Indirect Solar Dryer Research Articles

Drying kinetics and thermo-environmental analysis of a PV-operated tracking indirect solar dryer for tomato slices.

The purpose of this study is to investigate how a tracking indirect solar dryer (SD) powered by photovoltaic cells affected the drying kinetics (DK) and thermo-environmental conditions of tomato slices. In this current investigation, three air speeds (1, 1.5, and 2 m/s) are used, as well as three slice thicknesses (ST) (4, 6, and 8 mm) and two SD, one of which is integrated with fixed collector motion (FCM) and another with SD tracking collector motion (TCM). The obtained results showed that the drying time (DT) isn't significantly change with increasing air speeds from 1 to 2 m/s, this may be due to many reasons such as short DT, high temperature inside drying room, and little difference between the exanimated air speeds. When the ST is changed from 4 to 8 mm and maintaining constant air speeds, the DT for FCM and TCM rose by roughly 1.667 and 1.6 times, respectively. In addition, the drying coefficient of the TCM is higher than the FCM due to higher temperature. At 1.5 m/s air speed and 8 mm ST, the maximum values of moisture diffusivity (MD) are 7.15×10-10 and 9.30×10-10 m2/s for both FCM and TCM systems, respectively. During the study of DK, nine drying models and chose the best based on higher R2 and lower χ2 and RMSE are used. The findings of the DK analysis revealed that the modified two term II model fit the experimental data of various air speeds well when TF was dried using TCM and FCM systems at varying ST. These findings are based on recorded observations. Where the models' R2 values varied from 0.98005 to 0.99942 for FCM system and varied from 0.99386 to 0.99976 for TCM system. Regarding environmental analysis, it is found that the CO2 mitigation per lifetime is ranged between 5334.9-6795.4 tons for FCM and 6305.7-6323.3 tons for TCM.

Stabilization of Sewage Sludge from North Moroccan Wastewater Treatment Plants Using Convective Indirect Solar Drying

Stabilization of Sewage Sludge from North Moroccan Wastewater Treatment Plants Using Convective Indirect Solar Drying

Impact of trapezoidal ribs on the performance of solar air collector: A numerical solution with optimized rib dimensions for better performance

In the present study, a 2D numerical analysis of the solar air collector (SAC) of an indirect solar dryer having trapezoidal corrugations on the absorber plate was performed. Corrugation pitch, p (twelve values ranged from 20 to 160 mm) and height, e (six values ranged from 1 to 10 mm) were varied and analyzed for six values of Reynolds numbers (Re). The output characteristics such as Nusselt number (Nu), friction factor (f) and thermo-hydraulic performance index (Thp) were calculated for different p, e and Re. The total work was categorized into two parts (part-I for optimizing p and part-II for optimizing e). 18 domains (twelve for part-I and six for part-II simulations) were generated and 108 simulations were executed to find the optimum dimensions (p, e and corrugation angle, α) of the corrugation. ANSYS Fluent-v15 was used to solve the problem. The maximum Nu for the corrugated sheet was 2.663 times greater than the flat absorber plate. The maximum Thp range was from 1.435 to 1.699 and obtained at the optimal values of p = 140 mm, e = 4 mm and α = 38.66° The numerical results were compared with the existing literature.

Drying kinetics, energy, colour and FTIR spectroscopy analysis on indirect solar dryer with paraffin wax and glass pieces as thermal storage material

This research focuses on developing an innovative Indirect Solar Dryer (ISD) incorporating paraffin wax and glass pieces as Thermal Storage Material (TSM) within the solar collector towards sustainable food preservation for future usage. Experiments were conducted using three distinct configurations of solar dryers: one with glass pieces and paraffin wax, another with glass pieces only, and a third without TSM. Additionally, conventional Open Solar Drying (OSD) was examined for comparison. Comparative analyses were performed on drying kinetics and energy efficiency. Results from the drying kinetics demonstrated a significant decrease in the Moisture Content (MC) of turmeric, from 84.2 % (w.b.) to 8.3 % (w.b.) within 29 h employing the configuration incorporating paraffin wax and glass pieces as TSM. Furthermore, this same configuration exhibited the highest dryer efficiency of 68.3 %. In addition to drying kinetics, Moisture Ratio (MR) was forecasted using twelve drying mathematical models, with the logarithmic model producing the most accurate forecasts (χ2 = 0.0009843 and R2 = 0.9782). Colour and Fourier Transform Infrared (FTIR) analyses have been investigated to assess the quality of the dried turmeric specimens. The configuration utilizing glass pieces and paraffin wax as integrated TSM yielded the best colour quality. FTIR spectroscopy investigation discovered peaks of the C-H Stretch within the range of 2830–2900 cm−1 in the ISD configuration spectrum, whereas these peaks were absent in the OSD spectrum, indicative of uneven drying in OSD. Based on these experimental findings, the designed ISD configuration with integrated glass pieces and paraffin wax TSM demonstrates effective results in reduced drying time and improved food specimen quality. It suggests that the proposed ISD configuration could serve as a sustainable and preferable method for drying in various industries.

Solar Drying Technology for Agricultural Products: A Review

The application of solar drying technology for fruits, vegetables and other crops is one of the most attractive, cost-effective and eco-friendly. Many types of solar dryers have been designed and developed in different parts of the world, having different degrees of technical performance. There are four types of solar dryers: (1) direct solar dryers, (2) indirect solar dryers, (3) mixed-mode dryers and (4) hybrid solar dryers. A synthesis view of the classification of solar energy dryers is also presented. Two groups of solar energy dryers can be identified: Passive or natural-circulation solar energy dryers and active or forced convection solar energy dryers. This paper is a review of all these types of solar dryers, including aspects of the various designs, details of construction and operational principles. Therefore, the selection of dryers for a particular situation is primarily based on what is available and the types of dryers currently used are widely based on available circumstances. Some recent developments in solar drying technology and the appropriateness of each design type for application by farmers in developing countries are also discussed.

Erratum to “Experimental investigation of indirect solar dryer integrated with wicked heat pipe”

Erratum to “Experimental investigation of indirect solar dryer integrated with wicked heat pipe”

Assessment of an indirect solar dryer for small-scale resin production: Energy, exergy, economic (3E), and sustainability analysis

This study evaluates an innovative domestic indirect solar dryer (ISD) for drying grapes (Vitis Vinifera L.), focusing on energy, exergy, economic, and sustainability performance. Two trials with crop loads of 15% (Trial-1) and 33% (Trial-2) were conducted. Trial-2 exhibited higher energy efficiencies in the solar collector (SC) and drying chamber (DC) compared to Trial-1, with efficiencies of 61.4% and 58.5% for SC, and a 13% increase in DC efficiency. The daily average exergy efficiencies for SC and DC ranged from 11%–13% and 54%–58%, respectively. Trial-2 also showed a 113% higher life cycle savings, a 54.4% decrease in payback period, and a 23% lower waste exergy ratio compared to Trial-1. Pre-treatment of grapes resulted in superior dried product quality. The study highlights the ISD’s potential as an economically and environmentally sustainable solution for small-scale agricultural ventures, providing insights for renewable energy sectors

Experimental investigation of indirect solar dryer integrated with wicked heat pipe

Experimental investigation of indirect solar dryer integrated with wicked heat pipe

Review Paper on Diffierent Types of Solar Dryer

Abstract: One of the most appealing and economical uses of solar energy is drying agricultural goods. With differing degrees of technical performance, a multitude of solar dryer types have been devised and developed across the globe. In general, solar dryers come in four different varieties: (1) direct solar dryers, (2) indirect solar dryers, (3) mixed-mode dryers, and (4) hybrid solar dryers. The product being dried, as well as technical and financial concerns, are reviewed in this paper together with other solar dryer kinds. Technically speaking, integrated storage, high efficiency, compact collector design, and long-life drying systems are the main focuses in the development of solar-assisted drying systems for vegetables. There exist alternative systems to air-based solar collectors. By using a water-to-air heat exchanger, water-based collectors are another option. A water-to-air heat exchanger can be used to push hot air used for drying agricultural products to pass through it. As part of the solar drying system, the hot water tank stores heat

Influence of glazing type on the drying kinetics and thermal performance of indirect solar dryer for jelly candy

This research aims to evaluate drying kinetics and thermal performance, influenced by the type of glazing. A novel solar dryer that has a phase-change-materials (PCM), heat-recovery (HR), V-groove absorber, and photovoltaic (PV). The research was carried out on jelly candy objects treated with the influence of glazing (single-double-vacuum glazing). Jelly candy has an equilibrium moisture content using single, double, and vacuum glazing collectors, namely 11.59 % (wb), 9.94 % (wb), and 8.83 % (wb), respectively. Then, all types of glazing have an average drying rate value of 0.05 % (wb)/min for three working days. Based on the model accuracy test indicate that the Page and Verma et al. model are the best models for predicting drying kinetics in jelly candy. Specific heat (Cp) and thermal conductivity (k) decreased as the equilibrium moisture content decreased with a range of >1000–2250 J/kg°C and >0.05–0.11 W/m.K, respectively. The heat-utilization-factor (HUF) and coefficient-of-energy (COE) values show an average value of 0.79 and 0.21. Various glazing shows an average heat-gain-percentage (HGP) of 24.82 %. Drying efficiency of indirect solar dryers with single, double, and vacuum solar collectors, namely 83.6 %, 85.2 %, and 85.2 %, respectively. SEM-EDS analysis shows that the surface of the jelly candy is filled with sugar crystals and contains several elements (C,O,K,Fe).

Experimental and numerical investigation of the incorporation of an air temperature controller for indirect solar dryers

Solar drying systems often face the challenge of overheating due to uncontrolled solar collectors, which can degrade the quality of dried products by destroying enzymes, vitamins, and their chemical composition. To address this issue, we developed and validated a new control system for stabilizing drying air temperature using both experimental and CFD numerical methods. This system not only effectively maintains the desired air temperature but also extends the lifespan of solar collectors by adjusting their exposure during periods of excessive solar radiation. The experimental results demonstrated that without the control system, the air temperature peaked at 72 °C, leading to potential product degradation. In contrast, the control system has succeeded in stabilizing the air temperature at an optimum level. Additionally, the validated CFD model confirmed the effectiveness of this control technique in various climatic conditions, including cold semi-arid, typically Mediterranean, hot semi-arid, and sub-desert conditions. The findings underline the importance and necessity of temperature control in solar drying systems, as well as the effectiveness of the CFD method in predicting system performance. Furthermore, this work significantly enhances the efficiency and applicability of solar drying technology, offering a practical solution for improving product quality and system durability.

Proposing novel approach for indirect solar dryer integrated with active-fan and passive-chimney: An experimental and analytical investigation

Solar energy utilizing for drying products was considered the important friendly method to the environment in order to minimize the fossil fuels dependence. With removing the content of moisture, fruits life can be improved and these can be conserved and utilized for long time. Solar technique of drying not evaporates only but provides safe storage and products controlled. The aims of this experimental work were to determine how the proposed design of an indirect solar dryer (Chimney [natural convection] and Fan [forced convection]) influence on the drying performance and the rate of evaporation for drying grapes in Egypt. Compared to open sun solar dryer (OSSD), the dried grape product from the indirect sun drying process (in both cases) is protected from pollution and dust. In addition, the grape samples are dried faster by the recommended indirect SDs than by the OSSD. The results showed that the moisture content (MC) of the grape sample in the chimney-SD dropped from 79.80 % to 14.04 % and for the Fan-SD to 15.83 % during three days of the experiments. In contrast, the average MC for the tray in the OSSD was 70.76 % for the same time. Furthermore, the mean collector thermal efficiency for the Fan and Chimney-SDs was 27.02 % and 29.18 %, respectively. The production costs were estimated at 4.65 $/kg and 4.5$/kg of dried grapes for the Fan and Chimney-SDs, respectively. Finally, The CO2 mitigation were 286.25 kg/year and 337.18 kg/year for the Fan and Chimney-SDs, respectively.

Development of advanced machine learning for prognostic analysis of drying parameters for banana slices using indirect solar dryer

In this study, eXtreme Gradient Boosting (XGBoost) and Light Gradient Boosting (LightGBM) algorithms were used to model-predict the drying characteristics of banana slices with an indirect solar drier. The relationships between independent variables (temperature, moisture, product type, water flow rate, and mass of product) and dependent variables (energy consumption and size reduction) were established. For energy consumption, XGBoost demonstrates superior performance with an R2 of 0.9957 during training and 0.9971 during testing, alongside minimal MSE of 0.0034 during training and 0.0008 during the testing phase indicating high predictive accuracy and low error rates. Conversely, LGBM shows lower R2 values (0.9061 training, 0.8809 testing) and higher MSE of 0.0747 during training and 0.0337 during testing, reflecting poorer performance. Similarly, for shrinkage prediction, XGBoost outperforms LGBM, evidenced by higher R2 (0.9887 training, 0.9975 testing) and lower MSE (0.2527 training, 0.4878 testing). The comparative statistics showed that XGBoost regularly outperformed LightGBM. The game theory-based Shapley functions revealed that temperature and product types were the most influential features of the energy consumption model. These findings illustrate the practical applicability of the XGBoost and LightGBM models in food drying operations towards optimizing drying conditions, improving product quality, and reducing energy consumption.

Experimental testing on the performance of solar dryer equipped with evacuated tube collector, rock bed heat storage and reflectors

Agricultural products can be dried in an open sun; but such drying method has poor quality of the product causes to grow bacteria and microorganisms and long drying time. In order to alleviate those draw backs of open sun drying, direct solar dryers were developed; but this type of dryer reduces the product quality due to direct exposure of solar radiation. Then, an indirect solar dryer became more important and efficient method. However, the most solar dryers were developed with less efficient flat plate solar collectors. A few solar dryers were developed using efficient solar collector called evacuated tube solar collector (ETC) but they have low overall performance. The goal of this research is to create a dependable solar dryer system for drying agricultural products. It was a solar dryer system with an independent rock bed thermal storage unit and an evacuated tube collector having reflectors. In this case, a rock bed has been a well-insulated with thermal insulation and its top surface is covered by a transparent double-glass. This system is intended to dry potato slice that weigh of 7.5 kg sample having a wet base initial moisture level of 80.1 %, until it reaches the ideal moisture content of 7–13 %. The solar dryer has been developed from drying chamber having size of (length x breadth x height) of 85 cm×61 cm x 62 cm, evacuated tube collector area of 1.3 m2, and rock bed volume of 0.137 m3 (with a solar absorber area of 0.52 m2 and a depth of 0.26 m). The solar dryer system was built and tested with loading slices at various air flow rates and open sun. Here, at a 0.016 m3/s air flow rate as compared to lower and higher air flow rates, more moisture reduction (9.3 % within eight hours and 0.664 kg/h), higher efficiency of the solar collector (62.02 %), more heat production from the system (20.79 MJ, of which 4837.8 kJ was recovered from the rock bed), and higher dryer efficiency (23.87 %) were attained. Compared to open-sun drying, 20 % less time was needed for drying. In addition, the study examined the significance of the reflectors and the rock bed. In comparison to the situation of utilizing ETC alone and 30 % of the drying period in relation to the open sun, the introduction of a reflector on the collector increased the average net heat obtained from the collector by 5.1 %. In another instance, the slice's moisture content was lowered to 12.37 % in under eight hours using ETC alone, while the dryer's efficiency was 29.82 %. However, the drying rate rise by 3.7 % in comparison to the dryer equipped with ETC alone because of the enhanced heat output in the dryer, which used ETC with a rock bed's help.

Drying Kinetics and Quality Attributes of Solar-Dried Red Peppers: A Comparative Study with Traditional and Industrial Methods

Red pepper is a valuable ingredient known for its abundance of vitamins and antioxidants. But, it usually needs to be dried for longer preservation. Hence, this research is aimed at examining the drying kinetics and quality attributes of dried red peppers utilizing various solar drying methods, in comparison with traditional open sun drying (OSD) and industrial laboratory thin layer dryers (LTLD). Analysis parameters employed include determining moisture content, measuring color properties, evaluating antioxidant capacity, analyzing capsaicinoid content, and assessing microbial presence. The drying process took place in a sunny environment with fluctuations in temperature and relative humidity as evidence of the dynamic conditions experienced within the solar dryers. It was observed that the logarithmic model was the most accurate in predicting moisture ratio over time, estimating a drying time of 25 hours to achieve 10% moisture content. The result demonstrated that direct solar dryers (DSD), indirect solar dryers (ISD), and mix mode solar dryers (MMSD) methods showed moderate changes in color parameters, with average ΔL∗, Δa∗, and Δb∗ values of -5.08, -23.71, and -13.62, respectively. The average overall color difference (ΔE) for these methods was 27.96. In addition, after comparing it to the LTLD method, which showed the highest content of phenolic compounds at 47.89%, MMSD displayed a slightly lower content of 44.71%. Similarly, MMSD exhibited higher levels of DPPH radical scavenging activity and ferric reducing power, measuring at 44.22% and 1163.75 μmol Fe2+/L, respectively. The capsaicin content remained relatively consistent across all drying methods, with MMSD, DSD, and LTLD demonstrating similar levels of approximately 31 mg/g. Although MMSD had slightly higher mold and yeast counts compared to LTLD, ISD, and DSD, it remained lower than OSD (less than 0.56 log10cfu/g). Furthermore, MMSD showed a lower total microbial count in comparison to other drying methods. These findings suggest that MMSD shows promise as a drying technique for preserving the phenolic compounds and antioxidant activity of the dried product.

Drying characteristics and kinetics of bottle gourd using stand-alone indirect solar dryer

Drying food is an effective method to preserve fruits and vegetables, increasing their shelf life and preventing germination. Bottle gourds, known for their high nutritional value, can rot quickly due to their high moisture content, causing biochemical and microbial changes. To improve shelf life, moisture can be removed to prevent microbial activity. Different drying methods are used to preserve gourd family vegetables for long periods and off-season. Indirect solar drying shields foods from UV rays, dust, insects, and other contamination by avoiding direct exposure. This study aimed to utilize an indirect solar dryer to research the potential for drying bottle gourds and conduct physicochemical analyses for the dried products to compare the drying techniques. In this experiment, different samples of bottle gourd slices were dried using an indirect solar dryer and compared with sun and shade drying. Under physicochemical properties, moisture content (MC), retention of color, thickness, and shrinkage of dried samples were analyzed and compared. The result showed that the time taken to reach 10% moisture was 13 h for samples dried with sun drying. While shade and indirect solar drying took 17 h. The Midilli-Kucuk model outperforms other approaches for drying bottle gourd, with the greatest R2 values (0.9967, 0.9950, 0.9936) and the lowest RMSE values (0.0182, 0.0220, 0.0277) for direct sun, shade, and indirect solar drying, respectively. The indirect sun dryer showed good color retention compared to the fresh bottle gourd samples with L* value of 44.08, b* value of 15.40 and a* value of 7.01. The volumetric shrinkage was 97.64% in the direct sun drying method after 15 h, which is higher compared to sun and shade dryers due to the effect of time and temperature. In addition, there was a significant difference (p-value <0.05) between the thickness of the three drying methods. The use of indirect solar drying methods can be highly recommended to get high-quality dried food with zero energy cost. For future studies it is recommended to enhance the function and design of the indirect solar dryer to speed up drying times and improve the quality of dried samples.

Assessment of performance and sustainability of waste heat dryer coupled with air conditioner unit during drying of banana slices

The present work presents the effective application of waste heat rejected from window air conditioning (AC) in a waste heat dryer (WHD) for drying plantain banana slices. The comparison between drying with the waste heat dryer coupled with an AC unit (ACWHD) and a natural convective indirect solar dryer (SD) reveals significant differences in drying kinetics, supply air conditions, and thermodynamic performance. The drying kinetics of banana slices obtained with ACWHD and SD were validated by revisiting the concepts of dryer performance index (DPI) and generalized drying curve. The temperature of the hot air supplied to the drying chamber in ACWHD was 48 °C while the relative humidity of the supply air was below 30 %. The thermodynamic performance assessment revealed that the exergetic efficiency was about 45 % and 16 % for ACWHD and SD respectively. The results of exergy based sustainable index and environment impact factor indicated the potential application of the waste heat of residual air from AC units for drying applications. Thus, the results of the present study imply that this novel idea has appreciable potential for commercialization with large-scale central air conditioning units in commercial complexes and industries where the magnitude of heat rejection will be multi-fold.

Dynamic simulation and thermoeconomic analysis of a novel indirect hybrid solar dryer

Indirect solar dryers represent a clean and sustainable solution for drying foods, fruits, and vegetables. In this research, the performance of a novel indirect hybrid solar dryer has been investigated numerically on apple slices using TRNSYS software. The solar dryer consists of a flat plate solar collector, a vacuum tube solar collector, a cross-flow heat exchanger, an auxiliary heater, and a drying chamber. With the assumption that there is no access to fresh fruits and vegetables in winter, the simulation was carried out in three days on April 15, July 15, and October 15 (from 8 a.m. to 5 p.m.) as representatives of spring, summer and autumn, respectively. The humidity content of apple slices reduced from 86 % to 11 % in about 270 min at 70 °C. The minimum power received from the auxiliary heater was on July 15 with 1497 W, which was about 1.5 h without needing a backup heater. (from 11:30 a.m. to 1 p.m.). The maximum thermal efficiency of the drying system was obtained on July 15 at about 60 % for the flat plate collector, 78 % for the vacuity tube collector, and 25 % for the drying chamber. Also, the return on capital in Iran, USA, UAE, and Turkey was equal to 1.49, 0.74, 0.95 and 1.35, respectively.

Postharvest practices and loss determinants for interventions among smallholder potato farmers in Tiyo district, Arsi zone, Ethiopia

Postharvest loss reduction, which will contribute to several sustainable development goals (SDGs) including SDG 1, 2, 3, 9, 12 and 13, is an important strategy for food and nutrition security. It requires interventions designed based on timely and reliable statistical data. However, lack of produce-specific loss data and associated factors along the postharvest value chain stages remains a challenge to implement appropriate interventions. Therefore, a survey was conducted on socio-demographic characteristics, postharvest practices, extent and causes of losses, and factors influencing postharvest loss of potato crops in Tiyo district of Arsi Zone, Ethiopia in 2022. A multistage sampling method was used to select a total of 209 smallholder potato farming household heads through a combination of purposive and simple random sampling techniques. Quantitative data collection was carried out online using computer-assisted personal interviewing (CAPI) by programming a semi-structured questionnaire in KoboCollect software for tablets. Descriptive statistics and ordinal probit regression model were used to analyze the collected data and determinant factors influencing postharvest loss of potatoes at various farm-level stages, respectively. An aggregate of 15-46% loss exists between harvesting and marketing. Losses during harvesting, sorting, cleaning, packaging, field-to-storage transport, storage, and storage-to-market transport were 58.9%, 6.2%, 2.9%, 2.4%, 3.8%, 20.1%, and 5.7%, respectively. Elevated loss during harvesting and storage in the area is likely to reflect poor handling and storage practices. The primary causes of losses were poor harvesting and handling techniques, poor storage facility, and insects and worms. Moreover, regression model estimations of categorical losses, as perceived by farmers, reveal that socio-demographic variables and postharvest factors influenced potato loss. During the harvest stage, working family members significantly (p<0.01) increased loss while years of schooling (p<0.05) significantly reduced loss. In addition, harvesting using leaf color change observation as a criterion had significantly (p<0.01) mitigated potato loss. In storage, female respondents (p<0.05), land size (p<0.05), and lack of training (p<0.1) had accentuated loss. During transport, the age of household reduced (p<0.1) loss whereas farming experience promoted (p<0.1) it. To reduce the existing losses, farmers’ awareness should be increased concerning each stage. The study recommends the need for stakeholders’ intervention focusing on postharvest knowledge and skill capacity building, demonstration of simple innovative ventilated storage construction using locally available materials, appropriate packaging (such as reusable plastic crates) and transport methods, and simple value addition methods (such as potato drying using indirect solar dryers and potato flour processing for fortifying local cereals). Key words: CAPI, Ethiopia, ordinal probit regression, postharvest practices, potato loss determinants

Realization and Experimental Study of a Forced Convection Solar Dryer

Post-harvest losses represent a significant cause of food insecurity worldwide. These losses not only affect the availability of food, but they also impact the economic stability of farmers and communities dependent on these crops. Food drying presents itself as a viable solution to reduce these post-harvest losses and ensure greater availability of food for human consumption. It is in this context that our work on the creation of an indirect solar dryer with forced convection, integrating an automatic temperature control system, takes place. This study consisted of creating a prototype and subsequently carrying out drying experiments on onions in order to evaluate the performance of the device. Our experiments took place from October 25 to October 29, 2023 at Joseph KI-ZERBO University. After 8 hours of drying, only 12% of the initial mass of the onions remained. The solar thermal collector presented an efficiency of 62%. And a drying efficiency, estimated at 17% with an average sunshine of 600W/m2.