Double Diffusion Model Research Articles

Numerical simulation of double-diffusive dynamical model of a solar pond considering the effect of turbidity and wind

A solar pond, typical double-diffusive system, is a stable heat source that can collect and store the solar energy. When the thermal stable condition is not satisfied at the interface, the upper and lower convective zone (UCZ and LCZ) will erode the middle non-convective zone (NCZ), resulting in a drop or even a collapse of the thermal performance of solar pond. Wind strongly affects the erosion of NCZ from the entrainment of UCZ. The double-diffusion of heat and salt plays an important role in the erosion of NCZ from the entrainment of the lower-convective zone (LCZ). The turbidity of saline water in the pond not only could lower the thermal performance of solar pond, but have effect on the entrainment mechanism. In this paper, based on the double-diffusive model along with the wind-driven turbulent entrainment model, the effects of turbidity and external wind etc. on the thermal performance of solar pond and the entrainment mechanism are analyzed with the numerical simulation.

Adsorption of Dyes using Peat: Equilibrium and Kinetic Studies

In recent years, adsorption has been accepted as one of the most appropriate processes for decolorization of wastewaters. This paper presents experimental results on application of peat for removal of structurally diverse dyes (azo, oxazine, triphenylmethane, thiazine and others) with emphasis on relevant factors such as the adsorbate-adsorbent chemical properties and chemical interaction as well as adsorption conditions. The equilibrium experimental results were fitted to Langmuir and Freundlich isotherms to obtain the characteristic parameters of each model. According to the evaluation using the Langmuir equation, the maximum sorption capacity of basic dyes at 22°C was 667 (mg g-1) for Basic Blue 24, 526 (mg g-1) for Basic Green 4 and 714 (mg g-1) for Basic Violet 4. On the other hand for Acid Black 1 it was only 25 (mg g-1). Batch kinetics studies were undertaken and the data evaluated in compliance with chemical sorption mechanisms. For all of the systems studied the pseudo-second order model provided the best correlation of the kinetic experimental data. A film-pore double resistance diffusion model for mass transfer has also been used in this study to determine the effective diffusivity, Deff, for the adsorption of basic dyes in to peat.

Double-diffusion models from a highly-heterogeneous medium

A distributed microstructure model is obtained by homogenization from an exact micro-model with continuous temperature and flux for heat diffusion through a periodically distributed highly-heterogeneous medium. This composite medium consists of two flow regions separated by a third region which forms the doubly-porous matrix structure. The homogenized system recognizes the multiple scale processes and the microscale geometry of the local structure, and it quantifies the distributed heat exchange across the internal boundaries. The classical double-diffusion models of Rubinstein (1948) and Barenblatt (1960) are obtained in non-isotropic form for the special case of quasi-static coupling in this homogenized system.

Double-diffusion models from a highly-heterogeneous medium*1

A distributed microstructure model is obtained by homogenization from an exact micro-model with continuous temperature and flux for heat diffusion through a periodically distributed highly-heterogeneous medium. This composite medium consists of two flow regions separated by a third region which forms the doubly-porous matrix structure. The homogenized system recognizes the multiple scale processes and the microscale geometry of the local structure, and it quantifies the distributed heat exchange across the internal boundaries. The classical double-diffusion models of Rubinstein (1948) and Barenblatt (1960) are obtained in non-isotropic form for the special case of quasi-static coupling in this homogenized system.

Numerical Analysis of Natural Convection and Mixing in Two-Fluid Stratified Pools With Internal Heat Sources

Abstract The heat transport in two-layer fluid systems has been investigated numerically for slice-type semicircular pools with internal heat sources. The fixed interface model has been applied to study natural convection in the system of the immiscible fluids. The double-diffusion model has been employed to describe the heat transfer and mixing for the miscible fluids. The numerical results are compared to data measured in the SIMECO experiments. Based on the numerical simulations, the effect of the ratio of the fluid properties has been quantified. The results are of interest for the corium melt coolability in a postulated severe accident scenario in a light water reactor.

Application of double diffusivity model to superconductors

A continuum double diffusivity model proposed over twenty years ago by the third author is applied here to interpret the experimental results of oxygen self-diffusion through grain boundaries of YBa 2Cu 3O 7− x superconductors. The agreement between theory and experiment is quite satisfactory.

Further experimental evidence of the double diffusivity model

Further experimental evidence of the double diffusivity model

On the experimental validation of the double diffusivity model

On the experimental validation of the double diffusivity model

Color removal from dye wastewaters by adsorption using powdered activated carbon: Mass transfer studies

AbstractColor removal from synthetic dye wastewater which typically emanates from the Taiwan textile industry has been studied using powdered activated carbon (PAC) as an adsorbent. The CIE colorimetric system has been used in the measurement of color for the treatment of disperse‐red‐60 dye wastewater. The effect of contact time, dye concentrations and PAC dosage on color and color removal has been investigated. A film‐pore double resistance diffusion model for mass transfer has also been used in this study to determine the effective diffusivity, Deff, for the adsorption of disperse‐red‐60 dye wastewater to PAC.

A note on the random walk model arising in double diffusion

AbstractThe discrete random walk problem for the unrestricted particle formulated in the double diffusion model given in Hill [2] is solved explicitly. In this model it is assumed that a particle moves along two distinct horizontal paths, say the upper path I and lower path 2. For i = 1, 2, when the particle is in path i, it can move at each jump in one of four possible ways, one step to the right with probability pi, one step to the left with probability qi, remains in the same position with probability ri, or exchanges paths but remains in the same horizontal position with probability si (pi + qi + ri + si = 1). Using generating functions, the probability distribution of the position of an unrestricted particle is derived. Finally some special cases are discussed to illustrate the general result.

On the criterion for the reversal of the ∇T th heat flow in the double diffusion model of electron transport

The effective Coulomb logarithms for thermal and suprathermal electrons in the blow-off region of a high- Z laser-irradiated target may differ appreciably. This effect is included in the “double diffusion” model for electron transport and is shown to modify the criterion for the reversal of the ∇ T thermal heat flux.

Micro and macro strain-induced damping and dislocation structures in tungsten and molybdenum single crystals

The connections between micro-macro strain behaviour, damping spectra and dislocation structures have been examined in four orientations (the three principals and the easy glide orientation) of high purity molybdenum and tungsten single crystals ( R R = 10 +) for molybdenum and R R = 5 × 10 4 for tungsten). The samples were deformed in compression at 300.550 and 600 K in microplastic (ϵ ∼- 10 −4) and plastic (ϵ ∼- 10 −2) ranges prior to internal friction measurements (between 30 and 800 K.) and to transmission electron microscopy examination. Several peaks have been revealed, in particular a peak on the low temperature side of the α peak (α' peak) and a peak around room temperature (γ' peak). A direct connection for molybdenum and tungsten has been established between stress-strain behaviour, dislocation structure and internal friction spectra:screw dislocations controlling plastic flow are directly involved in high temperature peaks mechanisms, nonscrew dislocations induce low temperature peaks. Our observations are very well explained by the double kink generation and kink diffusion models in nonscrew dislocations respectively for the α and α' peak, by the double kink generation and point defect impurity dislocation interaction models in screw dislocations respectively for the γ and β peaks and by the kink diffusion model in screw dislocations for the γ' peak ( RT peak).