and Neural Network Modeling of a Large-scale Greenhouse Solar Dryer for Drying Natural Rubber Sheets

This paper presents experimental performance and artificial neural network modeling of a large-scale greenhouse solar dryer for drying of natural rubber sheets. The dryer consists of a parabolic roof structure covered with polycarbonate sheets on a concrete floor. The dryer is 9.0 m in width, 27.0 m in length and 3.5 m in height. Nine 15-W DC fans powered by three 50-W PV modules were used to ventilate the dryer. To investigate its performance, the dryer was used to dry six batches of natural rubber sheets. For each batch, 750 kg of rubber sheets were dried in the dryer. Results obtained from the experiments showed that drying temperatures varied from 32 ~C to 55 ~C and the use of the dryer led to a considerable reduction of drying time, as compared to the open air sun drying. In addition, the quality of the product from the dryer was high-quality dried products. A multilayer neural network model was developed to predict the performance of this dryer. The predictive power of the model was found to be high after it was adequately trained.

Application of Analytic Hierarchy Process in Selection of an Appropriate Drying Platform for Maize Drying in a Solar Bubble Dryer

The solar bubble dryer (SBD) is a convenient and better option to traditional open sun drying commonly practiced by smallholder farmers in Ghana and other developing countries. However, to operate the SBD, one is faced with the challenge of frequent mixing of grains using a rake to enhance uniform drying and prevent over-heating of the top-layer exposed to the sun. Additionally, condensation in the SBD can compromise the quality of grains during drying under humid conditions. In the present study, the Analytical Hierarchy Process (AHP) was used to select an appropriate drying platform, tarpaulin, or elevated drying rack for maize drying in the SBD. Using the AHP, the elevated drying rack was chosen as a suitable platform for drying maize in the SBD. The SBD with the elevated drying racks was used to dry 270 kg of maize from a moisture content of 18.2% to 12.6% (w.w.b) within 6 hours compared to 11 hours for the same quantity of grains dried on the tarpaulin of the SBD to reach an MC of 12.5% (w.w.b). An average drying rate and moisture extraction rate of 0.93%/h and 2.88 kg/h were achieved with the elevated drying rack system compared to 0.52%/h and 1.60 kg/h when drying on the tarpaulin of the SBD. An average temperature of 44.6°C recorded in the SBD was 9°C more compared to the ambient temperature. The thermal efficiency of the SBD collector was determined as 36.2%. Drying grains with the elevated racks showed advantages of reduced drying time, improved airflow through the drying bed, and prevention of condensation, which occurs when drying on the tarpaulin of the SBD.

Evaluating Low Cost and Sustainable High Quality Cassava Drying Technologies among Small and Medium Processors in Uganda

Cassava regarded as a white gold of Africa is driving the agricultural commercialization and industrialization with small to medium technologies in Uganda. There is an over-whelming demand for high quality cassava flour （HQCF） by Bakeries, beverage industry, paper board and composite end markets. The end market for HQCF dictates on its quality attributes and rewards for its quality in terms of price offered within their minimum standards. However, obtaining sustainable amounts of HQCF for these markets calls for devoted efforts. Limited types of HQCF processing technologies exist and if they exist, their efficiency, costs and sustainability are not well understood. We evaluated high quality cassava drying technologies in Northern and Eastern Uganda in two years using naturally ventilated wooden screen solar drying structures and open air sun drying structures. Naturally ventilated wooden screen solar dryers produced clean dry high quality cassava chips free off insect and bird contamination and caused faster drying to less than 14.3% MC in 1.5 hours than open outside drying conditions. We recommend naturally ventilated wooden screen solar dryers for small and medium cassava processors during dry and rainy season. Halftone to one tone cassava chips dryers per day drying unit can cost one 2,258-4,338 USD to make it functional. Also open outside raised metallic racks with black surface can give good results on a good sunny day especially for starters on small scale basis. A small durable unit of 150 kilograms per day can be made with 500 USD.

Development of an inflatable solar dryer for improved postharvest handling of paddy rice in humid climates

Rice is the staple food for more than three billion people worldwide.Although considerable progress has been made with respect to improved breeds and production practices,losses during postharvest handling remain considerable.Drying and storage of paddy are two key stages where management can be improved.For rice,grain moisture content of 14%prevents microbiological activity,while a level of about 12%minimizes quality losses over prolonged storage periods.Due to the need for simple and economical technologies,an inflatable solar dryer(ISD)was developed based on adaptations of the Hohenheim-type solar tunnel dryer.To form a drying tunnel,transparent polyethylene(PE)film attaches by zipper to a reinforced black polyvinyl chloride(PVC)film.To reduce heat loss,a flexible multilayer floor was used along the drying area.The tunnel does not need a substructure as it is stabilized adequately from pressure created by two axial flow ventilators.During experiments,paddy was spread on the floor and mixed with a special roller bar.The ISD has been evaluated for paddy in the Philippines during both rainy and dry seasons and was subsequently optimized.Sun drying and shade drying were carried out in parallel for comparison and product was evaluated for moisture content and quality in terms of milling recovery and head rice yield.Moisture content was reduced from 23%to 14%within 26-52 h of continuous operation during the rainy season and 16%to 14%within 4-26 h of drying during the dry season.In both seasons,the final moisture content of 12%was reached after prolonged drying periods.Quality was not found to be affected with respect to drying treatment.The ISD showed advantages over sun drying,despite longer drying periods.

Effect of drying technologies on the biochemical properties of Stolephorus commersonnii

Objectives:Two different methods,namely traditional sundrying and solar dryer drying were employed to investigate the effect of drying method on the quality of Indian anchovies,Stolephorus commersonnii.Materials and Methods:Fifty fish samples of Stolephorus commersonnii were purchased for the drying study.Traditionally dried fishes were bought from the local market.For solar drying the samples were kept in on the solar cabinet dryer KSD 25 designed and fabricated by the Central Institute of Fisheries Technology(CIFT).International standard AOAC methods were used for quality analysis of dried fish samples.Results:The method of drying by the solar dryer is more hygienic and faster than the traditional sun-drying method.The biochemical compositions and sensory evaluation of the products obtained showed significant variation between the two drying methods.Solar dryer-dried fish has got good organoleptic score than the traditional sundried fish.The overall quality of fish dried in the solar dryer was better than the traditionally sundried fish.Conclusions:The study clearly indicates that solar drying can be used as an environment-friendly method for fish processing which enhances food security.