•Post-harvest loss of fresh produce in East Africa is enormous.•Farmers solely depend on open sun drying, which is an inefficient method of drying food.•A modified solar dryer was prototyped and ...proposed as an alternative.•Modification of the hybrid solar dryer with multiple metallic solar concentrators boosts drying performance.
Reducing postharvest losses (PHL) of fresh perishable agro-produce is a key strategic pathway to increasing incomes, food and nutrition security in East Africa. In response, an improved Hybrid Indirect Passive (HIP) solar dryer with a modified solar collector plate and drying cabinet, has been developed and presented as a better food drying alternative against the traditional open sun drying (OSD) method. A conventional active-mode Solar Photovoltaic and Electric (SPE) dryer with an auxiliary thermal-backup system was also fabricated. The fruit drying performance of the HIP and SPE dryers was evaluated using pineapples and mangoes, and compared against the traditional open sun drying (OSD) method. The food drying duration for the SPE, HIP and OSD methods were 10 h, 18 and 30 h; respectively. Drying efficiency of the improved HIP dryer was comparable to the SPE dryer and was 18% higher than the OSD method. Therefore, modifying the solar collector plate with multiple metallic solar concentrators coupled with an improved greenhouse cabinet significantly improves the drying performance of the HIP dryer. The HIP dryer is, therefore recommended for mass adoption against the OSD method.
•PVT collector-based solar dryer has been developed for green tea drying application.•Glass to glass PVT collector has been investigated first time for drying application.•PVT system performance has ...been compared under sunny and cloudy days.•Mixed-mode and indirect mode drying are investigated under natural and forced mode.•Drying kinetics of green tea leaves is compared with proposed and published models.
A sustainable solar based PVT tea drying system has been developed to minimize the dependency on the non-renewable commercial tea drying system. In this work, the effect of operating conditions on the performance of a photovoltaic-thermal (PVT) collector-based solar dryer is investigated under sunny and cloudy weather conditions for three different cases- Case-I (natural convection), Case-II (forced convection with an air velocity of 0.096 m/s), and Case-III (forced convection with an air velocity of 0.014 m/s). Firstly, energy performance of the PVT system has been evaluated for all the three cases under sunny and cloudy days, which show that the energy performance has been enhanced to a maximum value of 58.71% and 53.95% for sunny days and cloudy days, respectively, and these are obtained in case of case-III. Then the drying of green tea under mixed-mode drying (MMD) and indirect mode drying (IMD) are presented under sunny days for each of the three cases and compared with open sun drying (OSD) and shade drying (SD). The moisture content has been reduced from 2.95 (d.b.) to 0.14 (d.b.) in all the cases of drying modes. Further, the drying kinetics of green tea leaves is compared using existing models, and a new drying model is proposed, which is found to predict the moisture ratio better. The maximum PVT dryer efficiency, moisture effective diffusivity, and specific moisture extraction rate (SMER) are 26.37%, 4.97 × 10−9 m2/s, and 0.6125 kg/kWh, respectively, for MMD process.
•A photovoltaic thermal – evacuated tube dryer with and without set points examined.•Two new model to predict the drying process of Tarkhineh was presented.•The life-cycle cost analysis (LCCA) of ...Tarkhineh was performed.•The payback period of the PV/T dryer and ET solar dryer were 2.3 and 2.5 years.
In this study, an indirect solar dryer was designed and manufactured using a Photovoltaic Thermal (PV/T) collector and Evacuated Tube (ET) collector. The main objectives of this system were to supply the thermal load of the indirect solar dryer, to find the best model for the drying process, to present a new model to predict the drying process of Tarkhineh (the drying material) and to perform its life-cycle cost analysis (LCCA). The manufactured system was tested under the weather conditions of Sanandaj city, Iran and was compared with open sun drying. When the auxiliary heater was not used, the new model 1 was the best model to describe the drying of Tarkhineh in the open sun mode and the new model 2 was the best model to describe the drying of Tarkhineh in the solar dryer designed and manufactured in this study. The new models 1 and 2 were found to be the best models for describing the drying process of Tarkhineh at set point temperatures 55 °C and 45 °C, supplied by the auxiliary heater, respectively. The payback period of the PV/T solar dryer and ET solar dryer, assuming 300 sunny days/year, were 2.3 and 2.5 years, respectively.
Solar dryers have always been criticized for their lower performances. There are numerous ways to define the performance of a solar drying system such as thermal performance, drying kinetics, ...environmental aspects, economic evaluations, and quality of the dried product. Different modeling techniques have also been developed to design and analyze solar dryers and drying processes. This article presents a systematic, comprehensive, and state-of-the-art overview of various performance indicators and modeling techniques used for the evaluation and analysis of solar dryers, especially domestic and low cost solar dryers. Environmental analysis has severe global implications, and product quality is one of the biggest concerns of consumers. But the environmental impact and product quality assessments for domestic solar dryers are observed to be rarely reported in the literature. The use of modeling techniques in solar drying has changed the way of analyzing any thermal system. Here, an attempt is made to establish an overall assessment criterion for domestic solar dryers and to give a one-stop solution for researchers and users around the world.
A review of solar drying technologies VijayaVenkataRaman, S.; Iniyan, S.; Goic, Ranko
Renewable & sustainable energy reviews,
06/2012, Volume:
16, Issue:
5
Journal Article
Peer reviewed
Agricultural products such as coffee, tobacco, tea, fruit, cocoa beans, rice, nuts, and timber generally require drying through a consistent application of relatively low heat. Traditionally, crop ...drying has been accomplished by burning wood and fossil fuels in ovens or open air drying under screened sunlight. These methods, however, have their shortcomings. The former is expensive and damages the environment and the latter is susceptible to the variety and unpredictability of the weather. Solar crop drying is a happy medium between these two methods and it dries crops with more efficiency, uniformity, and less expense. A solar crop drying system does not solely depend on solar energy to function; it combines fuel burning with the energy of the sun, thus reducing fossil fuel consumption. In this paper, the status of solar drying technologies in developing countries is presented. The various designs of solar dryers, its types and performance analysis are reviewed. Special attention is given to the solar drying technologies that facilitate drying of crops in off-sunshine hours. The solar dryers specifically designed or tested using specific crops like the vegetable dryer, fruit dryer, grain dryer, grape dryer, and so on are also reviewed with details about the specifications and the results. In short, the state of art technologies and development of solar dryers are presented in this paper.
A mixed-type solar dryer operating with three different modes of operation (mixed-mode natural convection (MM-NC); mixed-mode forced convection (MM-FC) and indirect-mode natural convection (IM-NC)) ...were evaluated to reduce the moisture content of pear of 82.15 ± 0.13% up to 8.86 ± 1.3% (wet basis). The drying times were 5.25, 4.5, and 6.6 h; the drying efficiencies were 13.6, 11.2, and 26.6%, and the average instantaneous thermal efficiencies of the solar air heater were 33.0%, 56.3%, and 30.9% for the MM-NC, MM-FC, and IM-NC modes, respectively. The drying chamber’s exergy efficiency values in the MM-NC mode was 65.2%, while the lowest values were in the MM-FC mode (54.4%). The MM-FC mode had a more significant improvement potential (308.76 kJ) than the other modes. The highest average value of the energy utilization ratio was 29.1% in the IM-NC mode. The experimental data shows that the MM-NC mode had a higher exergy efficiency than the other two operation modes. The IM-NC mode shows a lower improvement potential, taking better advantage of the supplied energy. Having these results would be expected that by increasing the load, the solar dryer’s thermal and exergy efficiency in the MM-NC mode and MM-FC mode could be improved.
•A mixed-type solar dryer was utilized for dehydrating pear slices under 3 different methods.•Exergy and energy analysis of three modes of operation was studied.•Values of energy utilization ratio, exergy loss and exergy efficiency were presented.•Effect of modes of operation on energy and exergy of dryer have been examined.•Operating the system in forced convection increases the thermal efficiency of the SAH.
•Energetic and exergetic analysis of the dryer system are investigated.•The proposed solar dryer is sustainable, since it only uses solar energy.•The most significant input exergy rate is due to the ...absorber plate.•Three control volumes were used to evaluate the exergetic efficiency.•Thermal and exergetic efficiency are greatly affected by the control volume used.
In this study, an energy and exergy analysis of the drying process of corn was developed for a hybrid dryer coupled with a PV system. The differential of the dryer is the fact that the PV system was used to feed an electrical heater and fans and also to preheat the drying air through the use of the PV panel rear side as heat exchanger, increasing the air temperature before the inlet of the solar collector. The performance of solar drying processes is extensively investigated in the literature, but usually the drying chamber is used as control volume in the analysis. The main contribution of this work is the assessment and comparison of the performance of the dryer using three different control volumes in the thermodynamic analysis: only the drying chamber, the drying chamber and the solar collector, referred to as solar dryer and the complete drying set, corresponding to the drying chamber, the solar collector and the PV module. The results indicated that the efficiency values found are greatly affected by the control volume used, with variations of the exergy efficiency ranging from 22.2% to 45.0%, depending on the control volume used. It was found that the higher efficiencies were found selecting the drying chamber as control volume (as usually chosen by most works from literature). For the complete drying set, the individual contributions of the exergy rates were evaluated. It was concluded that the main contribution to the input and output exergy are the heat transfer and the outflow exergy rates, respectively.
•Natural energy storage (NES) materials on food drying applications were reviewed.•The types, progress and benefits of NES materials were discussed.•Applications in direct, indirect, mixed-mode and ...hybrid solar dryers were analyzed.•Highlights, perspectives and challenges of NES materials were thoroughly reviewed.•Important results were tabulated and concluding remarks were reported.
The application of solar energy in food drying is a well-known technology. Open sun drying has some limitations but these limitations can be overcome in solar dryers. Thermal energy storage (TES) systems for solar dryers receive wide attraction as the TES system enhances the performance of dryers. Among TES materials, the natural energy storage materials are inexpensive and easy to collect in remote areas. This work extensively reviews solar dryers with various natural energy storage materials. It discusses thermo-physical properties of various natural energy storage materials. The performance analyses of direct, indirect, mixed-mode and hybrid mode solar dryers with and without natural energy storage materials are reviewed. natural energy storage materials placed in different locations such as kind 1, kind 2 and kind 3 are discussed. The performance of frequently used natural energy storage materials such as sand, sandstone, gravel, rocks, pebbles, limestone, clay, soil, bricks, quartz, reinforced concrete and water are reviewed. The drying time saving is in the range of 9.52−47.2% using natural energy storage materials compared to conventional solar dryers. The drying efficiency (ηd) and thermal efficiency (ηth) of the direct solar dryer with natural energy storage are in the range of 2.85−42% and 9.9 − 58.2%, respectively, for various food materials. The drying air temperatures inside the chamber are 5 to 20 °C higher than the atmospheric temperature even after sunset hours with the natural energy storage system. The progress, benefits, challenges and recommendations of natural energy storage materials for use in solar dryers are also addressed in this paper.
Synthetic textiles can shed numerous microfibers during conventional washing, but evaluating environmental consequences as well as source-control strategies requires understanding mass releases. ...Polyester apparel accounts for a large proportion of the polyester market, and synthetic jackets represent the broadest range in apparel construction, allowing for potential changes in manufacturing as a mitigation measure to reduce microfiber release during laundering. Here, detergent-free washing experiments were conducted and replicated in both front- and top-load conventional home machines for five new and mechanically aged jackets or sweaters: four from one name-brand clothing manufacturer (three majority polyester fleece, and one nylon shell with nonwoven polyester insulation) and one off-brand (100% polyester fleece). Wash water was filtered to recover two size fractions (>333 μm and between 20 and 333 μm); filters were then imaged, and microfiber masses were calculated. Across all treatments, the recovered microfiber mass per garment ranged from approximately 0 to 2 g, or exceeding 0.3% of the unwashed garment mass. Microfiber masses from top-load machines were approximately 7 times those from front-load machines; garments mechanically aged via a 24 h continuous wash had increased mass release under the same wash protocol as new garments. When published wastewater treatment plant influent characterization and microfiber removal studies are considered, washing synthetic jackets or sweaters as per this study would account for most microfibers entering the environment.
The proper treatment of organic or inorganic solid wastes is necessary for economic and environmental interests. Added-value by-products of market interest can be obtained through the recovery, ...reuse, and treatment of solid wastes, which are otherwise discarded inappropriately in large quantities into the environment. In this review, the drying process is presented as an alternative environmental technology for the thermal treatment of residues of different natures from different origins. The main techniques applied to solid waste drying are described and, in parallel, the most relevant studies found in the literature for this theme are analyzed. Moreover, the main dryers currently used are presented, as well as their most important characteristics. Some general aspects of the thermal and energetic performance of these dryers fundamental for process feasibility analysis are also discussed in this review. Essential aspects of the solid waste drying process are primarily presented with the purpose of showing the particularities that this approach offers when it comes to putting the theory into practice.
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