@article {1878, title = { Exergetic sustainability and economic analysis of hybrid solar-biomass dryer integrated with copper tubing as heat exchanger }, journal = {HELIYON}, volume = {6}, year = {2020}, abstract = {

The aim of this study is to present a new hybrid solar-biomass dryer and carry out thermal analysis based on energy and exergo-sustainability analysis considering all the available exergy stream of solar radiation, air stream through the collector, and exergy of the moisture in the product. The research also presented the environmental impact and economic analysis of using the dryer. Performance evaluations show that at collector efficiency of 20.81\%-21.89 \%, the developed solar dryers can save between 10-21hrs of drying time in drying 5 mm thick plantain slices to 15 \% moisture content from initial moisture content of 66 \% w.b when compared to drying under the open sun. The improvement potential ranged from 0.036 to 20.6W while the waste exergy ratios and sustainability index ranged from 0.38-0.55 and 2.3-6.11 respectively. Application of the solar dryers can save between 44-3074 of CO2 entering the atmosphere per year while 2.94 to 205.43$ could also be saved at 10-100\% rate of usage when compared to diesel fired dryer. The total energy consumption for drying ranges between 5.52 and 35.47 MJ, while the specific energy consumption ranged from 4.3 to 26.2 kWh/kg. The exergy efficiency ranges from 5.6-95.13 \% during the sunshine hours.

}, author = {M.C. NDUKWU and M. SIMO-TAGNE and F.I. ABAM and O.S. ONWUKA and S. PRINCE and L. BENNAMOUN} } @article {1862, title = { Numerical analysis and validation of a natural convection mix-mode solar dryer for drying red chilli under variable conditions }, journal = { RENEWABLE ENERGY }, volume = {151}, year = {2020}, pages = {659-673}, abstract = {

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.

}, url = {https://hal.archives-ouvertes.fr/hal-02521198/}, author = {M. SIMO-TAGNE and M.C. NDUKWU and A. ZOULALIAN and L. BENNAMOUN and F. KIFANI-SAHBAN and Y. ROGAUME} } @article {1803, title = { Determination and modeling of the isotherms of adsorption/desorption and thermodynamic properties of obeche and lotofa using nelson{\textquoteright}s sorption model }, journal = { HEAT AND MASS TRANSFER }, volume = {55}, year = {2019}, pages = {2185-2197}, abstract = {

Equilibrium moisture content (EMC), net isosteric heat of sorption (NIHS), net entropy of sorption (NES) and standard free energy of Gibbs (SFEG) of Triplochiton scleroxylon (obeche) and Sterculia rhinopetala (lotofa) are modeled using Nelson\&$\#$39;s sorption isotherm model. Experimental data are determined using a dynamic vapor sorption apparatus. Air relative humidity is ranged from 0 to 90\% and two air temperatures (20 degrees C and 40 degrees C) are used. Experimental data of EMCs obtained from adsorption and desorption for the mentioned woods were compared with the predicted results using Nelson\&$\#$39;s sorption model by the application of the same operating conditions (i.e. temperatures and relative humidity conditions). The results showed that the predicted ones were in good agreement with the experimental data, when the relative humidity varied from 1.2 to 90\%. Both adsorption and desorption phase presented a mean relative errors value inferior to 6.3\%. The parameters that define the sorption isotherm varied with the wood type and the sorption mode. Thus, Nelson\&$\#$39;s sorption isotherm model is a useful tool that can be used for prediction of the moisture change in wood under different environmental conditions and for predicting indirectly the thermodynamic parameters such as NIHS, NES and SFEG. In adsorption and desorption mode, the NIHS are estimated using Clausius-Clapeyron\&$\#$39;s equation. The desorption values were higher than the adsorption ones. NIHS versus EMC varied exponentially and the parameters of the function were presented variable with the sorption mode and the wood type. The total energy that we needed to extract and evaporate all bounded water is 12,398.6 J/mol for obeche and 11,627.7J/mol for lotofa. The total energy that we needed to condense and fix all bounded water taken from the state vapour is 11,829.34 J/mol for obeche and 11,379.39 J/mol for lotofa. Water molecules are more mobile during desorption than adsorption in the case of obeche. In the case of lotofa, these molecules are more mobile during adsorption. SFEG is higher in desorption than adsorption and it is influenced by species and less by the temperature. When the temperature increased, the SFEG increased as well. At low values of EMC, NIHS and SFEG are higher and decreased with the increase of EMC until reaching the fibre saturation point.

}, url = {https://hal.archives-ouvertes.fr/hal-02521244/}, author = {M. SIMO-TAGNE and L. BENNAMOUN and A. LEONARD and Y. ROGAUME} } @article {1788, title = { Modeling of coupled heat and mass transfer during drying of ebony wood using indirect natural convection solar dryer }, journal = { DRYING TECHNOLOGY }, volume = {37}, year = {2019}, pages = {1863-1878}, abstract = {

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 Yaounde in Cameroon, and the tested boards were ebony (Diospyros crassiflora). 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 x 10(-8) to 5.5 x 10(-8) m/s, respectively. The proposed model allowed designing and dimensioning 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.

}, url = {https://hal.archives-ouvertes.fr/hal-02521718/}, author = {M. SIMO-TAGNE and B. BONOMA and L. BENNAMOUN and L. MONKAM and A. LEONARD and A. ZOULALIAN and Y. ROGAUME} } @article {1728, title = { Numerical study of timber solar drying with application to different geographical and climatic conditions in Central Africa }, journal = { SOLAR ENERGY }, volume = {170}, year = {2018}, pages = {454-469}, abstract = {

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 cylindricwn). 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 and 0.48 kg/kg, the average final water contents are ranged from 0.15 to 0.18 kg/kg after 21 days in Yaounde 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 Yaounde 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/m(3) with a maximal thermal efficiency between 12 and 47\%. Ndjamena\&$\#$39;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 Yaounde 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.

}, author = {M. SIMO-TAGNE and L. BENNAMOUN} }