The concern of the present work is the convective drying of empty cocoa shells in an indirect solar dryer. Some drying experiments, using one sample, were carried out. During the experiments, the sample is introduced ...The concern of the present work is the convective drying of empty cocoa shells in an indirect solar dryer. Some drying experiments, using one sample, were carried out. During the experiments, the sample is introduced in the drying chamber. Then at steady time intervals, the sample is withdrawn from the drying chamber, for a rapid weighing. After each weighing, the sample is reintroduced in the dryer. At each time interval, the ambient temperature of the drying chamber and its relative humidity γ are measured by a thermo-hygrometer. From the experimental data, a theoretical determination of the moisture evaporated from the product was performed and a good agreement was found between the theoretical and experimental values, confirmed by the value of the RMSE. Those calculations used the constants in the Nusselt number found in literature. Then those constants were evaluated again, to get new values more suitable with the experimental data. The dimensionless numbers of Nusselt, Grashof and Prandtl were calculated. That allowed the calculation of the average value of the Nusselt number. The average convective heat transfer coefficient was determined.展开更多
This study was carried out at the Mamou Higher Institute of Technology during the period from March 10 to April 15, 2022, with the aim of designing and testing a solar dryer with forced convection by drying potatoes. ...This study was carried out at the Mamou Higher Institute of Technology during the period from March 10 to April 15, 2022, with the aim of designing and testing a solar dryer with forced convection by drying potatoes. The dryer was designed using local materials. Its main geometric parameters are: 1) height of the drying chamber (90 cm), 2) length of the drying chamber (50 cm), 3) width of the drying chamber (43 cm), 4) surface of the racks (0.1806 m<sup>2</sup>), 5) surface of the heat accumulator (0.2537 m<sup>2</sup>). The experiment focused on the vacuum test of the dryer for two days and that of the drying of the sweet potato for three days from 8:30 a.m. to 5:30 p.m. The average vacuum test temperature values of the three environments are respectively accumulator (43°C), dryer chamber (41°C) and ambient environment (34°C). Four kilograms (4 kg) of boiled sweet potato were dried. The average temperatures in the accumulator and in the drying chamber during the three days of drying are respectively 33°C and 39°C. The final mass of the dried product is 1.2 kg, with a quantity of water extracted of 2 liters or 63% of the initial mass of the product. The average drying rate is 0.074 kg/h. The drying kinetics showed a decreasing rate in the absence of the heating period and the constant rate period.展开更多
This study was carried out at the Mamou Higher Institute of Technology during the period from March 10 to April 15, 2022, with the aim of designing and testing a solar dryer with forced convection by drying potatoes. ...This study was carried out at the Mamou Higher Institute of Technology during the period from March 10 to April 15, 2022, with the aim of designing and testing a solar dryer with forced convection by drying potatoes. The dryer was designed using local materials. Its main geometric parameters are: 1) height of the drying chamber (90 cm), 2) length of the drying chamber (50 cm), 3) width of the drying chamber (43 cm), 4) surface of the racks (0.1806 m<sup>2</sup>), 5) surface of the heat accumulator (0.2537 m<sup>2</sup>). The experiment focused on the vacuum test of the dryer for two days and that of the drying of the sweet potato for three days from 8:30 a.m. to 5:30 p.m. The average vacuum test temperature values of the three environments are respectively accumulator (43°C), dryer chamber (41°C) and ambient environment (34°C). Four kilograms (4 kg) of boiled sweet potato were dried. The average temperatures in the accumulator and in the drying chamber during the three days of drying are respectively 33°C and 39°C. The final mass of the dried product is 1.2 kg, with a quantity of water extracted of 2 liters or 63% of the initial mass of the product. The average drying rate is 0.074 kg/h. The drying kinetics showed a decreasing rate in the absence of the heating period and the constant rate period.展开更多
Food losses in the developing country are thought to be 50% of the fruits and vegetables grown and 25% of harvested food grain. Food preservation can reduce wastage of a harvest surplus, allow storage for food shortag...Food losses in the developing country are thought to be 50% of the fruits and vegetables grown and 25% of harvested food grain. Food preservation can reduce wastage of a harvest surplus, allow storage for food shortages, and in some cases facilitate export to high-value markets. Drying is one of the oldest methods of food preservation. Drying makes produce lighter, smaller, and less likely to spoil and helps to minimize the moisture content in coffee beans as high moisture content during storage is certain to ruin the taste and appearance of coffee. This work presents the results of an experimental study of forced convection drying of coffee cherries in a modified Icaro solar dryer. The study aims to validate the numerical models developed for further research. The experimental tests envisaged also aim to determine the mass loss curves of the product by fixing or calculating its initial mass (1 kg), its initial water content (70%), the ambient temperature, the drying airflow (0.02 m<sup>3.</sup>s<sup>-1</sup> to 0.09 m<sup>3.</sup>s<sup>-1</sup>) and the exchange coefficients. The influence of these aerothermal parameters on the drying time of a most commercialized coffee variety (Robusta) was studied. Finally, the results revealed an increase in the efficiency of the heat transfer air and a reduction in the water content of the coffee cherry from 70% to 9.87%, after 30.2 hours.展开更多
This comprehensive review focuses on the performance of solar dryers, with a specific emphasis on their structural shape and orientation. Researchers have extensively examined these design parameters, often employing ...This comprehensive review focuses on the performance of solar dryers, with a specific emphasis on their structural shape and orientation. Researchers have extensively examined these design parameters, often employing Computational Fluid Dynamics (CFD) to assess thermal attributes and predict temperature distribution, airflow patterns, and temperature profiles within the structures. Geographical location significantly influences solar dryer shape preferences, with the parabolic shape finding favor in tropical regions for its superior solar radiation capture and storm resistance, while even-span and Quonset shapes are popular elsewhere. Solar dryer orientation is another crucial factor, with east-west alignment consistently proving optimal due to its ability to maximize year-round solar radiation absorption and, consequently, enhance drying efficiency. Economic considerations, however, fall beyond the scope of this review, which predominantly focuses on thermal aspects. This investigation reveals diverse global preferences for solar dryer shapes and orientation, highlighting the necessity of considering geographical factors in design choices. While CFD and shape/orientation dynamics have provided valuable insights, there remains room for future research to expand into transient state simulations under various conditions, contributing to a more comprehensive understanding of solar dryer performance. Such insights promise to promote sustainable and efficient drying processes, benefitting agricultural and drying applications across the globe.展开更多
The fluctuation in drying temperature influences the food products’quality and drying time significantly during the drying process using an indirect solar dryer.One of the effective methods to reduce these variations...The fluctuation in drying temperature influences the food products’quality and drying time significantly during the drying process using an indirect solar dryer.One of the effective methods to reduce these variations in the temperature is based on thermal storage materials to control the drying temperature.An experimental investigation is presented in this study to evaluate the performance of an indirect solar dryer with air double pass using multiple phase change materials(PCM)as thermal storage materials.Two PCMs with different melting points are used to store the available heat energy during peak sunshine periods and reduce the drying temperature fluctuations.Drying tests on a food product sample are conducted in three cases,the first was without PCMs using natural convection.The second and third cases are based on forced convection with and without using multiple PCMs under Baghdad city conditions.The results showed that;approximately a steady temperature of hot drying air was obtained during relatively low ambient temperatures when the dryer was incorporated with multiple PCMs.The drying time of the product sample for the natural,forced convection without PCMs and forced with PCMs was 87,72 and 47 h,respectively.The higher performance of the dryer was for the forced convection with PCMs.The reduction percentage in drying time was about 17.2%and 46%for the forced convection without and with PCMs respectively compared with natural convection.The average drying rate for the natural,forced without PCMs and forced convection with PCMs was 0.0093,0.0135 and 0.0172 kg/h,respectively.The enhancement in thermal efficiency of the solar collector and drying chamber with multiple PCMs was 43%and 25.5%,respectively,compared with a typical solar dryer.展开更多
The study investigates drying characteristics of common species of fish in the tropics, catfish (Clarias gariepinus) and tilapia fish (Oreochromis niloticus) using a direct solar dryer. The drying process was carried ...The study investigates drying characteristics of common species of fish in the tropics, catfish (Clarias gariepinus) and tilapia fish (Oreochromis niloticus) using a direct solar dryer. The drying process was carried out during the dry and wet season under natural (0 m/s) and forced convective drying (1.5 m/s, 2.5 m/s, 3.5 m/s fan speed). Results obtained showed that the drying air attained by the dryer was satisfactory and the maximum temperature difference between the dryer and the ambient temperatures was 35°C. The moisture content of the dried samples was 13.97% for catfish and 13.35% for tilapia fish during dry season and during the wet season it was 15.68% for catfish and 14.9% for tilapia fish while for the open sun dried samples it was 21.7% for catfish and 17.0% for tilapia fish. Maximum drying efficiency of 74.3% was recorded for the dryer during dry season and the dried samples at 3.5 m/s fan speed were better in drying rates. The proximate compositions of the fish before and after drying were determined. There was significant difference in proximate composition before and after drying (P < 0.05) and no significant difference in proximate composition at fan speeds considered for both fish species (P < 0.05).展开更多
Drying is one of the most energy-intensive processes in agro-products industry. For this reason, using solar energy appears as an attractive not polluting alternative to be used in drying processes. However, the daily...Drying is one of the most energy-intensive processes in agro-products industry. For this reason, using solar energy appears as an attractive not polluting alternative to be used in drying processes. However, the daily and seasonal fluctuations in the radiation level require using energy accumulators with phase change materials (paraffin wax), to have a continuous drying processes. In hybrid solar dryers with energy accumulation system, a control system is essential to coordinate the control valves that allow the income of air that comes from the solar panel or from the energy accumulator. In this work, we implemented an advances multivariable control system that uses fuzzy logic in the hybrid solar dryer. The dryer includes an energy accumulator panel with paraffin wax as phase change material. The input variables were ambient temperature and solar radiation, both not controllable. The controlled variables were the opening level of the solar panel and accumulator energy valves. The control program consisted in an algorithm implemented with the “Fuzzy” toolbox in Matlab. Data were acquired with OPTO 22. The control system performed adequately when used to dehydrate mushroom slices and plums. Closing or opening the respective valves as a response to the variations of solar radiation and ambient air temperature allowed optimizing the use of solar energy.展开更多
Rice is the staple food for more than three billion people worldwide.Although considerable progress has been made with respect to improved breeds and production practices,losses during postharvest handling remain cons...Rice is the staple food for more than three billion people worldwide.Although considerable progress has been made with respect to improved breeds and production practices,losses during postharvest handling remain considerable.Drying and storage of paddy are two key stages where management can be improved.For rice,grain moisture content of 14%prevents microbiological activity,while a level of about 12%minimizes quality losses over prolonged storage periods.Due to the need for simple and economical technologies,an inflatable solar dryer(ISD)was developed based on adaptations of the Hohenheim-type solar tunnel dryer.To form a drying tunnel,transparent polyethylene(PE)film attaches by zipper to a reinforced black polyvinyl chloride(PVC)film.To reduce heat loss,a flexible multilayer floor was used along the drying area.The tunnel does not need a substructure as it is stabilized adequately from pressure created by two axial flow ventilators.During experiments,paddy was spread on the floor and mixed with a special roller bar.The ISD has been evaluated for paddy in the Philippines during both rainy and dry seasons and was subsequently optimized.Sun drying and shade drying were carried out in parallel for comparison and product was evaluated for moisture content and quality in terms of milling recovery and head rice yield.Moisture content was reduced from 23%to 14%within 26-52 h of continuous operation during the rainy season and 16%to 14%within 4-26 h of drying during the dry season.In both seasons,the final moisture content of 12%was reached after prolonged drying periods.Quality was not found to be affected with respect to drying treatment.The ISD showed advantages over sun drying,despite longer drying periods.展开更多
The objective of this work is to analyse the extent to which a change in the drying air velocity may affect the drying kinetics of tomato in a forced-convective solar tunnel dryer. 2 m?s?1 (V1) and 3 m?s?1 (V2) air sp...The objective of this work is to analyse the extent to which a change in the drying air velocity may affect the drying kinetics of tomato in a forced-convective solar tunnel dryer. 2 m?s?1 (V1) and 3 m?s?1 (V2) air speeds were applied in similar drying air temperature and humidity conditions. Main drying constants calculated included the drying rate, the drying time and the effective water diffusivity based on the derivative form of the Fick’s second law of diffusion. Henderson and Pabis Model and Page Model were used to describe the drying kinetics of tomato. We found that solar drying of tomato occurred in both constant and falling-rate phases. The Page Model appeared to give a better description of tomato drying in a forced-convective solar tunnel dryer. At t = 800 min, the drying rate was approximately 0.0023 kg of water/kg dry matter when drying air velocity was at 2 m/s. At the same moment, the drying rate was higher than 0.0032 kg of water/kg dry matter when the drying air velocity was 3 m/s. As per the effective water diffusivity, its values changed from 2.918E?09 m2?s?1 to 3.921E?09 m2?s?1 when drying air velocity was at 2 and 3 m?s?1 respectively, which is equivalent to a 25% increase. The experimentations were conducted in Niamey, on the 1st and 5th of January 2019 for V2 and V1 respectively. For both two experiments, the starting time was 9:30 local time.展开更多
Erecting solar dryers for medicinal plants require the best design option to suit such plants.Investigations were carried out on some design parameters of the unglazed perforated solar dryers under the prevailing weat...Erecting solar dryers for medicinal plants require the best design option to suit such plants.Investigations were carried out on some design parameters of the unglazed perforated solar dryers under the prevailing weather conditions of Ismailia,Egypt.Effects of different parameters on the heat exchange effectiveness were investigated.Parameters considered in this study including hole(perforation)diameters,dimensions apart,material being used and its thickness all were investigated to reveal the effects of suitable suction velocity,prevailing wind speed and its direction under the simulated incident solar radiation of the investigation site.Based on the obtained results for heat exchange effectiveness under controllable conditions,solar drier was built and investigated outdoors under the prevailing weather conditions of the investigation site.Holes diameter of 3 mm for all the investigated plates and under the different conditions resulted the highest obtained heat exchange effectiveness.Diamond shape for Holes distribution with dimensions of 29 mm×29 mm apart gave higher heat exchange effectiveness above the commonly used distribution(square shape).Temperature increase above ambient per unit of incident radiation was found as(0.0162±0.0007)℃m^(2)/W,when the best designed performance was investigated in the open environment.Using that perforated surface as an absorber in constructed dryer to dry Rosemary(Rosmarinus officinalis L.),reduced the moisture content from 65%(wet basis)to 38.1%on eight hours on the first drying day of the 18th April,2010 while the reduction in moisture content of the sample dried in the shade area was from 65%(wet basis)to 42.2%under the same prevailing weather conditions at the same time.展开更多
Two passive solar dryers were designed and constructed with available local materials.The passive solar dryers which were direct and indirect types were tested with pepper(Capsicum annum L.),okro(Abelmoschus esculentu...Two passive solar dryers were designed and constructed with available local materials.The passive solar dryers which were direct and indirect types were tested with pepper(Capsicum annum L.),okro(Abelmoschus esculentus L.)and vegetables(Amaranthus hybridus L.)in order to evaluate the drying rate of these produces.The moisture content of 78.9%(w.b.)for 180 g freshly harvested peppers was reduced to 24.0%(w.b.).The drying rate in the direct passive solar dryer was found to be higher than the indirect passive solar dryer.The initial moisture content of 92%(w.b.)for 1000 g okro was reduced to 20%(w.b.).The drying rate in the direct passive solar dryer was also found to be higher than in the indirect passive solar dryer.The initial moisture content of 90%(w.b.)for 400 g vegetable was reduced to 20%(w.b.).The drying rate with the direct passive solar dryer was found to be higher than that with indirect passive solar dryer.During the course of drying,after each crop was kept inside the drying system,the temperature of the drying was monitored at an-hour interval;the moisture content was also monitored at a three-hour interval until there was no more change in the weight of the crop.The crops dried faster with the direct passive solar dryer than with the indirect passive solar dryer.As a result of the highest temperature attained in the direct passive solar dryer,the rate of moisture removal was the highest in this dryer.展开更多
A survey on the use of solar dryers for drying purposes was carried out in some communities in eastern Nigeria.The objective of the study was to ascertain the extent uses of solar dryers by local farmers and the rural...A survey on the use of solar dryers for drying purposes was carried out in some communities in eastern Nigeria.The objective of the study was to ascertain the extent uses of solar dryers by local farmers and the rural populace.The survey method included oral interview and questionnaire administration.The results of the study revealed that the practical use of solar dryers is absent domestically and industrially.However,great enthusiasm was shown by the farmers in the use of solar crop dryers if their performance is satisfactory with respect to quality and quantity of products dried at a given time interval.Most farmers rejected the idea of establishing communally maintained and operated systems but preferred commercialized systems where payments are made per unit quantity of products dried.The study therefore recommends the development of affordable solar crop dryers with auxiliary heat sources to mitigate the effects of daily and seasonal fluctuation in solar radiation in order to cope with the demands of a profit oriented commercial drying system.Such a system holds a lot of promises for entrepreneurs.展开更多
In this paper, a new design of a natural convection solar dryer used to dry fruits is presented;taking into account the local climatic conditions prevailed in Jordan during summer season. The dryer will have a capacit...In this paper, a new design of a natural convection solar dryer used to dry fruits is presented;taking into account the local climatic conditions prevailed in Jordan during summer season. The dryer will have a capacity of 100 kg of sliced apples and the simulation is based on mass and heat balances. It is deemed that such new design will be able to reduce the original moisture content, of the final product, to 10% within two days. The special tailored program could be used to calculate drying parameters for similar products under different climatic conditions. The next step will be focused on constructing the solar dryer in order to conduct actual experiments in the field.展开更多
The solar bubble dryer (SBD) is a convenient and better option to traditional open sun drying commonly practiced by smallholder farmers in Ghana and other developing countries. However, to operate the SBD, one is face...The solar bubble dryer (SBD) is a convenient and better option to traditional open sun drying commonly practiced by smallholder farmers in Ghana and other developing countries. However, to operate the SBD, one is faced with the challenge of frequent mixing of grains using a rake to enhance uniform drying and prevent over-heating of the top-layer exposed to the sun. Additionally, condensation in the SBD can compromise the quality of grains during drying under humid conditions. In the present study, the Analytical Hierarchy Process (AHP) was used to select an appropriate drying platform, tarpaulin, or elevated drying rack for maize drying in the SBD. Using the AHP, the elevated drying rack was chosen as a suitable platform for drying maize in the SBD. The SBD with the elevated drying racks was used to dry 270 kg of maize from a moisture content of 18.2% to 12.6% (w.w.b) within 6 hours compared to 11 hours for the same quantity of grains dried on the tarpaulin of the SBD to reach an MC of 12.5% (w.w.b). An average drying rate and moisture extraction rate of 0.93%/h and 2.88 kg/h were achieved with the elevated drying rack system compared to 0.52%/h and 1.60 kg/h when drying on the tarpaulin of the SBD. An average temperature of 44.6<span style="white-space:nowrap;">°</span>C recorded in the SBD was 9<span style="white-space:nowrap;">°</span>C more compared to the ambient temperature. The thermal efficiency of the SBD collector was determined as 36.2%. Drying grains with the elevated racks showed advantages of reduced drying time, improved airflow through the drying bed, and prevention of condensation, which occurs when drying on the tarpaulin of the SBD.展开更多
Though several maize varieties have been developed and introduced over the years in Ghana, farmers still face challenges of access to quality seed maize. Among the major constraint is lack of proper drying systems to ...Though several maize varieties have been developed and introduced over the years in Ghana, farmers still face challenges of access to quality seed maize. Among the major constraint is lack of proper drying systems to guarantee quality of seed produced. As in most parts of Africa, drying of maize in the open, on bare ground along shoulders of roads is still a common practice in Ghana. In this study, a 5-tonne capacity hybrid solar biomass dryer was developed for drying maize for seed and food/feed in Ghana. Effect of air temperature in the dryer on the physiological quality and germination of maize kernels was investigated. Maize grains were dried in the open sun simulating farmers practice and using the dryer at 4 varying levels (L1, L2, L3 and L4) with corresponding heights (0.6 m, 1.2 m, 1.8 m and 2.4 m, respectively) from the ground. Harvested maize at 22.8% moisture content was dried at the varying levels until reaching the final desired moisture content of 12.8% ± 0.2% (wb). Results showed that, air temperatures in the dryer increased in accordance with height with lowest mean temperature of 44.4°C ± 4.6°C recorded at L1 and mean maximum of 52.8°C ± 5.4°C at L4. Drying temperatures recorded at L1 - L3 and ambient had no significant effect (p < 0.05) on kernel damage and viability. Drying conditions at L1-L3 were considered optimum (<50°C) for kernel drying compared to the topmost tray, L4. Kernel stress crack index (multiple and checked) was therefore reduced on average by 14% while kernel germination increased by 33%. This satisfies the dryer’s potential to be used for commercial drying of maize grains for seed production for smallholder farmers in Ghana.展开更多
This paper presents an experimental analysis for comparisons of conventional flat plate solar collectors and collectors integrated with different numbers of baffles. Heat transfer between absorber plate and drying flu...This paper presents an experimental analysis for comparisons of conventional flat plate solar collectors and collectors integrated with different numbers of baffles. Heat transfer between absorber plate and drying fluid (air) has been one of the major challenges in the design and operations of the indirect solar dryer systems. In this experiment, efficiency of air flat plate solar collector integrated with 2, 3, 4 and 8 baffles was studied and compared with the ordinary collector. The results showed that integrating solar collector with baffles significantly increased the efficiency of the system. It was noted that collector with 2, 3, 4 and 8 baffles had a mean efficiency of 29.2%, 31.3%, 33.1% and 33.7% respectively while with no baffles was 28.9%. The analysis showed that when there were less than four baffles in the collector, heat transfer was dominant over pressure drop and hence high efficiency. However, when the number of baffles exceeded four, the effect associated with an increase in pressure drop highly observed compared to heat transfer coefficient, thus resulted to insignificant increase in efficiency. Therefore, the optimum number of four baffles was commended for the designed model for optimum efficiency.展开更多
Medical herbs are located in Egypt in different areas and they are very important to increase the national income of Egypt. It is necessary to dry the herbs in their growing locations. As the growing locations are loc...Medical herbs are located in Egypt in different areas and they are very important to increase the national income of Egypt. It is necessary to dry the herbs in their growing locations. As the growing locations are located far from the natural supply grid of Egypt, renewable energy sources such as PV&WIND are preferably utilized to achieve the drying process. Moreover, since the drying process is actually used to remove water from the herbs, thus it can preserve the herbs in storage drastically by preventing the attack of microorganisms during the moist conditions of herbs and also reduce their weight and bulk (for cheaper transport). Where, this paper selects, at first, the suitable drying site, and then it suggests. The suggested drying system is completely designed, and includes the following three systems: the solar thermal system, the dryer, and the renewable energy system.展开更多
文摘The concern of the present work is the convective drying of empty cocoa shells in an indirect solar dryer. Some drying experiments, using one sample, were carried out. During the experiments, the sample is introduced in the drying chamber. Then at steady time intervals, the sample is withdrawn from the drying chamber, for a rapid weighing. After each weighing, the sample is reintroduced in the dryer. At each time interval, the ambient temperature of the drying chamber and its relative humidity γ are measured by a thermo-hygrometer. From the experimental data, a theoretical determination of the moisture evaporated from the product was performed and a good agreement was found between the theoretical and experimental values, confirmed by the value of the RMSE. Those calculations used the constants in the Nusselt number found in literature. Then those constants were evaluated again, to get new values more suitable with the experimental data. The dimensionless numbers of Nusselt, Grashof and Prandtl were calculated. That allowed the calculation of the average value of the Nusselt number. The average convective heat transfer coefficient was determined.
文摘This study was carried out at the Mamou Higher Institute of Technology during the period from March 10 to April 15, 2022, with the aim of designing and testing a solar dryer with forced convection by drying potatoes. The dryer was designed using local materials. Its main geometric parameters are: 1) height of the drying chamber (90 cm), 2) length of the drying chamber (50 cm), 3) width of the drying chamber (43 cm), 4) surface of the racks (0.1806 m<sup>2</sup>), 5) surface of the heat accumulator (0.2537 m<sup>2</sup>). The experiment focused on the vacuum test of the dryer for two days and that of the drying of the sweet potato for three days from 8:30 a.m. to 5:30 p.m. The average vacuum test temperature values of the three environments are respectively accumulator (43°C), dryer chamber (41°C) and ambient environment (34°C). Four kilograms (4 kg) of boiled sweet potato were dried. The average temperatures in the accumulator and in the drying chamber during the three days of drying are respectively 33°C and 39°C. The final mass of the dried product is 1.2 kg, with a quantity of water extracted of 2 liters or 63% of the initial mass of the product. The average drying rate is 0.074 kg/h. The drying kinetics showed a decreasing rate in the absence of the heating period and the constant rate period.
文摘This study was carried out at the Mamou Higher Institute of Technology during the period from March 10 to April 15, 2022, with the aim of designing and testing a solar dryer with forced convection by drying potatoes. The dryer was designed using local materials. Its main geometric parameters are: 1) height of the drying chamber (90 cm), 2) length of the drying chamber (50 cm), 3) width of the drying chamber (43 cm), 4) surface of the racks (0.1806 m<sup>2</sup>), 5) surface of the heat accumulator (0.2537 m<sup>2</sup>). The experiment focused on the vacuum test of the dryer for two days and that of the drying of the sweet potato for three days from 8:30 a.m. to 5:30 p.m. The average vacuum test temperature values of the three environments are respectively accumulator (43°C), dryer chamber (41°C) and ambient environment (34°C). Four kilograms (4 kg) of boiled sweet potato were dried. The average temperatures in the accumulator and in the drying chamber during the three days of drying are respectively 33°C and 39°C. The final mass of the dried product is 1.2 kg, with a quantity of water extracted of 2 liters or 63% of the initial mass of the product. The average drying rate is 0.074 kg/h. The drying kinetics showed a decreasing rate in the absence of the heating period and the constant rate period.
文摘Food losses in the developing country are thought to be 50% of the fruits and vegetables grown and 25% of harvested food grain. Food preservation can reduce wastage of a harvest surplus, allow storage for food shortages, and in some cases facilitate export to high-value markets. Drying is one of the oldest methods of food preservation. Drying makes produce lighter, smaller, and less likely to spoil and helps to minimize the moisture content in coffee beans as high moisture content during storage is certain to ruin the taste and appearance of coffee. This work presents the results of an experimental study of forced convection drying of coffee cherries in a modified Icaro solar dryer. The study aims to validate the numerical models developed for further research. The experimental tests envisaged also aim to determine the mass loss curves of the product by fixing or calculating its initial mass (1 kg), its initial water content (70%), the ambient temperature, the drying airflow (0.02 m<sup>3.</sup>s<sup>-1</sup> to 0.09 m<sup>3.</sup>s<sup>-1</sup>) and the exchange coefficients. The influence of these aerothermal parameters on the drying time of a most commercialized coffee variety (Robusta) was studied. Finally, the results revealed an increase in the efficiency of the heat transfer air and a reduction in the water content of the coffee cherry from 70% to 9.87%, after 30.2 hours.
文摘This comprehensive review focuses on the performance of solar dryers, with a specific emphasis on their structural shape and orientation. Researchers have extensively examined these design parameters, often employing Computational Fluid Dynamics (CFD) to assess thermal attributes and predict temperature distribution, airflow patterns, and temperature profiles within the structures. Geographical location significantly influences solar dryer shape preferences, with the parabolic shape finding favor in tropical regions for its superior solar radiation capture and storm resistance, while even-span and Quonset shapes are popular elsewhere. Solar dryer orientation is another crucial factor, with east-west alignment consistently proving optimal due to its ability to maximize year-round solar radiation absorption and, consequently, enhance drying efficiency. Economic considerations, however, fall beyond the scope of this review, which predominantly focuses on thermal aspects. This investigation reveals diverse global preferences for solar dryer shapes and orientation, highlighting the necessity of considering geographical factors in design choices. While CFD and shape/orientation dynamics have provided valuable insights, there remains room for future research to expand into transient state simulations under various conditions, contributing to a more comprehensive understanding of solar dryer performance. Such insights promise to promote sustainable and efficient drying processes, benefitting agricultural and drying applications across the globe.
文摘The fluctuation in drying temperature influences the food products’quality and drying time significantly during the drying process using an indirect solar dryer.One of the effective methods to reduce these variations in the temperature is based on thermal storage materials to control the drying temperature.An experimental investigation is presented in this study to evaluate the performance of an indirect solar dryer with air double pass using multiple phase change materials(PCM)as thermal storage materials.Two PCMs with different melting points are used to store the available heat energy during peak sunshine periods and reduce the drying temperature fluctuations.Drying tests on a food product sample are conducted in three cases,the first was without PCMs using natural convection.The second and third cases are based on forced convection with and without using multiple PCMs under Baghdad city conditions.The results showed that;approximately a steady temperature of hot drying air was obtained during relatively low ambient temperatures when the dryer was incorporated with multiple PCMs.The drying time of the product sample for the natural,forced convection without PCMs and forced with PCMs was 87,72 and 47 h,respectively.The higher performance of the dryer was for the forced convection with PCMs.The reduction percentage in drying time was about 17.2%and 46%for the forced convection without and with PCMs respectively compared with natural convection.The average drying rate for the natural,forced without PCMs and forced convection with PCMs was 0.0093,0.0135 and 0.0172 kg/h,respectively.The enhancement in thermal efficiency of the solar collector and drying chamber with multiple PCMs was 43%and 25.5%,respectively,compared with a typical solar dryer.
文摘The study investigates drying characteristics of common species of fish in the tropics, catfish (Clarias gariepinus) and tilapia fish (Oreochromis niloticus) using a direct solar dryer. The drying process was carried out during the dry and wet season under natural (0 m/s) and forced convective drying (1.5 m/s, 2.5 m/s, 3.5 m/s fan speed). Results obtained showed that the drying air attained by the dryer was satisfactory and the maximum temperature difference between the dryer and the ambient temperatures was 35°C. The moisture content of the dried samples was 13.97% for catfish and 13.35% for tilapia fish during dry season and during the wet season it was 15.68% for catfish and 14.9% for tilapia fish while for the open sun dried samples it was 21.7% for catfish and 17.0% for tilapia fish. Maximum drying efficiency of 74.3% was recorded for the dryer during dry season and the dried samples at 3.5 m/s fan speed were better in drying rates. The proximate compositions of the fish before and after drying were determined. There was significant difference in proximate composition before and after drying (P < 0.05) and no significant difference in proximate composition at fan speeds considered for both fish species (P < 0.05).
文摘Drying is one of the most energy-intensive processes in agro-products industry. For this reason, using solar energy appears as an attractive not polluting alternative to be used in drying processes. However, the daily and seasonal fluctuations in the radiation level require using energy accumulators with phase change materials (paraffin wax), to have a continuous drying processes. In hybrid solar dryers with energy accumulation system, a control system is essential to coordinate the control valves that allow the income of air that comes from the solar panel or from the energy accumulator. In this work, we implemented an advances multivariable control system that uses fuzzy logic in the hybrid solar dryer. The dryer includes an energy accumulator panel with paraffin wax as phase change material. The input variables were ambient temperature and solar radiation, both not controllable. The controlled variables were the opening level of the solar panel and accumulator energy valves. The control program consisted in an algorithm implemented with the “Fuzzy” toolbox in Matlab. Data were acquired with OPTO 22. The control system performed adequately when used to dehydrate mushroom slices and plums. Closing or opening the respective valves as a response to the variations of solar radiation and ambient air temperature allowed optimizing the use of solar energy.
文摘Rice is the staple food for more than three billion people worldwide.Although considerable progress has been made with respect to improved breeds and production practices,losses during postharvest handling remain considerable.Drying and storage of paddy are two key stages where management can be improved.For rice,grain moisture content of 14%prevents microbiological activity,while a level of about 12%minimizes quality losses over prolonged storage periods.Due to the need for simple and economical technologies,an inflatable solar dryer(ISD)was developed based on adaptations of the Hohenheim-type solar tunnel dryer.To form a drying tunnel,transparent polyethylene(PE)film attaches by zipper to a reinforced black polyvinyl chloride(PVC)film.To reduce heat loss,a flexible multilayer floor was used along the drying area.The tunnel does not need a substructure as it is stabilized adequately from pressure created by two axial flow ventilators.During experiments,paddy was spread on the floor and mixed with a special roller bar.The ISD has been evaluated for paddy in the Philippines during both rainy and dry seasons and was subsequently optimized.Sun drying and shade drying were carried out in parallel for comparison and product was evaluated for moisture content and quality in terms of milling recovery and head rice yield.Moisture content was reduced from 23%to 14%within 26-52 h of continuous operation during the rainy season and 16%to 14%within 4-26 h of drying during the dry season.In both seasons,the final moisture content of 12%was reached after prolonged drying periods.Quality was not found to be affected with respect to drying treatment.The ISD showed advantages over sun drying,despite longer drying periods.
文摘The objective of this work is to analyse the extent to which a change in the drying air velocity may affect the drying kinetics of tomato in a forced-convective solar tunnel dryer. 2 m?s?1 (V1) and 3 m?s?1 (V2) air speeds were applied in similar drying air temperature and humidity conditions. Main drying constants calculated included the drying rate, the drying time and the effective water diffusivity based on the derivative form of the Fick’s second law of diffusion. Henderson and Pabis Model and Page Model were used to describe the drying kinetics of tomato. We found that solar drying of tomato occurred in both constant and falling-rate phases. The Page Model appeared to give a better description of tomato drying in a forced-convective solar tunnel dryer. At t = 800 min, the drying rate was approximately 0.0023 kg of water/kg dry matter when drying air velocity was at 2 m/s. At the same moment, the drying rate was higher than 0.0032 kg of water/kg dry matter when the drying air velocity was 3 m/s. As per the effective water diffusivity, its values changed from 2.918E?09 m2?s?1 to 3.921E?09 m2?s?1 when drying air velocity was at 2 and 3 m?s?1 respectively, which is equivalent to a 25% increase. The experimentations were conducted in Niamey, on the 1st and 5th of January 2019 for V2 and V1 respectively. For both two experiments, the starting time was 9:30 local time.
文摘Erecting solar dryers for medicinal plants require the best design option to suit such plants.Investigations were carried out on some design parameters of the unglazed perforated solar dryers under the prevailing weather conditions of Ismailia,Egypt.Effects of different parameters on the heat exchange effectiveness were investigated.Parameters considered in this study including hole(perforation)diameters,dimensions apart,material being used and its thickness all were investigated to reveal the effects of suitable suction velocity,prevailing wind speed and its direction under the simulated incident solar radiation of the investigation site.Based on the obtained results for heat exchange effectiveness under controllable conditions,solar drier was built and investigated outdoors under the prevailing weather conditions of the investigation site.Holes diameter of 3 mm for all the investigated plates and under the different conditions resulted the highest obtained heat exchange effectiveness.Diamond shape for Holes distribution with dimensions of 29 mm×29 mm apart gave higher heat exchange effectiveness above the commonly used distribution(square shape).Temperature increase above ambient per unit of incident radiation was found as(0.0162±0.0007)℃m^(2)/W,when the best designed performance was investigated in the open environment.Using that perforated surface as an absorber in constructed dryer to dry Rosemary(Rosmarinus officinalis L.),reduced the moisture content from 65%(wet basis)to 38.1%on eight hours on the first drying day of the 18th April,2010 while the reduction in moisture content of the sample dried in the shade area was from 65%(wet basis)to 42.2%under the same prevailing weather conditions at the same time.
文摘Two passive solar dryers were designed and constructed with available local materials.The passive solar dryers which were direct and indirect types were tested with pepper(Capsicum annum L.),okro(Abelmoschus esculentus L.)and vegetables(Amaranthus hybridus L.)in order to evaluate the drying rate of these produces.The moisture content of 78.9%(w.b.)for 180 g freshly harvested peppers was reduced to 24.0%(w.b.).The drying rate in the direct passive solar dryer was found to be higher than the indirect passive solar dryer.The initial moisture content of 92%(w.b.)for 1000 g okro was reduced to 20%(w.b.).The drying rate in the direct passive solar dryer was also found to be higher than in the indirect passive solar dryer.The initial moisture content of 90%(w.b.)for 400 g vegetable was reduced to 20%(w.b.).The drying rate with the direct passive solar dryer was found to be higher than that with indirect passive solar dryer.During the course of drying,after each crop was kept inside the drying system,the temperature of the drying was monitored at an-hour interval;the moisture content was also monitored at a three-hour interval until there was no more change in the weight of the crop.The crops dried faster with the direct passive solar dryer than with the indirect passive solar dryer.As a result of the highest temperature attained in the direct passive solar dryer,the rate of moisture removal was the highest in this dryer.
文摘A survey on the use of solar dryers for drying purposes was carried out in some communities in eastern Nigeria.The objective of the study was to ascertain the extent uses of solar dryers by local farmers and the rural populace.The survey method included oral interview and questionnaire administration.The results of the study revealed that the practical use of solar dryers is absent domestically and industrially.However,great enthusiasm was shown by the farmers in the use of solar crop dryers if their performance is satisfactory with respect to quality and quantity of products dried at a given time interval.Most farmers rejected the idea of establishing communally maintained and operated systems but preferred commercialized systems where payments are made per unit quantity of products dried.The study therefore recommends the development of affordable solar crop dryers with auxiliary heat sources to mitigate the effects of daily and seasonal fluctuation in solar radiation in order to cope with the demands of a profit oriented commercial drying system.Such a system holds a lot of promises for entrepreneurs.
文摘In this paper, a new design of a natural convection solar dryer used to dry fruits is presented;taking into account the local climatic conditions prevailed in Jordan during summer season. The dryer will have a capacity of 100 kg of sliced apples and the simulation is based on mass and heat balances. It is deemed that such new design will be able to reduce the original moisture content, of the final product, to 10% within two days. The special tailored program could be used to calculate drying parameters for similar products under different climatic conditions. The next step will be focused on constructing the solar dryer in order to conduct actual experiments in the field.
文摘The solar bubble dryer (SBD) is a convenient and better option to traditional open sun drying commonly practiced by smallholder farmers in Ghana and other developing countries. However, to operate the SBD, one is faced with the challenge of frequent mixing of grains using a rake to enhance uniform drying and prevent over-heating of the top-layer exposed to the sun. Additionally, condensation in the SBD can compromise the quality of grains during drying under humid conditions. In the present study, the Analytical Hierarchy Process (AHP) was used to select an appropriate drying platform, tarpaulin, or elevated drying rack for maize drying in the SBD. Using the AHP, the elevated drying rack was chosen as a suitable platform for drying maize in the SBD. The SBD with the elevated drying racks was used to dry 270 kg of maize from a moisture content of 18.2% to 12.6% (w.w.b) within 6 hours compared to 11 hours for the same quantity of grains dried on the tarpaulin of the SBD to reach an MC of 12.5% (w.w.b). An average drying rate and moisture extraction rate of 0.93%/h and 2.88 kg/h were achieved with the elevated drying rack system compared to 0.52%/h and 1.60 kg/h when drying on the tarpaulin of the SBD. An average temperature of 44.6<span style="white-space:nowrap;">°</span>C recorded in the SBD was 9<span style="white-space:nowrap;">°</span>C more compared to the ambient temperature. The thermal efficiency of the SBD collector was determined as 36.2%. Drying grains with the elevated racks showed advantages of reduced drying time, improved airflow through the drying bed, and prevention of condensation, which occurs when drying on the tarpaulin of the SBD.
文摘Though several maize varieties have been developed and introduced over the years in Ghana, farmers still face challenges of access to quality seed maize. Among the major constraint is lack of proper drying systems to guarantee quality of seed produced. As in most parts of Africa, drying of maize in the open, on bare ground along shoulders of roads is still a common practice in Ghana. In this study, a 5-tonne capacity hybrid solar biomass dryer was developed for drying maize for seed and food/feed in Ghana. Effect of air temperature in the dryer on the physiological quality and germination of maize kernels was investigated. Maize grains were dried in the open sun simulating farmers practice and using the dryer at 4 varying levels (L1, L2, L3 and L4) with corresponding heights (0.6 m, 1.2 m, 1.8 m and 2.4 m, respectively) from the ground. Harvested maize at 22.8% moisture content was dried at the varying levels until reaching the final desired moisture content of 12.8% ± 0.2% (wb). Results showed that, air temperatures in the dryer increased in accordance with height with lowest mean temperature of 44.4°C ± 4.6°C recorded at L1 and mean maximum of 52.8°C ± 5.4°C at L4. Drying temperatures recorded at L1 - L3 and ambient had no significant effect (p < 0.05) on kernel damage and viability. Drying conditions at L1-L3 were considered optimum (<50°C) for kernel drying compared to the topmost tray, L4. Kernel stress crack index (multiple and checked) was therefore reduced on average by 14% while kernel germination increased by 33%. This satisfies the dryer’s potential to be used for commercial drying of maize grains for seed production for smallholder farmers in Ghana.
文摘This paper presents an experimental analysis for comparisons of conventional flat plate solar collectors and collectors integrated with different numbers of baffles. Heat transfer between absorber plate and drying fluid (air) has been one of the major challenges in the design and operations of the indirect solar dryer systems. In this experiment, efficiency of air flat plate solar collector integrated with 2, 3, 4 and 8 baffles was studied and compared with the ordinary collector. The results showed that integrating solar collector with baffles significantly increased the efficiency of the system. It was noted that collector with 2, 3, 4 and 8 baffles had a mean efficiency of 29.2%, 31.3%, 33.1% and 33.7% respectively while with no baffles was 28.9%. The analysis showed that when there were less than four baffles in the collector, heat transfer was dominant over pressure drop and hence high efficiency. However, when the number of baffles exceeded four, the effect associated with an increase in pressure drop highly observed compared to heat transfer coefficient, thus resulted to insignificant increase in efficiency. Therefore, the optimum number of four baffles was commended for the designed model for optimum efficiency.
文摘Medical herbs are located in Egypt in different areas and they are very important to increase the national income of Egypt. It is necessary to dry the herbs in their growing locations. As the growing locations are located far from the natural supply grid of Egypt, renewable energy sources such as PV&WIND are preferably utilized to achieve the drying process. Moreover, since the drying process is actually used to remove water from the herbs, thus it can preserve the herbs in storage drastically by preventing the attack of microorganisms during the moist conditions of herbs and also reduce their weight and bulk (for cheaper transport). Where, this paper selects, at first, the suitable drying site, and then it suggests. The suggested drying system is completely designed, and includes the following three systems: the solar thermal system, the dryer, and the renewable energy system.
