Mechanism and mathematical model of heat and mass transfer during convective drying of porous materials

Zhang, Zhe; Yang, Shixi; Liu, Dengying

doi:10.1002/(sici)1523-1496(1999)28:5<337::aid-htj1>3.0.co;2-9

Cited by 21 publications

(12 citation statements)

References 15 publications

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“…The model has been implemented in a FORTRAN-based computer code. The formulation, presented in this study, has been validated successfully with experimental data over different ranges of conditions in drying of various porous materials, such as wood, , brick, food, and lignite . These works highlight the acceptance and validity of this model in drying of porous media.…”

Section: Numerical Solution Proceduresmentioning

confidence: 64%

“…Nowadays, Whitaker’s theory is a well-known model to describe drying processes in porous media. Because this model is the most rigorously formulated and comprehensive model in this field, it has been selected in this paper. Therefore, in this study, a one-dimensional drying process inside a single wood particle has been modeled on the basis of the multiphase transport theory of Whitaker.…”

Section: Mathematical Modelmentioning

confidence: 99%

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On the Uncertainty of a Mathematical Model for Drying of a Wood Particle

2013

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The reliability of the predictions of a mathematical model is a prerequisite to employ it. The drying process of a pine wood particle is modeled using a quasi-continuous multiphase porous media model. Different values and expressions from the literature of nine physical properties and transport coefficients are listed in this study. Lower and upper bounds of these model variables are determined and applied to the model, and a bounded output of the model is calculated. This study shows that taking arbitrary values of the model variables from the literature may lead to approximately 16 times differences in the calculated drying time of a single wood particle. By global sensitivity analysis, the most effective variables are determined. The variations of the coefficients of water vapor transport, except gas relative permeability, have a high impact on the presented drying model. For reliability of the predictions of the drying model, at least the values of the gas intrinsic permeability and water vapor diffusivity as well as capillary pressure have to be determined by own measurements in the studied conditions. One can use any of the reported values or expressions of effective thermal conductivity and specific heat capacity of wood as well as gas relative permeability and bound water diffusivity for modeling drying processes of wood particles, because all of them produce similar model predictions.

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Section: Numerical Solution Proceduresmentioning

confidence: 64%

Section: Mathematical Modelmentioning

confidence: 99%

On the Uncertainty of a Mathematical Model for Drying of a Wood Particle

2013

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“…Generally, the saturation for a phase varies between 0 (dry state / none of that phase) and 1 (saturated with that phase). In drying process, the free water exist when saturation is more than the critical value (S cri ) which is normally 0.3 [8] for ceramic materials whereas bound liquid water only exist when saturation is below the irreducible value (S irr =0.09) for hygroscopic materials [8]. An effective and commonly model related to capillary suction was proposed by VG [5] as equation below.…”

Section: Theoretical Formulationmentioning

confidence: 99%

Estimation of Water Desorption in Drying of Membrane Structure System

Harun¹,

Ong²,

Ahmad³

2014

AMR

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In general, ceramic membranes consist of top layer possess structure a hygroscopic zone which acts as a separator while the following bottom layers form a porous nonhygroscopic zone which provides the permeation paths and acting as supporting structures. Thus, the combination of these two different multilayer systems will exhibit different water desorption behavior especially in ceramic membrane preparation. Experimentally, this water characteristic is defined through water retention curve (WRC). Since there is no detailed study on the fitting parameters that associated with WRC on membrane structure has yet been reported, therefore, this paper investigates the effects of various parameters used in WRC equation that represent material properties of the membrane structure using mathematical model. The results showed that hygroscopic material has higher α and n value with lower m value compared with nonhygroscopic material. Hence, understanding the variation of the fitting parameters in the WRC equation is essential for the configuration of WRC slope associated with the material properties especially during drying process of membrane.

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“…In contrast to that, drying of hygroscopic materials not only involves free and capillarity water but also a tightly bound water that strongly attach to the solid matrix up to hydration temperature [1]. Previous studies on drying of hygroscopic and nonhygroscopic have present different equations and formulations as well as the concept that had been derived [1,2,3,4,5]. Bound water movement is expressed in terms of the diffusion of sorbed water driven by a gradient in the chemical potential of the sorbed water molecules [2].…”

Section: Introductionmentioning

confidence: 99%

Drying Comparison of Nonhygroscopic and Hygroscopic Materials

Harun

Ong

Ahmad

2013

AMM

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Abstract. This paper investigates and presents the simulation of drying for hygroscopic and nonhygroscopic materials. This present work used a coupled mathematical model of mass, heat and gas transfer that implemented to finite element method in two dimensional and numerically compute using Skyline solver to capture highly nonlinear transient process. Bound water contribution was taken into account in the drying of hygroscopic materials by incorporating constitutive equation of bound water. The results showed drying process can be divided into three periods named constant rate period (CRP), first falling rate period (FRP1) and second falling rate period (FRP2). Capillary action is dominated during CRP before vapour diffusion takes place in FRP1. Bound water movement is generated by vapour pressure gradient exists that represent hygroscopic material. IntroductionIn reality of porous material consists of three types of water that indentified as free, capillary and bound water. Free water is able to flow under an applied pressure gradient, capillary water is immobile water held by capillary forces in regions of microporosity, i.e. dead-end pores. Meanwhile, bound water includes both the water strongly held to negatively charged particles surfaces and the water of hydration associated with the mineral charge-balancing unit. The difference level of these types of water will exhibit different properties of porous material that generally known as hygroscopic and non hygroscopic materials. Drying of nonhyrosocpic materials only involve free and capillary water that easily experimentally can be determined and measured with specific equipment. In contrast to that, drying of hygroscopic materials not only involves free and capillarity water but also a tightly bound water that strongly attach to the solid matrix up to hydration temperature [1]. Previous studies on drying of hygroscopic and nonhygroscopic have present different equations and formulations as well as the concept that had been derived [1,2,3,4,5]. Bound water movement is expressed in terms of the diffusion of sorbed water driven by a gradient in the chemical potential of the sorbed water molecules [2]. This similar approach had been used by Kolhapure and Venkatesh[1] during studies of an unsaturated flow of low moisture for porous hygroscopic media. During low moisture contents, pores mainly consist of bound water and vapour. Stanish et al [3] in their development had derived a uniquely explicit expression for boundwater flux in terms of temperature and vapor pressure gradients. Meanwhile, Zhang et al [4] and Haghi [5] revealed that the bound water transport mechanism only effective when saturation irreducible is reached. The movement of bound water in hygroscopic materials is also known as liquid moisture transfer near dryness or sorption diffusion with driving force of vapor transport and without liquid transport [6]. Although substantial efforts have been made in the studies of hygroscopic materials, there are limited references available on modeling drying...

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Mechanism and mathematical model of heat and mass transfer during convective drying of porous materials

Cited by 21 publications

References 15 publications

On the Uncertainty of a Mathematical Model for Drying of a Wood Particle

On the Uncertainty of a Mathematical Model for Drying of a Wood Particle

Estimation of Water Desorption in Drying of Membrane Structure System

Drying Comparison of Nonhygroscopic and Hygroscopic Materials

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