Transactions of the ASABE (American Society of Agricultural and Biological Engineers)
The drying behavior of rough rice in a deep bed was analyzed numerically by solving the heat and ... more The drying behavior of rough rice in a deep bed was analyzed numerically by solving the heat and moisture transfer equations using a novel deep-bed model. The model consisted of two scales, where a computational fluid dynamics (CFD) model was used first to predict the convective coefficients of heat and mass transfer between an individual rough rice kernel and air in the rough rice bed. Subsequently, the predicted heat and mass transfer coefficients were then used for coupling the moisture and heat fluxes inside the rough rice kernel with the external convective heat and mass transfers at the kernels surfaces in a complete rough rice bed model using Comsol Multiphysics® simulation environment. The developed model was used to predict the grain moisture contents and temperatures at different heights in the bed during a drying process. The theoretical predictions of moisture profiles inside a deep bed of rough rice were validated against experimental data from literature. The results r...
Grain drying is a simultaneous heat and moisture transfer problem. The modeling of such a problem... more Grain drying is a simultaneous heat and moisture transfer problem. The modeling of such a problem is of significance in understanding and controlling the drying process. The main goal of this study was to predict the heat and mass transfer processes during deep-bed rice drying. To achieve this, first, CFD simulations were carried out to analyze the external flow and temperature fields at steady-state for a control volume of a stationary rice bed. The model was used to predict the convective heat and mass transfer coefficients in the rice bed, and correlations were developed for the convective heat and mass transfer coefficients as a function of drying air flow rate. Then, the coupled CFD and diffusion model developed by ElGamal, Ronsse, Radwan & Pieters (2013) to investigate the heat and mass transfer for thin-layer drying of rice was extended to volumetric heat and mass transfer in a deep-bed of rice using the predicted heat and mass transfer coefficients. All models were solved nu...
ABSTRACT The drying behavior of a single rice kernel subjected to convective drying was analyzed ... more ABSTRACT The drying behavior of a single rice kernel subjected to convective drying was analyzed numerically by solving heat and moisture transfer equations using a coupled CFD and diffusion model. The transfer coefficients were computed simultaneously with the external flow field and the internal diffusive field of the grain. The model was validated using results of a thin-layer drying experiments from literature. The effects of velocity and temperature of the drying air on the rice kernel were analyzed. It was found that the air temperature was the major variable that affected the drying rate of the rice kernel. The initial drying rates (in first 20 min) were 7%, 12% and 19% per hour at inlet air temperature of 30ºC, 45ºC, and 60ºC, respectively. Important temperature gradients within the grain existed only in the first few minutes of the drying process. The moisture content gradients reached a maximum value of 11.7% [d.b.].mm-1 at approximately 45 min along the short axis in the thickness direction. The variation of the inlet air velocity showed a minor effect on the drying rate of the rice kernel. The heat and mass transfer coefficients varied from 16.57 to 203.46 W•m-2•K-1 and from 0.0160 to 0.1959 m•s-1, respectively. The importance of the computation of the transfer coefficients with the heat and mass transfer model is demonstrated.
Abstract: Although the fluid bed technology has been successfully applied in the coating of parti... more Abstract: Although the fluid bed technology has been successfully applied in the coating of particulate solids, some problems like agglomeration and spray-drying still remain unresolved. In order to understand the fluidisation hydrodynamics of a specific fluid bed ...
A thermodynamic model is presented for the top-spray fluidised bed coating process. The model is ... more A thermodynamic model is presented for the top-spray fluidised bed coating process. The model is based on the bed's discretisation into horizontal layers (or control volumes). In each control volume, both particle population balances and heat and mass balances for the solid, gas and droplet phases are constructed. Model-predicted spray drying losses were compared against experimentally determined coating efficiencies.
Fluidized beds are amongst others used in industrial applications for coating particles. Little r... more Fluidized beds are amongst others used in industrial applications for coating particles. Little research has been performed in developing a quality model for a coating process. A quality model is able to predict the quality of the process in terms of coating thickness and uniformity and the occurrence of unwanted side-effects, including agglomeration, attrition and spray loss. The quality of the coating process in a fluidized bed is largely determined by the spray characteristics and the particle motion. A new quality model was developed for the coating process in a top-spray fluidized bed. The first step in the development of the new model was the creation of an accurate spray sub-model that describes the movement and the heat and mass balances of the droplets in the coating process. The second step was the creation of a particle sub-model that describes the movement and the heat and mass balances of the particles in the fluidized bed. The third and final step will be the developme...
The objective of this study was to investigate the effect of particle surface moisture content on... more The objective of this study was to investigate the effect of particle surface moisture content on growth rate during agglomeration. In order to establish the relationship between process conditions and particle surface moisture content and temperature (and their spatial distribution in the fluidized bed), the combined population balance and thermodynamic model, as described by Ronsse et al. (2007a,b), was used. Growth kinetics were experimentally verified using 100 µm glass beads and maltodextrin based aqueous binder solutions, under varying process conditions. Studied process variables included binder concentration, fluidization air temperature, liquid binder feed rate and liquid binder atomisation pressure.
It has been premised that lignocellulosic biomass is the main renewable energy resources availabl... more It has been premised that lignocellulosic biomass is the main renewable energy resources available here on earth and con be considered as one of few sources that can provide renewable liquid, gaseous and solid fuels. In contrast to fossil fuels, the use of biomass for energy renders significant environmental advantages. Plant growth needed to generate biomass feedstocks removes atmospheric carbon dioxide, which offsets the increase in atmospheric carbon dioxide that results from biomass fuel combustion. One promising and clean way to acquire bio-oil is by the fast pyrolysis of biomass, which is considered as a network of rich hemicellulose and cellulose bound by lignin. This process is carried out in the absence of oxygen, or when significantly less oxygen is present than required for complete combustion, and at elevated temperatures, thus yielding in gaseous products, liquids (bio-oil and water) and solid charcoal. The bio-oil contains a broad range of organic chemicals; hence they...
The main product of biomass fast pyrolysis is a liquid mixture of numerous organic molecules with... more The main product of biomass fast pyrolysis is a liquid mixture of numerous organic molecules with water that is usually called pyrolysis oil or bio-oil. The research discussed in this paper was meant (1) to validate a new, semicontinuously operated pyrolysis setup and (2) to investigate the effect of a repeatedly regenerated ZSM-5-based catalyst (eight reaction/regeneration cycles in total) on the yields and compositions of the pyrolysis products in relation to the applied process conditions and on the catalyst itself. The reliability of the setup has been proven by multiple repetition of noncatalytic and catalytic (in situ) pyrolysis experiments for pine wood at 500 degrees C under identical conditions. As a result, the mass balance closures for all experiments varied from 92 to 99 wt %, while the scatter in measured data was always less than 5%. Changes in the performance of the repeatedly regenerated catalyst have been observed via detailed analysis of the bio-oil (GC X GC-FID an...
Leaf wetness duration (LWD) is one of the most critical parameters involved in the development of... more Leaf wetness duration (LWD) is one of the most critical parameters involved in the development of plant diseases, since many pathogens require the presence of free water on plant organs to infect foliar tissue. For this reason LWD monitoring is extremely important in crop protection, particularly through the use of weather-related disease forecasting models. Because of the difficulties involved in the measurement of leaf wetness duration, simulation models, based on agrometeorological parameters, are often used as alternatives to field measurement. Furthermore, in greenhouse crop production, these LWD models can be used in predictive control of the greenhouse climate as to suppress the development and propagation of infectious plant diseases. In this study, the Gembloux Dynamic Greenhouse Climate Model (GDGCM) was applied to derive estimates of LWD and hence potential disease incidence, for a rose crop in a naturally ventilated Azrom type greenhouse in Zimbabwe. The model LWD estima...
Transactions of the ASABE (American Society of Agricultural and Biological Engineers)
The drying behavior of rough rice in a deep bed was analyzed numerically by solving the heat and ... more The drying behavior of rough rice in a deep bed was analyzed numerically by solving the heat and moisture transfer equations using a novel deep-bed model. The model consisted of two scales, where a computational fluid dynamics (CFD) model was used first to predict the convective coefficients of heat and mass transfer between an individual rough rice kernel and air in the rough rice bed. Subsequently, the predicted heat and mass transfer coefficients were then used for coupling the moisture and heat fluxes inside the rough rice kernel with the external convective heat and mass transfers at the kernels surfaces in a complete rough rice bed model using Comsol Multiphysics® simulation environment. The developed model was used to predict the grain moisture contents and temperatures at different heights in the bed during a drying process. The theoretical predictions of moisture profiles inside a deep bed of rough rice were validated against experimental data from literature. The results r...
Grain drying is a simultaneous heat and moisture transfer problem. The modeling of such a problem... more Grain drying is a simultaneous heat and moisture transfer problem. The modeling of such a problem is of significance in understanding and controlling the drying process. The main goal of this study was to predict the heat and mass transfer processes during deep-bed rice drying. To achieve this, first, CFD simulations were carried out to analyze the external flow and temperature fields at steady-state for a control volume of a stationary rice bed. The model was used to predict the convective heat and mass transfer coefficients in the rice bed, and correlations were developed for the convective heat and mass transfer coefficients as a function of drying air flow rate. Then, the coupled CFD and diffusion model developed by ElGamal, Ronsse, Radwan & Pieters (2013) to investigate the heat and mass transfer for thin-layer drying of rice was extended to volumetric heat and mass transfer in a deep-bed of rice using the predicted heat and mass transfer coefficients. All models were solved nu...
ABSTRACT The drying behavior of a single rice kernel subjected to convective drying was analyzed ... more ABSTRACT The drying behavior of a single rice kernel subjected to convective drying was analyzed numerically by solving heat and moisture transfer equations using a coupled CFD and diffusion model. The transfer coefficients were computed simultaneously with the external flow field and the internal diffusive field of the grain. The model was validated using results of a thin-layer drying experiments from literature. The effects of velocity and temperature of the drying air on the rice kernel were analyzed. It was found that the air temperature was the major variable that affected the drying rate of the rice kernel. The initial drying rates (in first 20 min) were 7%, 12% and 19% per hour at inlet air temperature of 30ºC, 45ºC, and 60ºC, respectively. Important temperature gradients within the grain existed only in the first few minutes of the drying process. The moisture content gradients reached a maximum value of 11.7% [d.b.].mm-1 at approximately 45 min along the short axis in the thickness direction. The variation of the inlet air velocity showed a minor effect on the drying rate of the rice kernel. The heat and mass transfer coefficients varied from 16.57 to 203.46 W•m-2•K-1 and from 0.0160 to 0.1959 m•s-1, respectively. The importance of the computation of the transfer coefficients with the heat and mass transfer model is demonstrated.
Abstract: Although the fluid bed technology has been successfully applied in the coating of parti... more Abstract: Although the fluid bed technology has been successfully applied in the coating of particulate solids, some problems like agglomeration and spray-drying still remain unresolved. In order to understand the fluidisation hydrodynamics of a specific fluid bed ...
A thermodynamic model is presented for the top-spray fluidised bed coating process. The model is ... more A thermodynamic model is presented for the top-spray fluidised bed coating process. The model is based on the bed's discretisation into horizontal layers (or control volumes). In each control volume, both particle population balances and heat and mass balances for the solid, gas and droplet phases are constructed. Model-predicted spray drying losses were compared against experimentally determined coating efficiencies.
Fluidized beds are amongst others used in industrial applications for coating particles. Little r... more Fluidized beds are amongst others used in industrial applications for coating particles. Little research has been performed in developing a quality model for a coating process. A quality model is able to predict the quality of the process in terms of coating thickness and uniformity and the occurrence of unwanted side-effects, including agglomeration, attrition and spray loss. The quality of the coating process in a fluidized bed is largely determined by the spray characteristics and the particle motion. A new quality model was developed for the coating process in a top-spray fluidized bed. The first step in the development of the new model was the creation of an accurate spray sub-model that describes the movement and the heat and mass balances of the droplets in the coating process. The second step was the creation of a particle sub-model that describes the movement and the heat and mass balances of the particles in the fluidized bed. The third and final step will be the developme...
The objective of this study was to investigate the effect of particle surface moisture content on... more The objective of this study was to investigate the effect of particle surface moisture content on growth rate during agglomeration. In order to establish the relationship between process conditions and particle surface moisture content and temperature (and their spatial distribution in the fluidized bed), the combined population balance and thermodynamic model, as described by Ronsse et al. (2007a,b), was used. Growth kinetics were experimentally verified using 100 µm glass beads and maltodextrin based aqueous binder solutions, under varying process conditions. Studied process variables included binder concentration, fluidization air temperature, liquid binder feed rate and liquid binder atomisation pressure.
It has been premised that lignocellulosic biomass is the main renewable energy resources availabl... more It has been premised that lignocellulosic biomass is the main renewable energy resources available here on earth and con be considered as one of few sources that can provide renewable liquid, gaseous and solid fuels. In contrast to fossil fuels, the use of biomass for energy renders significant environmental advantages. Plant growth needed to generate biomass feedstocks removes atmospheric carbon dioxide, which offsets the increase in atmospheric carbon dioxide that results from biomass fuel combustion. One promising and clean way to acquire bio-oil is by the fast pyrolysis of biomass, which is considered as a network of rich hemicellulose and cellulose bound by lignin. This process is carried out in the absence of oxygen, or when significantly less oxygen is present than required for complete combustion, and at elevated temperatures, thus yielding in gaseous products, liquids (bio-oil and water) and solid charcoal. The bio-oil contains a broad range of organic chemicals; hence they...
The main product of biomass fast pyrolysis is a liquid mixture of numerous organic molecules with... more The main product of biomass fast pyrolysis is a liquid mixture of numerous organic molecules with water that is usually called pyrolysis oil or bio-oil. The research discussed in this paper was meant (1) to validate a new, semicontinuously operated pyrolysis setup and (2) to investigate the effect of a repeatedly regenerated ZSM-5-based catalyst (eight reaction/regeneration cycles in total) on the yields and compositions of the pyrolysis products in relation to the applied process conditions and on the catalyst itself. The reliability of the setup has been proven by multiple repetition of noncatalytic and catalytic (in situ) pyrolysis experiments for pine wood at 500 degrees C under identical conditions. As a result, the mass balance closures for all experiments varied from 92 to 99 wt %, while the scatter in measured data was always less than 5%. Changes in the performance of the repeatedly regenerated catalyst have been observed via detailed analysis of the bio-oil (GC X GC-FID an...
Leaf wetness duration (LWD) is one of the most critical parameters involved in the development of... more Leaf wetness duration (LWD) is one of the most critical parameters involved in the development of plant diseases, since many pathogens require the presence of free water on plant organs to infect foliar tissue. For this reason LWD monitoring is extremely important in crop protection, particularly through the use of weather-related disease forecasting models. Because of the difficulties involved in the measurement of leaf wetness duration, simulation models, based on agrometeorological parameters, are often used as alternatives to field measurement. Furthermore, in greenhouse crop production, these LWD models can be used in predictive control of the greenhouse climate as to suppress the development and propagation of infectious plant diseases. In this study, the Gembloux Dynamic Greenhouse Climate Model (GDGCM) was applied to derive estimates of LWD and hence potential disease incidence, for a rose crop in a naturally ventilated Azrom type greenhouse in Zimbabwe. The model LWD estima...
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