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Solar drying in a ventilated attic: case study of cassava slices
Abstract
In constantly sunny regions of the world such as most African countries, due to the availability of sunlight, metal roofs that are constantly exposed to the sun offer opportunities for many solar thermal applications. This study focuses on the numerical and experimental investigation of solar drying in a ventilated attic. The constructed prototype attic has three PVC pipes used as chimneys, and the roof is painted black. It was modeled using the equations of heat and mass transfers occurring during drying. The food commodity subjected to drying was cassava. The resulting system of equations was solved using the classical fourth-order Runge–Kutta method. The MATLAB R2014a language is used for the simulations. The drying of 6 kg of cassava in the prototype took 3 days. The obtained experimental results were compared with the theoretical points. The mean relative error (E%) was used as a parameter for model validation. Its values of less than 14% obtained for temperatures and humidities are evidence that the theoretical points accurately represented the behavior of the attic during solar drying. The drying efficiency varied from 25% on the first day to 0.2% on the last day. The calculated payback period is 2 months. This method can be easily implemented and would be helpful to farmers in rural Africa.
... Solar thermal energy systems harness the sun's radiant and transport it to a fluid, such as oil, water, and air through a device known as a solar collector. These collectors efficiently transport and utilize harvested heat in various applications, including domestic water, space heating, and drying [4][5][6]. ...
... In the case of collectors shorter than 10 m, both theoretical and experimental studies, such as those conducted by Ong et al. [38], Alvarez et al. [39], and Stryi-Hipp et al. [40] assumed a scenario with a uniformly distributed wall temperature and a linear variation in airflow temperature along the collector. The mean air temperature is given as the arithmetic mean, as indicated in Eq. (6). ...
... However, this metric can vary significantly due attributable to aspects such as airflow rate, weather conditions, and temperature differences. To offer a more comprehensive evaluation of collector performance, daily efficiency computed by integrating instantaneous efficiency values over a specified time, following the method outlined in reference [6]. Fig. 12. Notably, the FESAC demonstrated an improvement in daily efficiency ranging from 3.1 % to 3.7 % compared to the SESAC, attributed to the change in airflow entrance from the side to the front entrance. ...
In assessing the status of solar energy in Nigeria, efforts have been made to review researchers' works. This review article presents the status of solar energy in Nigeria. Also, it provides an all-inclusive contemporary analysis of the extensive research carried out in this field by Nigerians and renewable energy researchers in general. With her large population, Nigeria requires enormous energy for sustainability; this has caused somewhat an over-dependence on crude oil and natural gas for energy. This overdependence constantly puts the country in an energy consumption crisis when these resources are not readily available. It has its disadvantages as it affects climate change and her economy. Solar energy growth and application/adoption from the global, African, West African, and Nigerian perspectives were expounded with that of Nigeria buttressed on to bring into view the contrast between her adoption of this technology and the world. Albeit, the electricity generation from solar energy in Nigeria has also been estimated from solar radiation data, results of this analysis showed some areas in Northern Nigeria as the regions with the highest electricity generation capacity; the estimation using 1 kWp (Kilowatt-peak) PV (photovoltaic) modules were made from obtained data for possible electricity generation in kWh. The challenges to adopting these technologies were noted together with some recommendations/policies on how to curb these challenges and their implications. This review article will be of massive benefit to both the government and researchers in this research area and scientists who are currently working on renewable-related projects.
In this work, an indirect solar dryer for drying cassava root chips was modelled and experimentally validated using the environmental conditions of Yaoundé in Cameroon and Yamoussoukro in Ivory Coast. The dryers were operational in natural convection mode. Resolution of the equations was achieved by finite differences and the 4th order of Runge–Kutta methods. A model was proposed for performing heat and mass transfer using thermophysical properties of cassava roots, and the obtained results were satisfactory for all conditions, with moisture content difference of less than 0.2 kg/kg between the experimental and theoretical results. The model showed that the core of the product takes more time to dry, which always prolongs the drying duration. The heat and mass transfer coefficients vary during the entire process of solar drying. The drying kinetics vary during the drying with values lower than 1.2 × 10⁻⁴ kg/(kg.s). The great gradients of humidity were observed in the thickness of the sample with a regular distribution of the temperature each drying time in the thickness of the sample.
The main objective of this study is to design and fabricate a low-cost hybrid solar drying system and present the drying kinetics, heat transfer coefficient and thin layer models for the dried product. For this purpose, two solar dryers one equipped with biomass heater and the other without biomass heater were constructed and tested. The results show that the developed solar dryers can save between 27.78 % and 58.33 % of drying time compared to open sun drying method at ambient temperature ranging between 30 to 40 °C and a humidity ranging from 55 to 70%. Under these operating conditions, the collector efficiency is 20.81% - 21.89 %. The values for the heat transfer coefficient ranged from 0.64 to 10.5 W/m2 oC. Verma et al model gave the best result for drying with biomass heater while logarithmic model was best for drying without biomass heater.
Performances of solar dryers for the drying of medicinal and aromatic plants (MAP) in Africa were reviewed. Policy formulation indicators, including the economic and the environmental impact analysis that was lacking in almost all researches, were presented in this study. Three countries of Nigeria, Egypt and Algeria were used as case studies. Key indicators analyzed were the amount of money saved and CO2 reduction based on 10 % to 100 % rate of utilization and cost of a kWh of energy in each country. Results showed that as the rate of usage increased from 10 % to 100 % for drying lemongrass in Egypt, the amount of money saved increased from 1025/year. While, in the same country at the same drying condition and mass, it increased from 1235.44/year for drying Oregano. Drying of chilli in the coastal area of Nigeria saved more money than drying of basil in Egypt under the same rate of usage. About 40702.38 to 407023.8 kg of CO2 per year can be reduced in the drying of grape in Egypt, while 2308.5 to 23085 kg of CO2 can be reduced for drying of chilli in Nigeria.
Two identical units of a hybrid photovoltaic-thermal (PV/T) solar dryer designed and constructed at ICAR-Central Arid Zone Research Institute, Jodhpur, were used to dry Indian jujube (Zizyphus mauritiana) fruit, one operated under natural and the other under forced convection modes. The fruits were dried to safe moisture content (24 %) in a period of 192 h in forced convection mode, and in 240 h in natural convection mode with drying load of 18 kg. There was a significant difference in performance of the dryer under forced and natural convection mode. The average thermal efficiency of solar energy utilization under forced convection mode was higher (16.7 %) than that of natural convection solar dryer (15.6 %). Logarithmic drying model was suitable for describing the thin layer drying behaviour of the fruit. Effective moisture diffusivity of forced convection dryer was 3.34 × 10-7 m 2 .s-1. Economic evaluation of the solar dryer indicated high value of IRR (54.5 %), and low value of payback period (2.26 years), suggesting the dryer to be cost efficient.
Cocoa beans moisture content behavior during drying in natural convection was estimated by integration of differential semi-empiric equation and mass flow formula. The new model was found to give better result (correlation coefficient is 0.97) respectively under experimental condition (55, 70 and 105°C), solar dryer, and sun drying. In addition, knowing that the drying kinetic was inversely dependent on the temperature, we have found the high drying temperatures lead to shortening of drying phases. Finally we conclude that the exponential two-member function is the improved model to describe falling drying rate.
The drying behavior of cassava chips was investigated using two cutting shapes—rectangular and circular—with evaluation under different air temperatures of 60 °C, 80 °C, 100 °C and 120 °C. The results showed that the rectangular chips with a drying air temperature of 100 °C was optimal because they had a soft, white color desirable for cassava flour manufacture and required less drying time compared to the circular chips Four classical drying models—Approximation of Diffusion, Henderson and Pabis, Page, and Verma—were fitted to experimental data and evaluated by comparing the coefficient of determination, reduced chi-square and root mean square error between the experimental and predicted values. The Page model was able to satisfactorily describe the drying behavior of cassava chips.
Drying is a main process of conservation used for cocoa beans and it is so essential to control its drying parameters. In this study, shrinkage, density, porosity, heat and mass transfer coefficients of cocoa beans during indirect solar drying were investigated. The results showed that shrinkage and porosity increased with decreasing in reduced moisture content. The real density varied during drying process. Its value decreased from 825.10 kg/m³ at the beginning of the drying to about 696.25 kg/m³ at the end of the drying process. The cocoa beans had a final porosity approaching 25 % and most of its removed water during drying was replaced by gas. Also, the values of heat and mass transfer coefficients increased from 1.92x10⁻⁴ to 8.08x10⁻² W/m²K and from 1.88x10⁻⁷ to 7.88x10⁻⁵ m/s, respectively, for an indirect solar drying of cocoa beans. The effective moisture diffusivity was influenced by shrinkage. Effective moisture diffusivities were calculated by Fick’s diffusion law and their values varied from 5.49x10⁻¹⁰ to 4.26x10⁻¹⁰ m²/s. The cocoa beans thermophysical properties were obtained and fitted to non-linear correlations, describing their behaviour as a function of moisture content.
An indirect forced convection solar dryer consisting of an air flat plate collector and a drying cabin was designed and fabricated to investigate its performance under the climate of Algiers. Drying experiments have been performed for spearmint leaves at different air flow rates in order to determine the drying velocity, the characteristic drying curve, the effective diffusion coefficient and the activation energy. A mathematical model based on thermal and mass balances over the component of the solar collector and the cabinet dryer was developed. Simulations are carried out for meteorological data of Algiers (Algeria). We analyse the effect of air mass flow rate, air temperature, products mass, collector area, air recycling rate on the drying time, the solar fraction and the efficiency of the dryer.
Errata pdf inserted. Η βιβλιοθήκη διαθέτει αντίτυπο του βιβλίου σε έντυπη μορφή με ταξινομικό αριθμό: TJ810 .K35 2009 With the threat of global warming, and the gradual depletion of petroleum supplies, solar electric power is rapidly becoming significant part of our energy mix. The range of solar cells spans different materials and different structures in the quest to extract maximum power from the device while keeping the cost to a minimum. Devices with efficiency exceeding 30% have been demonstrated in the laboratory. Solar Energy Engineering: Processes and Systems. Solar Energy Processes and Systems includes all areas of solar energy engineering. All subjects are presented from the fundamental level to the highest level of current research. The book includes subjects such as energy related environmental problems, solar collectors, solar water heating, solar space heating and cooling, industrial process heat, solar desalination, photovoltaics, solar thermal power systems and modelling of solar systems including the use of artificial intelligence systems in solar energy systems modelling and performance prediction.
Cost analysis and CO 2 mitigation potential of the solar dryer were presented. The
drying kinetics, drying rates, CO 2 emissions mitigation, thermal efficiency and
payback period are estimated in Yaoundé climate in Cameroon. It was difficult to have
the moisture content of the product in equilibrium with ambient air using only natural
convection. The best mode of functioning is to use forced convection during sunny
period and natural convection during not sunny period. It took 32 h of drying time to
obtained final moisture content of 0.15 kg/kg (db) using forced convection during the
day and natural convection during the night for each month. The gradients of humidity
and temperature are sufficient to have a homogeneous drying in the established product layers. The specific energy consumption range between 5 and 15 kWh per kg of humidity extracted for the combined natural and forced convection. The thermal efficiency of the solar collector is above 30%, while the global thermal efficiency ranges from 5% to 18%. The CO 2 emissions mitigation potential per mass of evaporated water ranged between 15 to 25 g of CO 2 per kg of water evaporated in a day. The calculated payback period was 2.19 years.
In this study, green chillies and okra were dried using an indirect type solar dryer ITSD dryer and their drying kinetics were evaluated. The initial moisture content (MC) of green chilli was 8.3984 kg/kg of dry basis (db) and it was reduced to final MC of 0.2218 kg/kg of db. Also, MC of okra reduced from 10.1234 to 0.3348 kg/kg of db. The efficiency of solar air collector and the drying efficiency were estimated during the drying of green chilli and okra. The activation energy was found to be 32.484 and 25.330 kJ/mol and effective moisture diffusion coefficient was found to be 1.464 × 10-⁻⁹ and 5.1798 × 10-⁻⁹ m²/s for green chilli and okra, respectively. The surface transfer coefficients (both heat and mass) of green chilli and okra were estimated. Uncertainty analysis was performed on all the measured and derived drying parameters.
This paper presents the energy, exergy, and economic analysis of conventional solar still (CSS) and Modified solar still integrated with sand bed earth (MSSIE). The energy analysis has been done with the help of Dunkle and Kumar & Tiwari after using modified relations of Tsilingiris. Throughout the experimentation, the internal efficiency of MSSIE is higher than CSS (viz. 14.67%). The MSSIE shows a 41.9% higher value of exergy efficiency after 14:00 h than CSS. The distillate yield recorded from MSSIE is 12.64% higher than CSS. The AWC has been evaluated as 1.2, 1.33, 1.47 and 1.29, 1.44, 1.59 INR/l at an interest rate of 8, 10 and 12% for CSS and MSSIE with GI tray, respectively. Whereas, AWC for MSSIE get reduced by 9.2, 8.3 and 8.8% compared to CSS for the same rate of interest without GI tray.
This research study presents the experimental assessment of two sensible heat materials originating from the State of Yucatán, Mexico, which were incorporated into three compartments within an indirect type solar dryer with a storage system (ITSD-TSS). The experimental tests were carried out under different environmental conditions and were compared with the results obtained from a conventional solar dryer without thermal storage. Temperature and humidity were measured during the different tests and various indicators were used to compare both drying systems. The results revealed that the solar dryer that used limestone as storage material indicated better performance than the dryer that utilized beach sand, since the drying efficiency with limestone was higher by 1.55% and allowed to extract 0.0257 kg more water per unit kWh. Similarly, beach sand stored 1.5 times more energy than limestone, however, this material is very susceptible to variations of solar radiation, so it is not recommended to implement it in areas with high cloudiness. Finally, the implementation of the three storage compartments in the ITSD-TSS allowed an increase between 3 and 4% of the drying efficiency as compared to the conventional solar dryer. The findings of the work can contribute to sustainable development in the agricultural drying process in rural communities.
Global energy demand continues to increase with the expansion of the economy activities and sustainable development. Meanwhile, the world is suffering from pollution and harmful greenhouse gases originated from burning of fossil fuels where the consequences of climate changes are also alarming. Solar energy is an alternative energy source that is abundant, safer and cleaner. This article provides a comprehensive review of works pertaining to solar thermal energy utilization in the drying process. In this article, the classification of solar dryers, the main components which includes solar collector, drying chamber and auxiliary systems, prospects, challenges, recent advancement and performance are discussed. The existing literature reported that solar dryer and solar collector maximum efficiency of 54% and 81% respectively, with superior products quality than the open solar drying. Solar drying is economical method with the payback period of 0.54–4.69 years. Solar dryer can also reduce 34% of CO2 emission to the atmosphere with less consumption of fossil fuel. Improvements such as in the design of solar collector, drying chamber, new auxiliary system, and material are essential to elevate the solar drying system performance. A review of the technologies can provide a base for the next generation of sustainable solar drying systems and helps policymakers to frame strategies aiming for clean technology and sustainable development.
The main objective of this paper is to present a numerical model and simulation of coupled heat and mass transfer of solar dryer with various solar concentrator shapes considering the thermo-physical properties of apricot and climatic conditions of Nancy France. The resolution of the model will permit the prediction of the temperature and humidity of the solar air heater at the collector and drying chamber and also determine the moisture profile during the drying process. The thermal performance of each concentrator design was compared for best performance. A solar dryer with a non-coaxial conical concentrator presented for drying of apricot under the variable external conditions was used for the validation of the model. The numerical results showed a good agreement with experimental data taken from Togrul and Pehlivan (2002) for Elazig town. Numerically the global results were satisfying for moisture content and air temperature for the solar dryers. Parabolic concentrator had comparatively poor drying kinetics when compared with conical concentrators while co-axial design outperforming the non-coaxial design for drying kinetics. When applied in Nancy France environment to dry 30 kg of apricot with an initial moisture content of 3.5 kg/kg (db), lower energy consumption of 8.143 MJ per kg of water removed was determined for non-hybrid drying with non-coaxial conical concentrator while intermittent deployment for 2 MW electrical power consumed more energy with the higher energy of 18.668 MJ per kg of water extracted. For simulation on the environmental condition of Nancy France under the winter, summer, autumn and spring periods drying kinetic were better for drying with 1 MW continuous drying, while drying with 2 MW discontinuous drying performed better in the autumn period. Generally, non –hybrid drying performed poorly compared to others but is more energy utilization efficient compared to others.
The aim of this research was to develop a direct solar dryer assisted by photovoltaic module and evaluate its performance under natural and forced convection experiments. The photovoltaic module provides electrical power to eight coolers that allow the renewal of air inside the equipment. In this configuration, the dryer is capable of operating independently of electrical energy distribution grid. Moisture and colorimetric parameters were monitored during drying of green onion. Drying kinetics showed a constant rate period followed by a falling rate period for both operating conditions. The convection experiment showed a higher rate and external mechanisms may have controlled the process. Straight lines were adjusted to constants rate periods with R2 of 0.999. Page and Overhults models best described the falling rate periods, with R2 between 0.932 and 0.999. The effective diffusivity values were 5.15 × 10−9 m2/s and 1.15 × 10−8 m2/s for drying with natural and forced convection runs. The average efficiencies of the solar dryer and the specific energy consumption were 34.2%, 18.3 kWh/kg for the drying process with natural convection, and 38.3%, 16.4 kWh/kg for the drying process with forced convection. Little color variation was observed between fresh and dried green onions in the two operating conditions, which is consistent with the need to maintain the green color of the material.
The objective of this paper is to model a natural convection mix-mode solar dryer (NCMMSD) for drying agricultural products in an environment with short sunshine duration. The solar dryer was used to dry red chilli and was operating under the climate of the coastal area of South Eastern Nigeria characterized by low solar radiation intensity with a short duration of sunshine hours. The model took into consideration the thermophysical properties of the drying air and dried red chilli. The simultaneous heat and mass transfer equations were solved using the fourth-order Runge-Kutha method. The numerical solution allows for the determination of temperature and relative humidity of drying air at different points within the dryer as well as the moisture profile of the dried product. The experimental values of moisture ratios, temperature, and relative humidity during the mix-mode solar drying process with and without NaCl were used to validate the proposed model. Numerical simulation results were in close agreement with experimental results. The present model can serve as good reference bases to explain the drying phenomenon of mix-mode solar drying of other agricultural products when necessary thermophysical properties of these products are known. Using this model, the potential of mitigating gross fossil (coal) CO2 in Africa is annually estimated to 1280148 tons of CO2.
This paper presents a modeling and a numerical study that allows following the variation of the moisture content, temperature, drying rate and heat and mass transfer coefficients of four African tropical woods coming from Douala Cameroon. Experimental setup was developed in order to verify the drying curves and calculation of mass and heat transfer coefficients for both moisture content gradient and temperature gradient. The thermophysical properties were selected after performing an exhaustive literature review linked to the tested materials. The drying conditions were 25 °C, 33.5 °C and 0.25 m/s, representing wet temperature, dry temperature and air velocity respectively. Wood thickness ranged between 22 and 25 mm. According to modeling and simulation results, the predicted moisture content shows an average relative error on each drying curve less than 10% compared to the experimental results. Mass and heat transfer coefficients evolutions are physically explained with satisfaction. Mass transfer coefficients for temperature gradient can be neglected in steady drying conditions contrarily to the others transfer coefficients. Water permeability and brake factor of diffusivity of the air vapor in wood are determined using an inverse method. The presented drying model can be used to simulate in particular the tropical woods drying.
This study presented the behavior of a laboratory scale solar dryer, which was designed with the objective of meeting the needs of low income carpenters of the tropical region of Africa. The following materials were used to build the solar dryer: aluminum sheets painted in black, a wooden support, and a plastic polyethylene used as a cover. Drying was carried out in the city of Yaound e in Cameroon, and the tested boards were ebony (Diospyros cras-siflora). Drying must be performed with the following conditions: slow process at a low temperature in order to maintain the proper air relative humidity. Since, no apparatus was used to force the circulation of the air, natural convection was the mode used by the dryer. The solar dryer was mathematically modeled by applying heat and mass transfer balance to the different components of the solar dryer. It is important to mention that the used heat and mass coefficients were proposed as variable with the operating conditions. The mathematical model was a reasonable description of the physical phenomena taking place in the dryer. The results show that the average relative error between numerical and experimental moisture contents was equal to 2.102%. Heat transfer convective coefficients and global mass transfer coefficients varied with drying time from 0.25 to 5.5 W/(m 2 K) and from 1 Â 10 À8 to 5.5 Â 10 À8 m/s, respectively. The proposed model allowed designing and dimen-sioning the solar dryer, to the industrial scale. It allowed following the evolution of the different temperatures and moisture content of the tested material and then optimizing the design of the dryer and the drying process conditions. Based on the model, proposing the opening of the drying chamber during the night time and the use of substances capable of retaining heat in the chamber were some proposed solutions in order to have more efficient drying process. The modeling results showed also that an improvement can be obtained at the addition of a solar collector. ARTICLE HISTORY
This paper presents a numerical investigation of an indirect solar dryer for wood, using an absorber
placed directly behind the transparent cover on the top of the dryer with a layer of air separating it from
the cover. The floor and north wall are insulated and painted in black. The dryer is very simple to build
and electrical energy is only used for the fan. Applications are done on three tropical woods with 50 mm
thick most utilized in Central Africa: obeche (Triplochilon scleroxylon), iroko (Chlorophora excelsa)
and sapele (Entandrophragma cylindricum). Comparisons between the numerical results and those
experimentally obtained are given and the performances of this solar dryer are discussed under the
weather conditions of seven towns in Central Africa region located in six different countries.
Satisfactory agreement between experimental and numerical results is then obtained. With an average
initial moisture content ranging between 0.4 to 0.48 kg/kg, the average final water contents are ranged
from 0.15 to 0.18 kg/kg after 21 days in Yaoundé during the months of November and December 2004.
Modeling was applied from November 1st to the November 30th, to Sapele wood with 50 mm thick and
0.4 kg/kg initial moisture content dried in Bangui, Brazzaville, Douala, Kinshasa, Libreville and
Yaoundé until the final moisture content, which can vary from 0.13 to 0.1 kg/kg. Solar energy per cubic
meter of wood was ranging from 2 to 4.3 GJ/m3 with a maximal thermal efficiency between 12 and
47%. Ndjamena’s climate is not good to use solar drying because of its low air absolute humidity that
gives a fast drop in the moisture content and consequently destroys the wood board quality. Bangui,
Brazzaville, Douala, Kinshasa, Libreville and Yaoundé give satisfactory alternative drying conditions
using the studied solar dryer. However, it is important to use a solar collector in those six towns in order
to reduce the effect of the air absolute humidity and improve the drying kinetic.
Innovative technologies are needed to make life of mankind easy. Those innovations are best useful if they run on renewable source of energy. Greenhouse solar dryer is a device used for drying purpose. Computational fluid dynamics (CFD) analysis simulation is performed on green house solar dryer when exposed to ambient temperature on a hot sunny day for free convection and forced convection processes. The mass flow rate and thickness of polycarbonate roof sheet material have been varied. The average temperature of the dryer is analyzed using simulation. The maximum temperature is obtained in forced convection as71°C for 0.025kg/s mass flow rate. The temperature attained in forced convection is 41% more than the temperature obtained by natural convection.
Solar dryers are used to enable the preservation of agricultural crops, food processing industries for dehydration of fruits and vegetables, fish and meat drying, production of milk powder for dairy industries, seasoning of wood and timber and drying of textile materials for textile industries. The fundamental concepts and contexts of their use to dry crops are discussed in the chapter. It is shown that solar drying is the outcome of complex interactions particular between the intensity and duration of solar energy, the prevailing ambient relative humidity and temperature, the characteristics of the particular crop and its pre-preparation and the design and operation of the solar dryer.
Drying reduces the moisture content of harvested crops thus slowing decay processes to enable longer-term storage. Solar dryers contain the crop being dried, to enhance solar energy collection incurring lower crop losses than are associated with open-sun drying and recurrent costs than are inherent to uses of fossil-fuels for drying. The influences of key environmental, operational and design parameters for solar dryers are discussed including: (i) psychrometry of drying processes and ambient conditions, (ii) how initial crop properties are converted to final desired product attributes, (iii) feasibility of using powered components such as fans and (iv) air-heating solar collector selection.
Indicators of drying potential for a region based on a model of free water evaporation in a solar dryer are presented. In these indicators,
the total solar radiation and the saturation deficit of ambient air are considered as driving forces for solar drying process. The
indicators were used to define the solar dryer performance considering the drying potential of the site. The performance definition was
applied to a forced solar dryer placed in the town of San Carlos, (Salta, north-western Argentina) and was loaded with 30 kg of trays
filled with water. The results were compared with other performance definitions. A standard dryer of 0.1 kg s�1 airflow was defined to
estimate the potential indicators for 18 locations of the north-western Argentina using daily historical data. A mapping of dryer potential
was obtained for the entire region through interpolating of results, showing similarity in relation to the distribution of phytogeographic
areas. September was the month with the highest potential for solar drying on account of the end of the dried season and the influence of
the local warm wind. The indicators also were obtained for San Carlos using recently measured data. Deviations from these potentials
with respect to those obtained from the historical database were analyzed and similar results were obtained. The usefulness of these indicators
was showed as a tool to be considered when variables other than solar radiation – such as temperature and relative humidity – are
taken as energy sources.
Sorption isotherms of cassava were determined experimentally using a static gravimetric method at 30, 45 and 60 °C and within the range of 0.10–0.90 water activity. At a constant water activity, equilibrium moisture content decreased with increasing temperature. The equilibrium moisture content increased with increasing water activity at a given temperature. The experimental results were modelled using seven sorption models using non-linear regression technique. Results demonstrated that the GAB model adequately predicted equilibrium moisture content of cassava for the range of temperatures and water activities studied. The thermodynamic functions such as net isosteric heat of sorption, differential entropy of sorption, net integral enthalpy and entropy were evaluated to provide an understanding of the properties of water and energy requirements associated with the sorption behaviour. Net isosteric heat and differential entropy decreased with increasing equilibrium moisture content. The net integral enthalpy decreased while net integral entropy increased with increasing equilibrium moisture content. Net integral entropy was negative in value. All thermodynamic functions were adequately characterised by a power law model. The point of maximum stability was found between 0.053 and 0.154 kg water/kg db for cassava.
The present study investigated the kinetics of heat pump drying of cocoa beans under stepwise drying conditions and the heat and mass transfer analysis carried out using 3-D computer simulation. The fermented cocoa beans were subject to drying at constant temperature (56 °C), step up temperature (30.7 °C–43.6°C–56.9 °C) and step down temperature (54.9 °C–43.9 °C) drying profiles. Shrinkage factor was incorporated into the heat and mass transfer models. Simulation results showed that the mean relative errors determined ranged from 3.1% to 12.1% in the predicted moisture ratio profiles in both models with and without shrinkage factor. In the bean temperature profiles, results showed excellent agreement between the predicted and experimental data with mean relative errors less than 5%. The present study showed that shrinkage played a lesser role in the analysis due to the small shrinkage ratio observed before and after drying.
We present a numerical simulation of the functioning of a wood solar dryer in atmospheric conditions of Moroccan climate. A comparison of our numerical results with experimental measurements carried out on a wood solar dryer shows a good agreement. Results show that drying period is closely linked to glass partitions and timber thickness. The type of ventilation has no effect on the drying period (initial timber humidity lower than 40%). The substitution of east and west glass faces by concrete walls has practically no effect on drying period.
An experimental and numerical study for the drying process of a solid food, Chilean papaya slices, was carried out in a range of air temperatures from 40 to 80 °C. The unsteady temperature and moisture distributions results inside the sample were predicted by using an unsteady tri-dimensional coupled heat conduction and mass diffusion mathematical model. The validation procedure includes a comparison with experimental and numerical temperature and moisture content results obtained from experimental data. The samples thermophysical properties as density, specific heat, and thermal conductivity are assumed to vary non-linearly with temperature. The convective heat and mass transfer coefficients were found by the analytical model. The water effective diffusion coefficient, the drying curves and the center temperature were measured by physical experiments. It was found from the experimental results that slices of papaya present an isotropic behavior with an uncertainty between 6.0% and 9.0%. According to statistical test results (RE%), the finite volume method based calculations gave a very good fit quality.
The moisture equilibrium isotherms of chitosan were determined at 20, 30, 40, 50 and 60°C, using the gravimetric static method. Experimental data were analyzed by the GAB, Oswin, Halsey and Smith equations. Isosteric heat and differential entropy of sorption were determined from the GAB model using the Clausius-Clapeyron and Gibbs-Helmholtz equations, and pore size distribution was calculated by the Kelvin and Halsey equations. The GAB and Oswin equations showed best fit to the experimental data with R2≈99% and low mean relative deviation values (E%
The first analysis of meteorological conditions and solar energy balance was carried out in the new capital of Ivory Coast (Yamoussoukro, 6°45′N and 5'21'W). Differentparameters (temperature, humidity, aerosols and solar radiation) were considered and discussed.
Contribution à l’étude du séchage solaire de la banane plantain, de la mangue et du manioc: essais de désorption, sorption et modélisation. Thèse de doctorat troisième cycle. Laboratoire d’énergie solaire
- K.-N S Apollinaire
Étude expérimentale d’un grenier séchoir solaire à convection naturelle: application au séchage du cacao et du manioc
- Z A Tieu
- P Gbaha
- K A Diby
Notions de transfert thermique par convection, Techniques de l’Ingenieur, traité de Génie énergetique A 1 540
- J Huetz
- J P Petit
Expérimentation et modélisation du comportement énergétique et thermique d’un séchoir solaire sous le climat de la région de Rabat
- K Kabidi
- Université Thèse De Doctorat
- Faculté Mohammed V - Agdal
- Rabat Des Sciences
Sénégale: Potential Improvements to Traditional Solar Crop Dryers in Cameroon: Research and Development
- C J Minka
Thermodynamic analysis of sorption isotherms of cassava (Manihot esculenta)
- BK Koua
- EPM Koffi
- P Gbaha
- S Touré
Modeling of humidity evolution during solar drying of cassava in a ventilated attic
- A Tieu
- A S Yapi
- P Gbaha
Evolution of shrinkage, real density, porosity, heat and mass transfer coefficients during indirect solar drying of cocoa beans
- BK Koua
- EPM Koffi
- P Gbaha
Les séchoirs solaires: théorie et pratique
- M Daguenet