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In geopolymer bricks (GPBs), fly ash content, which is waste from power plants, is converted into bricks by chemical treatment. GPBs can be dried by using appropriate curing methods. Conventionally, electric oven curing is one of the prominent methods. Using a solar dryer instead of an electric oven provides the added advantage of saving high-grade electrical energy. So, in this work, a solar dryer with the phase change material (PCM) paraffin wax and without a PCM is used for curing applications. GPBs gain an added advantage when compared to conventional bricks like cement and sand bricks in terms of strength. A GPB has been taken as a specimen for comparing the compressive strength, tensile split strength, and flexural strength of electrical-energy-based curing and solar-energy-based curing. It has been experimentally observed that solar-energy-based curing with and without a PCM exhibits higher compressive strength, higher tensile split strength, and flexural strength when compared to electrical-energy-based curing. Solar curing with a PCM shows higher compressive strength, higher tensile split strength, and higher flexural strength when compared to solar curing without a PCM. Open solar curing is a traditional technique, but nowadays, aggressive climatic conditions can lead to severe damage to geopolymers. The novelty of this work is the study of the effect of PCMs like paraffin wax in solar drying on the curing time and the mechanical properties of GPBs. [ABSTRACT FROM AUTHOR]

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

In the central jungle region of Peru, within the wet processing of coffee, the coffee pulp is discarded. This objective is to design a dual solar and gas dryer with continuous operation, for the dehydration of waste from wet processing of coffee for human use. The proposed objective is part of a broader project to apply the circular economy in the use of waste from wet coffee processing financed by Pro Ciencia. The following procedure was followed. At first, a 100 kg/Bach capacity gas and solar system dryer was designed applying the proposed technology development methodology in mechanical engineering and secondly arriving at the construction of the prototype. The results are to have a design methodology and the built prototype of the dual dryer (solar and gas) of continuous and semi-automated operation that has a control panel to allow programming and monitoring the drying process in real time. At the end of the project, the proposal will allow a continuous dehydration of the coffee pulp with quality, low cost and the industrialization of its by-products such as coffee pulp flour, filters and functional drinks.

The use of solar energy for drying is considered one of the most environmentally friendly ways to reduce dependence on fossil fuels. The purpose of this experimental study is to determine how absorption plate design affects the evaporation rate of a solar food dryer in Baghdad, Iraq. Tests were performed on four different absorbent panel models. This dryer design consists of a section for heating solar air and one for preserving food. There is insulation at the back of the dining cabinet, which is made of wood. As food samples, orange slices were selected. Except for the absorb plate design, all four models have identical measurements. Matte black aluminum absorbent plate is featured on the Model-1. Both Models 2 and 3 have perforated cylindrical fins arranged uniformly and vertically in Model 2 and horizontally in Model 3. Model 4 uses horizontal fins and an absorber plate coated with 15 % silicon content. A fruit cabinet holds sliced fruit in five movable mesh trays. According to experimental results, the shape of the absorbent plate directly affects the temperature of the outlet air, which in turn affects the rate at which water is evaporated from fruit slices and the overall drying process. Model-1 solar air heaters could be improved by approximately 17 % by coating them with 15 % silicon. The efficiency of Models 2, 3, and 4 is increased by 20 %, 40 %, and 65 % by adding fins and tint over Model 1. Models 1, 2, 3, and 4 had moisture contents of 28 %, 25 %, 20 %, and 18 %, respectively, at 15 p.m. A solar dryer has been demonstrated to be suitable for successfully drying fruits and vegetables in Iraq's atmosphere through practical experiments.

With ever expanding population and accelerating energy challenges, the ultimate need to adopt green-energy solutions for the preservation and storage techniques for fruits and vegetables has become vital. Sun drying is an age-old method to preserve food and it has revived the popularity within the industrial sector to overcome the high energy consuming operations. This work presents the experimental investigations of a solar dryer with integrated thermal storage chamber. The thermal storage chamber employed paraffin wax as a phase change material (PCM). Incorporating PCM enhances the efficiency and efficacy of the solar dryer. PCM absorbs heat, causing it to melt during peak sunshine hours. Then, during periods of reduced sunlight, the PCM releases the stored heat, enabling continuous product drying. Particularly, the solar dryer successfully dried onions, apricots, and peas, with moisture removal percentages of 69.6 %, 65 %, and 75 % respectively from the total mass.

Food industry being one of the world's largest energy intensive industries, lack of proper preservation and storage techniques have led to huge amount of food losses and wastage. Dehydration of food and vegetables has been an effective technique of preservation as this reduces post-harvest losses, make them easier to transport, store and can prevent the growth of microbes. Abundant solar energy being available for free of cost, solar drying is desirable in terms of environment friendliness, economic benefits and is compatible for remote locations. Solar dryers optimize this process with efficient utilization of solar energy and provides higher quality products. Different configurations of solar dryers with diverse configurations and applications have been designed and implemented over the years. Based on the difference in supply and utilization of solar energy, the most prominent solar dryer configurations are direct and indirect solar dryers. This work intends to review the features, design and performance of existing direct and indirect solar dryers. Major challenges such as intermittency and unsteady availability of solar energy has been addressed through thermal energy storage by many research studies, which has also been effectively reviewed. Materials used for construction, design constraints, thermal energy storage integration and experimental results have been discussed and tabulated. The review revealed highly efficient solar collectors such as tube type absorber and evacuated tube collectors, solar concentrators employed dryers capable of achieving elevated temperatures, greenhouse and solar tent dryers with huge capacity and novel dryer and collector designs of superior performance. Various integration techniques of different thermal energy storage materials and their enhancement in performance were eminently observed in the review. As a source of technological attributes and constructional features, this review paper intends to aid the development of solar dryers and food preservation employing renewable energy. [ABSTRACT FROM AUTHOR]

Solar energy provides desired thermal energy for diverse applications, including industrial heating, domestic cooking, power generation, desalination, and agri-food preservation. Despite extensive research on solar drying from the scientific community, there are limited practical applications for small-scale use. This review attempts to analyze the design features of three specific types of dryers for food drying applications: solar evacuated tube dryers, biomass dryers, and hybrid solar dryers. The thermal performance of the three dryers is evaluated in terms of drying time, moisture removal, and temperature attained during drying. The review also assesses the prospects of solar dryers, highlighting the need for further research into innovative designs and advanced drying capabilities. The study provides valuable information for enhancing dryer performance with various integrated solutions. [ABSTRACT FROM AUTHOR]

Drying agricultural products in open sun drying (OSD) is a well-known and ancient technology. OSD has a lot of limitations and these can be eliminated by employing various solar dryers. Integration of thermal energy storage (TES) units with solar dryers is an interesting and emerging area of research as it makes the dryers functional throughout the day. Among the sensible and latent heat storage substances, paraffin wax is widely used in solar dryers because of its easy availability, cheapness and its high TES capacity per unit volume. This work extensively reviews the solar dryers integrated with the TES units where paraffin wax is used. The different types of paraffin wax and their thermo-physical properties are presented. The thermal performances of various solar dryers with and without paraffin wax are reviewed and their effect on the drying time and drying efficiency is reported. Various kinds of TES unit locations inside the dryer were reviewed. Different methods available to enhance the thermal conductivity and heat transfer rate between paraffin wax and drying air are reviewed. Perspectives and challenges of solar drying with paraffin wax are also addressed. The thermal efficiency of solar dryers was enhanced up to 50% when paraffin, n-docosane with kerosene were mixed with a 2:1 ratio. [ABSTRACT FROM AUTHOR]

Due to the expansion of residents, the consumption of non-renewable energy increased enormously, thus indirectly increasing pollution and affecting the surroundings. To reduce pollutions in the surroundings, it is recommended to choose non-conventional energy sources. By satisfying this, we can probably decrease the non-renewable sources of energy, by consuming the solar power in day-to-day life in the application of food drying process. In this review article, we have discussed the classification of solar dryer and the impact of design modifications performed in the components of solar dryer and assessed the various types of solar dryer performance, cost estimations and designs performed in solar dryer of food applications which were not discussed in the earlier research. The primary and critical task in designing the solar dryer is to achieve higher efficiency at minimum cost. Hence, proper analysis of drying application, selection of suitable components and suitable design must be carried out to attain efficient dryer. Considering these characteristics, this paper primarily focuses on the effective design parameters incorporated with various efficiency enhancement processes of the solar dryer in the applications of food drying techniques. Thus, this review paper delivers the various classifications, design parameters, performance enhancement methods, properties and valuable assets of solar dryer, which helps to develop the sustainable green eco-friendly environment most primarily, in the application of food drying process. This review article concreted the way for upcoming considerations and provided the techniques for the studies to convey the work for promoting method enhancements. [ABSTRACT FROM AUTHOR]

Energy and environomical analysis play important role in designing a solar thermal drying system as these analyses identify the high energy-consuming area, formulate energy-saving measures and evaluate the size of any potential savings. In this study, a greenhouse solar dryer with a double-pass multi-hollow collector for leaf drying was evaluated using environmental-economic analysis. Environmental analysis includes the determination of embodied energy, energy payback time (EPBT) period, as well as CO2 emissions per year, carbon mitigation and carbon credit. The embodied energy of a passive dryer is 606.86 kWh and EPBT of 16.68 years, while for an active dryer, the values are determined at 636.17 kWh and 10.39 years, respectively. CO2 emission for the passive dryer is 47.17 kg per year, net CO2 mitigation of 124.6 kg, and earned carbon credit of RM 2.58 – RM 12.38. The active dryer has CO2 emission of 47.14 kg, net CO2 mitigation of 594 kg, and earned carbon credit of RM 51.95 – RM 247.66. Economic analysis of this dryer shows that the energy cost associated with its operation ranges from RM 1.59 to RM 4.77, monthly.

Background: In the past 30–40 years, conflicts over limited conventional energy sources and the negative climate change caused by them have attracted researchers and analysts to new, clean, and green energy technologies. Thereby reducing the consumption of conventional fuel and the negative impact on the climate. The production of alternative energy in the form of thermal energy storage using phase change materials (PCMs) is one of the techniques that not only reduces the gap between the supply and demand of energy but also increases the stability of the energy supply. The tendency of PCMs to melt and solidify over a wide temperature range makes them more attractive for use in many applications. The effective and efficient storage of solar energy by PCM has the potential to significantly advance the use of renewable energy. Methods: Organic non-paraffin compound beeswax (BW) mixed with other non-paraffin compounds stearic acid (SA), Palmitic acid (PA), Myristic acid (MA), and Lauric acid (LA) in different compositions with the help of magnetic stirrer at 50–60°C for 3–4 hours to prepare BWSA, BWPA, BWMA, and BWLA eutectic PCM. Results: Prepared eutectics melt and solidify in the temperature range 36–56°C and with latent heat in the range of 155–211 kJ/Kg. Conclusions: Due to suitable temperature and good latent heat storage range, it is a good choice as thermal energy storage, for solar drying applications.

In solar drying, the moisture content of a product is reduced through the use of sunlight. Solar drying is practiced since civilization for the drying of crops. The dried crop has a longer shelf life and requires less storage space. For crop drying, hot air is required in the moderate temperature range of 40 to 75℃. Solar dryer makes it possible to obtain better product quality. Over the past 20 years, numerous experimental projects have been carried out in the field of solar dryers. Most conventional dryers are not able to operate continuously during the off sunshine time. However, attempts were made to develop uninterrupted solar drying systems by incorporating an energy storage facility and a hybrid mode of operation. Sensible and latent heat storage methods are widely used to store solar energy. Heat storage materials store energy in the form of heat during sunshine and release it whenever it is required. Biogas backup, Chemical heat pump, Photo Voltaic, and Fluidized bed methods were integrated with solar dryers for uninterrupted operation. In this article, the discussion is made about different dryers. Also, the challenges and scope in the area of the solar dryer are highlighted.

The current study examined reduction of moisture from agricultural energy and food crops in a conventional oven to a solar dryer at various treatment periods at temperature between 40 ± 10 oC. Sugarcane bagasse and Phragmites Australis had initial moisture of 50.8 % and 6.07 % by dry weight, respectively, with higher heating values (HHV) 6548.5 kJ/kg and 17653.02 kJ/kg respectively. The moisture content of bagasse and phragmites were decreased by 51.31% and 68.69% respectively using oven drying, while the moisture content of bagasse and phragmites was reduced by 48.01% and 66.22% respectively, using solar drying with 5 hrs treatment time. Corresponding increase in HHV’s observed in bagasse to 11195.6 KJ/kg (oven drying) and 10998.1 KJ/kg (solar drying), while HHV of phragmites increased to 18706.79KJ/kg (oven drying) and 18685.36KJ/kg (solar drying). Green chillies had a moisture content reduction by 33.69 % (oven) and 8.28 % (solar), whereas grapes had a reduction by 31.20 % (oven) and 7.88 % (solar) with 5 hrs treatment time. The oven drying approach revealed higher carbohydrate content in food crops when compared to solar drying, while both treatments showed a similar drop in protein, fat, and vitamin C contents. Statistical and energy analysis observed that comparing solar drying; the oven drying eliminates slightly higher moisture content and have less drying energy requirements. The amount of heat energy required for drying unit mass of bagasse was 0.476 kJ/kg (oven) and 0.556 kJ/kg (solar), for phragmites it was 0.074 kJ/kg (oven) and 0.092 kJ/kg (solar), for chilles 0.524 kJ/kg (oven) and 0.576 kJ/kg (solar) and for grapes 0.123 kJ/kg (oven) and 0.157 MJ/kg (solar). According to the results solar drying required greater quantity of heat energy than oven drying. Mass transfer analysis showed drying constant of bagasse and phragmites were higher initially, then showed reducing trend with respect time. Furthermore, it was observed that the effective diffusivity and mass transfer coefficient were found reducing with respect to increasing drying treatment time. The research findings of renewable solar drying, on the other hand, are comparable to those of oven drying, demonstrating that there is still enough untapped heat energy available for its utilization in biomass thermo-chemical conversion methods.

A solar air heater that operates in the mixed-mode double pass and an absorber plate has aluminum cans at the top and bottom of the absorber for red pepper drying experiments was conducted in Bahir Dar, Ethiopia climatic conditions. A total dying period of red pepper in a mixed-mode solar greenhouse dryer takes less time than an open solar drying system. From the experiment, the average daily dryer chamber temperature ranges between 39.93 0C and 47.02 0C and the average daily ambient temperature ranges between 24.890C and 27.530C. Solar insolation reached 973 W/m2 when the sun was at mid-day and minimum solar insolation was 220 W/m2 and 0.0383 kg per second of air are expelled. A newly designed mixed-mode double pass, integrated with an Aluminum can dryer and the traditional open sun dryer, achieves an efficiency of 46% and 28%, respectively. In the open sun dryer system and the mixed-mode solar dryer, the drying rates are 0.0003395 kg/s and 0.0000365 kg/s respectively. On eleven mathematical models, Microsoft Excel was used to perform the statistical analysis. Logarithmic models were found to be the best explanation of red pepper behavior in both mixed-mode and open-sun solar dryer systems. These models were tested by comparing the maximum value of the coefficient of determination R2 and the minimum value of reduced chi-square X2 and root mean square error RMSE between experimental and predicted moisture ratios.

The heat and moisture sensitivity of spices and a consistent supply of electrical energy is the challenging factors in developing a relevant drying system for rural applications. A novel solar‐assisted fluidized bed dryer was developed for drying locally harvested unique spices like bird's eye chili (Capsicum frutescens L.). The chili was pretreated by the osmosonication method prior to drying to expedite the elimination of intercellular and intracellular moisture. In order to make the dryer more reliable, the recirculation strategy and dehumidified air supplied by liquid desiccant were acclimatized to constrict the heat loss through outflowing moist drying air. The experiments were conducted up to the permissible water activity (0.4–0.6) under variable drying conditions (50–70°C). By raising the ambient inlet temperature (maximum 25.9°C), the developed solar FBD was able to supply the drying air up to 50°C (in continuous mode) and a maximum of up to 65°C without aiding any heat energy sources except solar. It was found that osmosonication opened up the possibility of reducing the required drying temperature (↓10°C) and energy consumption (up to ↓31.7%). The dried red chili was fortified by pretreatment, as it could retain more capsaicin (>6%) and reddishness (>5%) compared to untreated samples. The Fourier transform infrared (FTIR) analysis showed the structural integrity of pretreated samples. The relative humidity of the drying air could be reduced by as much as 5% using the composite lithium chloride and calcium chloride (35% + 5%) desiccant dehumidifier. Dehumidification of air was found advantageous, with an inclination to shorten the drying duration (about ↓0.5 h) and energy (↓12.43%). Practical Applications: There are various commercially valuable unique agro‐products that are exclusively being produced in rural areas. The inaccessibility of relevant drying technology and inconsistency of grid electricity are the main constraints in the value addition of those products. Open sun drying is most popular in rural areas; however, it is not reliable, and the product quality can't maintain. The developed solar‐assisted fluidized bed dryer utilizing dehumidifying air and integrated with osmosonication pretreatment could be a relevant technology for drying heat and moisture‐sensitive products like spices. Cost‐effective drying using locally accessible solar energy compared to open sun drying and superior dried product quality can be achieved by using the current drying system. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Solar drying represents an attractive way to implement an efficient and green development strategy. The viability of open sorption thermal energy storage (OSTES) can compensate for the inherent shortcomings of intermittency and instability of solar energy for ensuring the continuity of the drying process. Nevertheless, the existing solar-powered OSTES technologies only allow a batch mode while being severely restricted by sunlight's availability, thereby heavily limiting the flexibility in managing OSTES on demand. Herein, a novel proof-of-concept that a standalone solar dryer integrated with a reversible solid-gas OSTES unit is presented. Using in situ electrothermal heating (in situ ETH) could rapidly release adsorbed water of activated carbon fibers (ACFs) in an energy-efficient manner to achieve a charging process with faster kinetics. Applying electrical power by a photovoltaic (PV) module, particularly during sunlight-absent or insufficient time, allowed multiple OSTES cycles to proceed. Moreover, ACFs cylindrical cartridges can be flexibly interconnected in either series or parallel, forming universal assemblies with well-controlled in situ ETH capacity. The mass storage density of ACFs with a water sorption capacity of 570 mg/g is 0.24 kW·h·kg-1. The desorption efficiencies of ACFs are higher than 90%, corresponding to 0.057 kW·h maximum energy consumption. The resulting prototype can diminish the fluctuation of air humidity along the night and provide a relatively steady and lower air humidity for the drying chamber. The energy-exergy and environment analysis of the drying section for both setups are estimated, respectively. [ABSTRACT FROM AUTHOR]

This present work deals with experimental investigation of photovoltaic thermal collector design and development with solar dryer (PVTCSD). An solar experimental investigation is done on coriander seeds by natural, forced and open sun drying to estimate different parametric investigations such as solar radiation intensity, removal of moisture and the air outlet in the collector. Solar radiation is utilized as a source of energy to propel the photovoltaic thermal collector dryer; which was analysed in a drying testing chamber temperature in the range of 32°C to 59°C to dry 4 kg of coriander seeds. From the experimental study, it was understood that coriander seeds posses much more starting moisture 68% by weight and also the results proved that final moisture content has been decreased by 9% by weight during six bright days in the month of May 2021. The PVTCSD was used during the 9 a.m. to 4 p.m. In terms of understanding PVTCSD, solar sun drying with the forced convection achieved superior results than other two modes of operation. [ABSTRACT FROM AUTHOR]

The drying process is considered an effective technique for preserving foods and agricultural products from spoilage. Moreover, the drying process lessens the products' weight, volume, and packaging, which prompts a reduction in the products' transportation costs. The drying technique with solar energy represents an ancient method, still alluring due to solar energy abundance and cost‐effectiveness. In this article, the previous manuscripts concerned with studying and analyzing indirect solar dryer systems that utilize innovative solar air heaters (SAHs) are reviewed. The results and conclusions are discussed intensively to clarify the significance of utilizing this type of drying technique. The effect of many parameters on the thermal performance and efficiency of the dryer systems has been investigated. The investigated parameters included the incident solar radiation, air flow rates, outlet solar air heater temperature, absorber plate material, moisture content of the agricultural products, and the shape and configuration of the SAH. Moreover, the manuscript outlines the drying rate mathematical models that were used to validate the experimental findings. Based on the review, it is found that solar dryer systems with modified SAHs designs rather than flat plate SAH have considerable effects on enhancing thermal performance and efficiency. [ABSTRACT FROM AUTHOR]

Agricultural technological development is a crucial strategy for agricultural commercialization and socio-economic transformation in Africa. However, a key challenge to technology use in agriculture remains the limited farmer acceptance of unfamiliar technologies. This paper uses a sample of 245 okra farmers drawn from northern Uganda to assess the drivers of the farmer acceptance of solar drying technology. On the basis of drying performance, farmers perceive the solar dryer to perform better than the open sun-drying method. Structural equation modelling results show that the drying rate and perceived product quality are the main determinants of farmer perceptions on product marketability. Further, product marketability drives acceptance of solar dryers among farmers. We conclude that acceptance of solar dryers is dependent on: i) the drying rate, ii) favorable perceptions towards product quality, and iii) perceived marketability of the solar-dried product. We call for policy action on intensification of efforts that promote solar drying technology, including supporting local artisans to fabricate dryers, to enable increased value addition and consumption of nutritious foods.

This recent study evaluated a hybrid solar-assisted heat pump dryer (HS-AHPD) for drying paddy and its product quality. R22 is used as a working fluid in the heat pump system during the drying experiment. The HS-AHPD decreased the paddy's weight from 420 kg (31.67% db) to 370.60 kg (16.18% db) in 5.5 h with an average air temperature of 62.9 °C and an average relative humidity of 16.1% at a mass flow rate of 0.195 kg/s. The average drying rate, specific moisture extraction rate (SMER), and specific energy consumption (SEC) were 8.34 kg/s, 0.44 kg/kWh, and 4.69 kWh/kg, respectively. The HS-AHPD's average thermal efficiency and the exergy efficiency of the drying section were found up to 29.1% and 18.4%, respectively. The furnace and the solar collector contributed 19.7% and 12.9% of energy to the HS-AHPD, respectively. The improvement potential (IP) was in the range of 628.8–824.4W. The drying resulted in higher-quality products due to higher head rice yield (93.10 ± 1.044%), lower broken rice (4.41 ± 0.737%), and lower rice grouts (1.11 ± 0.271%).

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

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India like other developing countries adopts many food preservation technologies using fossil fuels. But the fossil fuel resource depletes over the years and is non-renewable. Therefore, solar drying technology is preferred as a sustainable method for food preservation. The present study is aimed at a sustainable livelihood initiative for drying fruits and vegetables through solar technology intervention using an indirect forced convection type solar dryer. Such a dryer of 15 kg capacity has been designed and fabricated for drying mangoes. Performance indicators such as instantaneous collector efficiency, drying efficiency, drying rate, COP, heat utilization factor, and moisture content on a dry basis are evaluated as 59%, 32.25%, 0.15178 kg/hr, 0.77, 0.229, and 2.55, respectively by considering maximum outlet collector temperature, drying chamber temperature and atmospheric temperature. Economic indicators such as pay-back period and cost-benefit ratio are also evaluated as 1.439 and 2.0008, respectively. The dryer can be used by rural people of Odisha for earning their livelihood. [ABSTRACT FROM AUTHOR]

• Mixed mode UV sheet tent house solar dryer using natural convection is investigated. • Potato chips are dried in a natural convection solar dryer with different thickness. • For 2.5 mm and 5.0 mm thick sliced potatoes, solar drying took 6h less time than OSD. • Upper and lower trays ranged from 34.2°C to 59.7°C and 33.6°C to 57.1°C respectively. • All the performance parameters are superior for 2.5 mm thick sliced potatoes. A mixed mode natural convection ultraviolet (UV) tent house solar dryer is designed and installed at University Teaching Department, Chhattisgarh Swami Vivekanand Technical University, Bhilai, Chhattisgarh (21°27′N, 81°43′E) India for drying potato slices. This solar dryer is equipped with a solar flat plate collector (area 1.12 m2), covered with 5.0 mm thick glass and consists of two trays of the same size (0.57 m X 1.11 m) in a drying chamber on which equal quantities of potato slices were placed. The local atmospheric conditions including relative humidity, atmospheric temperatures, solar intensity, and wind velocity have been recorded for analyzing various parameters. The solar intensity and atmospheric temperature ranges from 134 to 993 W/m2 and 36.2 °C to 44.9 °C respectively. The initial moisture content value of 85.25% reaches 14.75% for 2.5 mm thick potato slices and for 5.0 mm thickness, the initial & final moisture content values are 85.10% & 14.90% respectively. The upper and lower tray temperature varies from 34.2 °C to 59.7 °C and 33.6 °C to 57.1 °C respectively. The open sun drying took 6 h longer than the solar natural convection drying. Moisture ratio for 2.5 mm thickness and 5.0 mm thickness lies 0.475–0.001 and 0.650–0.003 respectively. The maximum dryer efficiency is 26.62% and 21.61% for 2.5 mm and 5.0 mm thick potato slices respectively. All the drying kinetics is superior in the 2.5 mm thickness of the potato in process of drying using natural convection. [ABSTRACT FROM AUTHOR]

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

The paper develops a Mixed Mode Solar Crop Dryer (MMSCD) using blackcoated pebbles. The experiments were conducted in Ujire, Karnataka, India. Potato slices were used for test sample with an air speed of 4 m/s. Open Sun Drying (OSD) was used and the working temperature range of MMSCD was 36-64 o C, which is suitable for drying a wide variety of fruits and vegetables like green peas, cauliflower, chillies, apples, sweet potatoes and grapes. The dryer was able to provide hot air from 9:00 to 19:00 hours in a day. The overall maximum efficiency of the dryer was 56%. To reduce the moisture content from initial (75%) to storable level (below 10%), MMSCD took 6 h. However, 24 h (3 days of sunshine) were taken under OSD to attain the safe moisture content. [ABSTRACT FROM AUTHOR]

[Display omitted] • 70.5% reduction in drying time by the integration of latent heat and sensible heat energy storage. • Highest average drying temperature and drying rate by combined energy storage. • Drying efficiency of 14.2% with the use of black pebbles and lauric acid PCM. • Lowest payback period of 0.7 years. • Highest vitamin C retention when dried with energy storage materials. The effect on drying kinetics, economic characteristics and nutritional quality of dried cucumbers in a mixed mode solar dryer with both sensible and latent heat energy storage is investigated in this study. A thick bed of black pebbles at the base of drying chamber facilitated sensible heat energy storage and Lauric acid PCM filled in custom made chamber which was connected in series to the solar collector allowed latent heat energy storage. The dryer was operated without energy storage (Test 1), with sensible heat energy storage alone (Test 2) and with both sensible and latent heat energy storage (Test 3), in this study. Compared to open sun drying test 1, 2 and 3 reduced the drying time by 29.4 %, 47 % and 70.5 %, respectively. An average dryer temperature of 42.3 °C, 45.9 °C and 50.9 °C were recorded in test 1, test 2 and test 3, respectively. Rate of drying was significantly enhanced up to.76 kg of moisture per hour by integrating latent heat and sensible heat energy storage materials and also exhibited the highest drying efficiency of 14.2 %. Test 3 had the lowest payback period of 0.7 years with remarkable economic benefits compared to test 1 and test 2 configurations. The quality analysis of the products revealed higher vitamin C content in dried products from all three tests when compared to dried products under open sun, with highest retention of vitamin C reported in products from test 3. [ABSTRACT FROM AUTHOR]

It is estimated that in Portugal per year, 132 kg/person of food is wasted due to imperfections in weight, shape and due to their perishability, resulting in foods that cannot be marketed. Solar drying can be used to extend food life. However, it usually does not meet the current productivity and quality requirements of the dried product. Solar energy is renewable, very available in Portugal, which can make an important contribution to reducing the specific energy consumption and carbon footprint intensity associated with drying. This work aims to optimize the drying process using a solar dryer with electric support. The conditions of temperature and humidity in the dryer and their influence on the physical and chemical properties of blueberries and raspberries were studied, namely the ash, protein, fat, sugars, total phenolic compounds content and antioxidant capacity.It was concluded that the blueberries and raspberries, after drying underwent slight changes in some chemical parameters, namely the reduction of fats and phenolic compounds. The results of the drying tests showed a strong dependence on atmospheric conditions. Under the most favorable conditions, it was possible to record reductions in electricity consumption of 35%.

Photovoltaic-thermal (PV-T) solar air/water collectors have received increasing attention in recent years. Efficiency is the most important parameter usually considered in PV-T technologies. The present paper expressed energy efficiency and thermal-electrical exergy of PV-T collectors, and compared the studies of researchers on the performance of these systems. The figures are provided to give an overview of how PV-T performance is improved. Changes in heat transfer fluid play a major role in electrical and thermal efficiency. A brief overview of the most promising fluids used in PV-T is reported in this article. Nowadays, improving PV- T performance by optimizing the adsorbent plate and cooling fluid and using nanofluid has been considered by researchers. The application of these schemes in implementation, especially in agriculture, can help significantly in increasing the efficiency of solar radiation. Therefore, future work should be aimed at increasing efficiency and reducing costs to increase their competitiveness and use as a renewable and environmentally friendly energy device.

This experimental study aimed to evaluate the efficacy of natural and forced convective drying techniques in reducing the moisture content of the grapes in comparison with the conventional open sun drying method. Moisture effective diffusivity and activation energy were graphically determined using the Arrhenius equation. In the initial three-day period, forced convection drying significantly reduced moisture from 2000 g to 353 g, with a minimum loss of 14 g. In the next three days, natural convection reduced moisture from 2787 g to 468 g, with a minimum loss of 11 g. These outcomes were then compared to the results of open-sun drying. The investigation showed that open drying and natural convection methods eliminated 25.05 % and 82.35 % of the moisture content, respectively. However, for three days, open-sun drying removed 30.5 % of grape moisture, while forced convection achieved an impressive 83.21 % reduction. The study's innovative mathematical model explained drying curve characteristics, supported by correlation coefficients and parity plots. The comparison shows that the experimental moisture ratios and those predicted by the new correlation exhibit R2 values ranging from 0.984 to 0.994. [ABSTRACT FROM AUTHOR]

In this article the energy & exergy analysis of forced convection solar dryer for drying of garlic has been investigated. The exergy parameter, air velocity has been taken to conduct the experiments and its effect on thermal efficiency. Forced draft fans were used in all the two working conditions. During the two conditions, with and without sensible heat storage system, the average air-velocities were 4.5, 9.5 and 11.4 m/s selected as ideal and subsequently its entire effect on thermal efficiency and outlet. The ambient temperatures were between (17-25) °C during the month of October and November. A DC fan is directly connected to the photovoltaic cell in the solar dryer. The thermal energy storage bed was packed with gravels with 1.5 in of thickness up to the surface of flat plate collector, the storage system becomes space-efficient. The average thermal efficiency with sensible heat storage materials was high as compared to system without sensible heat storage. The highest thermal efficiency of 61% was achieved. The maximum collector temperature obtained was 55 °C, with a mean temperature of 42 °C in the drying chamber. The collector’s greatest exergy loss was 30.38 kJ/kg and highest exergy efficiency was 70%.

Sun drying in the open air is quite popular worldwide. However, the use of solar dryers to preserve various perishable agricultural products is a relatively new area of study, and the long-term effects of this method are not yet fully understood. The slow drying process in direct sunlight can contaminate the dried materials by soil and insects. To overcome these challenges, we devised a sun drying system that included a heating part, a drying area, a portable stand, fans, and a 50-W photovoltaic panel. An alternate energy source was used to power the drying process during cloudy days and at night. Fresh Freestone peach, Golden apple, and Anaheim chilies weighing 10 kg each with the initial moisture content of 89%, 87%, and 75% on a wet basis (w.b), respectively, were used in the experiments. The final moisture content of the samples was reduced by an average of 16%, 15%, and 11% for Freestone peaches, Golden apples, and Anaheim chilies, respectively. The quality analysis was carried out to determine sample composition, total bacteria, and color of dried products. The results indicated that the dried products met the recommended quality standards for food products in terms of composition, total bacteria, and color. This research supports the use of a hybrid mixed-mode solar dryer for drying a wide range of perishable agricultural products.

The treatment and disposal of sewage sludge is one of the most important and critical problems of wastewater treatment plants. 8.7 million tonnes of dry matter of sewage sludge were produced annually in the European Union in the year 2020. Due to the fact that sewage sludge contains a large number of substances that are not beneficial for human health, the conditions for sludge management will be significantly tightened in the EU countries. One option for sludge liquidation is the production of biofuel in a form of granules or pellets from sewage sludge enriched by waste celluloses. The achieved results show that the resulting quality of such alternative biofuel is fully comparable to conventional fossil fuels. The economic analysis is based on the simulation of cash flows associated with the implementation of the project over the lifetime and the calculation of levelised cost (LCOE). Results shows (under the current economic situation) that solar dryer technology ensures the lowest LCOE at the level of 26 EUR/GJ in fuel. If the LCOE of the alternative biofuel includes the price of the saved emission allowance and the future costs of sewage sludge disposal, the resulting price is directly competitive with lignite. The results thus clearly show that there is an ecological and economically competitive substitute for solid fossil fuels, which may be an important step for the future use of local combustion sources such as district heating plants. [ABSTRACT FROM AUTHOR]

It is the oldest and most common traditional food preservation method known to dry by laying food products under the sun. However, if the food product is in direct contact with the sun light, there is a decrease in the color and nutrient values of the product. To solve these problems, solar dryers have been developed which can be utilized due to indirectly the effect of the sun. In this study, kiwi rings were dried by using osmosolar dehydration as a combination of osmotic dehydration and solar drying. Kiwi rings were first immersed in sucrose solutions and then dried in a solar dryer. Response Surface Methodology used to determine effects of the conditions ondrying performance and find out optimum levels drying conditions for the responses to a safe level. In the response surface method, the drying conditions were selected as the kiwi slice thickness (A), sucrose concentrations (B), immersed time (C) and solar drying time (D). The response to be optimized was chosen as water loss, diameter shrinkage ratio and greenness (a) color change. A successful mathematical model was obtained by the response surface method between the drying conditions and the responses. The suitable model is chosen quadratic for water loss, 2FI model for color change model and shrinkage ratio. The model R² value is 0.952 for water loss, 0.737 for a color change and 0.856 for shrinkage ratio. The regression coefficients, along with the corresponding P-values, for the model of production water loss, a color change and shrinkage ratio are described by ANOVA. Values of "Prob>F" less than 0.0500 indicate model terms are significant. In this case B, C, C² are significant model terms for water loss. A, B, C, AB, AC, AD, BC and CD are significant model terms for color change and B, C, AC, AD, BD, CD are significant model terms for shrinkage ratio. The optimum drying conditions levels was determined to sucrose concentration 12.7 %w/v, ring slice thickness 4.06 mm, solar drying time 125 min and immersed time 70.9 min, respectively. In addition, pretreatment of osmotic dehydration was found to be effective in drying kiwi rings with solar tray dryer. [ABSTRACT FROM AUTHOR]

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