Solar Tunnel Research Articles

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.

Assessing the Physicochemical Characteristics: A Comparative Analysis of Various Drying Methods in Osmotic Treated Fruit Slices

Background: Due to their high perishability, we cannot store fruits in their fresh form for long. The different drying techniques have affected the physical and nutritional qualities of the dried fruit pieces. Adoption of osmotic dehydration will help to protect and improve the quality characteristics of the final products. Methods: Selected fruit slices, viz., apple, pineapple, guava, mango and banana, were subjected to sugar osmosis (60°Bx for up to 48 hours), followed by drying in different drying methods, viz., open sun (ODT), solar tunnel (SDT) and hot air drying (CDT) and the physical and chemical characteristics of the end products were analysed. Result: The osmosis process improved the total soluble solids content, while CDT and SDT improved both the rehydration of the dried fruit slices and the percentage of weight loss. The desirable physical attributes of the dried products significantly varied among the different drying methods and within the fruit slices. The CDT-dried samples had better nutritional properties in terms of total phenol content and antioxidant activity than did the other drying methods and fresh samples, except for vitamin C content, which was greater in fresh fruit slices. The results recommended using CDT techniques in osmosis-treated fruit slices, which could improve fruit's physical and nutritional properties and be useful as good functional foods for a long time.

Peningkatan teknologi bagi agroindustri pliek-u sebagai upaya pelestarian kearifan lokal di Aceh [Technology improvement on pliek-u agroindustry as an effort to maintain a local wisdom in Aceh

Pliek-u is a specialty food product in Aceh with local wisdom values that should be preserved. The Program of Community Service Based Product (PKMBP) aimed to improve the pliek-u agro-industry by adapting simple processing technologies so that it could lighten work, produce quality products, and attract the interest of the younger generation as pliek-u entrepreneurs in future. The method applied consist of surveys, preparation of tools and materials, assembly of a solar tunnel dryer type Hohenheim Aceh and a hydraulic press, training and dissemination of technology through field schools, and evaluation of the program with pre-tests and post-tests. Data analysis was carried out using the Wilcoxon rank test with alpha of 5%. The results of the program were the construction of 1 unit of Hohenheim Aceh tunnel dryer, 1 unit of hydraulic press, and the implementation of training and dissemination activities which have been published in the form of videos on YouTube media and press releases through online media. The results of the Wilcoxon rank test also showed that of the 13 participants whose data were valid, 100% of participants received positive rankings and the pre-test scores were significantly different from the post-test scores. Thus, it can be concluded that the program carried out has contributed to increasing the knowledge, expertise capacity, and interest of participants in pliek-u processing technologies since the profile of conventional agroindustry can be transformed to be better agroindustry by the use of solar tunnel dryer type Hohenheim Aceh and hydraulic press. In addition, the use of technologies will ensure the halal requirement of pliek-u.

Studies on the drying behaviour of red chilli and it’s effect on quality

Processing of chilli is an important aspect in the production of good quality chilli. Harvested chilli has moisture content about 80% (w.b) which has to be properly dried to keep away from aflatoxin infestation. Open yard sun drying is the conventional method being practised which takes long time for drying. Pre-treatment like destalking could reduce the drying time considerably resulting in uniformly dried product. The present work was aimed to find the effect of drying on the quality of chilli. Red chilli (variety: Sannam) was dried with stalk and without stalk under open sun and solar tunnel dryer. The drying behaviour of chilli was studied. The influence of drying on the quality parameters viz., vitamin C content, colour (L*, a*, b* values), shrinkage and ASTA colour was found. Drying studies resulted in reduction in moisture content from 323% (d.b) to 8% (d.b). The time taken for drying under open sun drying and solar drying was 33 and 17 hours respectively for chilli dried with stalk. Similarly, the time taken for drying chilli without stalk under open sun drying and solar drying was 29 and 16 hours respectively. Quality analysis of dried samples showed higher vit.C (13 mg/100g) and ASTA colour value (67.4) for solar dried chilli without stalk.

Influence of a double-stage solar tunnel dryer on the preservation of quality characteristics and the Modelling of colour variations in red chili peppers

In this work, the influence of two-stage solar tunnel drying on the preservation of quality attributes of both chili pepper varieties, Mareko Fana (MF) and Bako Local (BL), was studied. Both varieties were dried in different drying modalities, i.e. solar tunnel and open sun drying. The quality attributes were evaluated during the drying process using FTIR and spectrophotometry techniques. Different colour evolution models were implemented and a suitable model was selected. The results showed that after drying of the Mareko Fana chili variety, the lightness retention was found in the range of 81 %–89 %, the redness retention between 25 % and 42 % and the yellowness retention between 14 % and 38 %. For the Bako Local variety, the values were in the range of 78 %–82 %, 42 %–60 % and 36 %–55 %, respectively. The first order model gave a higher correlation coefficient (R2 > 0.96), which indicated the suitability of the model for predicting the color variation for both varieties. The volatile aromatic compounds in the chili peppers were greatly lost during open sun drying, while solar tunnel drying maintained these compounds for both varieties. However, during the solar tunnel drying process, a significant amount of alkyl halides or alkyl-chlorides were lost. The amount of dihydrocapsaicin and capsaicin from the chili peppers ranged from 10,172 μg/kg to 16,313 μg/kg and 16,676 μg/kg to 27,189 μg/kg for both dihydrocapsaicin and capsaicin, respectively. In tunnel, open-air, and uncontrolled open-air solar drying, the MF chili variety lost copsaicinoid content by 3.4 %, 14.8 %, and 38.3 %, respectively; in the BL variety, comparable losses were 1.8 %, 4.4 %, and 13.6 %. A minimum loss of ascorbic acids was recorded during solar tunnel drying. The results showed that well-designed double stage solar tunnel dryers are important for effective drying processes that preserve quality attributes of the chili pepper.

Performance study of solar tunnel dryer for medicinal plants

A solar tunnel dryer is a poly house framed structure covered with UV-stabilized polythene sheet, where agricultural and industrial products on large scale could be dried under at least partially controlled environment. A solar tunnel dryer accelerates and improves the drying process, it protects the product from insects and other pests-infestation thereby, reducing the contamination or product loss. As a result, the solar tunnel dryer lowers post-harvest losses compared to traditional sun drying. In this study, Adhatoda vasica and Moringa oleifera leaves were dried using a simple, low-cost solar tunnel drier and then it was compared with the open sun-dried products. The drying efficiency and the pick-up efficiency of the solar tunnel dryer for the drying of medicinal plant leaves was found to be 12.14% and 26.45%, respectively. The total drying cost of Adhatoda vasica and Moringa oleifera leaves was calculated as Rs. 16.26/- and Rs.16.87/- per kg, respectively as compared to the cost of sun drying which was Rs.114.1/- and Rs. 135.68/- per kg, respectively. The payback period of the dryer was found to be 1 year and 20 days.

The quality of pliek-u processed by using adaptive technologies

Abstract This study aimed to evaluate the quality of pliek-u processed by using adaptive technologies namely a solar tunnel dryer type Hohenheim Aceh for drying pliek-u and a hydraulic press for separating the pliek oil from pliek-u. About 100 coconuts were grated and fermented for 9days, then dried by using a solar tunnel dryer type Hohenheim Aceh and pressed by the hydraulic press. Parameters observed were moisture, total acidity, acidity, fat content, ash content, and yield. An organoleptic test was also conduct on 30 consumers. Results showed that the moisture of pliek-u ranged from 8.61 to 12.29%. The total acidity and pH-value of pliek-u were 0.52% and 5.5, respectively. Pliek-u has fat content about 43.65% and ash content approximately 5.3%, while the yield of pliek-u was 31.33%. The consumer test showed that the average preferences score of pliek-u for all sensory properties were 4 (like). In conclusion, the quality of pliek-u processed by using adaptive technologies were good as it was processed conventionally. Moreover, some quality properties such as pH-value and fat content can be improved so that the shelf-life of pliek-u could be extended.

Comparison of clam drying in solar, solar-hybrid, and infrared dryer: Drying characteristics, quality aspects, and techno-economic analysis

This study describes clam drying using various dryers (Open sun, solar tunnel dryer, solar-LPG dryer, infrared dryer). The parameters like moisture content of clam after drying, drying efficiency, rate of drying, energy consumption, proximate composition, microbial load, and sensory characteristics of dried clam were analyzed and also studied the economic aspects of clam drying using various dryers. The moisture content of clam reduced drastically to the level ranging from 9 −17 %wb in various dryers. Protein, ash, and fat content of dried clam were increased and moisture content was reduced compared to fresh clam under all drying methods. Drying reduced the microbial load of clam under various drying methods compared to fresh clam. Sensory parameters of dried clam are highly acceptable in infrared drying followed by solar-LPG hybrid drying. In general, infrared drying has resulted in the best drying, physical, quality, microbiological, and sensory characteristics of clam but economical indicator values were less than solar-LPG drying. The selection of a suitable drying method is not only based on the quality and drying characteristics but also by considering the economical feasibility of the dryers. Hence, it can be concluded that the solar-LPG dryer was found to the best drying method for clam drying with the final moisture content of 12.23 %wb, drying efficiency of 35.86 %, maximum drying rate of 1.26 (kg water/kg dry matter. h), specific energy consumption of 4.73 (kWh/kg of water evaporated), shrinkage of 16.52 %, rehydration ratio of 2.25 %, payback period of 1.14 years, and benefit-cost ratio of 2.

Functional, Morphological, Nutritional and Storage Evaluation of Developed Cauliflower Powder in Cabinet air Dryer and Solar Tunnel Dryer

Functional, Morphological, Nutritional and Storage Evaluation of Developed Cauliflower Powder in Cabinet air Dryer and Solar Tunnel Dryer

Energy, Exergy and Economic Analysis of a Mixed-mode Natural Convection Solar Tunnel Dryer for Banana Slices

The energy, exergy and economic analysis of a mixed-mode natural convection solar tunnel dryer for drying banana slices is presented. The collector, drying chamber and chimney energy and exergy are analysed for a load of 3.75 kg of fresh banana slices. Further, the economic analysis in terms of Net Present Value (NPV), Profitability Index (PI), the Payback Period (PB) and the Discounted Payback Period are presented. Drying experiments were done in a period of two days. During the experiment, solar radiation varied from 206.1 W/m2 to 934.5 W/m2; drying chamber temperature varied from 51.7ºC to 81.84ºC while the ambient temperature varied from 21.7ºC to 31.9ºC. The relative humidity ranged from 4.63% to 28.46% for the drying chamber and, 14.9% to 31.8% for the ambient. Under these conditions, the moisture content of the bananas was reduced from 73.89% to 14.27% in seven hours of drying on the first day. Energy and exergy efficiencies ranged from 5.56% to 57.32%, and 0.33% to 2.81%, respectively on Day 1. For Day 2 the energy and exergy efficiencies were from 14.15% to 59.16%, and 0.75% to 3.76%, respectively. For the drying chamber, the efficiency increased gradually in the first two hours to a maximum of 5.36%, corresponding to the period when there was maximum evaporation. The chimney, which is a bare flat plate type without glazing and insulation, lost heat from its surfaces. Nonetheless, it generated enough buoyancy to move air through the dryer. With the solar dryer lifespan of 10 years and the Discounted Payback Period of four years, the project is attractive and worth investing in.

Drying gayo coffee under natural processing by using modified Hohenheim solar tunnel dryer in Gayo highland

Gayo highland has relatively low daily temperature which is not effective for drying coffee. The objective of this study was to examine the operation of modified type Hohenheim solar tunnel dryer with 33% absorber area for drying coffee under natural processing in Gayo highland. About 9kg coffee cherries were dried by using the dryer and about 1 kg was dried under sun drying method. Results showed that the drying temperature of modified type Hohenheim solar tunnel dryer was higher about 9 to 14°C than the temperature of sun drying method. However, the relative humidity was about 40% both inside the drying chamber and outside the dryer. In order to reach the moisture below 14%, the drying time of coffee cherries by using the Hohenheim solar tunnel dryer may take for 8—9 days (64—72h) whereas the drying time by using sun drying method needs about 40 days (320h). It was found that the drying rate of coffee cherries dried by using Hohenheim solar tunnel dryer was higher than that of dried by sun drying method. In conclusion, the modified type Hohenheim solar tunnel dryer is promising to be used by farmers in Gayo highland.

Energy, Exergy and Economic Analysis of a Mixed-mode Natural Convection Solar Tunnel Dryer for Banana Slices

Energy, Exergy and Economic Analysis of a Mixed-mode Natural Convection Solar Tunnel Dryer for Banana Slices

Energy-efficient chamber dryer with combined heating heat transfer

Chamber dryers are widely used in the processing of vegetables and fruits in Ukraine, the USA, China, France, etc. They are intended for drying lumpy (artificial) products (bread, chopped vegetables and fruits, etc.). A chamber dryer is a connection of one or more dryer cabinets in location mode. In a 2-zone chamber dryer, it is possible to dry large volumes of raw materials, which consumes less energy compared to the power that the entire drying cabinet has when it is operated separately. But high energy costs for the process of drying materials with high prices for the second encourage to solve the task of increasing energy efficiency when creating new chamber dryers using electronic heaters of the coolant. The Institute of Technical Thermal Physics of the National Academy of Sciences of Ukraine suggests using steam heat generators in the operation of a multi-zone tunnel dryer, which, in comparison with organic fuel heat generators, make it possible to save heat consumption by 1.7-2.3 times compared to existing analogues. Energy consumption of heat in the tunnel dryer is 3800 kJ/kg of evaporated moisture. To reduce energy costs, solar tunnel dryers with an increase in the heat exchange surface due to the maximum separation of pallets with raw materials at different angles have become widespread. Due to the influence of solar energy, the temperature of the drying agent can reach 70 °С. The main direction of the development of drying plant materials is the combination of existing technologies with renewable energy sources, in particular the use of solar energy, heat pumps, as well as microwave, infrared and sublimation drying. Combined drying technology is the combination of two or more different drying processes that can provide a synergistic effect, resulting in reduced energy requirements and reduced drying time while maintaining most of the quality characteristics, such as taste, nutrients, color, aroma, texture, etc. Different methods of combined drying are considered, such as: solar-infrared, convective-infrared, infrared-microwave, convective-microwave and multifunctional, which combines microwave-sublimation drying under vacuum. The comparison of the combined methods showed a significant decrease in the duration of drying and a reduction in energy consumption, which can be used in the design of tunnel energy-efficient dryers.

Studies on semi-cylindrical solar tunnel dryer for drying wastewater sludge

Drying plays an important process for wastewater sludge management, as it can minimise the volume of wastewater sludge before disposal, and consequently the cost of storage, handling and transport. In this study, the wastewater sludge was dried by using a solar tunnel greenhouse drying system. The performance of the dryer for drying wastewater sludge has been analyzed through no load and full load test. The three full load drying tests recorded that the temperature inside the tunnel dryer fluctuated around 55±5°C; while the no load drying test, the temperature of the drying tunnel maintained within 60±5°C; as compared to the ambient temperature of 30±5°C. The average moisture content of solar dried sludge decreased from 88.69 - 90.84% to 7.78 – 13.30% in the mixing conditions and 14.78 – 19.52% in the non-mixing conditions, in 5 days. The study suggests that the semi-cylindrical solar tunnel dryer of wastewater sludge has given satisfactory results within five days.

Comprehensive analysis of the greenhouse solar tunnel dryer (GSTD) using Tomato, snake Gourd, and Cucumber: Insights into energy Efficiency, exergy Performance, economic Viability, and environmental impact

With the goal of sustainability, an innovative walk-in type Greenhouse Solar Tunnel Dryer (GSTD) with GI pipe and MS plate foundation, polycarbonate walls and roof, and cudappah stone flooring was developed and investigated. A comparison of GSTD and open sun drying was performed with tomato, snake gourd, and cucumber. The greenhouse drier drastically reduced the moisture content of the products, decreasing it from roughly 90 % to 2 % or less in 24 h. The developed GSTD was subjected to extensive energy, exergy, economic, and environmental assessments in order to examine its thermodynamic performance, economic viability, and environmental impact under forced convection by drying the three products chosen. The average efficiency of energy and exergy is 30.86 % and 14.76 %, respectively. The cost of utilizing GSTD to dry 1 kg of tomato, snack gourd, and cucumber was computed using the annualised cost technique to be 0.41, 0.1075 and 0.1232 USD, respectively. The lifetime savings range from 18,497 to 38,296 USD relying on the type of dried goods. The payback period for tomato is 1.34 years, snake gourd is 2.73 years and cucumber is 1.63 years. The lifetime carbon mitigation for tomato, snake gourd, and cucumber is 61.72 tonnes, 726.92 tonnes, and 175.74 tonnes, respectively, while the carbon credit earned is 1234.4 USD, 14538.4 USD, and 3514.8 USD.

Numerical and Experimental Validation of Solar Tunnel Dryer for Drying Agricultural Products under Togo Climatic Conditions

Numerical and Experimental Validation of Solar Tunnel Dryer for Drying Agricultural Products under Togo Climatic Conditions

Design, construction, and performance evaluation of a solar tunnel dryer with an auxiliary flat-plate solar air heater for bitter gourd drying (<em>Momordica charantia</em>)

A solar tunnel dryer and an auxiliary solar air heating unit compatible with the tunnel dryer were designed and constructed. The solar tunnel dryer has a collector chamber and a drying chamber, which are separated by a board with holes in top for air circulation. The drying experiments were conducted for sliced bitter gourd (Momordica charantia) samples in the solar drying system with and without using the auxiliary air heating unit for eight hours in the premises of Eastern University. In order to compare and analyze the performance of the solar drying system, controlled drying experiments were also carried out in open sun on equal mass samples of bitter gourd kept adjacent to the solar drying system. The temperature profiles of the inlet, interface, and outlet of the solar tunnel dryer were compared with ambient temperature, and the wet basis moisture content obtained during the system drying were compared with the open sun drying. The performance of the dryer system has been investigated in terms of temperature profile in the drying area; moisture contents, moisture ratio and effective moisture diffusivity of bitter gourd samples with time of the day. Analysis on bitter gourd samples reveal that the system with the auxiliary air heating unit exhibits enhanced performance compared to the dryer without the auxiliary unit. The moisture ratio decreases exponentially as predicted by logarithmic model. The effective moisture diffusivity values of bitter gourd drying were determined based on Fick’s Second Diffusion model.

Harmonizing Drying Time, Layer Thickness, and Drier Zones for Drying Kinetics: Quality and Safety of Solar Tunnel-Dried Wet-Processed Parchment Coffee (Coffea arabica L.).

Tunnel solar dryer is the recently used drying method for better quality and safety of parchment coffee. However, the higher variation of drying temperature and RH along the long tunnel solar dryer results in a heterogeneous environment in the tunnel, which could make parchment coffee dried at different times or with different moisture contents. This study is aimed at investigating the effect of solar tunnel dryer zones at different zones of the dryer, divided into three zones from the inlet to the exit side of the drier and drying layer thicknesses on the drying time, drying kinetics, physicochemical, sensory, and fungal growth loads of parchment coffee. Furthermore, seven mathematical models were evaluated to select the best-fitting model for a specific zone to predict drying time. Results showed that dryer zones significantly (p < 0.05) interacted with layer thickness for most of the measured parameters except titratable acidity and sensory properties. The dryer zone, coupled with the reduction in drying layer thickness, caused an increase in effective diffusivity and moisture removal rate and reduced drying time. The drying time to reach constant moisture content varied from 14 to 17 hours. Overall raw bean, cup, and total quality varied from 36.3 to 37, 48 to 51, and 84.3 to 87.3%, respectively. Values for physicochemical parameters ranged from 5.3 to 6.9 (pH), 2.1 to 2.6% (titratable acidity), 2.3 to 4.3°Brix TSS, 10.9 to 15.2% (ether extract), 39.2 to 53.5GAE/g (total phenolic content), and 38.5 to 59.2 (DPPH scavenging capacity). The fungal infection percentage at the end of drying varied from 4 to 93.3%, which could be associated with potential mycotoxin formation if recommended conditions were not maintained. In general, for better quality, similar drying times, and a lesser fungal load, it is recommended to use 4, 5, and 6 cm layer thickness in zones one, two, and three, respectively. The drying kinetics of parchment coffee in different dryer zones with different drying layer thicknesses showed variation. Zone one at 2 and 4 cm layer thicknesses is best described by the Verma model. Four- and six-centimetre layer thicknesses in zones 2 and 3 are best described by the modified Midilli model.

Effects of Slice Thickness and Pre-Treatment Concentration on the Quality Characteristics of Solar Dried Pineapple

The overall goal of this study was to determine the quality changes (vitamin C retention, browning, rehydration ratio) that occur during solar drying of pineapple as influenced by different processing conditions (slice thickness and pre-treatment concentration). Pineapple fruits were sliced to varying thicknesses (5 and 10 mm), pre-treated at different concentrations of citric acid (2, 5, and 10 g/l), and dried for 2 days in a Hohenheim model type solar tunnel dryer until a safe moisture level about ≤15% was reached. Samples were analyzed for changes in quality characteristics using standard AOAC methods. Dried pineapple slices were found to differ significantly in terms of browning scores and vitamin C retention (p≤0.05) while no differences were observed in the rehydration ratio (p&gt;0.05). Slice thickness and pre-treatment concentration were observed to have a significant interaction effect on the browning score/index of pineapple slices during drying (p≤0.05). Overall vitamin C concentration increased for samples during the drying process with the maximum vitamin C concentration being 36.85 mg/100 g recorded in 5mm thickness samples pre-treated with 5% citric acid solution. Maximum vitamin C retention was recorded in samples sliced to 5mm thickness and pre-treated with 5 g/l citric acid solution (15.68) while minimum vitamin C retention (2.41) was recorded in 5mm slices treated with a 10 g/l citric acid solution. Rehydration ratio ranged from 1.60 to 2.53. There was no significant difference between the rehydration ratio between the different treatments at P≤0.05. The lowest browning index was observed in samples sliced to 10 mm thickness and treated at 5 g/l while the highest browning index was observed in samples sliced to 5mm and treated at 5 g/l of citric acid. The best-optimized conditions obtained for the given criteria were 5 mm slice thickness and 2 g/l pre-treatment concentration based on a maximum desirability of 0.639. For the optimized combination of drying parameters, the vitamin C content, the rehydration ratio, and the browning were 9.14, 2.43 and 0.47, respectively.

Abrupt Te doping of GaInP grown by molecular beam epitaxy for solar cell applications

We report abrupt Te doping of GaInP solar cells grown by molecular beam epitaxy (MBE) through the use of a low substrate temperature of 420 °C and subsequent elimination of surface segregation. First, a Te surface pre-dose layer and reduced substrate temperature were required to achieve abrupt profiles at doping &amp;gt;1 × 1018 cm−3 in calibration samples, while reduced doping of 5.7 × 1017 cm−3 did not require the surface layer. Next, we demonstrate front-junction n+/p GaInP cells with an improved internal quantum efficiency (IQE) after Te doping of the n-type emitter directly attributable to an ∼2.5× higher carrier diffusion length, with IQE-derived short-circuit current density increasing from 13.2 to 14.1 mA/cm2. Rapid thermal annealing further boosted the performance through improvements in the minority carrier lifetime of the p-GaInP base. The use of low substrate temperature in MBE-grown GaInP enables abrupt Te doping profiles to be attained in a straightforward manner and is promising for both solar cells and tunnel junctions.