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1.
A. J. J. van der Zanden A. M. E. Schoenmakers P. I. A. M. Kerkhof 《Drying Technology》1996,14(3):647-676
A model is presented to describe the moisture transport inside a partially saturated porous material. The transport is caused by vapour diffusion and liquid diffusion. The evaporation inside the porous material is described with a mass transfer coefficient and a specific evaporating surface. Predictions of the model for moisture profiles are compared to experimentally oblained profiles found in the literature. The model needs further extension in the form of incorporating sorption isotherms. 相似文献
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ABSTRACT A model is presented to describe the moisture transport inside a partially saturated porous material. The transport is caused by vapour diffusion and liquid diffusion. The evaporation inside the porous material is described with a mass transfer coefficient and a specific evaporating surface. Predictions of the model for moisture profiles are compared to experimentally oblained profiles found in the literature. The model needs further extension in the form of incorporating sorption isotherms. 相似文献
3.
ABSTRACT A model is presented to describe the moisture transport inside a partially saturated porous material. The transport is caused by vapour diffusion and liquid diffusion. The evaporation inside the porous material is described with a mass transfer coefficient and a specific evaporating surface. Predictions of the model for moisture profiles are compared to experimentally obtained profiles found in the literature. The model needs further extension in the form of incorporating sorption isotherms. 相似文献
4.
In this paper we have examined the influence of gravity on the moisture transport process during the isenthalpic drying period, and we have considered the use of diffusion models both to predict saturation pro- files and to extract apparent diffusivities from experi- mental data. For granular or unconsolidated porous media, the one-dimensional moisture transport process can be characterized by two dimensionless groups that account for capillary forces, gravitational forces and viscous forces. Detailed numerical solutions of the saturation transport equation indicate under what circumstances the diffusion model can be used with confidence, and under what circumstances the diffusion model can be used to predict saturation profiles even though it is an incorrect representation of the moisture transport process. In addition to exploring the predictive capabilities of the diffusion model, we have 相似文献
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In this paper we have examined the influence of gravity on the moisture transport process during the isenthalpic drying period, and we have considered the use of diffusion models both to predict saturation pro- files and to extract apparent diffusivities from experi- mental data. For granular or unconsolidated porous media, the one-dimensional moisture transport process can be characterized by two dimensionless groups that account for capillary forces, gravitational forces and viscous forces. Detailed numerical solutions of the saturation transport equation indicate under what circumstances the diffusion model can be used with confidence, and under what circumstances the diffusion model can be used to predict saturation profiles even though it is an incorrect representation of the moisture transport process. In addition to exploring the predictive capabilities of the diffusion model, we have 相似文献
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Studies of chloride-induced corrosion in reinforced concrete structures are performed based on the reliable predictions of chloride and moisture distributions in concrete. This paper adopted the Laplace Transformation and the inverse Laplace Transformation to obtain the analytical solutions of the moisture-chloride two-way coupled transport processes. Additionally, the model has involved with realistic material parameters to predict the internal distributions of relative humidity and free chloride ions in concrete samples. To illustrate the accuracy of the present model, the calculations were compared with the available experimental results, and good agreements were obtained. It indicates that the present analytical model can successfully characterize the two-way coupling effects between chloride transport and moisture diffusion in concrete; and the model can provide the distribution profiles of both chloride and relative humidity in concrete, which are useful for predicting the service life of reinforced concrete structures. 相似文献
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A. Lengyel 《Drying Technology》2013,31(7-8):1275-1280
When using the convective drying method, the mass transfer between drying air and moisture diffusion of the material is very important. The moisture moves inside the material because of the volume change caused by the increased temperature. This movement is additionally affected by the texture of the material. According to the research dealing with colloid capillary porous texture of vegetables and fruit, the humidity migration inside the material occurs in both fluid and steam condition at the same time. This migration is stimulated by the heating and decreasing humidity along with the flow. In this research, winter varieties of apples (Jonathan, Golden Delicious, and Idared) were studied by heating of a 20 × 20 × 20 piece of apple with a thermocouple in it. On the basis of the measurements it can be stated that for the fruits with a high percentage of moisture (75–90%), when making the drying condition, the moisture gradient is influenced by the fractured cells of the cut area. It was found that the variety of apple is very important in relation to the heating and water loss gradient. According to the results, the wet volume change due to the heating highly influences the water loss. The models that describe the temperature of the material have a connection with the water loss. 相似文献
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《Drying Technology》2007,25(7):1275-1280
When using the convective drying method, the mass transfer between drying air and moisture diffusion of the material is very important. The moisture moves inside the material because of the volume change caused by the increased temperature. This movement is additionally affected by the texture of the material. According to the research dealing with colloid capillary porous texture of vegetables and fruit, the humidity migration inside the material occurs in both fluid and steam condition at the same time. This migration is stimulated by the heating and decreasing humidity along with the flow. In this research, winter varieties of apples (Jonathan, Golden Delicious, and Idared) were studied by heating of a 20 × 20 × 20 piece of apple with a thermocouple in it. On the basis of the measurements it can be stated that for the fruits with a high percentage of moisture (75-90%), when making the drying condition, the moisture gradient is influenced by the fractured cells of the cut area. It was found that the variety of apple is very important in relation to the heating and water loss gradient. According to the results, the wet volume change due to the heating highly influences the water loss. The models that describe the temperature of the material have a connection with the water loss. 相似文献
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A.J.J. van der Zanden W.J. Coumans P.J.A.M. Kerkhof A.M.E. Schoenmakers 《Drying Technology》1996,14(7):1525-1542
The prediction of a hydrodynamic model for the isothermal transport of liquid in partially saturated porous media is compared with experimentally obtained values of water transport in clay. The transport obeys the diffusion equation, The diffusion coefficient is described as a function of porosity, permeability and pore size distribution. The comparison indicates that the model needs some refinement. 相似文献
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A.J.J. van der Zanden W.J. Coumans P.J.A.M. Kerkhof A.M.E. Schoenmakers 《Drying Technology》2013,31(7-8):1525-1542
ABSTRACT The prediction of a hydrodynamic model for the isothermal transport of liquid in partially saturated porous media is compared with experimentally obtained values of water transport in clay. The transport obeys the diffusion equation, The diffusion coefficient is described as a function of porosity, permeability and pore size distribution. The comparison indicates that the model needs some refinement. 相似文献
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Vineet Rakesh Ashim K. Datta Jeffrey H. Walton Kathryn L. McCarthy Michael J. McCarthy 《American Institute of Chemical Engineers》2012,58(4):1262-1278
The work includes development of a multiphase porous media model and magnetic resonance imaging (MRI) experiments to study microwave combination heating. Combination of electromagnetic, convective and radiant heating was considered. The material being heated was modeled as a hygroscopic porous medium with different phases: solid matrix, water and gas, and included pressure driven flow, binary diffusion and phase change. The three‐dimensional transport model was fully coupled with electromagnetics to include the effect of variable properties. MRI was used to obtain spatial temperature and moisture distributions to validate the model. The model demonstrated that high and low moisture materials behave differently under different combinations of heating and general guidelines for combining heating modes were obtained. Low moisture materials can be heated effectively using higher microwave power which is not possible in high moisture material. Cycling of microwave was found to be useful in distribution of excessive volumetric heat generated by microwaves. © 2011 American Institute of Chemical Engineers AIChE J, 2012 相似文献
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A mathematical model able to predict solid and drying gas temperature and moisture content axial profiles along a direct contact rotary dryer was developed. The study was focused on the drying kinetics based on phenomenological models. Two different drying mechanisms in the decreasing drying rate period were tested: proponional to the unbound moisture content and moisture diffusion inside the particle. Experimental data collected in a pilot-scale direct contact rotary dryer was used to validate the model. Soya and fish meals were used as drying material. 相似文献
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ABSTRACT A mathematical model able to predict solid and drying gas temperature and moisture content axial profiles along a direct contact rotary dryer was developed. The study was focused on the drying kinetics based on phenomenological models. Two different drying mechanisms in the decreasing drying rate period were tested: proponional to the unbound moisture content and moisture diffusion inside the particle. Experimental data collected in a pilot-scale direct contact rotary dryer was used to validate the model. Soya and fish meals were used as drying material. 相似文献
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流化床氛围下多孔物料干燥传热传质的数值模拟 总被引:4,自引:1,他引:4
用有限差分法数值求解一个热、质传递耦合模型,理论研究多孔物料流化床干燥过程。方程离散采用全隐格式的控制容积方法,三对角矩阵法(TDMA)用来求解线性方程组。选用球形的苹果丁作为多孔物料。在典型操作条件下,通过分析温度、饱和度和压力的分布侧形,讨论了物料内部的热、质传递机理。在对比条件下,考察了气体入口温度、气速和床面积因子对干燥过程的影响。结果表明:干燥过程受气、固相间的耦合传热传质的影响十分明显,干燥时间随气体入口温度和气速的提高而减少;随床面积因子的增大而增加。 相似文献
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The effects of temperatures and volumetric expansion on the diffusion of fluids through solid polymers
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Yiming Fan Antonio Gomez Serena Ferraro Brian Pinto Anastasia Muliana Valeria La Saponara 《应用聚合物科学杂志》2017,134(31)
This study examines moisture sorption behaviors of two glassy polymers, epoxy and vinylester, immersed in different fluids at two temperatures below the glass transition temperatures of the polymers. The main purpose of this study is to understand the effect of volume‐dependent temperatures and deformations on the diffusion process of solid polymers. Diffusivity coefficients are first determined by assuming the diffusion to follow the classical Fickian diffusion. In some cases, moisture sorption led to quite significant changes of volume, and the diffusion process cannot be well described by the Fickian diffusion. In such situation, the coupled deformation–diffusion model for linear elastic isotropic materials presented by Gurtin 1 is adopted, as a first approximation. This coupled deformation‐diffusion model reduces to a Fickian diffusion model when the coupling parameters are absent and the volume changes in the solid polymers during diffusion are negligible. A finite difference method is used in order to solve for the coupled deformation‐diffusion model. The model is used to predict the one‐dimensional moisture diffusion in thin plates and the multiaxial three‐dimensional moisture diffusion in dogbone specimens. The multiaxial diffusion in the dogbone specimens is used to validate the calibrated material parameters from the standard thin plate diffusion characterization. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45151. 相似文献
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A pore-network model is developed to study the liquid water movement and flooding in a gas diffusion layer (GDL), with the GDL morphology taken into account. The dynamics of liquid water transport at the pore-scale and evolution of saturation profile in a GDL under realistic fuel cell operating conditions is examined for the first time. It is found that capillary forces control liquid water transport in the GDL and that liquid water moves in connected clusters with finger-like liquid waterfronts, rendering concave-shaped saturation profiles characteristic of fractal capillary fingering. The effect of liquid coverage at the GDL–channel interface on the liquid water transport inside GDL is also studied, and it is found that liquid coverage at the GDL–channel interface results in pressure buildup inside the GDL causing the liquid water to break out from preferential locations. 相似文献
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Multiscale and multilayer structural modeling and simulation on drying of grain packing porous media
Yuejin Yuan Libin Tan Zhe Zhao Yingying Xu Yu Zhao Yueding Yuan 《Drying Technology》2016,34(14):1664-1676
ABSTRACTAiming at the problem of multilayer physical structure for the skeleton of porous media, a multiscale and multilayer structural model of heat and mass transfer processes for drying of grain packing porous media was established by applying the pore network method and multiscale theory. An experimental study on rice drying was conducted in order to validate this model. The simulation and experimental results indicated that the established model could explain the mechanical properties of rice drying well. The rate of heat transfer was faster than the rate of mass transfer and there was a higher moisture gradient inside the rice grain. The diffusion coefficient of rice embryo played an important role in the drying process, and whose effect on drying was larger than the diffusion coefficient of rice hull and chaff. The moisture was imprisoned effectively inside the rice when the diffusion coefficient of rice embryo was very small. 相似文献