Solar Dryer Research Articles

Finding Critical Factors for Developing Dynamic Models to Optimize Greenhouse Solar Dryer’s Environmental Conditions

This paper is focused on the formulation of a mathematical model for greenhouse solar dryer systems in the context of determining the principal drivers of efficiency of the solar dryer. The model was built by evaluating the correlation coefficients of each term and only those terms which had high levels of significance were retained. To test this model, experiments were replicated with measurements being taken in the different sections of the greenhouse to provide a large spectrum of the environmental conditions involved. The values of the technical coefficients are predicated on internal air temperature, humidity ratio and weight of the product with fixed scales, avoiding sophisticated complex models prone to overfitting. By using terms with high correlation, the model is less likely to be affected by outliers and total correlation or cross correlation is low, thereby making the model practical. The outcomes of this research, therefore, offer a scientifically viable and a practical approach to enhancing drying processes in greenhouse solar dryer systems.

Protocol Refinement for the Development of Coconut Inflorescence Powder

Aims: Coconut inflorescence holds significant potential as a nutraceutical due to its rich composition of bioactive compounds, including vitamins, minerals, and antioxidants. Its use in promoting health and preventing diseases has made it a valuable ingredient in both traditional medicine and modern functional foods. The aim of the study is the protocol refinement for the development of coconut inflorescence powder with acceptable moisture content and superior sensory quality. Study Design: Completely randomized design (CRD). Place and Duration of Study: Department of Plantation, Spices, Medicinal and Aromatic Crops, College of Agriculture, Vellayani, Kerala Agricultural University, between May 2024 and October 2024. Methodology: In the present study, coconut inflorescence was harvested at 5-6 months before inflorescence opening, size reduced (1 cm3 pieces), and precooked by adopting different methods, viz., steaming, boiling, dry roasting, and microwave cooking (non-precooked inflorescence was used as the control). The precooked inflorescence pieces were dried by different drying methods viz., hot-air oven drying at 600C (Control), cabinet drier at 600C, 700C, 800C and solar drying for developing coconut inflorescence powder (CIP). CIP was analyzed for moisture content and sensory quality. Results: CIP prepared by steaming the coconut inflorescence pieces for 30 minutes and drying in cabinet dryer at 600C (C1D1) recorded the least moisture content, 1.83±0.07 per cent. However, CIP prepared by boiling (95-1000C) the inflorescence pieces by submerging for 30 minutes and drying in cabinet dryer at 600C (C2D1) showed the highest mean rank value for all the sensory attributes viz., colour (735.50), consistency (730.63), flavour (730.68), mouthfeel (734.75) and taste (735.23) on a nine-point hedonic scale with a moisture content, 4.20±0.04 per cent. The lowest mean rank value for colour was recorded by C1D1 and C2D0 (211.06). The lowest values for consistency, mouthfeel, flavour and taste were observed for the treatments C4D1 (289.81), C4D1 (290.61), C4D0 (226.05) and C0D0 (216.50), respectively. Hence, C2D1 was identified as the best precooking and drying method for the preparation of coconut inflorescence powder.

Assessing thermal and economic performance of solar dryers in sustainable strategies for bottle gourd and tomato preservation.

The traditional approach of open-sun drying is facing contemporary challenges arising from the widespread adoption of energy-intensive methods and the quality of drying. In response, solar dryers have emerged as a sustainable alternative, utilizing solar thermal energy to effectively dehydrate vegetables. This study investigates the performance of a single-basin, double-slope solar dryer utilizing natural convection for drying bottle gourds and tomatoes, presenting a sustainable alternative to traditional open-sun drying. The solar dryer exhibited superior moisture removal efficiency, achieving a 94.42% reduction in tomatoes and 83.87% in bottle gourds, compared to open-sun drying. Drying rates were significantly enhanced, with maximum air and plate temperatures reaching 54.42°C and 63.38°C, respectively, accelerating the dehydration process. Moisture diffusivity analysis revealed a marked improvement in drying behavior under solar drying, with values ranging from 3.12 × 10-11 to 4.31 × 10-11 m2/s for bottle gourds, and 4.65 × 10-11 to 2.31 × 10-11 m2/s for tomatoes. Energy efficiency assessments highlighted the solar dryer's advantage, with exergy efficiency peaking at 61.78% for bottle gourds and 68.5% for tomatoes. Furthermore, the activation energy required for drying was significantly lower in the solar dryer (29.14-46.41kJ/mol for bottle gourds and 27.16-55.42kJ/mol for tomatoes) compared to open-sun drying, enhancing energy conservation. Visual inspections confirmed the superior quality of the solar-dried vegetables, free from dust and impurities. An economic analysis underscored the system's viability, with payback periods of 2 years for bottle gourds and 1.6 years for tomatoes. Overall, this study demonstrates the efficacy of solar dryers in optimizing vegetable preservation while promoting energy efficiency, aligning with global sustainability goals by reducing post-harvest losses and supporting eco-friendly practices.

PERFORMANCE EVALUATION OF NATURAL AND FORCED CONVECTION IN SOLAR DRYERS FOR MULLET FISH

Ombak Damai Trading, a Malaysian company specialising in dried mullet fish, needed to dry the fish faster to meet growing demand. They reduced the drying time from 1-2 days to 3-4 hours using a solar dryer. The dryer was equipped with an IoT (Internet of things) weighing system for precise monitoring and data collection. Two inlet fans were added for forced convection drying. Measurements of weight, temperature, and humidity were taken for ten days. The forced convection system was found to be 85.78% effective, compared to 59.36% for natural convection. Moisture analysis revealed that the forced convection system removed more moisture, with a maximum percentage of 36% compared to 22% for natural convection. Forced convection also had a higher drying rate of 60.17 g/hour compared to 37.83 g/hour for natural convection. These findings can help seafood businesses optimise the drying process and achieve target moisture levels. Further studies are recommended to examine the forced convection system's commercial scalability, as well as the effects of drying on nutritional content and sensory qualities.

Research advances in solar dryer technologies integrated with solar air heater: a state-of-the art review on design variations, performance and feasibility assessments

Research advances in solar dryer technologies integrated with solar air heater: a state-of-the art review on design variations, performance and feasibility assessments

Thermal Evaluation of Solar Dryer’s Curve-Front utilized Heat Transfer Analysis

The sun is most sustainable renewable energy, environmentally friendly and utilized for preservation of food and agricultural crops. The main objective of this experiment research work has focused on using renewable energy for evaporated moisture of foods fruit vegetables and herbs by drying system. The heat transfer equation are analyzed to effectively harness the temperature from the sun. Experimental data obtained were used to evaluate the properties of dry air on boundary region condition. Initial, testing was carried out under without load condition, and the result shows that the ambient and dryer’s internal temperature range between 29.3-40.2˚C and 37.4-60.3 ˚C, respectively, in Thailand a latitude of 14°0'48.46" North and longitude of 100°31'49.76" East (recorded average solar radiations and temperature on January 2023 - June 2024), average solar radiations range between 312 W/m2 and 513 W/m2. The indirect natural convection was design and calculated energy base on average temperature not higher than 55˚C, utilized sun daylight at 08:00 a.m. to 04:00 p.m. local time and clear sky or partially cloudy. Second, determination of design parameters; heat energy equation and steam table analysis. Final, utilization of the design under local time, solar radiation and the climatic local conditions and test with ginger slices (represent product in order to examine weight loss). The solar dryer’s curve front shape conduced on without load showed the heat transfer coefficient natural convections range between 3.7 and 4.5 W/m2 ˚C, the energy of dry air analysis range between 54.7 and 155.2 J/s and performance of drying rate range between 0.06 and 0.82 g/s, under increasing and decreasing trends of solar radiations from the time, date and climatic local region condition.

Thermal Conductivity, Density and Calorific Value of Sargassum Fluitans and Sargassum Natans Species

In this study, we obtained the values of the thermodynamic properties of sargassum that includes S. fluitans and S. natans species, which are the ones that most arrive at the coasts of the Mexican Caribbean. The sargassum samples, collected at the coast, were dried in a direct type of solar dryer and their final relative humidity was 15% dry base. Two physical models were designed to construct biscuits of 0.0127 m in diameter and 0.0063 m in length, which were used to obtain the density and calorific value and those used for thermal conductivity, were 0.069 m in diameter and 0.008 m thick. The density resulted in 660.62 𝑘𝑔/𝑚3 . To determine the calorific value, a commercial calorimetric pump was used, and the value obtained was 17,950 𝑘𝐽/𝑘𝑔. For thermal conductivity, a device that employs the hot plate and guard method was designed and built and its value was 0.346 𝑊/𝑚°𝐶. These values indicate that it is possible to use dehydrated sargassum to produce energy, which has approximately a value of 75% of that obtained for sugar cane bagasse. With these three values and using the thermal diffusivity definition equation, this last parameter was calculated in 2.917 × 10−11 𝑚2 /𝑠.

Investigation of thermodynamics performance of solar dryer equipped with double pass flat, v-corrugated, and low-e coated collectors

In this study, a solar dryer incorporating a flat plate heat exchanger to recover heat from exhaust air was investigated to explore the usability of different types of collectors in the system. Their usability was further evaluated through economic and environmental analyses. Moreover, the thermodynamic performance of the solar dryers was evaluated under two weather conditions in Nepal. Apple drying experiments were conducted for 8 hours from 09:00 to 17:00 from February to April 2023 on solar dryers and with open sun drying (OSD) in Dhulikhel, Nepal. The results showed that the low emissivity (low-e) coated aluminum collector was more efficient in terms of collector efficiency and drying rate than collectors with flat or v-corrugated GI absorbers. The average collector efficiency and drying rate were found to be 89% and 107 g/(h×m2) using the low-e coated aluminum collectors, while the values were 50% and 84 g/(h×m2) for the GI sheet collector. The results indicated a slight improvement in the performance of v-corrugated collectors, with values of 53% and 89 g/(h×m2). The drying rate for OSD was found to be 78 g/(h×m2), which was lower than for the dryers with all collectors used in this study. In terms of economic analysis, the dryer equipped with the low-e coated collector was found to be superior, with a payback time of 1.61 years compared to the dryers with flat or v-corrugated GI collectors. Reducing the thermal losses due to radiation by using the low-e coated absorber was shown to be more important than increasing the absorber area using v-corrugated GI sheets.

Performance investigation of newly developed novel hemispherical solar dryer for sustainable food preservation: Comparative analysis with traditional methods

To preserve the world’s food resources, drying agricultural products is crucial for prolonging their shelf life. A novel concept of 1.5 m hemispherical solar dryer surmounts the limitations of conventional dryers like long drying time, solar tracking, large space requirement etc. Trials were performed on Thomson grapes to convert into raisins. For the purpose of fair accuracy in comparison, experiments were conducted on hemispherical solar dryer (active and passive mode), traditional cabinet solar dryer as well as open sun drying (OSD) by maintaining the uniform test conditions. An average moisture removal rate of 0.1935096 kg/h was obtained in hemispherical dryer. The hemispherical solar dryer significantly reduced drying time for converging grapes into raisins to 13 days, compared to 18 days in a cabinet solar dryer and 19 days with OSD. The hemispherical dryer, through a gap, creates a greenhouse effect, reaching a 70.1 °C maximum temperature and an average of 60.7 °C at 796 W/m2 average solar energy. The hemispherical dryer attained a drying efficiency of 5.67 %. Six mathematical models were employed for hemispherical and cabinet dryers. Amongst these Two term and Wang & Singh models were found suitable for the experimental data and provided precise prediction of moisture ratio.

Evaluating Drying Behavior and Efficiency in Varied Shaped Samples Using Solar Drying: A Morphological and Kinetic Study

Evaluating Drying Behavior and Efficiency in Varied Shaped Samples Using Solar Drying: A Morphological and Kinetic Study

Analysis of the Design and Technological Parameters of the Designed Solar Dryer with a Heat Pump

Analysis of the Design and Technological Parameters of the Designed Solar Dryer with a Heat Pump

Experimental and numerical study of performance enhancement in a direct solar dryer integrated with obstacles

Experimental and numerical study of performance enhancement in a direct solar dryer integrated with obstacles

Exergy Efficiency and Energy Efficiency of Double Air Pass Solar Tunnel Air Dryer: A CFD Analysis

This work presents, the computational fluid dynamics simulation of a forced convection double air pass solar tunnel drying system to study the temperature distribution, the flow behaviour of the air stream, and the exergy performance. Realizable k-epsilon non-equilibrium wall function turbulence model, discrete ordinate radiation model, and species transport were used. The average temperature, thermal efficiency, and exergy efficiency were found to 59.2 oC, 30%, and 9.41%, respectively. The result revealed that the uniform temperature and velocity distribution throughout the heating and drying chamber. Therefore, the newly developed double air pass solar tunnel dryer enhances the air temperature and the exergy performance leads to the increment of drying rate and reduction of drying period.

Potential Utilisation of Solar-Assisted Kiln Dryer in Bamboo Drying

Bamboo is increasingly used as an alternative material for producing renewable and environmentally friendly products. Bamboo should be dried before use to increase its stability and improve its resistance against biodeterioration agents. The most common drying method for bamboo is through air-drying. Alternatively, artificial drying, such as solar drying, can produce optimum drying results regarding the drying rate and quality of bamboo throughput. This study investigated the potential utilisation of solar drying methods for processing local bamboo. The drying characteristics and physical and mechanical properties of solar-dried Gigantochloa levis bamboo culms’ bottom, middle, and top sections were determined. The drying time of G. levis culm has been reduced to about 40 days compared to the conventional air drying of 70 days using the solar-assisted kiln dryer. Solar-dried culms have a lower final moisture content of 20% than air-dried ones. The average circumference and diameter shrinkage values of solar-dried G. levis culms from green to approximately 12% moisture content were 3.22% and 4.29%, respectively, and the wall thickness shrinkage was 8.12%. The mean values of modulus of rupture and modulus of elasticity of solar-dried G. levis culm were 63.75 and 12567.99 N mm-2, respectively, while its mean values of compression and shear parallel to fibre were 45.87 and 10.01 N mm-2, respectively. The quality of solar-dried G. levis culms produced in this study showed the viability of using a solar-assisted kiln-dryer as a potential alternative processing method for drying local bamboo species in Malaysia.

Solar Dryers: Technical Insights and Bibliometric Trends in Energy Technologies

This review article provides a comprehensive analysis of the technical advancements and research trends in solar drying technologies for agricultural products. The study encompasses various innovations in energy storage systems, including phase change materials (PCMs) and the use of computational fluid dynamics (CFD) for optimizing the drying process. Through a bibliometric analysis of 126 scientific papers published between 1984 and 2024, five major research clusters were identified: energy generation, heat transfer, thermal storage, simulation modeling, and the integration of hybrid systems. The results demonstrate a marked increase in scientific output over the past decade, emphasizing a growing interest in the sustainable use of solar energy for drying applications. Key findings highlight that while PCM-based storage solutions significantly enhance the thermal stability of dryers, the high implementation costs and technical complexities limit their adoption, especially in small-scale operations. Similarly, CFD models have proven effective in optimizing air and temperature distribution within dryers; however, their performance is hindered by real-world fluctuations in solar radiation and humidity levels. To address these limitations, future research should focus on the development of cost-effective PCM materials and the improvement of CFD models for dynamic environmental conditions. The review concludes by emphasizing the importance of interdisciplinary collaboration in the design and application of these technologies, recommending the inclusion of real-world case studies to better illustrate the practical implications and economic benefits of solar drying technologies for agricultural production.

Assessment of solar drying of Brazilian pulp mill primary sludge

AbstractPulp mill sludge is a challenging by-product in wastewater treatment plants (WWTP), due to high moisture content, and poor dewatering characteristics. Solar drying was identified as an appropriate pre-treatment to reduce sludge moisture and enhance its energy efficiency for combustion purposes. Brazil is the world’s second-largest pulp producer, and its high intensity of annual solar irradiation makes it a prime candidate for the application of solar sludge drying technology. This study evaluates the main characteristics of primary sludge (PS) from pulp mills at 65% and 95% moisture content. An active passive solar dryer, followed by ASPEN Plus software simulation was used to evaluate drying properties and combustion potential. CO2 emission impact was explored, and the environmental effects of primary sludge combustion after solar drying were estimated. As indicated by the findings, the sludge commenced with a solids concentration of 21%, eventually reaching 95.5%, thereby enhancing its suitability for combustion. From the simulation, a heat rate expenditure in sludge combustion reported 24672 kW and 16295 kW for a solids content of 65% and 95%, respectively. Therefore, employing solar drying before the sludge incineration is crucial for minimizing energy consumption during combustion. Additionally, solar energy being cost-free, offers an opportunity to alleviate environmental harm.

Thermal evaluation of solar dryers and the effect on the antioxidant and some physicochemical properties of Agastache mexicana and Rosmarinus officinalis.

Lemon balm (Agastache mexicana) and rosemary (Rosmarinus officinalis) were dried using a mixed-mode solar dryer. A 23-factorial design was carried out: operation mode (mesh shade and direct irradiance), airflow (natural convection and forced convection), and type of flat plate solar collector cover (polycarbonate and glass). The drying kinetics of lemon balm and rosemary ranged from 4.5 to 6.5h and 4 to 7h, respectively, according to the operation mode of the solar dryer. The highest percentage of antioxidant activity in the 2,2-diphenyl-1-picrylhydrazil tests was lemon balm, with values between 88% and 93% (100µg/mL), and rosemary, 88% and 92% (100µg/mL). When forced convection was applied, solar collector thermal efficiency increased from 3.97%-5.11% to 17.20%-24.75%, dryer efficiencies ranged from 4.78% to 6.05%, and drying efficiencies between 14.17% and 44.23%. The lowest color difference (6.01) for lemon balm was shown with the mesh shade, forced convection, and glass cover collector, and for rosemary, the lowest color difference (12.87) resulted from using the mesh shade and natural convection; according to the analysis of variance, the cover collector did not affect significantly the color difference. Dehydrated lemon balm and rosemary could be used as an additive for medicinal, gastronomic, and food preservative applications. PRACTICAL APPLICATION: The results are significant for designing dryers for community centers in areas where the production and losses of fruits, vegetables, aromatic herbs, and edible flowers are high. The novelty of this research is to introduce a new product for the consumer; in this case, the traditional dried rosemary and lemon balm in powder form as a nutritional source, both for the preparation of remedies and for direct consumption in dishes, powders, or healthy pills and food supplements.

MATHEMATICAL MODELLING OF DRYING PROCESS

The aim of this study is to experimentally investigate the drying kinetics of common basil using a solar drying unit. The tests consist in studying the effect of constant and variable drying air temperature on the drying kinetics. In this empirical approach, we aim to determine and compare drying characteristic curves under conditions where the drying air temperature is constant or variable. Subsequently, correlations describing the drying rate will be developed, these will be used at a later stage to size and model the solar dryer. Few numerical models have been used in the literature to explain the drying kinetics of common basil, in fact, given the complexity of the transport mechanisms and the diversity of products, a single model cannot represent all situations. This justifies an experimental study in the laboratory to determine the drying kinetics of a particular product.

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.

Performance evaluation of solar dryer integrated with solar panel for drying of carrot (Daucus carota) vegetable

ABSTRACT Solar energy is a well-known and economically efficient energy source. Solar energy is harvested in two modes: one is direct and another is indirect. In the direct type, the global radiation is used directly to dry the food samples, while in indirect mode, solar energy is converted into electricity to operate the integrated exhaust fan for enhancement of the drying rate. Thermal analyses of the various components of the PVT hybrid dryer have been incorporated into this performance evaluation. Carrot has been chosen as a food sample because it has good moisture content and is used for nutritive purposes. The maximum ambient temperature has been monitored as 41°C at maximum global radiation conditions. The effect of the PVT system with solar dryer in both cases i.e. natural convection and forced convection have also been discussed in terms of temperature profiles of the drying chamber, sample temperature, and thermal efficiency. The thermal efficiency has been found as 55.3% for forced convection and 53.4% for natural convection. Similarly, a 3°C temperature increment has been found in food samples. Results have been supported and analyzed by the comparison between outcomes of natural and induced convection.