Experimental investigation of double-diffusive groundwater fingers

1988 ◽  
Vol 188 ◽  
pp. 363-382 ◽  
Author(s):  
Paul T. Imhoff ◽  
Theodore Green
Keyword(s):  
Experimental Investigation ◽  
Viscous Fluid ◽  
Molecular Diffusion ◽  
Saturated Porous Medium ◽  
Flux Ratio ◽  
Buoyancy Flux ◽  
Tank Model ◽  
Density Anomaly ◽  
Double Diffusive ◽  
Good Agreement

Using a sand-tank model and the salt-sugar system, double-diffusive fingers formed in a saturated porous medium. In contrast to the quasi-steady fingering typically observed in a viscous fluid, the fingering here was quite unsteady. The fingers’ structure was observed, and measurements of the sugar flux indicate that double-diffusive groundwater fingers can transport solutes at rates as much as two orders of magnitude larger than those associated with molecular diffusion in motionless groundwater. The buoyancy-flux ratio, r = αFT/βFS, increased from r = 0.65 ± 0.02 (at Rρ = 1.02) to r = 0.81 ± 0.06 (at Rρ = 1.50), where Rρ is the density-anomaly ratio. (Using the salt-sugar system in a viscous fluid, r was previously shown to decrease with increasing Rρ.) The buoyancy flux due to sugar varied approximately as R−5.6ρ, which is almost identical with the variation found for salt-sugar fingers in a viscous fluid. The model of Green (1984) was applied to the experiments and predicted buoyancy-flux ratios and finger widths that were in fairly good agreement with the measured values, although the predicted buoyancy fluxes due to sugar were significantly larger than the measured fluxes.

Transport and profile measurements of the diffusive interface in double diffusive convection with similar diffusivities

1973 ◽  
Vol 57 (1) ◽  
pp. 27-43 ◽  
Author(s):  
T. G. L. Shirtcliffe
Keyword(s):  
Molecular Diffusion ◽  
Flux Ratio ◽  
Optical Measurements ◽  
Salt Flux ◽  
Density Anomaly ◽  
Diffusive Convection ◽  
Diffusive Interface ◽  
Double Diffusive ◽  
Vertical Gradients ◽  
Diffusivity Ratio

The transport properties of a diffusive interface with diffusivity ratio $\kappa_S/\kappa_T = {\textstyle\frac{1}{3}}$ have been measured, using salt and sugar as the diffusing components. The flux ratio is constant and equal to (κS/κT)½. The normalized salt flux is related to the density anomaly ratio Rρ = βΔS/αΔT by the power law F*T = 2·59Rρ−12.6 over four decades. Optical measurements show that the vertical gradients of concentration of salt and sugar within the interface are those required if molecular diffusion is to account for the whole flux of each component.

Numerical investigation of double-diffusive mixed convection in horizontal annulus partially filled with a porous medium

2017 ◽  
Vol 27 (4) ◽  
pp. 773-794 ◽  
Author(s):  
Mourad Moderres ◽  
Said Abboudi ◽  
Malika Ihdene ◽  
Sofiane Aberkane ◽  
Abderahmane Ghezal
Keyword(s):  
Mass Transfer ◽  
Porous Medium ◽  
Fluid Flow ◽  
Saturated Porous Medium ◽  
Lewis Number ◽  
Content Type ◽  
Transfer Rates ◽  
Diffusive Convection ◽  
Double Diffusive ◽  
Good Agreement

Purpose Double-diffusive convection within a tri-dimensional in a horizontal annulus partially filled with a fluid-saturated porous medium is numerically investigated. The aim of this work is to understand the effects of a source of heat and solute on the fluid flow and heat and mass transfer rates. Design/methodology/approach In the formulation of the problem, the Darcy–Brinkman–Forchheimer model is adopted to the fluid flow in the porous annulus. The laminar flow regime is considered under steady state conditions. Moreover, the transport equation for continuity, momentum, energy and mass transfer are solved using the Patankar–Spalding technique. Findings Through this investigation, the predicted results for both average Nusselt and Sherwood numbers were correlated in terms of Lewis number, thermal Grashof number and buoyancy ration. A comparison was made with the published results and a good agreement was found. Originality/value The paper’s results are validated by favorable comparisons with previously published results. The results of the problem are presented in graphical forms and discussed. This paper aims to study the behavior of the flow structure and heat transfer and mass for different parameters.

Accurate fluxes across a salt-sugar finger interface deduced from direct density measurements

1980 ◽  
Vol 99 (1) ◽  
pp. 85-95 ◽  
Author(s):  
R. W. Griffiths ◽  
B. R. Ruddick
Keyword(s):  
Flux Ratio ◽  
Buoyancy Flux ◽  
Density Measurements ◽  
Density Anomaly

The buoyancy flux ratio, r = αFT/βFS, across a salt-sugar fingering interface is determined from accurate measurements of the density variations in a two-layer run-down experiment. Since r is close to 1, the net buoyancy flux, βFS − αFT, which is proportional to 1 − r, gives r with a resolution that is much improved over that of previous measurements. The value of r is found to decrease from r ≈ 0·94 ± 0·01 at Rρ = 1·02 to r = 0·88 ± 0·01 at Rρ = 2, where Rρ is the density anomaly ratio. The latter is smaller than the previous (constant) value of 0·92. The buoyancy flux due to sugar is found to decrease rapidly with increasing Rρ, varying approximately as R−6ρ.

Experimental investigation and modelling of light scattering in a-Si:H solar cells deposited on glass/ZnO:Al substrates

2002 ◽  
Vol 715 ◽  
Author(s):  
J. Krc ◽  
M. Zeman ◽  
O. Kluth ◽  
F. Smole ◽  
M. Topic
Keyword(s):  
Surface Roughness ◽  
Experimental Investigation ◽  
Solar Cells ◽  
Angular Distribution ◽  
Light Scattering ◽  
Optical Model ◽  
Distribution Functions ◽  
Interface Roughness ◽  
Scattering Parameters ◽  
Good Agreement

AbstractThe descriptive scattering parameters, haze and angular distribution functions of textured ZnO:Al transparent conductive oxides with different surface roughness are measured. An approach to determine the scattering parameters of all internal interfaces in p-i-n a-Si:H solar cells deposited on the glass/ZnO:Al substrates is presented. Using the determined scattering parameters as the input parameters of the optical model, a good agreement between the measured and simulated quantum efficiencies of the p-i-n a-Si:H solar cells with different interface roughness is achieved.

Experimental Investigation on the Effect of Arm Length on Accuracy of Torque Wrench

2016 ◽  
Vol 853 ◽  
pp. 216-220 ◽  
Author(s):  
You Gang Peng ◽  
Yong Wang
Keyword(s):  
Experimental Investigation ◽  
Structural Design ◽  
Bending Moment ◽  
Theoretical Solution ◽  
Calibration Laboratory ◽  
Moment Measurement ◽  
Torque Wrench ◽  
Actual Use ◽  
Good Agreement

Experiments were carried out to investigate the effect of arm length on the accuracy of two typical conventional torque wrenches, namely, setting type torque wrench (STW) and indicating type torque wrench (ITW). The experiment results demonstrate that the measurement values of STW rises rapidly with decreasing arm length while measured torque of ITW shows irrelevant to arm length. Theoretical solution with respect to STW shows quite good agreement with experiment results. Irrelevance of arm length regard to ITW may be attributable to compensation of bending moment measurement due to proper arrangement of circuit and structural design. In order to conduct a proper assessment at a calibration laboratory or ensure its reliability with reference to actual use conditions, a torque wrench should be used by a customer at the loading point as recommended.

Double-Diffusive Fluxes in a Salt Gradient Solar Pond

1988 ◽  
Vol 110 (1) ◽  
pp. 17-22 ◽  
Author(s):  
J. F. Atkinson ◽  
E. Eric Adams ◽  
D. R. F. Harleman
Keyword(s):  
Mixed Layer ◽  
Molecular Diffusion ◽  
Numerical Models ◽  
Mechanical Stirring ◽  
Solar Pond ◽  
Salt Gradient ◽  
Layer Region ◽  
Diffusive Fluxes ◽  
Effective Diffusivities ◽  
Double Diffusive

The possible influence of double-diffusive stratification on the vertical transport of salt and heat in a mixed-layer simulation model for a salt gradient solar pond is examined. The study is concerned primarily with the interfacial fluxes across the boundary between the gradient zone and upper convecting zone of solar ponds, though the arguments presented should be applicable to other “diffusive” interfaces as well. In the absence of mechanical stirring in the upper convecting zone (e.g., by wind), double diffusive instabilities could govern the vertical flux of heat and salt by adjusting interfacial gradients of temperature and salinity which control transport by molecular diffusion. Because these gradients are generally too sharp to be resolved by numerical models, the fluxes can either be modeled directly or be parameterized by grid-dependent “effective diffusivities.” It is shown that when mechanical stirring is present in the mixed layer, double-diffusive instabilities will not be allowed to grow in the interfacial boundary layer region. Thus, double-diffusive fluxes become important only in the absence of stirring and, in effect, provide a lower bound to the fluxes that would be expected across the interface.

scholarly journals Simulations of a double-diffusive interface in the diffusive convection regime

2012 ◽  
Vol 711 ◽  
pp. 411-436 ◽  
Author(s):  
J. R. Carpenter ◽  
T. Sommer ◽  
A. Wüest
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Molecular Diffusion ◽  
Layer Structure ◽  
Previous Theory ◽  
Convection Regime ◽  
Graphic Interface ◽  
Diffusive Convection ◽  
Diffusive Interface ◽  
Double Diffusive

AbstractThree-dimensional direct numerical simulations are performed that give us an in-depth account of the evolution and structure of the double-diffusive interface. We examine the diffusive convection regime, which, in the oceanographically relevant case, consists of relatively cold fresh water above warm salty water. A ‘double-boundary-layer’ structure is found in all of the simulations, in which the temperature ($T$) interface has a greater thickness than the salinity ($S$) interface. Therefore, thin gravitationally unstable boundary layers are maintained at the edges of the diffusive interface. The $TS$-interface thickness ratio is found to scale with the diffusivity ratio in a consistent manner once the shear across the boundary layers is accounted for. The turbulence present in the mixed layers is not able to penetrate the stable stratification of the interface core, and the $TS$-fluxes through the core are given by their molecular diffusion values. Interface growth in time is found to be determined by molecular diffusion of the $S$-interface, in agreement with a previous theory. The stability of the boundary layers is also considered, where we find boundary layer Rayleigh numbers that are an order of magnitude lower than previously assumed.

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