Solar Greenhouse 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.

Energy and enviro‐economic (3E) assessment of greenhouse solar dryer (GHSD) for drying and quality evaluation of medicinal Ocimum sanctum leaves: A sustainable path for preservation

Energy and enviro‐economic (<scp>3E</scp>) assessment of greenhouse solar dryer (<scp>GHSD</scp>) for drying and quality evaluation of medicinal Ocimum sanctum leaves: A sustainable path for preservation

IoT-based Environmental Monitoring and Prediction of Banana Moisture Content in a Solar Greenhouse Dryer

IoT-based Environmental Monitoring and Prediction of Banana Moisture Content in a Solar Greenhouse Dryer

Assessing mathematical models for the intermittent drying of cocoa (Theobroma cacao L.) beans

Fine flavor cocoa quality is significantly impacted by its postharvest drying process which can be enhanced through mathematical modeling. The objective of this study was to carry out the mathematical modeling of cocoa bean drying kinetics for a greenhouse dryer and considering intermittent drying. In this study, a natural convection solar greenhouse dryer was used to dry cocoa beans with negligible losses to an acceptable moisture content (6.6%) and cotyledon pH (5.25). Models based on Fick’s second law of diffusion, Newton’s model, and Hii, Law and Cloke’s model were developed considering (i) the entire drying period, and (ii) intermittent drying for Fick’s and Newton’s. Effective diffusivities and drying constants increased up to 1.01 ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} 10–11 m2/s and 0.0165 1/h respectively during drying. Newton’s model slightly outperformed Fick’s model, and the models considering intermittency showed slight improvement over the models for the entire drying period. Considering intermittency when modeling cocoa drying may be useful since a better fit to experimental data resulted, and variation of effective diffusivity and the drying constant was observed over the drying period.

Drying kinetics (mathematical modeling) and quality evaluation of herbal leaves (Adulsa and Durva) dried in small‐scale greenhouse solar dryer (GHSD): Experimental investigation and comparative analysis

AbstractThe study presents the performance of a small‐scale greenhouse solar dryer (GHSD) to demonstrate hygiene and superiority over traditional methods for medicinal Adulsa and Durva leaves. The GHSD dryer lowered the initial moisture of Adulsa leaves from 73.99% (w.b.) to the final 10.63% (w.b.) under natural and forced convection in 3 and 2.5 h, respectively. Similarly, the initial moisture of Durva leaves was reduced from 67.33% (w.b.) to 11.65% (w.b.) under natural and forced convection in 2.75 and 2.5 h, respectively. Furthermore, mathematical modeling with non‐linear regression was implemented to characterize the drying of Adulsa and Durva leaves, which showed that Midilli–Kucuk and Modified Midilli were the most superior fits for reporting the drying of Adulsa leaves in GHSD and open sun drying, respectively, whereas Verma and Midilli–Kucuk models were superior fits for characterizing the drying of Durva leaves in GHSD and open sun, respectively. Furthermore, the quality of the dried Adulsa and Durva leaves was evaluated, where total phenolic content (TPC) and total flavonoid content (TFC) values were marked higher in the leaves dried by the GHSD as compared to open sun drying for both Adulsa and Durva leaves. Moreover, during antioxidant analysis, the IC50 values among the leaves dried in GHSD were recorded to be greater for the natural convection greenhouse solar dryer (NCGHSD) for both Adulsa and Durva (40.67 and 122.24 μg/mL) compared to open sun drying (101.88 and 158.20 μg/mL). A quality assessment was performed on dried Adulsa and Durva leaf samples, and they exhibited appropriateness for pharmaceutical industry drug production.Practical applicationsGreenhouse solar dryer is an eco‐friendly, sustainable, clean, and hygienic way to dry herbs and medicinal plants. The greenhouse solar dryer can shorten the drying time by 50%–60% compared to natural stand in the sun (open sun drying) and improve the quality of the dried herbs, medicinal plants, and reduce the decay rate of the dried products. These leaves can be best suited for Ayurveda medicine industries for herbal powder (Churna). Being an economically advantageous greenhouse solar dryer improves the shelf life of the dried leaves, reduces their density, and lower transportation costs, leading to boost farmers' income in herbal farming and nutritional security.

Comparative Performance Evaluation of Active Greenhouse Solar Dryer with and without Reflective Floor Material

Comparative Performance Evaluation of Active Greenhouse Solar Dryer with and without Reflective Floor Material

دراسة التأثير الحراري لعملية تجفيف الطماطم باستخدام نظام الطاقة الشمسي

This study developed a hybrid solar greenhouse dryer (lean-to) incorporated with a solar collector and photovoltaic (PV) system for smallholder processors of tomatoes and evaluated the thermal performance of forced convection mixed-mode solar dryer with two pretreatments of fresh tomatoes (halves and slices) with salt and sugar. Tomatoes dipped in a 40% sucrose solution for 72 hours before drying exhibited a greater initial drying rate than those treated with salt. The hourly average incident solar radiation without a reflector was 673.8 (±214.2) W/m2 outside and 754.6 (±284.5) W/m2 inside the lean-to solar dehydrator during operation. The incident solar radiation in the collector ranged from 390.3 to 1156.0 W/m2, indicating higher levels at the tilt angle. The hourly average air temperatures outside and inside the solar dehydrator and solar collector during the experiment, respectively, were 30.7 (±2.3), 52.7 (±10.1), and 30.7 (±2.3), 79.7 (±26.9)°C for the salt treatment and 31.0 (±2.0), 55.1 (±15.3), and 31.0 (±2.0), 84.8 (±28.0)°C for the sugar treatment. Thus, the solar dehydrator and the solar collector raised the dehydrating air temperatures over the outside for the salt and sugar treatment by an average of 22.0, 49.0, 24.1, and 53.8ºC, respectively. The average hourly air-relative humidity inside the solar dehydrator was 33.5%, while outside was 47.2%. The pretreated tomatoes had an initial moisture content of 93.1% (w.b). The solar dehydrator's thermal efficiency was 72.21%, and its drying efficiency was 56.48%. Consequently, solar energy contributed 84.28 and 71.18% of the generated heating power. The solar dehydrator lost 15.72 and 28.82% of its remaining solar energy due to exhausted air. The solar dehydrator had a daily average energy of 59.375 kWh, and the heating power was 47.473 kWh during the experimental period (29 h).

Sustainable valorisation of kitchen waste through greenhouse solar drying and microwave pyrolysis- technology readiness level for the production of biochar.

Sustainable valorisation of kitchen waste through greenhouse solar drying and microwave pyrolysis- technology readiness level for the production of biochar.

Review of Solar Greenhouse Drying Systems in Conjunction with Hybrid Technological Features, Designs, Operations, and Economic Implications for Agro‐Food Product Processing Application

This review reports recent developments in solar greenhouse drying systems in conjunction with hybrid technological features and their designs, operations, and economic implications as well as application in agro‐food product processing. Solar energy is one of the most efficient renewable energy sources to be used as an alternative to fossil fuels. This form of energy is the finest option for space heating and electricity generation among the available renewable energy sources. Solar energy can be used directly or indirectly for dehydrating agricultural and nonagricultural products. However, the products are susceptible to natural disasters such as rain, insects, and animals in open‐air sun drying. Solar greenhouse drying systems in conjunction with hybrid technological features are one of the most recent applications used in the agro‐food processing sectors. The review shows that the quality of products dried in conservatories is superior to that of products traditionally dried under the sun. Further, higher sustainability of the solar greenhouse‐oriented hybrid drying system in terms of embodied energy, energy return time, CO2 emission, net CO2 mitigation, and carbon credit can also be observed with the strengths, weaknesses, opportunities, and threats analysis, i.e., strengths, weaknesses, opportunities, and threats of solar dryers. This shows the framework for abundant real‐world applications.

Drying Performance and Economic Analysis of a Greenhouse Solar Dryer for Tomatoes

Purpose: The purpose of this study was to assess the drying performance and economic feasibility of a Greenhouse Solar Dryer for Tomatoes. With a focus on small-scale tomato drying, the study aimed to evaluate the effectiveness of the greenhouse in comparison to traditional sun drying methods. Additionally, the economic analysis sought to determine the investment attractiveness of the greenhouse dryer by considering the initial investment, operational costs, and potential revenue generation. Methodology: The methodology involved conducting drying experiments using the Greenhouse Solar Dryer for Tomatoes under existing weather conditions. The dryer's components include the steel frame, greenhouse plastic cover, and concrete floor. The temperature and relative humidity contributed to the environment inside the greenhouse that facilitated the drying process. Moisture content measurements were taken at regular intervals to assess the drying kinetics and effectiveness of the greenhouse. Economic analysis was conducted to evaluate the project's financial viability, considering initial investment, revenue generation, and operational costs. Findings: The findings revealed that the Greenhouse Solar Dryer outperformed sun drying methods, achieving higher temperatures and faster drying times for tomatoes. Specifically, the greenhouse reached maximum temperatures of 38.4 °C and 45.5 °C on the first and second days, respectively, leading to a moisture content of 14.9% wet basis within 11 hours on the second day. In contrast, sun drying resulted in a significantly higher moisture content of 37.9% at the same time, highlighting the effectiveness of the greenhouse. Economic analysis demonstrated that the project had a payback period of 1.6 years, indicating its attractiveness as an investment opportunity for farmers. Unique Contribution to theory, practice and policy: This study makes a unique contribution to knowledge by providing empirical evidence of the drying performance and economic viability of a Greenhouse Solar Dryer for Tomatoes. By demonstrating the effectiveness of the greenhouse in achieving faster drying times and lower moisture content compared to sun drying methods, the study underscores the potential of solar drying technologies in small-scale agricultural settings. Additionally, the economic analysis offers valuable insights into the financial feasibility of adopting greenhouse dryers, particularly for farmers seeking to enhance their income through value-added tomato products.

Calidad física y sensorial del café secado en tres prototipos de secadores solares tipo invernadero

Reducing the drying time of coffee without causing negative effects on cup quality has been the subject of several investigations. The objective was to determine the effect of three variants of a greenhouse-type solar dryer prototype on the physical, sensory and microbiological quality of coffee. The solar dryer prototype with three variants, prototype 1 (P1) greenhouse solar dryer, prototype 2 (P2) solar dryer with air extractor and prototype 3 (P3) solar dryer with air extractor and solar powered heaters, was compared to traditional drying (T0) (cement floor). Drying time, physical grain defects, yield, sensory and microbiological quality were evaluated. The best results were obtained in P3 with a drying time of 52 h (2 ¼ days), with dry parchment coffee beans without primary defects, higher yield in exportable gold coffee (83.24 %), sensory profile of 84.25 points qualified as specialty coffee (with Q Premium grade) and better safety than coffee obtained by traditional drying; demonstrating that the greenhouse type solar dryer with air extractor and solar energy heaters is a sustainable alternative to improve the efficiency of coffee drying while preserving its sensory quality, an essential value for producers to achieve better prices.

Efficient simulation of bitter gourd drying in active solar dryer: A state-of-the-art model

Greenhouse drying system is used to dry agricultural products or low-temperature thermal drying using a greenhouse structure. In this paper, an experimental and simulation study is carried out to evaluate the drying performances of an active solar greenhouse dryer using COMSOL Multiphysics. The experimental setup includes a compact thermal storage-based greenhouse dryer (1.5 m × 1.0 m x 0.5 m) equipped with a black gravel-covered Aluminium jacket and 35 kg of paraffin wax for heat retention which is located on the floor of the dryer. The experiments were conducted in Ranchi, India (23.34 °N, 85.30 °E) under clear sky conditions in the month of May. The amount of solar radiation (global solar radiation) varied from (630 W/m2 to 1052 W/m2) with an average of 936 W/m2, ambient air temperature (30.2 °C–38.2 °C), air relative humidity (31.6 %–34.6 %), and wind speed (0.9–1.0 m/s). The inside dryer temperature, humidity, wind speed, and floor temperature were also measured every hour. The average values of these parameters were 59.1 °C, 30.2 %, 0.91 m/s, and 69.1 °C, respectively. The FE (finite element) modelling finds out the maximum temperature in drying products, floor and dryer's outlet is 55.3 °C,72.4 °C and 67.4 °C, respectively at 13:00 h. The proposed dryer costs 19633.50 INR with an embodied energy of 1358.01 kW h. The proposed dryer has a break-even period of 1.87 years, and its lifespan is 35 years. During this time, the net CO2 emission was found to be 21.45 tonnes, and the earned carbon credit varies from 1505.01 to 30030.00 INR. The result shows that the drying efficiency is 42.52 %, reducing the initial moisture content from 88.64 % to 2.28 % within five consecutive hours. The energy and exergy efficiencies of the dryer are found to be 61.84 % and 56 % respectively. The system is a viable, sustainable choice for the large-scale production of bitter gourd flakes.

Environmental and economic assessment of single-slope solar greenhouse dryer for ginger and turmeric drying in north-eastern region of India

In the present work environmental and economic assessment of a single-slope solar greenhouse dryer (GHD) for drying ginger and turmeric have been attempted under the natural convection (NC) and forced convection (FC) of different air flow rates; FC1 (0.073 m3/s), FC2 (0.089 m3/s), and FC3 (0.107 m3/s). This system was investigated in the climatic conditions of the North East India region to dry the products at zero energy cost by installing this system for greater utility in different drying industries. The moisture reduction was 0.11 (d.b.) or 0.01 (w.b.) and 0.14 (d.b.) or 0.02 (w.b.) from initial values of 10.11 (d.b.) or 0.91 (w.b.) and 6.14 (d.b.) or 0.86 (w.b.) for ginger and turmeric, respectively. The drying time was 6.00 h in GHD under FC3 case and 11.50 h in OSD for ginger and 6.50 h in GHD under FC3 case and 12.50 h in OSD for turmeric. The drying efficiency for ginger and turmeric under the FC3 case was 34.13–37.17% and 30.71–33.28%, respectively. The energy efficiency and energy utilization ratio of the GHD under the FC3 case was 66.66–89.84% and 55.39–72.96%, respectively. The payback periods of 0.81 yr and 0.55 yr were determined for turmeric and ginger, respectively. Furthermore, over the 20 years of the system's life, the system reduced CO2 emissions by 29.48 tonnes compared to 11.10 kg of CO2 emissions produced for the embodied energy used to develop the GHD.

Experimental performance investigation of a novel movable greenhouse solar dryer for drying potato slices in the arid climate of India

In the present study, the drying of 5 kg potato slices in a small-size movable greenhouse solar dryer is performed experimentally to determine its performance. The study was carried out at Ajmer, India, in May 2022, and the results demonstrated that the dryer could heat the air to a maximum temperature of 59.5°C with a daily average air temperature of 56.2°C under the no-load test for an average ambient temperature and a solar intensity of 39.8°C and 676 W/m2. Under load, the moisture content of potato slices was reduced to 6.3%, 21.1% and 55.9% from an initial moisture content of 85% (w.b.) in the greenhouse solar dryer, open sun and under shade, respectively, in 5 h. However, for complete drying up to 6.3% moisture content, open sun drying and shade drying took 6 and 9.5 h, respectively. Maximum exergy inflow and outflow of 13.2 W and 9.2 W and maximum exergy efficiency of 69.6% were attained during the drying. The payback period for the developed greenhouse solar dryer was 0.35 years for an expected life of 10 years. Also, the efficiency of the developed greenhouse dryer under load was 26.9%.

Performance evaluation and development of FE modeling for passive greenhouse solar dryer for potato chips drying

AbstractFood losses and hunger around the world are majorly attributed to the lack of diverse food processing technologies and standardized methods. Solar energy is a potential solution for drying agricultural products, but traditional solar drying methods are not yet widely used. This study developed a finite element model using COMSOL Multiphysics to assess the performance of a passive greenhouse dryer for drying food products. The proposed model was used to simulate the drying of potato slices, and the results showed that the dryer was able to reduce the moisture content of the potato slices from 1 to 0.005 in 3 h. The drying efficiency was 20.52%, the relative humidity inside the drying chamber was 25.2%, and the energy and exergy efficiencies were 63.46% and 94.01%, respectively. Overall, the results of this study suggest that the passive greenhouse dryer is a suitable drying method for potato chips. The model developed in this study can be used to further optimize the design of the dryer and to evaluate its performance for other food products.

Drying Kinetics of Pear Slices in Greenhouse Solar Dryer

An experimental study was performed to determine the drying characteristics of pear using greenhouse based solar dryer and under open sun with natural convection. Prior to drying, sliced pear samples were pre-treated: i) control inside dryer i.e. with no dip, ii) blanching, iii) soaking in 2% KMS (Potassium Metabisulphite) solution, iv) blanching and soaking in 1% KMS solution, v) control outside dryer i.e. with no dip. The experimental drying data of pear were fitted to five different mathematical models viz. Exponential, Generalized exponential, Page’s, Logarithmic and Power law models, and drying rate constants and coefficient of models tested were determined by non-linear regression analysis. Among the various models tested to interpret the drying behaviour of pear, Page’s model was selected which gave best statistical indices of coefficient of determination (R2) and standard error of estimation (SEE) values.

Red pepper drying with a double pass solar air heater integrated with aluminium cans

In this paper, an experimental evaluation of a newly developed flat plate double pass solar air heater combined with aluminum cans for drying red pepper was presented. The proposed solar dryer system was designed, modeled, and evaluated. Solar air heater trials were carried out using the absorber’s top and bottom plate and aluminum cans for red pepper drying at Bahir Dar, Ethiopia. To test the solar dryer, 100 pieces of red paper were obtained from the Bahir Dar region of Ethiopia for the purpose of experimentation. Microsoft Excel was used to perform statistical analysis of eleven mathematical models. The results show that the mixed-mode solar greenhouse dryer takes less time to dry red pepper than the open solar dryer. In the midday, the solar insolation reached 973 W/m2 and the minimum solar insolation was 220 W/m2 and air is expelled at a rate of 0.0383 kg/s. According to the experimental results, the dryers chamber temperature ranged from 30.9 to 54 °C, while the ambient temperature was between 22.6 and 28.2 °C. The mixed-mode double pass achieves up to 46% and 28% efficiency when used with aluminum can dryers and conventional open sun dryers, respectively. A drying rate of 0.0003395 kg/s was achieved for the open sun dryer system and 0.0000365 kg/s for the mixed mode solar dryer. Using mixed-mode and open-sun solar dryers, the logarithmic model was found to be most effective in explaining the red pepper behavior. Furthermore, a comparison was made between the experimental and predicted moisture ratios through the calculation of the coefficient of determination (R2), the reduced chi-square (X2), and the root mean square error (RMSE). The results show that the logarithmic model achieved the highest value of the correlation coefficient (R2), which was determined to be 0.9978 and 0.9989, while the logarithmic model achieved the lowest value of Chi-square (X2).

Effect of citric acid pretreatment on drying kinetics of tamarillo in a greenhouse solar dryer

The production and consumption of tamarillo (Solanum betaceum) is gaining momentum due to its immense nutritional, health, and commercial potential. However, like many other horticultural products, high postharvest losses are incurred in tamarillo production. In particular, decay is a major problem. Drying is a viable option that can address this problem and significantly increase the shelf life of tamarillo. Consequently, the objective of this study was to evaluate the effect of citric acid pretreatment on the drying kinetics and quality of tamarillo slices. The tamarillos were dried in a passively operated even-span greenhouse solar dryer (8 m long, 4 m wide, and 3.6 m high to the ridge) covered with a 200 μm thick ultraviolet-stabilised polyethylene film. Solar radiation, temperature, relative humidity, moisture content, colour, firmness, and vitamin C content were periodically measured, and the data were analysed statistically. The citric acid-pretreated and control (untreated) tamarillo slices were dried from an initial moisture content of 655% (db) to a final moisture content of 16.25% and 22.50% (db), respectively, in 10 hours. In addition, the pretreated slices attained a higher average drying rate of 42.01±0.23 g/g/hr compared to 40.23±0.12 g/g/hr attained by the control slices. Further, the Page model best described the drying kinetics of both tamarillo samples with R², χ2, and RMSE values of 0.9975, 0.0004, and 0.0005, respectively. The pre-treated samples had better colour retention with a total colour change of 15.07±1.12 compared to 35.99±0.98 attained in the control samples. Moreover, the pretreated tamarillo slices attained a lower percentage firmness increment of 281.82±3.21% compared to 337.5%±1.54 attained in the untreated samples. Further, the pretreated tamarillo slices had 42.94±0.41% vitamin C retention compared to 40.17±0.67% retention in the control samples. Generally, pre-treating tamarillo slices with citric acid improves their drying kinetics and both physical and nutritional qualities.

Experimental and computational validation of thermal performance of an active greenhouse solar dryer in no-load conditions

Abstract This study focused on developing a finite element (FE) model using COMSOL Multiphysics to simulate the active mode of a greenhouse dryer under no-load conditions in Ranchi humid subtropical climate. The model visualized the temperature and humidity distribution within the dryer and was validated against real-world experimental results. Under unloaded conditions, the performance assessment revealed a 29.14% efficiency for the proposed dryer and a maximum overall convective heat transfer coefficient of 5.0 W/m2 °C. The internal temperature ranged from 50°C to 70°C, while the relative humidity hovered between 30% and 45%. The COMSOL Multiphysics-based FE model demonstrated close agreement between experimental and predicted results, with minimal statistical error. Overall, the findings suggest that the active mode of the greenhouse dryer could be a valuable tool for crop drying in humid subtropical climates. Additionally, the FE model presents a promising approach for future research and development.

A Comparative Management Analysis on the Performance of Different Solar Drying Methods for Drying Vegetables and Fruits

Drying is the process of moisture removal which is applied to many foodstuffs including fruits and vegetables for preservation and storage purposes. Since solar energy is one type of environmentally friendly renewable energy, open-type solar dryers, natural convective type solar dryers and greenhouse type solar dryers were designed and fabricated in this study for the preservation of fruits and vegetables. A comparative study among various solar drying methods was performed to study the drying performance by maintaining the quality and texture of the dried foodstuffs. Factors such as solar radiation, ambient temperature, moisture in the air, materials used for glazing, inclination, etc., were considered during the fabrication of the solar dryer so that a better estimate of the performance of the solar dryer could be obtained. The lowest drying rate was observed when convective drying was used as an indirect mode of heating. The maximum drying rate observed in open drying was 0.088 kg/kgh, whereas in convective drying under the same conditions, it was 0.03 kg/kgh, which was almost 65% less. This in turn also resulted in the dried samples displaying a better texture and better color. The shrinkage effect on the samples was less pronounced for those samples in the convective dryer than it was for those in the open and greenhouse dryers, as the method uses indirect drying. Comparing convective and greenhouse drying, more shrinkage and a greater browning effect were observed for the open drying method. Out of three types of solar dryers, the greenhouse dryer was selected to study thermal performance because of its better drying rate. DHT11 sensors controlled through Arduino programming were employed in this study to record the temperature and moisture at various locations in the greenhouse dryer setup. The range of energy efficiency of the greenhouse solar dryer was estimated to be from around 15% to 25% on average. This might be due to a greater extent of energy losses. No significant difference was observed in the energy efficiency with respect to the samples used for drying.