Greenhouse-type Solar Dryer Research Articles

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.

Simulation and Optimization of a Greenhouse-Type Solar Dryer with Comsol Multiphysics

Solar drying remains for developing African countries the only economical means of preserving foodstuffs for which post-harvest losses sometimes reach 60%.
 It was modeled in this work, the different elements that constitute a solar drying system by natural convection. This model is described by heat, mass and momentum balance equations between the different exchange media.
 The model initially made it possible to describe the dynamic behavior and calorific value of greenhouse-type solar dryers.
 The optimization study through simulations also made it possible to compare the drying power of more than 180 solar dryers. The analysis of the simulation results gave the dryer a small size (h = 2.5 m and l = 3 m) with large identical openings (inlet = loutlet = 25 cm) positioned at the two extremes: bottom for the inlet (Ye = 0.1 m) and high for the air outlet (Ys = 1.65 m), as an energy-efficient dryer (Taverage = 50.73 oC). The fluidity of the air (Vaverage = 0.58 m.s-1) in this dryer is also remarkable and could be used for drying food products.

Development and effectiveness of greenhouse type solar dryer for coriander leaves

Aim: Sun drying system is not able to provide the best drying performance and quality dried produce of leafy vegetables. To facilitate better options to the farmers, this study aims to develop and evaluate a cost-effective greenhouse type solar dryer to improve shelf stability of coriander leaves. Methodology: A greenhouse type solar dryer (5m x 3m x 2.3m) was developed with the provision of rigid frame, 200 µ UV stabilized LDPE glazing material, solar collector cum drying chamber, inlet air and outlet air openings. The dryer was evaluated for its performance, drying characteristics of coriander leaves and qualitative evaluation of dried product as compared to open sun drying. Results: The greenhouse type solar dryer performed well for coriander drying with increased level of temperature inside the dryer (42oC) and 24% reduced drying time as compared to sun drying (29oC).The loading capacity, efficiency, payback period and B:C ratio of the dryer were found to be 100 kg, 70.47 %, 1.26 yr and 1.79, respectively. The drying of coriander leaves occured mostly in falling rate period. Coriander leaves dried under the dryer possessed higher values of chlorophyll content (1.356 mg g-1 of tissue), ascorbic acid content (111.257 mg 100g-1), rehydration ratio (5.302) and coefficient of rehydration (0.762) than sun dried coriander leaves with the respective values of these quality parameters being 1.097 mg g-1 of tissue, 62.37 mg 100g-1, 4.715 and 0.689, respectively.

Drying kinetics of natural rubber sheets under two solar thermal drying systems

This work describes the thermal behavior and evaluation of kinetics drying of natural rubber sheets using two solar drying technologies: direct and indirect. The solar drying tests were carried out simultaneously in order to compare the behavior under same weather conditions. The moisture content of the rubber sheets was reduced from 45.8 to 0.59% and from 49.7 to 0.33% on a dry basis (d.b.) for direct solar drying and indirect solar drying, respectively. The direct drying mode was carried out for 12 days with average temperature and relative humidity inside the greenhouse, during sunny hours, of 37.04 °C and 14.1%, respectively. Meanwhile, the indirect drying operation was carried out in 9 days (61.62 h intermittently) with 61 °C and 4.77%, respectively. The average global energy efficiency of the field of SAH was 33.77%. Thirteen thin layer models were used to evaluate the drying behavior of which the Modified Henderson and Pabis model was the best to describe the solar drying of rubber sheets for the direct and indirect system. As a conclusion, the direct greenhouse-type solar dryer is recommended for small producers and the indirect tunnel-type solar dryer for companies with high and continuous production.

Performance evaluation of parabolic greenhouse-type solar dryer used for drying of cayenne pepper

This study examines the performance of a parabolic greenhouse-type solar dryer used for drying of cayenne pepper (Capsicum annuum) in Nan (northern Thailand). The dryer has a base area of 6.0 m × 8.2 m and a height of 3.25 m with the loading capacity of 100–200 kg for fruit or vegetables. It has a parabolic roof structure covered with polycarbonate sheets and is placed on a concrete floor. It is ventilated by three DC fans powered by a 50-Watt solar cell module. The produce is placed on trays with wire mesh base and located on steel supports. Among the advantages of this type of dryer is that the product is protected from rain, dust and insects. The pepper samples consisted of whole pods or cut pods. The drying experiments were carried out in the solar dryer and in an electrical (convective) tray dryer. The study was focusing on drying kinetics and on the effects of the drying treatments on one of the main quality attributes namely the capsaicin content in the dried products.

Modelo matemático de la capa delgada de piña (Ananas comosus, L.): Experimento en un secador solar tipo invernadero a gran escala

The objectives of this research were two: first to investigate experimentally the behavior of pineappl (Ananas comosus, L.) thin layer drying in a greenhouse-type solar dryer and second to describe the best fitting kinetic and mathematical model taken from literature. A large scale greenhouse dryer designed and installed at Silpakorn University, Nakhon Pathom, Thailand was used to dry slices 1 cm width at temperature range between 25-60 °C with relative humidity between 50-90%. Nine statistical models, either empirical or semi-empirical, were tested in order to validate the experimental data. A non-linear regression analysis conducted by a statistical computer program was applied to evaluate the constants of all the models. The parameter values, root mean square error (RMSE), mean absolute error (MAE) and modelling efficiency (EFF) of the nine models were calculated. Comparison outcomes of two experiments are displayed between the predicted moisture content and the observed pineapple moisture content. Hasibuan and Daud drying model proved to describe the best pineapple solar drying curves. The two experiments were carried out on sunny days, the second experiment on the third day showed cloudiness decreasing the solar radiation. Mathematical models of pineapple drying in a greenhouse dryer have not been found so far in the literature. Drying curves obtained from experiments showed that the constant drying and the falling drying rate periods exist. Nine thin-layer drying models were fitted to two experimental data in order to describe the drying characteristics of pineapple founding that the Hasibuan and Daud model was the best fitting.

Modelo matemático de la capa delgada de piña (Ananas comosus, L.): Experimento en un secador solar tipo invernadero a gran escala

The objectives of this research were two: first to investigate experimentally the behavior of pineappl (Ananas comosus, L.) thin layer drying in a greenhouse-type solar dryer and second to describe the best fitting kinetic and mathematical model taken from literature. A large scale greenhouse dryer designed and installed at Silpakorn University, Nakhon Pathom, Thailand was used to dry slices 1 cm width at temperature range between 25-60 °C with relative humidity between 50-90%. Nine statistical models, either empirical or semi-empirical, were tested in order to validate the experimental data. A non-linear regression analysis conducted by a statistical computer program was applied to evaluate the constants of all the models. The parameter values, root mean square error (RMSE), mean absolute error (MAE) and modelling efficiency (EFF) of the nine models were calculated. Comparison outcomes of two experiments are displayed between the predicted moisture content and the observed pineapple moisture content. Hasibuan and Daud drying model proved to describe the best pineapple solar drying curves. The two experiments were carried out on sunny days, the second experiment on the third day showed cloudiness decreasing the solar radiation. Mathematical models of pineapple drying in a greenhouse dryer have not been found so far in the literature. Drying curves obtained from experiments showed that the constant drying and the falling drying rate periods exist. Nine thin-layer drying models were fitted to two experimental data in order to describe the drying characteristics of pineapple founding that the Hasibuan and Daud model was the best fitting.

EFFECT OF SOLAR DRYING ON THE QUALITY OF CORN SEEDS

The main objective of this investigation was carried out to study the ability of utilizing greenhouse solar dryers for drying of corn in order to obtain the best quality of dried grains for using it as seeds with the least drying time, and comparing with the natural sun drying method. Thus, contributing to increase the productivity. Corn cv. (Giza 168) was used for the experimental work at initial moisture content of 31.73% on dry basis (d.b). Two different drying methods of corn were tested for drying of ear and shelled corn. The two methods were natural sun drying and solar drying using greenhouse type solar dryers at different air velocities (0.5, 1.0 and 1.5 m/s). The experiments were carried out in rice mechanization center at Meet El- Dyba, Kafr El-Sheikh Governorate, Egypt during September 2016. Experiment included the flowing variables Two different drying methods (Solar drying method using greenhouse type solar dryer and natural sun drying method). Two different conditions of corn (complete ear-shelled corn). Three different air velocity (0.5, 1.0 and 1.5 m/s). High moisture ear and shelled corn was dried by using solar energy for heating air inside a greenhouse and compared with natural sun drying method. The results of quality tests that included standard germination test, vigor test and tetrazolium test for both drying methods for ear and shelled corn recorded high percentages for all treatments except solar drying of ear corn at air velocities 0.5 and 1.0 m/s. The average air temperature inside the solar dryer at air velocities 0.5 and 1.0 m/s reached to 43.9 and 42.4 ˚C respectively. High temperatures killed the germ of corn so the quality tests were reduced. Germination percentage of natural sun dried ear corn was 97 % and for solar dried samples at air velocities 0.5, 1.0 and 1.5 m/s was 79, 81, and 89%, respectively. The corresponding values for shelled corn were 93, 97 and 98 %.and 95 % for natural sun dried ones. The vigor test of dried ear corn recorded 90 for natural sun drying method and 34, 45, and 66% for solar drying at air velocities of 0.5, 1.0 and 1.5 m/s, respectively. The corresponding values for shelled corn were 86, 96 and 97% respectively, and 82 for natural sun dried samples. The recorded drying times were 26, 24 and 28 hours to reduce the moisture content from an initial level of 31.73 to final level of 14.07% (d.b.) for ear corn and for shelled corn were 20, 16 and 24 hours to reduce the moisture content from an initial level of an initial level of 31.73 to final level of 14.07% (d.b.) for ear corn and for shelled corn were 20, 16 and 24 hours to reduce the moisture content from an initial level of 27.23% to 14.12% compared with 46 and 38 hours for ear and shelled corn dried by natural sun drying method. Hourly costs of ear corn drying were 0.95, 0.88, 1.00 and 1.03 L.E/ kg for solar drying at air velocities 0.5, 1.0 , 1.5m/s and natural sun drying respectively. The corresponding values for shelled corn were 0.74, 0.58, 0.89 and 0.96 L.E/ kg.

Energy and exergy analysis of a mixed-mode greenhouse-type solar dryer, integrated with partially covered N-PVT air collector

In the present communication, a hybrid mixed mode greenhouse solar dryer, integrated with partially covered number of photovoltaic thermal (N-PVT) solar air collectors has been proposed for drying and different performance parameters are evaluated for the climatic conditions of New Delhi, India. Thermal modelling has been done for the drying system and analytical expressions for different parameters such as crop temperature, greenhouse temperature, outlet air temperature of collector and cell temperature have been obtained. The set of governing equations has been solved with the help of MATLAB 2013a. Further, the effect of mass flow rate and variation of number of air collectors on thermal energy, electrical energy, equivalent thermal energy, thermal exergy efficiency and overall thermal efficiency have been calculated. It was found that with variation of number of air collectors from 1 to 5, equivalent thermal energy, equivalent thermal efficiency and equivalent exergy efficiency changes from 3.24 to 10.57 kWh/day, 61.56%–42.22% and 28.96%–19.11% respectively.

Initial Investigation of the Solar Drying Method for the Drying of Olive Oil By-Products

In this study, a greenhouse-type solar dryer was developed in order to demonstrate an olive oil by-product and agro-residue Managing System, which uses solar drying processes for the treatment of olive oil mill residues to decrease the high energy consumption of the drying operations, thus decreasing the environmental impact of these residues. The resulting by-products, once dried out, have a final application as fuel. The greenhouse, with a roof height of 3.5 m and total area of 150 m2, consisted of three 3.0 × 1.5 × 0.20 m concrete tanks, where the drying of olive pomace (two- and three-phase olive mills), leaves and biomass from pruning for the production of solid biofuels was examined. The two-phase olive mill by-products required more drying time than three-phase olive mill by-products due to higher moisture content. Moreover, the moisture rate was positively related to minimum relative humidity and the highest material and ambient temperature. Using free solar energy for drying olive oil by-products can be beneficial from the point of view of energy consumption and, consequently, the drying system cost. The main innovation of the process is using the most abundantly available energy source in Greece—and the Mediterranean basin generally—the sun.

Effect of temperature and relative humidity on fenugreek (Trigonella Foenum Graecum L.) Leaves during dehydration process

The study of this research, dehydrated Fenugreek leaves was prepared by different drying conditions with pre-treatments. The moisture removing process from the products. Low-temperature drying allows foods such as green leafy vegetables to be dried without losing the original color and texture. The system proposed in this paper consists of desiccant dehumidifier which removes the moisture from the air and increases its adsorption capacity. Drying reduces the bacterial growth in the products. Fenugreek leaves are commonly consumed fresh; over 62% of the Fenugreek leaves consumption comes from processed products such as powder, RTS, medicinal products and serum etc. Recent studies have indicated the potential health benefits of a diet that is rich in Fenugreek leaves. It will helpful for preserving the products for long time. Dehydration process was carried out using a cabinet tray dryer, green house type solar dryer. Low Humidity Air (LHA) dried fenugreek had superior green color and a more porous and uniform structure than those obtained from Radiofrequency (RF) and Hot air (HA) drying. In order to improve the drying rate of fenugreek leaves under low-temperature conditions, the driving force for mass transfer can be enhanced by several strategies. Reducing the relative humidity of hot air is one such approach, which increases the moisture-absorbing capacity of drying air.

Study of the Solar Energy Drying Device and Its Application in Traditional Chinese Medicine in Drying

Background: We referred to nearly 40 years of development and application progress of solar dryer in China literature, especially its application in the field of Chinese herbal medicine drying. Objective: We explored the development direction of China’s development and application of solar dryers, especially focusing on its development and application in traditional Chinese medicine drying. Method: Five types of solar dryers including the greenhouse type solar dryer, the collector type solar dryer, the collector-greenhouse type hybrid solar dryer, the integrated solar dryer and the focusing type solar dryer accounted for the development and application of solar dryers up to 95% in China. The first three types of solar dryers are low temperature dryer (less than or equal to 70°C), while the latter two kinds of solar dryers are high temperature dryer (more than 70°C). In this paper, we respectively introduced and compared the structure, working principle, applications, advantages and disadvantages, and the research status of these five dryer. Results: The integrated solar dryer and the focusing type solar dryer belong to the high temperature dryer types are the future direction of development. Among them, the integrated solar dryer is relatively simple structure and has more promotion prospects. These two kinds of key drying device used in the dryer is the development direction of high efficient vacuum tube. On the other hand, because of their low cost, simple structure and the dry material requirements etc., the three types of low temperature dryers at low temperature for drying materials are also indispensable in the practical application. In contrast, the collector-greenhouse type hybrid solar dryer has more advantages, is the development direction of low temperature drying category. Conclusion: The collector tube which is the key element of the dryer was the core technology of solar dryer. Our country develops more successful of the all-glass vacuum solar thermal collectors and heat pipe-glass vacuum tube. Efficient vacuum tube collector technology is the future developed direction and is equally important to improve the quality of traditional Chinese medicine and dried.

The Drying Characteristics of Amaranth Leaves under Greenhouse Type Solar Dryer and Open Sun

The dehydrated leafy vegetables have the potential to become an important product because of relatively inexpensive, easily and quickly cookable and rich in several nutrients which are essential for human health. The proper drying techniques are the most important aspect of leafy vegetable preservation. The use of solar dryer helps to reduce the losses and improves the quality of product. A Greenhouse type solar dryer was used and the experiments were conducted to develop dehydrated amaranth leaves so as to enhance the availability of amaranth leaves during off season. In the present study, fresh amaranth leaves were pretreated in two ways viz; (i) dipping in a solution (leaves to water 1:5 (w/w)) containing 0.1% Mgcl 2 + 0.1% NaHCO 3 + 2% KMS in distilled water for 15 minute and (ii) blanching in boiling water containing 3% sodium bisulphate for 2 min. The leaves were dried at 1.5, 2.0 and 2.5 kg/m 2 loading density, under greenhouse type solar dryer and in open sun. Untreated amaranth leaves were also

Experimental investigation of the performance of a large-scale greenhouse type solar dryer for drying chilli in Thailand

Solar drying is considered to be a useful solar energy technology for developing counties. In this work, the performance of a large-scale greenhouse type solar dryer for drying chilli was investigated. The dryer has a parabolic shape and it is covered with polycarbonate sheets. The base of the dryer is a concrete floor with an area of 8×20 m2. Nine DC fans powered by three 50W solar cell modules were used to ventilate the dryer. The dryer was installed at Ubon Ratchathani, Thailand. Three batches of chilli were dried in the dryer. It was found that five hundred kilograms of chilli with the initial moisture content of 74% (wb) were dried within 3 days while the natural sun dried needed 5 days. The chilli dried in this dryer was completely protected from insects, animals and rain. In addition, good quality of chilli was obtained.

Solar Drying Technology

Drying is the oldest preservation technique of agricultural products, and sun drying is still widely used for preservation of agricultural products in the tropics and subtropics. Previous efforts on solar drying of cereal grains, fruits, vegetables, spices, medicinal plants, and fish are critically examined. Recent developments of solar dryers such as solar tunnel dryer, improved version of solar tunnel dryer, roof-integrated solar dryer, and greenhouse-type solar dryer for drying of fruits, vegetables, spices, medicinal plants, and fish are also critically examined in terms of drying performance and product quality, and economics in the rural areas of the tropics and subtropics. Experimental performances of different types of solar dryers, which have demonstrated their potentialities for drying of fruits, vegetables, spices, medicinal plants, and fish in the tropics and subtropics, are addressed, and also the simulated performances of the different types of solar dryers are discussed. The agreement between the simulated and experimental results was very good, and it is within the acceptable limit (10%). The simulation models developed can be used to provide design data and also for optimal design of the dryer components. A multilayer neural network approach was used to predict the performance of the solar tunnel dryer. Using solar drying data of jackfruit and jackfruit leather, the model was trained using back propagation algorithm. The prediction of the performance of the dryer was found to be excellent after it was adequately trained and can be used to predict the potential of the dryer for different locations and can also be used in a predictive optimal control algorithm. Finally, prospects of solar dryers for drying of fruits, vegetables, spices, medicinal plants, and fish in the tropics and subtropics are discussed.

Solar drying of pine lumber: Verification of a mathematical model

This work presents verification of a mathematical model for drying of a wood stack in a greenhouse type solar dryer. A simplified heat and mass transfer numerical model has been developed with input parameters based on the actual metrological data of a Moroccan climate. For its validation, a comparative study is performed in this work; the present model is solved to simulate the solar drying of pine wood using experimental data of previous wood drying experiments. The average relative discrepancies between the model predicted and experimental data are 1,2% for wood moisture content, 1% for drying air temperature and 5% for the air relative humidity. The close agreement between the predicted and experimental results shows the ability of the model to reproduce experimental drying data for wood.

Analysis of Fish Fillet Drying Rates under Three Solar Energy Drying Systems

A small Box type solar dryer with controllable air inlet was designed and tested. The dryer had a mild steel absorber plate and a polyvinyl chloride (pvc) transparent cover and could be adjusted to allow variation in airflow rate through the drying chamber. A convectional green house covered with transparent pvc and into which a drying tray stand at a height of 90 cm above the ground was placed made up the second drying method. The rate of air flow through the green house could be controlled by adjusting the opening at either end of the tunnel. The third method of drying which also served as the control is sun drying in which case the drying trays was placed 90 cm above the ground but left unenclosed to allow free flow of ambient air. The air temperature at points just above the drying rack was monitored for all three drying systems under no load conditions from morning to late afternoon. The temperature was also monitored during drying when the trays were loaded with fish of different fillet thicknesses. The rate of loss of moisture was also monitored by weighing the fillets at regular interval until the moisture dropped to 20%, dry basis or lower. The average temperature inside the plenum chamber of the box type solar dryer was found to have a high daily value of 71.1OC although an absolute maximum value of 74.4OC was recorded. This maximum value could be reached on cloudless days between the hours of 13:00 and 1400. The green house recorded a slightly lower average temperature and its peak value occurred latter in the day. Both the green house and the box-type solar dryer had average drying chamber temperatures that were more than 30 centigrade degrees above ambient conditions. Both the box-type and green house type solar dryer could dry thin slices of fish fillet in 1-3 days as opposed to the 7-9 days normally required under sun drying conditions. The quality of the dry fillet was satisfactory and CIE LAB colour values did not change significantly during drying.

Solar dryers in the Asia-Pacific region

The traditional method of solar drying in the Asia-Pacific region is by open-air drying where the product to be dried is exposed directly to the sun. The disadvantages of this traditional form of drying are many. Dirt, dust, and wind-blown debris, insect infestation, human and animal interference, will result in contamination of the product. Speed of drying and quality of dried product will be reduced due to over/under drying, intermittent sunshine, interruption and wetting by rain. Mechanical solar drying using natural convection or forced circulation would minimise these disadvantages. The author of this paper visited a number of countries and studied the numerous designs available for solar drying in the region. Three types of solar dryers considered by the author as having the best potential for development in the Asia-Pacific Region are discussed. These are the natural convection cabinet-type solar dryer, the forced convection indirect solar dryer, and the greenhouse-type solar dryer.

Development of a greenhouse-type solar dryer for medicinal plants and herbs

The economy of medicinal plant production is burdened considerably by the energy costs of drying. To substitute fossil energy, a solar heated dryer was developed, taking a plastic film greenhouse as superstructure to lower the initial costs. The solar air heaters, being incorporated into the roof, consists of a black absorber tissue, which is placed between the transparent cover of the greenhouse and an insulating air-bubble foil. To obtain a modular design, the system is structured along the ridge into segments of 2 m width. Each segment forms an independent solar air heater/batch dryer unit and is operated by a fan with a power consumption of 500 W. A prototype was tested in Yugoslavia, drying mint, sage and hops. The drying process from an initial moisture content of 80% w.b. to a final moisture content of 11% w.b. took 3–4 days. The load is 250–500 kg fresh material per segment. Maximum temperatures have been within a range of 40–60°C. The total pressure drop is 50 Pa at an air flow rate of 3300 m 3 /hr per segment. Compared to conventionally dried crude drugs, the percentage of active ingredients was up to 40% higher. The low investment and operating cost and the high quality of the crude drugs permit the solar dryer to be used in agriculture.