The Experts below are selected from a list of 1848 Experts worldwide ranked by ideXlab platform
Roland Wimmerstedt - One of the best experts on this subject based on the ideXlab platform.
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Steam Drying a bed of porous spheres theory and experiment
Chemical Engineering Science, 2000Co-Authors: Jorgen Hager, Roland Wimmerstedt, Stephen WhitakerAbstract:The process of Steam Drying a bed of porous spheres is analysed in terms of a hybrid model that makes use of volume averaged transport equations for the fluid flowing in the bed and point equations for the heat and mass transport taking place in the spheres. To verify the model, a series of experiments with varying mass flux and Steam temperature were carried out at atmospheric pressure using ceramic and Al2O3 porous spheres. The comparison between theory and experiment gives good agreement for the total Drying rate and the outlet Steam temperature for both materials, while the prediction of the internal particle temperatures shows some deviation from the experimental results. (C) 2000 Elsevier Science Ltd. All rights reserved.
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modelling Steam Drying of a single porous ceramic sphere experiments and simulations
Chemical Engineering Science, 1997Co-Authors: Jorgen Hager, Magnus Hermansson, Roland WimmerstedtAbstract:In order to investigate and describe the Drying kinetics occurring in a porous material during superheated Steam Drying, a model was developed based on the fundamental transport equations for mass and heat. The driving forces in the model are gradients of moisture, temperature and pressure. The transport coefficients employed were either measured experimentally or were derived theoretically from the pore size distribution of the material. The porous material was viewed as having cylindrical pores that wind according to a tortuosity factor, which was the only adjustable parameter used in the simulations. Local thermodynamic equilibrium was assumed to be present throughout the material. To describe this, an experimental sorption isobar was measured. Single ceramic spheres (10 mm diameter), which served as the porous model material, were dried in a thermobalance which enabled weight changes during Drying to be determined very accurately. All the experiments were carried out under atmospheric conditions, but both the Steam temperature and the Steam mass flux were varied within a broad range. Internal temperatures in the sphere were also measured by use of thin thermocouples (0.5 mm), in order to determine the shape of the internal temperature rise and obtain an indication of the temperature gradient. Good agreement was obtained between results of the experiments and of the simulations, both for the Drying rate and for internal temperature under varying external conditions, providing support for the model. The model was also used to study the magnitude and influence of the different transport mechanisms during Steam Drying. (C) 1997 Elsevier Science Ltd. (Less)
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Steam Drying: modelling and applications
Drying Technology, 1996Co-Authors: Roland Wimmerstedt, J. HagerAbstract:ABSTRACT The concept of Steam Drying originates from the mid of the last century. However, a broad industrial acceptance of the technique has so far not taken place. The paper deals with modelling the Steam Drying process and applications of Steam Drying with in certain industrial sectors where the technique has been deemed to hove special opponunities. In the modelling scction the mass and heat transfer proceases are described along with equilibrium, capillarity and sorption phenomena occurring in porous materials during the Steam Drying process. In addition existing models in the literslure are presented. The applications discussed involve Drying of fuels with high moisture contcna, cattle feed exemplified by sugar beet pulp. lumber. paper pulp. paper and sludges. Steam Drying is compared to flue gas Drying of biofuels prior to combustion in a boiler. With reference to a current insrallation in Sweden. the exergy losses. as manifested by loss of co-generation cupacity. are discussed. The energy saving p...
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Steam Drying — History and Future
Drying Technology, 1995Co-Authors: Roland WimmerstedtAbstract:ABSTRACT The concept of Steam Drying originates from the mid of the last century. However, a broad industrial acceptance of the technique has so far not taken place. The paper deals with applications of Steam Drying within certain industrial sectors where the technique has been deemed to have special opportunities. The applications discussed involve Drying of fuels with high moisture contents, cattle feed exemplified by sugar beet pulp, lumber, paper pulp, paper and sludges. Steam Drying is compared to flue gas Drying of biofuels prior to combustion in a boiler. With reference to a current installation in Sweden, the energy losscs, as manifested by loss of co-generation capacity, are discussed. The energy saving potential when using Steam Drying of sugar beet pulp as compared to other possible plant configurations is demonstrated. Mechanical vapour recompression applied to Steam Drying is analysed with reference to reported data from industrial plants. Finally, environmental advantages when using Steam dr...
Evangelos Tsotsas - One of the best experts on this subject based on the ideXlab platform.
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Continuous modeling of superheated Steam Drying of single rice grains
Drying Technology, 2018Co-Authors: Neli Hampel, Kieu Hiep Le, Abdolreza Kharaghani, Evangelos TsotsasAbstract:AbstractIn this work, a transient macroscopic model is proposed for studying the conjugated heat and mass transfer phenomena that occur inside a single rice grain during the superheated Steam Drying process. The governing equations of this model are derived based on the volume-averaging approach. Since rice is a highly hygroscopic material, more than 80% of water is accumulated as bound water in rice grain. Both the bound water diffusive flow in the solid matrix and the convective flow of water vapor and liquid water in the void volume are taken into account in this model. Thermophysical properties of rice which serve as model inputs are measured, except the absolute permeability and the bound-water diffusivity coefficients. These two properties are determined by minimizing the square of residuals between simulation results and experimental data, which were obtained by means of a magnetic suspension balance system at a Drying temperature of 160 °C. The validity of these two estimated parameters is reflect...
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Continuous modeling of superheated Steam Drying of single rice grains
Drying Technology, 2018Co-Authors: Neli Hampel, Abdolreza Kharaghani, Evangelos TsotsasAbstract:In this work, a transient macroscopic model is proposed for studying the conjugated heat and mass transfer phenomena that occur inside a single rice grain during the superheated Steam Drying proces...
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Continuum-scale modeling of superheated Steam Drying of cellular plant porous media
International Journal of Heat and Mass Transfer, 2018Co-Authors: Kieu Hiep Le, Evangelos Tsotsas, Abdolreza KharaghaniAbstract:Abstract In this work, a continuous model is developed to describe the dynamics of heat and mass transfer in cellular plant porous media during the superheated Steam Drying process at atmospheric pressure. This model accounts for the advective liquid and vapor flows in the intercellular void space as well as for the diffusive liquid flow across the solid cell membranes of the porous medium. The numerical results are verified against Drying experiments for potato samples, which were carried out by a magnetic suspension balance at three different superheated Steam temperatures (160 °C, 180 °C, 200 °C). A comparison between the simulation results and the measured data shows that the Drying characteristics of a plant porous medium can fairly be predicted by using the continuous model developed herein. The influence of the cell membrane water conductivity on the spatio-temporal distribution of the moisture content and of the temperature within the porous medium is studied by numerical simulations. It is observed that the water diffusion across the cell membranes controls the dynamics of the heat and mass transfer in the porous medium, and thus the Drying kinetics.
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Superheated Steam Drying of single wood particles: A characteristic Drying curve model deduced from continuum model simulations and assessed by experiments
Drying Technology, 2018Co-Authors: Kieu Hiep Le, Neli Hampel, Andreas Bück, Abdolreza Kharaghani, Evangelos TsotsasAbstract:ABSTRACTComputational fluid dynamics (CFD) and CFD coupled with discrete element method (DEM) are powerful approaches to describe the Drying behavior of real Drying towers. In these approaches, the heat and mass interaction between fluid phase and the wet solid is required as an essential input. In this work, a new methodology for establishing simple Drying model of single wood particles is presented. First, a spatially resolved continuum-scale model that describes the coupled heat and mass transfer within a single porous wood particle during superheated Steam Drying under atmospheric pressure is developed. The thermophysical properties of wood particle required as input data for the continuum model are determined experimentally. Then sophisticated continuum model is reduced to a simpler lumped model, which is referred to as the characteristic Drying curve (CDC) model. The continuum model simulations are performed in a board range of operating Drying conditions and the associated results are used to estab...
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Discrete pore network modeling of superheated Steam Drying
Drying Technology, 2016Co-Authors: Kieu Hiep Le, Christoph Kirsch, Abdolreza Kharaghani, Evangelos TsotsasAbstract:ABSTRACTA nonisothermal two-dimensional pore network model is developed to describe the superheated Steam Drying of a capillary porous medium. The complex void space is approximated by a network of spherical pores interconnected by cylindrical throats. In this model, the condensation of water vapor at the network surface as well as the network Drying are taken into account. During the network Drying period, the liquid transport is driven by capillary action, whereas vapor transport occurs because of convection. The condensation of water vapor within the pores is modeled based on newly formulated liquid invasion rules. The simulation results, presented as temperature and moisture content profiles over time, indicate qualitative agreement with available experimental observations. The inclusion of the liquid invasion rules is shown to accommodate more of the condensed water mass compared to earlier models, in which condensation is only partly treated. Due to the viscous vapor flow, the vapor overpressure wit...
Jorgen Hager - One of the best experts on this subject based on the ideXlab platform.
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Steam Drying a bed of porous spheres theory and experiment
Chemical Engineering Science, 2000Co-Authors: Jorgen Hager, Roland Wimmerstedt, Stephen WhitakerAbstract:The process of Steam Drying a bed of porous spheres is analysed in terms of a hybrid model that makes use of volume averaged transport equations for the fluid flowing in the bed and point equations for the heat and mass transport taking place in the spheres. To verify the model, a series of experiments with varying mass flux and Steam temperature were carried out at atmospheric pressure using ceramic and Al2O3 porous spheres. The comparison between theory and experiment gives good agreement for the total Drying rate and the outlet Steam temperature for both materials, while the prediction of the internal particle temperatures shows some deviation from the experimental results. (C) 2000 Elsevier Science Ltd. All rights reserved.
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Steam Drying of Porous Media
1998Co-Authors: Jorgen HagerAbstract:The present study concerns heat and mass transfer in porous media dried by superheated Steam. Specifically, the Steam Drying process of a packed bed of porous particles was studied in order to obtain design data for a band drier. The small scale averaged governing equations describing the heat and mass transfer within the porous particles were derived. The inherent transport coefficients were either measured or derived from the pore size distribution, the tortuosity being the only adjustable parameter. The vapour pressure reduction due to sorption phenomena was described by an experimentally measured sorption isobar. The single particle model was verified in experiments carried out in a thermo-balance using ceramic spheres. Close agreement was obtained between results from the experiments and from the simulations, both for the Drying rate and for internal temperatures under varying external conditions, providing support for the derived model. The large scale averaged equations describing the flowing fluid in the bed were derived and the constraints pointing out the validity domain for the resulting bed model were analysed. As the transport coefficients within the porous particles varied significantly in the large scale averaging volume, spherically symmetric fields within the porous spheres had to be assumed in order to join the single particle model with the bed model, together constituting the hybrid model. The hybrid model was verified with pilot-scale experiments using two materials, ceramic and aluminium oxide spheres, with significantly different pore size distribution. Close agreement was found between the experiments and the simulations concerning Drying rate and Steam outlet temperature, for varying external Drying conditions. (Less)
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modelling Steam Drying of a single porous ceramic sphere experiments and simulations
Chemical Engineering Science, 1997Co-Authors: Jorgen Hager, Magnus Hermansson, Roland WimmerstedtAbstract:In order to investigate and describe the Drying kinetics occurring in a porous material during superheated Steam Drying, a model was developed based on the fundamental transport equations for mass and heat. The driving forces in the model are gradients of moisture, temperature and pressure. The transport coefficients employed were either measured experimentally or were derived theoretically from the pore size distribution of the material. The porous material was viewed as having cylindrical pores that wind according to a tortuosity factor, which was the only adjustable parameter used in the simulations. Local thermodynamic equilibrium was assumed to be present throughout the material. To describe this, an experimental sorption isobar was measured. Single ceramic spheres (10 mm diameter), which served as the porous model material, were dried in a thermobalance which enabled weight changes during Drying to be determined very accurately. All the experiments were carried out under atmospheric conditions, but both the Steam temperature and the Steam mass flux were varied within a broad range. Internal temperatures in the sphere were also measured by use of thin thermocouples (0.5 mm), in order to determine the shape of the internal temperature rise and obtain an indication of the temperature gradient. Good agreement was obtained between results of the experiments and of the simulations, both for the Drying rate and for internal temperature under varying external conditions, providing support for the model. The model was also used to study the magnitude and influence of the different transport mechanisms during Steam Drying. (C) 1997 Elsevier Science Ltd. (Less)
Lothar Mörl - One of the best experts on this subject based on the ideXlab platform.
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Studies of Steam Drying in a fluidized bed
Drying Technology, 2002Co-Authors: Stefan Heinrich, Matthias Ihlow, Markus Henneberg, Mirko Peglow, Eike Machnow, Lothar MörlAbstract:In general, Drying processes are described by the quantity of air humidity of the exiting gases. This approach is not possible however by the Drying medium of water in Steam Drying, since the air humidity naturally possesses a constant value of 100%. This paper presents a model which represents the Drying processes on the basis of the observation of temperature profiles of the material and energetic balancing of all components involved as well as the wall of the apparatus. The modeling differentiates three intervals: the condensation phase, the 1st Drying period and the 2nd Drying period. In addition, a validation of the model on the basis of experiments in an experimental plant DN100 belonging to the university is dealt with. The satisfying concurrence of the theoretical and practical results shows that, with the help of the theoretical model, discontinuous Steam Drying processes can be theoretically described with sufficient accuracy.
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An optimization model of the operating costs of a fluidized bed Steam-Drying plant
The Canadian Journal of Chemical Engineering, 2002Co-Authors: Stefan Heinrich, Matthias Ihlow, Markus Henneberg, Gerhard Krüger, Lothar MörlAbstract:A model is developed to determine an optimum apparatus geometry and, for given apparatus dimensions, a financially optimal fluidized bed height. The parameters that effect the operating costs are the bed mass, the apparatus diameter and the gas mass flow rate. To implement such cost optimization, a physics-based mathematical model for describing the thermodynamic processes in fluidized bed Steam-Drying is briefly explained and presented. The most important conclusion is not to operate the fluidized bed for a Drying process below a certain minimum cost, calculated with the help of the modelling. The problem, when describing the Drying process and consequently the mass transfer, is that in the superheated Steam Drying case studied here, water is evaporated as moisture and withdrawn into an atmosphere of vapor water. On a mis au point un modele pour determiner une geometrie d'appareil optimale et, pour des dimensions d'appareil donnees, une hauteur de lit fluidise optimale sur le plan economique. Les parametres influant sur les couts de fonctionnement sont la masse du lit, le diametre de l'appareil et le debit massique du gaz. Pour mettre en aeuvre une telle optimisation des couts, on decrit brievement un modele mathematique base sur la physique des procedes thermodynamiques intervenant en sechage a la vapeur en lit fluidise. La conclusion la plus importante est qu'il ne faut pas utiliser le lit fluidise pour un procede de chauffage en dessous d'un certain cout minimum, calcule a l'aide de la modelisation. Le probleme lorsqu'on decrit le procede de sechage et donc le transfert de matiere, est que dans le cas du sechage a la vapeur surchauffee etudie ici, l'eau s'evapore en humidite et disparait sous forme d'une atmosphere faite de vapeur d'eau
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Fluidized Bed‐Steam Drying – Modeling and Experimental Studies
Chemical Engineering & Technology, 2001Co-Authors: Eike Machnow, Stefan Heinrich, Matthias Ihlow, Markus Henneberg, Lothar MörlAbstract:Fluidized bed-Steam Drying combines the energetic and operationally safe advantages of Steam Drying with the excellent heat and mass transfer conditions of fluidized bed technology. The existing moisture loading of the particles, as dependent variables in Drying processes, is relatively difficult to determine through balancing the quantity of the escaping gas, since, in the case of the superheated Steam Drying observed in this paper, both the particle moisture and the Drying medium are water. Temperature progressions however can be determined easily and without great demand on the apparatus. The experiments presented in this paper serve to establish a connection between the temperature and moisture progression, as well as between all other relevant Drying parameters such as gas mass flow, gas temperature or particle mass. To do this, the components involved (fluidization gas, fluidized bed particles and apparatus wall) are balanced for mass and energy. With the help of modeling based on physical laws, the mechanism of fluidized bed Drying with superheated Steam as fluidizing and Drying medium are resolved. The result is that any Drying time progression can be simulated. Discontinuous fluidized bed Drying in batches serves as the basis for the experiments. In order to use also the mathematical modeling of a discontinuous fluidized bed apparatus for continuously operated processes, a longitudinal mixture of the material being dried in a continuous Drying apparatus, e.g. in a fluidized bed channel, must be suppressed or presumably disregarded. The local coordinate of the continuous fluidized bed apparatus and the time coordinate of the discontinuous fluidized bed apparatus are then connected to one another by the product velocity being set to a constant.
Sakamon Devahastin - One of the best experts on this subject based on the ideXlab platform.
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Improvement of a mathematical model for low-pressure superheated Steam Drying of a biomaterial
Chemical Engineering Science, 2009Co-Authors: Sommart Kittiworrawatt, Sakamon DevahastinAbstract:Although there currently are a number of works reporting experimental study of low-pressure superheated Steam Drying (LPSSD), which has proved to be an attractive alternative to Drying heat-sensitive biomaterials, there are a very few works reporting the development of a mathematical model to predict the evolutions of product moisture content and temperature during LPSSD. Moreover, the predictions of those few developed models are still not satisfactory because, most of the time, the models do not include the effect of initial Steam condensation; the use of mass transfer boundary condition is, in some cases, also not quite realistic. The aim of the present study was thus to develop a more realistic liquid diffusion based model to simulate the transport of heat and mass within a product undergoing LPSSD. The effect of initial Steam condensation, in terms of film condensation, was included and a more realistic mass transfer boundary condition, in terms of the vapor pressure gradient and the physical condition at the Drying surface, was applied in the newly developed model. The effect of the product shrinkage was also included directly in the model. The predictability of the model was tested against the available experimental data. The model with initial Steam condensation was found to be able to predict the center temperature and average moisture content of the product undergoing LPSSD very well. However, at higher temperatures and lower pressures the product core temperature was still under predicted.
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Effect of starch retrogradation on texture of potato chips produced by low-pressure superheated Steam Drying
Journal of Food Engineering, 2008Co-Authors: Rungthip Kingcam, Sakamon Devahastin, Naphaporn ChiewchanAbstract:The effects of the degree of starch retrogradation, initial slice thickness and final moisture content on the texture of potato chips dried by low-pressure superheated Steam Drying (LPSSD) were investigated in this study. Potato slices of different initial thicknesses (1.5, 2.5 and 3.5 mm) were pretreated with three different methods (blanching and then freezing for 24 h, blanching and then repeated freezing/thawing either for 3 or 5 cycles) to study the effects of these pretreatment methods on the degree of starch retrogradation. The potato slices were then dried by LPSSD at 90 °C and absolute pressure of 7 kPa to three levels of final moisture content (1.5%, 2.5% and 3.5% (d.b.)) to investigate the Drying kinetics and the quality of dried potato chips in terms of hardness, toughness and crispness as well as degree of crystallinity by X-ray diffraction technique. The various pretreatment methods were found to have an obvious effect on the rates of moisture reduction of the samples. Higher degrees of starch retrogradation led to an increase in the hardness and toughness of dried chips, but did not show any significant effect on the crispness of the chips. An increase in the degree of starch retrogradation led to higher degree of crystallinity of dried potato chips.
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A mathematical model for low-pressure superheated Steam Drying of a biomaterial
Chemical Engineering and Processing, 2007Co-Authors: Peamsuk Suvarnakuta, Sakamon Devahastin, Arun S. MujumdarAbstract:Abstract Low-pressure superheated Steam Drying (LPSSD) has recently received much attention as an alternative Drying technique for heat-sensitive biomaterials. Although there are a number of works that report studies of this Drying technique experimentally, there are a very limited number of works that report attempts to model this Drying process. The aim of the present study was therefore to propose the use of a simple three-dimensional liquid diffusion based model to predict the evolutions of the moisture content and temperature of a product undergoing LPSSD. The effect of the product shrinkage was also included directly in the model and the effect of this inclusion on the predictability of the model is shown. The model was found to be able to predict the heat and mass transfer behavior as well as the change of a selected chemical quality, i.e., β-carotene, of a model biomaterial viz., carrot cube reasonably well over some range of moisture content if accurate values of the heat transfer coefficient were used.
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Effects of combined pretreatments on Drying kinetics and quality of potato chips undergoing low-pressure superheated Steam Drying
Journal of Food Engineering, 2007Co-Authors: Phet Pimpaporn, Sakamon Devahastin, Naphaporn ChiewchanAbstract:Due to an increasing demand from health-conscious consumers more attention has been placed on investigating alternative techniques to replace conventional deep-fat frying to produce health-friendly snack products including potato chips. Recently, low-pressure superheated Steam Drying (LPSSD) has proved to have potential to produce fat-free potato chips if performed in combination with appropriate pre-Drying treatments. In this study, the influences of various pretreatments and Drying temperature on the LPSSD Drying kinetics and quality parameters of dried potato chips were investigated. LPSSD of potato chips underwent various combined pretreatments, i.e., (a) blanching, (b) combined blanching and freezing, (c) blanching followed by immersion in glycerol solution and then freezing, and (d) combined blanching, immersion in monoglyceride solution and freezing, were carried out at different Drying temperatures (70, 80, and 90 °C) at an absolute pressure of 7 kPa. The quality of the dried chips was then evaluated in terms of colors, texture (hardness, toughness and crispness) and microstructure. In terms of the Drying behavior and the dried product quality, LPSSD at 90 °C with combined blanching and freezing pretreatments was proposed as the most favorable conditions for Drying potato chips.
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Simulation of a mixed air and superheated Steam Drying system
Drying Technology, 2005Co-Authors: Yuvanaree Namsanguan, Sumran Tichangtong, Warunee Tia, Somchart Soponronnarit, Sakamon DevahastinAbstract:Numerical simulation of a cabinet-type superheated Steam Drying system was conducted and validated experimentally using shrimp as the test material. The experimental and simulated Drying temperatures used were in the range of 140-160°C while the volume flow rate of Steam of 1.04 m 3 /s was used throughout. The initial masses of the Drying product were 50.7 and 31.2kg, with initial moisture contents of 4.0 kg/kg and 3.61 kg/kg dry basis, respectively; the final moisture content of the dried product was 0.25 kg/kg dry basis. The simulated moisture content of shrimp, the Drying medium temperature at the outlet of the dryer, and the performance of the dryer in terms of Drying time, Drying rate, specific energy consumption, and Drying efficiency, were verified using available experimental data. The results showed that the simulated results agreed well with the experimental results. Based on the present study, the desirable operating conditions were also evaluated for the dryer for shrimp by considering the optimized performance and good product quality.