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Fil: Nelli, Silvana Sofia. Universidad Nacional de Misiones. Facultad de Ingeniería. Laboratorio de Gestión Tecnológica y Estadística Aplicada; Argentina. Fil: Mantulak, Mario José. Universidad Nacional de Misiones. Facultad de Ingeniería. Laboratorio de Gestión Tecnológica y Estadística Aplicada; Argentina. Fil: Feltan, Corina M. Universidad Nacional de Misiones. Facultad de Ingeniería. Departamento Ingeniería Electromecánica; Argentina. Fil: Bresciani, Julio Cesar. Universidad Nacional de Misiones. Facultad de Ingeniería. Laboratorio de Gestión Tecnológica y Estadística Aplicada; Argentina. En la República Argentina, Provincia de Misiones, la industria forestal es una actividad muy importante, sin embargo, son pocos los aserraderos que cuentan con un sistema apropiado de secado de madera. Estos aserraderos son los de mayor envergadura, mientras que los más pequeños en general realizan el secado al aire libre. En este trabajo se han realizado ensayos del funcionamiento de un prototipo de secador solar de madera con el objetivo de comparar las condiciones de secado en el prototipo con respecto al secado al aire libre y así brindar una alternativa sustentable a estos pequeños aserraderos. Dichos ensayos consistieron en realizar el secado de madera de pino mediante el prototipo y se contrastaron dichos resultados con un grupo testigo de secado natural. El secado fue por radiación solar y convección forzada de aire caliente generados por los colectores solares. Las variables medidas fueron humedad, temperatura ambiente y en el interior del secador solar. Los principales resultados obtenidos fueron, una reducción de humedad que ronda el 50 por ciento, mientras que la temperatura se incrementó alrededor de un 90 por ciento en el interior del prototipo, en comparación con las mediciones realizadas al aire libre. In the Argentine Republic,In Misiones Province, the forestry industry constitutes a highly important activity; however, few sawmills have an appropriate wood drying system. These sawmills are the largest ones, while the smallest generally use an air-drying system. In order to provide a sustainable alternative for small sawmills, in this work, tests were carried out on the operation of a solar wood dryer prototype.Themes to obtain a functionality and performance determination of this prototype; andtothisend, pinewood was used to perform the tests. The results were contrasted with the natural drying control group. Solar Radiation And convection hot air generated by the solar collectors were used for frying. The variables measured were humidity, ambient temperature and temperature inside the solar dryer. Compared to air-drying measurements, the main results were a humidity reduction of around 50 percent and a temperature increase of around 90percent inside the prototype. In addition, it was found that wood dried with air-drying system presented stains and fungal growth,while wood dried in the prototype did not show these drawbacks.

Onion slices were dried in a low-humidity air-assisted hybrid solar dryer. Drying occurred in the falling rate period, and the drying rate was attenuated with the initial moisture content of the samples. The effects of different drying air temperatures (50, 60, 70°C) and KMS pre-treatments (0.1, 0.3, 0.5%) on drying characteristics of onion slices were also studied. Eight thin layer drying mathematical models viz. Newton, Page, Modified Page, Exponential, Asymptotic, Logistic, Wang and Singh, and two-term exponential were investigated and the results were compared to their goodness of fit in terms of coefficient of correlation (r), standard error (es), and the mean square of the deviation χ2. Drying characteristics of onion slices were better delineated by Page’s regression model for hybrid solar drying with values for the coefficient of correlation (0.9962–0.9999), standard error (0.0048–0.0431), and χ² (5.98E-05 to 2.16E-03). Effective moisture diffusivity values of onion slices ranged between 1.33E-08 m2.s-1 to 2.49E-08 m2.s-1 for the drying conditions under investigation.

The novel hybrid greenhouse solar dryer (HGSD) attached with evacuated tube collector (ETC) is developed for faster drying of high moisture content crops. The slow drying rate of high moisture crops lead to microbial attack on crop surface and have more chance of deterioration. Hence the HGSD is designed and tested for faster drying of crops. The experiments are performed to evaluate the performance of HGSD under active and passive mode. Ginger has been taken as a high moisture crops for the experimentation on two cases. In both the cases the ginger is dried from 79.8% to 9.82% moisture level (wb). In active mode, dryer takes 43.47% less time than the passive mode. The overall efficiency of the dryer in active and passive mode is 4.81% and 3.39% respectively. The lower drying time makes this dryer suitable for rural as well as commercial applications for drying agricultural or non-agro based products.

Indian jujube (Ziziphus mauritiana) and Date palm (Phoenix dactylifera L.) the most important fruit crops that can grow in India's hot arid regions. The perishable nature of Indian jujube and date fruits leads to post-harvest loss. Both of these fruits are highly perishable, containing more than 80% moisture. Moisture needs to be reduced to less than 20% for storing it for a longer period of time. A phase change material (PCM) based hybrid solar dryer was developed, which consisted of the collector of area 1.06 m2 and two drying trays made of SS (0.50 m2) and that two half trays (0.24 m2). The performance of the developed PCM dryer was evaluated by drying fresh Indian jujube and date palm fruits having an initial moisture content of 65–80% (wet basis) and compared with the developed dryer without PCM. The drying system works so that phase-change material stores the thermal energy during sunshine hours and releases it at night. Therefore, the dryer is effectively operative for the next 5–6 h. The temperature of the drying chamber was observed as 6 °C higher than the ambient temperature in July 2020 during date palm drying after sunshine hours till midnight and it falls gradually, and temperature in the drying chamber was observed as 5°Celsius higher than the ambient temperature in January 2021 during Indian jujube drying. The variations in moisture content (wet basis) of the Indian jujube fruit are reduced from 80% to 22% within seven days by using the dryer with PCM and in 9 days dryer without PCM. In date palm fruit, MC reduced from 65 to 20% in 6 days in the dryer with PCM and eight days without PCM. The thermal efficiency (η) of PCM based hybrid photovoltaic thermal (PV/T) solar dryer (η = 18.0%) was found better than that of natural convection mode without PCM based hybrid solar dryer (η = 15.8%). The developed solar dryer provides a promising alternative for drying other arid food produced after sunshine hours with a real-time data acquisition system. It is also found to be superior in retaining quality.

The present work reports on an experimental study carried out on a solar dryer with an external reflector to remove the moisture content available in the grapes. The thermal behavior of the solar dryer with external reflector and open solar drying technique were compared. Using an external reflector on the solar dryer increased the energy input. Results showed that using a solar dryer with external reflectors reduced the drying time while compared to that of open solar drying. The temperature of the dryer tray using an external reflector is increased to about 20% than open basket solar drying. Similarly, the relative humidity of open solar drying is higher as compared to that of the drying chamber with an external reflector. The time required for removing the moisture using a modified solar dryer is found as 5 days, whereas, using open basket solar drying, the time required to remove moisture is 8 days.

Phosphate sludge generated at the end of the phosphate enrichment operations can be reused after being subject to drying processes. For efficient drying treatment and also for saving storage, the hygroscopic properties of the phosphate sludge have to be determined. In this paper, the adsorption and desorption behaviors were studied. The drying of phosphate sludge in a hybrid solar dryer requires between 90 min at 60 °C and 180 min at 40 °C. The isosteric energy was calculated from the experimental tests and varies from 2 kJ/mol to 25 kJ/mol respectively from the wetted to dried product. From the moisture content evolution, the computed water diffusivity inside tailing varies from 1.70 10-7 m2/s at 30 °C to reach 2.49 10-7 m2/s at 60 °C.

This study presents experimental investigation into a novel UV cabinet type solar dryer designed for drying banana slices at the Chhattisgarh Swami Vivekanand Technical University (21 27′N, 81 43′ E). An experiment for the performance assessment of banana drying was conducted at the clear sky conditions. The solar dryer consists of 6 trays with the one drying chamber. The same technique is used for forced convection drying using the fan and the PV panel. Experimentally evaluated local metrological conditions such as solar radiation, atmospheric temperature, wind speed and air humidity. In the six trays for drying, 2 kg of banana slices were evenly divided and after a period of 16 h of drying, banana slices dried in the forced convection to moisture content of 13.75 % from an initial moisture content of 86.2%. On the other hand, natural convection drying reaches to 17.5% of the final moisture content, in the same time. Moisture ratio for the forced and natural convection drying varies in the range of 0.79–0.001 and 0.85–0.05, respectively. For the forced convection drying of banana slices the optimal and minimum drying efficiency of the designed solar dryer are 16.32 % and 0.29% whereas 13.75% and 0.15% of drying efficiency for natural convection drying are measured. The more efficient is forced convection drying in comparison with natural convection drying.

Photovoltaic-thermal (PVT) collectors can be applied in order to concurrently generation of electrical and thermal energy. In the present study, a vertical hybrid PVT solar dryer has been developed and analyzed by utilizing numerical and experimental approaches. ANSYS Fluent software has been employed to visualize both flow and thermal behavior inside the vertical PVTs. The main aim of using vertical structure of PVT dryer is its space-saving potential. For enhancing heat transfer, fins have been integrated over the absorber plate and PV panel. The obtained experimental findings showed that thermal efficiency values of the finless and finned vertical PVT collectors were in the ranges of 47.46-54.86% and 50.25-58.16%, respectively. Moreover, sustainability index values of finless and finned drying systems were achieved between 2.16-2.75 and 2.38-3.25, respectively. The obtained results showed that applying high air flow rate in finned vertical dryer notably improved the drying performance. In addition, the deviation between numerical and experimental findings obtained in the range of 4.2-8.7%. (c) 2021 Elsevier Ltd. All rights reserved.

This study proposes an indirect solar drying system containing a solar photovoltaic/thermal air collector, a monocrystalline silicon photovoltaic system, a drying oven and two batteries. The drying kinetics and drying quality of turnip slices obtained using the proposed solar drying equipment and via natural drying were compared and analyzed along with the energy provided and required for turnip drying using a solar dryer. The results reveal that the turnip drying time is shorter when using the solar dryer than when using natural drying. The moisture content on dry basis of the turnips decreased to 0.197 from 20.370 using the solar dryer. However, when subjected to natural drying, the moisture content on dry basis took more time to dry from a moistire content of 21.320 to 0.250. The Midilli and Kucuk model was deemed appropriate for depicting the turnip slices’ drying using solar drying equipment and via natural sunlight. Furthermore, the dried turnips obtained via natural drying and using the solar drying system exhibited the highest and lowest values of total colour difference, respectively. Following open sun drying, scanning electron microscopy revealed some obvious molds on the surface of the turnip cells, and the turnip cells were subsequently destroyed. The drying quality of turnips attained via open sun drying was severely reduced. The drying method using the solar drying equipment was thus better than natural drying, particularly in cloudy weather.

In this study, the design, development, and performance analysis of novel thermal energy storage integrated evacuated tube heat pipe solar dryer was investigated. A new common condenser heat pipe system having thermal energy storage was incorporated into the solar collector of the dryer. Therminol 55 was used as the thermal storage medium. The performance analysis was carried out with air mass flow rates between 0.003 kg/s to 0.02 kg/s and a combination of two mass flow rates 0.015 kg/s and 0.0065 kg/s. The maximum outlet temperature of the air delivered by the solar collector during the study was 118 °C. The average energy and exergy efficiency of the solar collector varied between 10%-30% and 1.9%-5.6% respectively. Agricultural products like tomatoes and carrots were dried in the dryer. The effect of moisture diffusivity variation for tomatoes and carrots with the mass flow rate of air and product thickness was analyzed in this study. The Newton model fairly demonstrated the solar drying characteristics of tomatoes. The combined mass flow rate method increased the average collector outlet temperature to 67 °C against 56 °C during a single mass flow rate and decreased the drying time by 2 h. The payback period for the dryer was 2.6 years.

Progress in Applied Science and Technology, 13, 2, C25-C32

Olive Mill wastewater is considered as a hazardous olive by-product due to its high organic load and its toxic activity. The drying of this effluent under a greenhouse dryer can be an interesting low-cost treatment to obtain a high added value product. In order to provide an efficient design of the dryer that can consistently meet the needs of the customers, a numerical model was developed, as a first step before project implementation, to simulate the drying process inside a modified even span solar greenhouse dryer. The governing conservation equations were thus solved using COMSOL Multiphysics. To understand and then control the coupled heat and mass transfer as well as the flow, simulations have been first performed for five typical days of July for the proposed dryer as well as under the open sun. Higher air and OMWW temperatures and better air circulation inside the solar dryer reduced more effectively the drying time needed to evaporate 28.7 kg m−1 from 120 hinder open sun to 90 h inside the tested dryer. The overall efficiency of the studied greenhouse dryer and under the traditional open sun drying reached 68.1 and 50.1%, respectively, after the drying period. The study of the effect of some geometrical and Tunisian climatic conditions on the evaporated quantity showed that separated shallow basins in a greenhouse dryer during July make more effective the drying process and provide significant improvement. The obtained results allowed not only a better understanding of the drying kinetics for both studied drying processes but also an optimization of the dryer design.

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 nanofluidþsilver 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 info:eu-repo/semantics/publishedVersion

Due to continuous growth in population and sharp increase in energy and food demand, research on alternative energy sources independent of fossil fuels has increased over the last decade. Moreover, limitations on greenhouse gas emissions by developed and developing countries are imposing much pressure on the energy sector worldwide to use renewable energy sources such as solar, wind, biomass, hydro, and geothermal. Food production is one of the biggest industries in the world, and it consumes a large amount of energy in the form of heat and electricity. In this work, agro-product drying technologies powered by solar energy are presented and discussed. Different types of solar dryers based on direct, indirect and mixed modes are described. Moreover, energy, exergy, economic, and environmental analyses for these technologies are presented to determine the main parameters affecting the dryer performance. The results indicate that the air mass flow rate, temperature, moisture content, and drying time are the most important parameters in solar dryer performance. Finally, a comparative assessment of the performance of different existing solar dryer has been highlighted with a detail scope of future works.

Solar dryers utilise solar radiation for producing hot air to dry various food and agricultural products. The limitation of solar dryers is their inability to achieve continuous drying during off sunshine hours. Thus, solar dryers are integrated with thermal energy storage units to achieve continuous drying operation. The thermal energy storage unit employed in solar dryer consists of either sensible, latent heat storage systems or the combination of these two. The article provides an extensive review on the various sensible and latent storage units and materials used in different solar dryers viz., direct type, indirect and mixed-mode type dryers operated in both natural and forced convection. A detailed discussion on different dryer types, product dried, operating parameters, sensible and latent heat storage materials used, and their outcomes are reported and tabulated. Further, the article also provides a detailed summary on the implementation of thermal storage units in solar dryers. The future challenges and recommendations on the selection, implementation and testing of the thermal storage unit for different solar dryers are also reported.

Cassava roots are processed by peeling using knives, chopping into small pieces, then dried and milled into flour with dried maize, sorghum or millet. This traditional method of drying takes 7 to 14 days and is prone to contamination. The objective of this study was to add value to small scale farmers’ cassava in Busia County through solar drying. Fresh cassava roots were peeled and washed in running water and sliced using a motorized chipper. The chips were randomly distributed on two trays and uniformly spread. Temperatures were taken daily at an interval of 30 min. After introduction of wet cassava (wet weight 4.6 kg) chipping in the dryer, pick temperatures were; first day, 41.7°C, second day 49.3°C and third day 41.5°C. The experiment was terminated at 11.00 am in the third day after achieving a moisture content of 16% dry and dry weight of 1.985 kg. From the results, it was observed that it took the fabricated dryer two and a half days to dry the cassava chippings compared to traditional method’s ten days of drying. The efficient solar dryer is recommended for use by small scale cassava farmers in the County. Key words: Cassava, drying, dryer, contamination, fabricated

Jaggery is a traditional Indian sweetener prepared from sugarcane juice through evaporation process and is considered as medicinal sugar due to its nutritional and thereupatic properties. To improve the shelf-life of solid jaggery , making jaggery in the form of granules with moisture content of 1–2% was recommended. A Polyhouse solar dryer for drying granular jaggery with a capacity of 200 kg was developed at Regional Agricultural Research Station, Anakapalle, Andhra Pradesh, India. Traditionally, granular jaggery was dried in openyard resulting in contamination with dust, insects, birds and rain. A comparative study was carried for drying granular jaggery with initial moisture of 9.3 to 10.5% (db) in both polyhouse solar dryer and in an open yard during the month of March– April, 2019. The study revealed that the rate of drying was faster in poly house compared to open yard drying. The temperature inside the polyhouse dryer was 59% higher than the ambient conditions. The percent saving in time for drying of granular jaggery in poly house dryer was 38% to attain optimum moisture content of 1.7% for stable shelf life besides maintaining hygienic conditions. The quality parameters of jaggery in terms of sucrose and reducing sugars percentage showed insignificant changes in both methods. However, the color of the granular jaggery was well retained in polyhouse dryer compared to open yard drying. Hence, this study will be helpful for small and micro entrepreneurs for large scale drying of granular jaggery under hygienic conditions utilizing renewable energy resources.

Solar energy is a widely used green energy resource that is used for drying processes. Through this assessment, the performance of an Indirect Solar Dryer (ISD) with three different cases, namely solar collector - without Thermal Energy Storage (TES), with TES unit having Phase Change Material (PCM) and with TES having fins inserted PCM have been experimentally analyzed during spring and summer seasons for drying Momordica charantia. Totally six experiments were undertaken to compare temperature, drying kinetics, and energy analyses. The initial moisture level of 2 kg of specimen decreased from 1.84 kg of water (92% w. b) to 0.24 kg of water (12% w. b) in 10.5 h utilizing ISD with TES having fins inserted PCM (Test 6). The maximum thermal efficiency achieved about 19.41% on Test 6. Exergy efficiency increased from 8.66% to 79.02% at Test 6. Environmental impacts assessment has revealed that the Energy Payback Time for the ISD was 1.42 years. The CO2 emission, mitigation, and carbon credit gained (Test 6) are 23.88 kg/year, 20.13 tons, and $100.642 to $402.569 for the 35 years’ intended lifespan. The assessment report showed that the device established was a potentially effective commercial drying technique, both in energy utilization and environmental sustainability.

The aim of the present study is to investigate the experimental performance of a solar dryer by using a novel type of a drying chamber for increasing the drying performance and ensuring homogeneous...

Solar drying has received great interest as a viable alternative solution to fossil fuel dryers. However, due to the intermittency of the solar resource, solar dryers suffer from discontinued drying and thus, long drying time. In this paper, the use of sorption materials to enhance the performance of solar dryers is reviewed. The main aspects regarding their use as thermal energy storage or dehumidification materials are highlighted. The paper shows that solid adsorbents, especially silica gel, are the most used materials. The use of composite materials, for instance the mixture of bentonite, CaCl2, vermiculite, and cement proved to be promising. The incorporation of a sorption dehumidifier in a solar dryer, usually at the solar collector inlet, generally leads to a reduction of the drying time of 15–30%, although values up to 50% and even 64% have been reported. On the other hand, introducing sorption materials as thermal storage in a solar dryer, mostly integrated at the top in the drying chamber, usually leads to a reduction of the drying time in a range of 30–45%. There are still various aspects to be investigated in depth before a large-scale utilization of these techniques in solar drying technology.

This work reports the use of tubular solar dryer for drying the Mexican mint (Plectranthus amboinicus) under various mass of leaves. Experiments were carried out in a tubular solar dryer under natural convection mode with direct solar heating. Parameters such as the temperature of dryer tray, relative humidity, and moisture content were recorded for 0.25, 0.5, 0.75 and 1 kg of P. amboinicus leaves placed in the dryer tray. Results showed that under an increased mass of P. amboinicus leaves in the tray the parameters such as dryer tray temperature are reduced, and the moisture content available with 0.75 kg of P. amboinicus leaves is higher as compared to 0.25 kg of P. amboinicus leaves. Also, it is found that the relative humidity inside the drying chamber is higher with increased mass of P. amboinicus leaves in the drying chamber.

OBJECTIVE: The primary objective of this study was to minimize post-harvest damages and improve the handling of agricultural commodities. The secondary objective was to assess the performance of the dryer by varying inlet velocity of air on temperature, final moisture of the product, drying period, and drying rate METHODS: The present research was carried out for the development, fabrication, and testing of a multi-portioned type solar dryer. The multi-portioned dryer consisted of a collector unit, air storage chamber, drying cabins, and a chimney. A fan assembly was also attached at the inlet of the collector and at the outlet of the drying compartment to control the air velocity and to remove the moist air. RESULTS: The data obtained from the experiments revealed that the maximum temperature elevation of 36.5oC was attained during a no-load test. The results obtained after carrying out load tests revealed that the maximum drying rate of 47 g/hr was achieved at the air inlet velocity of 3.2 m/s. The initial moisture content of 80.50% was brought down to 3.31% in five sunshine hours of 150 gram sliced potatoes. Each portion received air at varying speeds, and it was observed that the portion receiving air at the lowest speed had the maximum temperature. CONCLUSION: The lowest temperature elevation was recorded for the portion receiving air at the highest speed. The dryer was also found to be suitable for the on-field practical application for the drying of perishable commodities.

Drying foods and medicinal plants is a process with high energy consumption because high amount of energy is needed for evaporating the water from the surface of the fresh materials. Therefore, developing cost-effective and simple-structured drying systems with low energy demand is a crucial matter. In the present study, compact type solar dryers have been designed, manufactured and tested experimentally. Within this context, thermal and flow behavior of compact dryers with and without baffles have been analyzed using CFD method. Then, fabricated compact dryers have been experimented at different conditions to determine their performance. Experimental and numerical findings of this study illustrated the effective design of the developed compact solar dryers. However, compact solar dryer with baffles exhibited better performance than the solar dryer without baffles. According to the experimental results, mean specific moisture extraction rate in compact dryers with and without baffles obtained between the ranges of 0.55–0.69 and 0.47–0.62 kg/kWh, respectively. In addition, average exergy efficiency of drying chambers was attained over the range of 44.91–55.28%. Overall findings of this study indicated successfulness of a compact solar dryer which developed using simple and lightweight materials.

Solar energy as a clean energy source is widely investigated to find out the effective mechanisms to meet a large part of energy demand in the near future. In the present research, a square-spiral finned quadruple-flow solar collector assisted dryer has been designed, and numerically compared with finless collector. Main aim of the current work is to develop and analyze a sustainable solar drying system. In this study, different from similar works, heat transfer surface area has been enhanced by using square spiral geometry which is an unconventional fin type. According to the numerical findings, a finned quadruple-flow collector which found more efficient has been manufactured, integrated with a drying chamber and performance experiments have been conducted. In the manufactured solar dryer, a PV panel has been used to run utilized fan. CFD simulation and empirical outcomes of this research exhibited the successful design of finned quadruple-flow collector. Experimentally obtained average efficiency of quadruple-flow collector varied in the range of 73.27-78.19%. Also, mean exergy efficiency of drying chamber was found between 44.16 and 58.38%. Sustainability index and waste exergy ratio values as important factors were attained between the ranges of 1.93-2.73 and 0.52-0.56, respectively. (c) 2021 Elsevier Ltd. All rights reserved.

The wood drying process consumes a great deal of energy with pollutants carrying bi-products. To preserve tropical and temperate forests and protect the environment, it is important to optimize the use of energy using solar dryers that are less expensive and easy to construct. In this paper, mathematical modeling of a novel solar dryer for firewood has been examined and experimentally validated using average relative error analysis. The solar dryer functioning in forced convection is constructed with wood and wood panels, and it is constituted of a solar collector. This field experimental solar dryer is numerically simulated for climatic conditions existing in Yaounde and Nancy environments. The role of the solar collector is methodically identified ultimately permitting its usage as an effective dryer in a temperate environment. Our results indicate that in the tropical environment, and during the summer and spring seasons, the thermal efficiency is higher than 40 %, but lower than 30 % during the winter and autumn seasons. The construction of this solar dryer type of 7 steres capacity functioning all the year is capable of reducing the production of pollutants near 26.106 tons of CO2 and 58.433 tons of CO2 for Nancy and Yaounde respectively. Constructed for a life duration of 10 years, the payback period is equal to 1.893 years and 0.971 years when the dryer is used all the year from Nancy and Yaounde respectively.

Research on solar dryer technology proliferates since it reduces the drying period while keeping nutritional values in the agricultural products. This paper presented a review of recent advances in the solar drying system. This review is composed of working principles and classifications of solar dryers. They were classified into two main elements: airflow modes, either passive or active, and the way heat is transferred: direct, indirect, mixed-mode, and hybrid. The hybrid system used several types of elements to supply additional heat in the drying system, as elaborated in this paper, such as the electrical heater, biomass, and photovoltaic system. The advantages and disadvantages of the solar dryer also being discussed in this paper

A cylindrical-parabolic solar-thermal converter, with 0.5m2 of capture surface, was manufactured and attached to a furnace, constituting an indirect solar dryer. Thermal balances of the elements of the receiver, housed in the focal point of this collector, are settled. A campaign of vacuum tests of this dryer indicated temperatures of the heat-bearing air in natural convection, along the absorber tube (70°C) and inside the drying cage (almost 60°C,on average). The average thermal efficiency of said converter has been evaluated at 50%.The higher the efficiency, the less the converter's capture surface is required and, therefore, less investment is required. These promising results testify to the effective performance of this new dryer compared to dryers with flat collectors, whose efficiencies could not exceed 40% despite the large surface area of these collectors.

For low temperature agricultural crop and meat drying, dryers utilizing the renewable energy source (solar energy) appear to be an efficient technique as it is ecofriendly, energy efficient, and available in free of cost. This work presents the experimental investigation on a solar food dryer equipped with external reflectors to enhance the rate of drying efficiency by removing the moisture content available in the anchovy fish. A comparison of conventional open solar drying is carried out to assess the parameters such as drying efficiency, moisture removal rate, and heat energy required for drying the anchovy fish using the modified solar dryer using the natural convection technique. From the experimental results it is observed that the relative humidity greatly influence the rate of drying. The average relative humidity during the experiments using open solar drying is found as 50–65% whereas, the using solar dryer the average relative humidity inside the chamber is found as 20–35%. The relative humidity of the fish using open solar drying is higher as compared to solar dryer drying as the drying products are kept in open atmosphere. The physical examination results on the dried products proved that using a modified solar dryers, the dried product is free from insects, and dust. Also, it is found that the loss of color from the product is a minimum while compared to conventional open solar drying. The results showed that the thermal efficiency of top tray (dryer 1) and bottom tray (dryer 2) is comparatively higher as compared to that of conventional open solar drying and found as 16.73 and 19.34 %, respectively. Results also showed that nearly 20.05% of the energy could be saved using the modified solar dryer as compared to the open solar drying technique.

This research study presents the experimental assessment of two sensible heat materials originating from the State of Yucatan, Mexico, which were incorporated into three compartments within an indirect type solar dryer with a storage system (ITSD-TSS). The experimental tests were carried out under different environmental conditions and were compared with the results obtained from a conventional solar dryer without thermal storage. Temperature and humidity were measured during the different tests and various indicators were used to compare both drying systems. The results revealed that the solar dryer that used limestone as storage material indicated better performance than the dryer that utilized beach sand, since the drying efficiency with limestone was higher by 1.55% and allowed to extract 0.0257 kg more water per unit kWh. Similarly, beach sand stored 1.5 times more energy than limestone, however, this material is very susceptible to variations of solar radiation, so it is not recommended to implement it in areas with high cloudiness. Finally, the implementation of the three storage compartments in the ITSD-TSS allowed an increase between 3 and 4% of the drying efficiency as compared to the conventional solar dryer. The findings of the work can contribute to sustainable development in the agricultural drying process in rural communities.

Solar drying is an important industrial technology with expanding segment in the industrial solar market. The main drawback in commercializing solar dryers is the non-appropriate design of the drying chamber to perform uniform drying and hence producing a nonhomogeneous product. Uniformity of airflow inside the drying chamber has a significant role in the drying process. The current article presents an experimental and computational analysis of a hybrid solar-thermal dryer with a multi-chamber drying cabinet. A prototype was designed and fabricated to including three separate chambers, and each has one angular-movable tray for experimental measurements. The computational model was developed in ANSYS Fluent software for CFD simulation and validated by comparing the experimental results. A statistical analysis of the simulation results has been performed. The focus was made on the effect of tray inclination angle, 0°, 10°, 20°, 30° and 35°, air velocity and turbulence intensity distribution inside the drying cabinet at various operational conditions. Experimental and numerical analysis results indicate that the best uniformity is achieved in the tray with 30° inclination. Statistical analysis results revealed that around 93% of velocity frequency is obtained at 0.7–0.8 m/s air velocity level for 30° tray angle.

The objective of the paper is to carry out the heat transfer analysis of novel designed hybrid active greenhouse solar dryer (HAGSD) attached with water-in-tube type evacuated collector. The experimentation is carried out to investigate the performance of dryer with and without evacuated tube collector (ETC) under active mode. Three high moisture seasonal crops namely tomato, ginger and bottle gourd have been dried inside the dryer for the two cases and also in open sun drying. Also the drying kinetic of crops has been fitted with ten drying rate models given by researchers. A new drying rate model is also obtained which gives a very close fit with experimental drying rate. The average values of convective heat transfer coefficients for dryer with ETC are 153%, 3.8% and 305.4% higher than the dryer without ETC for tomato, ginger and bottle gourd respectively. The drying time in case of dryer with ETC for tomato, ginger and bottle gourd is 9, 12 and 6 h respectively less than the dryer without ETC. The overall efficiency of the dryer for the three crops varies between 14.22 and 27.99% for dryer with ETC, while for dryer without ETC, it varies between 9.63 and 24.88%.

This Paper attempts to study the variation of simulation and fabricated jet impingement dryer to define how to increase efficiency, temperature and best quality of the dryer. The jet impingement is helps to increase the overall temperature of the exhaust air. where increasing the temperature slightly and velocity ranges of drying time as been reduced. The experimental process has been carried in the copra.From the CFD analysis end results establish the flow jet impingement processing on the absorber where a strong function of heat transfer enhancement. The present process concludes that the mass flow ranges of air as been influence the heat transfer rates. At solar radiation 500-1000 (W/M2), 348K ambient temperature and 0.048(Kg/S) mass flow ranges has been get at the end analysis.Now a day the new model innovations are needed in solar dryer to fulfil the requirements of drying industrial and agricultural products. The new design process analysis and assumptions are very necessary to design any system. By comparison solar drying fulfil the requirements than sun drying processing. Under the such process and conditions Effect of mass flow ranges of air, solar radiation on exit air temperature, and efficiency has been analyzed.

Solar Drying or solar dehydration is one of the important processes required for preservation of food and agriculture products. Bacterial growth and moisture is being removed in this process. It helps for preserving the food products for more long time. Solar drying is the oldest & effective method used for drying food products. The device used for preservation of food products using solar energy is called as solar dryer or solar dehydrator. The solar dryer is classified on the basis of mode of drying, circulation of air, type and arrangement of solar air collector. In this project, a solar powered indirect type food dryer is designed and developed. The dryer design is consisting of solar collector unit along with absorber made up of extended surface of aluminum sheet with staging, drying chamber with three columns of each rack shelves, chimney for exhaust air, a solar powered fan. The dryer collector and drying chamber are connected with a hose pipe clamped to both ends. The project model of solar dryer is consisting of a monitoring unit for data logging of continuous updatation of parameters like temperature inside the dryer and temperature at ambient condition, humidity at inside and outside of dryer also the atmospheric pressure, etc. At the end we are going to investigate the effectiveness of solar dryer with above parameters.

In this study, green chillies and okra were dried using an indirect type solar dryer ITSD dryer and their drying kinetics were evaluated. The initial moisture content (MC) of green chilli was 8.398...

A sensor based solar dryer was designed to control the drying environment for precision drying of agricultural produce. The system entirely used solar energy utilizing both thermal and electrical effect. Paraffin wax (PCM) was used for storage of thermal energy whereas solar battery was used to store the electrical energy. Hot air blower was also provided to supply heat when there is less or no solar radiation. Temperature sensors were provided to control the environment of drying chamber. The exhaust fan started operating depending on the set temperature and thus control the drying environment. Load cells were provided below each tray to measure the dry weight. The drying chamber was made of mild steel with glass wool insulation. The capacity of the designed dryer was 10-15 kg with 6 trays. The designed dryer has target temperature of 55-60oC.

This paper presents experimentation on model developed to compare the performance of solar drying with and without dehumidification system. Basic components of system consist of flat plate solar collector, drying chamber, desiccant bed and blower to maintain forced air circulation inside the system. Humidity of fresh air supplied to collector reduced by passing it through two stationary desiccant beds, which work alternately for adsorption and regeneration. Exhaust heat used for regeneration thereby overall efficiency of system increased. Drying rate obtained from solar drying with desiccant bed, solar drying without desiccant bed and open sun drying are 0.1094 Kg/hour, 0.09375 Kg/hour, and 0.0775 Kg/hour respectively. It concluded that by use of desiccant bed increases drying rate that takes near about three hours less to reach same moisture content compared with solar drying without desiccant bed. From results obtained it further found that desiccant bed based solar dryer gives higher drying chamber efficiency than without desiccant bed system due to increased moisture pick-up capacity. Also, in built latent heat thermal storage was able to provide 7 to 8 0C higher temperature than surrounding after sunset for about 2 hours.

The main objective of this paper is to present a numerical model and simulation of coupled heat and mass transfer of solar dryer with various solar concentrator shapes considering the thermo-physic...

Global energy demand continues to increase with the expansion of the economy activities and sustainable development. Meanwhile, the world is suffering from pollution and harmful greenhouse gases originated from burning of fossil fuels where the consequences of climate changes are also alarming. Solar energy is an alternative energy source that is abundant, safer and cleaner. This article provides a comprehensive review of works pertaining to solar thermal energy utilization in the drying process. In this article, the classification of solar dryers, the main components which includes solar collector, drying chamber and auxiliary systems, prospects, challenges, recent advancement and performance are discussed. The existing literature reported that solar dryer and solar collector maximum efficiency of 54% and 81% respectively, with superior products quality than the open solar drying. Solar drying is economical method with the payback period of 0.54–4.69 years. Solar dryer can also reduce 34% of CO2 emission to the atmosphere with less consumption of fossil fuel. Improvements such as in the design of solar collector, drying chamber, new auxiliary system, and material are essential to elevate the solar drying system performance. A review of the technologies can provide a base for the next generation of sustainable solar drying systems and helps policymakers to frame strategies aiming for clean technology and sustainable development.

Cover material of solar dryers influences on fruit properties due to the temperature and ultraviolet radiation (UV) during drying. Polyethylene (P) is the most used material for covering solar dryers. Cellular polycarbonate (CP) is a material that promotes UV protection; hence, it has recently been proposed as a covering material for greenhouse dryers. However, it is unknown whether CP cover will have any effect on bioactive compounds of foods treated by solar drying. Especially, if CP has advantages in preserving sensitive compounds compared to traditional materials as P. In this work the effect of CP and P covers on anthocyanins (TA) and total phenolic compounds (TPC) of strawberries during solar drying was evaluated. Open sun drying was used as a reference. Drying temperature, solar radiation, external and internal UV radiation was measured. The results indicated that the drying temperature and UV radiation influenced the moisture content and bioactive compounds. Direct radiation increased the drying temperature and reduced the final moisture content, while the partial incidence of UV radiation in the dried samples with P covers favored the remaining 40.7% of TA and 42.5% of TPC. With CP covers, where the ultraviolet radiation was zero, the 15.5% of TA and 14.4% of TPC were retained. Activation energy indicated that bioactives were more stable in the solar dryer with P and transparent cellular polycarbonate covers, demonstrated that they can be used as coatings in solar dryers destined for drying fruits, producing high-quality dehydrated products and efficient solar drying processes.

Agriculture contributes to large export earnings for many countries and provides food all over the world. However, most agricultural products need some post-harvest processing, such as drying, to extend their shelf life while still maintaining their respective nutrient quality. One popular post-harvest processing method is drying using solar energy. It is a type of renewable energy that is abundant and free. Conventional dryers use grid electricity and can be expensive to operate. Consequently, there is a growing need for cost-effective solar-powered agricultural dryers that is reasonable for smaller-scale farmers. Although current solar dryers are still not on par with modern electricity-powered dryers, solar dryers have lower running costs and are sustainable and able to generate electricity. They can also be used practically anywhere with abundant solar energy. As numerous solar drying technologies have been proposed over the past decade, it is necessary to assess the current state of solar drying technology in the agricultural sector to identify current advancements and potential research gaps. In this paper, a review of existing solar dryers mechanism and the state of the art of solar drying technology research for agricultural products is presented.

Natural convection indirect type solar dryer integrated with reflectors that can be used for drying fruits and vegetables was designed, constructed, and evaluated. The study mainly tried to improve the performance of a prototype natural convection indirect solar dryer. The solar dryer was integrated with reflectors and its thermal performance was experimentally analyzed and results were compared with the same dryer without reflectors. The experiments conducted included a no-load test to determine the stagnation temperature that can be reached and drying tests using tomato slices. During the drying test, moisture content at the initial and final stages was measured using a moisture balance instrument. The mass of the tomato slices was measured every two hours to find the drying efficiency. Temperatures were measured using thermocouples located at the absorber plate and at the trays inside the drying cabinet. Solar radiation was also measured using a pyranometer located near the dryer. During no load experiments, the maximum temperature reached the collector was around 98oC for the dryer without reflectors. The maximum temperature was improved to around 154oC during the test with reflectors. Similar temperature improvement was obtained during the drying tests as well. Due to the improvement in the temperature in the collector, the drying rate was also improved by 8% for 10 kg and 14% for 5 kg load. The experimental results indicate that the dryer performance was improved when the reflectors were added.

Low thermal efficiency is one of the main problems in using solar collectors in different fields. In the present study, the effect of using phase change materials (PCM) inside the Flat plate collector (FPC) on the thermal performance and overall drying efficiency of FPC was investigated. Four PCM positions were considered inside of the collector, and the results compared with the collector without PCM. Experimental results implied that specific energy consumption for drying tomato slices is between 11.12 and 9.01 MJ/kg. The drying time of the slices using the collector with PCM at the end section was decreased about 21.87%. Based on the position of PCM, the thermal efficiency of FPC increased by about 5.02%-10.13%. The overall efficiency varied from 21.92% to 25.72% for different PCM positions. CFD simulation of the system was performed by Ansys 2015, and it showed that the thermal performance of the collector could be predicted with good accuracy (R2 > 0.9432). Moreover, the result of evolutionary polynomial regression models applied for each PCM position. It confirmed that outlet temperature and thermal efficiency of collector predicted with acceptable accuracy (R2 > 0.98). Due to the use of PCM at the end section of the collector, a homogeneous drying process, normal temperature, and short drying time resulted. The quality of tomato slices dried by the solar dryer was higher than other positions.

In this study, the manufacturing and testing of an infrared dryer equipped with a PV/T solar collector were investigated. The total energy for the drying process is provided by solar energy. This study sought to compare the experimental results of glazed and unglazed modes and observe the effect of volume flow rate variations on the drying process of the products to determine the dryer’s energy and exergy efficiency and analyze the drying kinetic of potato slices. The amount of inlet airflow to the PV/T was controlled during the experiment. The power of the fan is supplied directly from two photovoltaic panels and the surplus amount of electrical energy is assigned to an infrared radiation source to enhance the process. Despite the low energy consumption of the current system, the products’ drying time was significantly reduced compared to similar systems. As a result, in glazed experiments, the drying time is prolonged in a range of 12–25% for 3 mm thicknesses and between 5 and 25% for 7 mm thicknesses compared to unglazed experiments. The maximum system energy efficiency and system exergy efficiency were 9% and 0.5%, respectively, calculated for 7 mm slices in unglazed tests.

Improper handling of fruits and vegetables causes a significant postharvest loss. Among the postharvest preservation mechanisms, solar dryers are reported as sustainable and suitable preservation systems for fruit and vegetable products. This paper summarizes the recent advances, opportunities, and challenges in solar drying of fruit and vegetable products. Besides, the review discusses the commonly used mathematical models for the evaluation, design, and optimization of solar dryers. The review discusses the factors that affect the performance of solar drying systems concerning drying time, drying rate, and product quality attributes. Short drying time, uniform drying air velocity, temperature, and product moisture distribution in the drying chamber are the critical parameters that are required for an efficient operation of a solar dryer. There is a good prospect in the application of mathematical modeling techniques such as computational fluid dynamics (CFD) in identifying the optimum solar drying conditions and dryer design that can maintain the required quality of the product. CFD has been used extensively in studying the airflow, heat, and mass transfer processes for optimizing the design and operation of different drying systems, similarly different quality models have been applied to evaluate the quality of dried products. However, most CFD studies did not include the quality aspect for dryer performance evaluation or optimization studies. To get the best result, CFD based performance evaluation or optimization studies of the solar dryers should have the capacity to predict the product quality in addition to the airflow, heat, and moisture transfer characteristics.

Hybrid air heater is a device taking advantage of two or more energy sources directly or indirectly for heating air. This study aims to analyze energy and exergy for a hybrid air heater. It is assumed that no thermal gradient exists along glass thickness and one-directional variation of temperature is in flow direction and thermal capacity of glass, absorber plate, and thermal insulations are negligible. To avoid food oxidation in dryers, effects of heating fluid such as air, carbon dioxide, and nitrogen on temperature, heat transfer, and thermodynamic first and second law efficiencies are also investigated along with the effects of hybrid heating on the aforementioned parameters. The problem is solved using MATLAB software and invoking iterative method with convergence criterion of 0.0001 for temperature. Results indicate the positive effects of using carbon dioxide. Applying hybrid system is also shown to increase the efficiency of air heater.

The design and development of an evacuated tube collector-based solar dryer with heat pipe for drying of garlic clove were carried out in the present work. For the experimental performance evaluation, garlic cloves (10 kg) were dried from 69% to 8% moisture content (wb). The thermal performance of the evacuated tube solar dryer (ETSD) was tested on no-load and full load conditions at different air flow velocities (1, 2, and 3 m/s). The highest temperature of 86.7 °C, at no load condition, was obtained in the drying chamber at 2 m/s air flow velocity with the maximum solar radiation of 1204 W/m2 while the maximum peak sun hour was 6.27. The maximum drying rate, solar collector efficiency, and dryer efficiency were found to be 1.56 kg H2O/kg dry solid/h, 45.86%, and 56% respectively at 2 m/s air flow velocity. The highest average exergy efficiency of 56.59% was found at 2 m/s, and the average lowest exergy loss of 4.74 W was found at 1 m/s. ETSD performed efficiently at 2 m/s air velocity and was capable to dry the garlic clove within 8 h. The payback period of the developed ESTD was found to be 1.3 years.

Solar air heaters (SAHs) are commonly utilized in different applications due to their simple structure and low setup cost. Optimizing operating parameters of the SAH is highly linked to the desired application. The aim of this study is to determine the optimal geometric and operational parameters of finned SAH for food drying. In order to achieve this goal, response surface methodology was combined with an experimentally validated thermal model of the SAH system. Multi-objective optimization is carried out according to energy-exergy analysis, improvement potential (IP) and outlet temperature suitable for food drying (40–70 °C). Length/width ratio (L/W) (1–5), height of air duct (0.02–0.2), and number of fins (0-60) were the operating variables. The experimental tests were carried out on the indirect type solar dryer composed of SAH and the drying chamber. The developed code led to consistent numerical results that have been confirmed by experimental tests. The optimal parameters were defined as 1.28 L/W, 0.067 m air duct height and 49 fins. In these optimal conditions, the outlet temperature, thermal efficiency, and IP were 52 °C, 51.78% and 1397.34W, respectively. The optimal design improved the thermal efficiency by 15.76% and IP by 19.33%.