Search

Abstract: The non-isothermal phase change phenomena during the vertical Bridgman growth process for HgCdTe are numerically investigated using an interface capturing finite element scheme. The influence of the growth parameters such as Bi, Ste, U and the flow parameters including Gr T and Gr S on the non-isothermal phase change phenomena are obtained. Some new features about the melt/crystal interface shape, the temperature field near the interface and the flow field are revealed by comparing the non-isothermal phase change with the isothermal phase change. Furthermore, the comparison of the non-isothermal interfacial characteristics between the pure diffusion, the natural convection and the double-diffusive convection is made and the obvious differences are presented. [Copyright &y& Elsevier]

The present paper examines the effect of vertical harmonic vibration on the onset of convection in an infinite horizontal layer of a binary fluid mixture saturating a porous medium. A constant temperature and concentration distribution are assigned on the rigid boundaries, so that there exist vertical temperature and concentration gradients. The mathematical model is described by equations of filtration convection in the Darcy-Oberbeck-Boussinesq approximation. The linear stability analysis for the quasi-equilibrium solution is performed using Floquet theory. Employing the method of continued fractions allows derivation of the dispersion equation for the Floquet exponent in an explicit form. The neutral curves of the Rayleigh number versus horizontal wave number are constructed for the three types of instability modes: synchronous, subharmonic, and complex conjugate. Asymptotic formulas for these curves are derived for large values of vibration frequency using the method of averaging. It is shown that, at some finite frequencies of vibration, there exist regions of parametric instability. Investigations carried out in the paper demonstrate that, depending on the governing parameters of the problem, vertical vibration can significantly affect the stability of the system by increasing or decreasing its susceptibility to convection. In addition, even in the presence of vibration, the onset of convection in the system is affected by variations in the concentration of the solute in the mixture. [ABSTRACT FROM AUTHOR]

Abstract: We present new electron microprobe and Sr-isotope analytical results from mixing experiments using natural volcanic samples. In order to constrain the dynamics of such mixing events, we applied a Taylor–Couette flow, simulating forced convection under very low Reynolds numbers, in a time series ranging from 1 h up to 1 week. The end-member melts derive from samples of the Campanian Ignimbrite (CI), in Italy. The CI is thought to represent a layered reservoir formed in 3 stages: 1) a resident phono-trachytic magma reservoir (end-member A); replenished by 2) a less evolved trachybasaltic–trachytic magma (end-member B of trachytic composition); 3) short-term pre-eruptive mixing in the shallow chamber between a new trachytic and the phono-trachytic resident magmas. Our experiments are motivated by this hypothesis. The two end-members are stirred together, under constant low flow velocity (0.5 rotations per minute). This initially generates single convection cells, which cause progressive homogenization of some major components. This is the case after 1, 4 and 9 h. After 16 h the 87Sr/86Sr-isotopic system is homogenized and the starting compositions are fully mixed. Then separate convection cells and compositional layering for major and minor elements emerged. Based on microprobe measurements of quenched melts (glass) from the 16-hour, 25-hour and 1-week long experiments, we confirm the separation of layers having different densities. This phenomenon is locally complicated by the production of micro-volumes of unmixed melts. Our results support the effectiveness of the interplay between convection and diffusion, enhanced by a double-diffusive–convection-driven differentiation for moderately high-silica magmas under high (near-liquidus) temperatures, attesting that differentiation initiates in the liquidus before the onset of fractional crystallization. [Copyright &y& Elsevier]

The consistent splitting scheme involving a mixed finite element method for considering the influence of the Forchheimer-extended Brinkman–Darcy model in the momentum equation is applied to double-diffusive convection in a fluid-saturated porous medium. It is shown that the method is robust and can accurately predict flow, pressure distribution, temperature and concentration fields. The numerical scheme may be an alternative to some other existing methods for the solution of porous thermosolutal convection problems since its implementation is very handy. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper describes the so-called consistent splitting scheme (CSS) for solving unsteady double-diffusive convection (DDC) problems using the mixed finite element method. The CSS was chosen to numerically solve the primitive form of the unsteady governing equations for decoupling the velocity variables and the pressure. Both first- and second-order accurate temporal and spatial approximations have been implemented for unsteady DDC problems. The results obtained with the described numerical methods compare favourably with the existing numerical result. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the theoretical investigation of the double-diffusive convection in a micropolar ferromagnetic fluid layer heated and soluted from below saturating a porous medium subjected to a transverse uniform magnetic field. For a flat fluid layer contained between two free boundaries, an exact solution is obtained. A linear stability analysis theory and normal mode analysis method have been carried out to study the onset of convection. The influence of various parameters like medium permeability, solute gradient, non-buoyancy magnetization and micropolar parameters (i.e. coupling parameter, spin diffusion parameter and micropolar heat conduction parameter) has been analyzed on the onset of stationary convection. The critical magnetic thermal Rayleigh number for the onset of instability is also determined numerically for sufficiently large values of buoyancy magnetization parameter and results are depicted graphically. The principle of exchange of stabilities is found to hold true for the micropolar ferromagnetic fluid saturating a porous medium heated from below in the absence of micropolar viscous effect, microinertia and solute gradient. The oscillatory modes are introduced due to the presence of the micropolar viscous effect, microinertia and solute gradient, which were non-existent in their absence. In this paper, an attempt is also made to obtain the sufficient conditions for the non-existence of overstability. [Copyright &y& Elsevier]

Abstract: This paper deals with the theoretical investigation of the double-diffusive convection in a micropolar ferromagnetic fluid layer heated and soluted from below subjected to a transverse uniform magnetic field. For a flat fluid layer contained between two free boundaries, an exact solution is obtained. A linear stability analysis theory and normal mode analysis method have been carried out to study the onset of convection. The influence of various parameters like solute gradient, non-buoyancy magnetization and micropolar parameters (i.e. coupling parameter, spin diffusion parameter and micropolar heat conduction parameter) has been analyzed on the onset of stationary convection. The critical magnetic thermal Rayleigh number for the onset of instability is also determined numerically for sufficiently large values of buoyancy magnetization parameter M 1 and results are depicted graphically. The principle of exchange of stabilities is found to hold true for the micropolar ferromagnetic fluid heated from below in the absence of micropolar viscous effect, microinertia and solute gradient. The oscillatory modes are introduced due to the presence of the micropolar viscous effect, microinertia and solute gradient, which were non-existent in their absence. In this paper, an attempt is also made to obtain the sufficient conditions for the non-existence of overstability. [Copyright &y& Elsevier]

Abstract: Convection in a horizontal fluid layer of a binary mixture is studied analytically and numerically. In the formulation of the problem, use is made of the Boussinesq approximation. Neumman boundary conditions are specified for the temperature on all walls of the cavity. In addition of the Soret contribution, a shear stress, τ, is applied on the upper free surface of the layer. The flows are found to be dependent of the Darcy–Rayleigh number, R T, the Lewis number, Le, the solutal to thermal buoyancy ratio, ϕ, the shear stress, τ and the thermal boundary conditions. Numerical results for finite amplitude convection, obtained by solving numerically the full governing equations, are found to be in good agreement with the analytical solution based on the parallel flow approach. For given sets of the control parameters, the occurrence of multiple steady state solutions is demonstrated. The existence of subcritical bifurcations for both stabilizing and destabilizing mass flux is also demonstrated. [Copyright &y& Elsevier]

The structure of double diffusive convection in a circular cylinder cavity has been numerically studied. The numerical results exhibit some new characters of non-horizontal stratifications of thermal and solutal fields: in the stratification state, the isothermal lines near the sidewall are higher than that near the symmetry axis, while the isoconcentration lines near the symmetry axis are relatively high. The mechanism of these non-horizontal stratifications is illustrated by comparing double-diffusive convection with natural convection driven by thermal buoyancy or solutal buoyancy alone. The effects of Lewis number Le and buoyancy ratio N on the non-horizontal stratifications of thermal and solutal fields are also investigated. The results show that: at a given time (t = 0.2), with an increase in Le (Le = 0-15), the area influenced by solute diffusion decreases; for isothermal line, the gradients of it initially increase, but it tends to be horizontal at the top of the cavity when the Lewis number is higher than 10. When N varies from 0 to 2, the isoconcentration lines tend to be horizontal while the gradients of isothermal line increase. [ABSTRACT FROM AUTHOR]

Abstract: The characteristics of transient double-diffusive convection in a vertical cylinder are numerically simulated using a finite element method. Initially the fluid in the cavity is at uniform temperature and solute concentration, then constant temperature and solute concentration, which are lower than their initial values, are imposed along the sidewall and bottom wall, respectively. The time evolution of the double-diffusive convection is investigated for specific parameters, which are the Prandtl number, Pr =7, the Lewis number, Le =5, the thermal Grashof number, Gr T =107, and the aspect ratio, A =2, of the enclosure. The objective of the work is to identify the effect of the buoyancy ratio (the ratio of solutal Grashof to thermal Grashof numbers: N = Gr S/Gr T) on the evolution of the flow field, temperature and solute field in the cavity. It is found that initially the fluid near the bottom wall is squeezed by the cold flow from the sidewall, a crest of the solute field forms and then pushed to the symmetry line. In the case of N >0, a domain with higher temperature and weak flow (dead region) forms on the bottom wall near the symmetry line, and the area of dead region increases when N varies from 0.5 to 1.5. More crests of the solute field are formed and the flow near the bottom wall fluctuates continuously for N <0. The frequency of the fluctuation increases when N varies from −0.5 to −1.5. Corresponding to the variety of the thermal and solutal boundary layers, the average rates of heat transfer (Nu) at the sidewall remain almost unchanged while the average rates of mass transfer (Sh) at the bottom wall change much in the cases of N =1,0,−1. [Copyright &y& Elsevier]

The onset of double-diffusive convection in a horizontal fluid layer is studied. The density is assumed to depend quadratically on the temperature and linearly on the solute concentration. Under the Boussinesq approximation, the linear stability of the conduction state is investigated with respect to the oscillatory and steady convection modes. For steady onset, the critical thermal Rayleigh number is found to be a double-valued function of the solutal Rayleigh number as long as the relative maximum of the density profile exists within the fluid layer. Driving mechanisms of the steady convections are discussed. [Copyright &y& Elsevier]

We present the results of an experiment conducted to explore the temporal and spatial development of double-diffusive finger convection in a Hele–Shaw cell. Two solutions each containing a different density affecting component were layered in a density stable configuration (sucrose solution over a more dense salt solution) with a nearly perturbation-free interface between. The mismatch of diffusive time scales for the two components leads to local density instabilities that generate upward and downward convecting fingers. Throughout the course of the experiment, a full-field quantitative light transmission technique was used to measure concentration fields of a dye tracer dissolved in the salt solution. Analysis of these fields yielded the temporal evolution of length scales associated with the vertical and horizontal finger structure as well as mass transfer. Distinct developmental stages are identified with strong correlation between all measures. These data provide a baseline that can be used to develop and evaluate both process-level models that simulate the full complexity of the evolving flow field and large-scale effective models that integrate over small-scale behavior. [ABSTRACT FROM AUTHOR]

Some modelling deficiencies in various recent papers, on convective flows in porous media, are pointed out and discussed. These deficiencies are related to the Forchheimer coefficient, mixed double-diffusive convection, magnetohydrodynamic mixed convection, convection in a rarefied gas, and geophysical phenomena. [ABSTRACT FROM AUTHOR]

Here is investigated the characteristics of double-diffusive convection in thermally-stable stratified horizontal fluid layer. By employing an electrochemical technique, and adopting aqueous CuSO-HSO solution as electrolyte, experiments on ionic mass transfer have been conducted systematically. And, also a new mass transfer correlation in double-diffusive situations has been derived by extending the model of micro-scales of turbulence, which was proposed by Arpaci. The resulting correlation of the Sherwood number as a function of the thermal Rayleigh number and the solutal Rayleigh number was in good agreement with the present experimental results. The present study provides plausible understanding in controlling both mass and heat transfer rates for practical situations including double-diffusive convection. [ABSTRACT FROM AUTHOR]

• The paper investigated double-diffusive convection of a shear-thinning fluid. • All parameters of the Carreau model influence the convective flows. • When Ra T very high, the Carreau and power-law models give almost the same results. • The results of scale analysis and numerical solution are in good agreement. We study heat and mass transfers by natural convection for shear-thinning non-Newtonian binary fluids confined in a square cavity. Thermal and solutal boundary conditions of the Dirichlet type are applied on the vertical walls of the cavity while the horizontal ones are assumed adiabatic and impermeable. We used the rheological Carreau model, adequate for many non-Newtonian fluids to characterize the shear-thinning behavior. The first part from this study is devoted to the numerical solution of the governing equations, and the effect of the governing parameters, namely, the thermal Rayleigh number Ra T , Prandtl number Pr , Lewis number Le , buoyancy ratio N and the various parameters of Carreau model. Numerical calculations are also carried out by considering the same problem on the basis of the power-law model, and a comparison of the results predicted by the two rheological models is performed. In the second part, a scale analysis is proposed to obtain correlations giving the heat and mass transfers. The results of this approach are validated numerically and a good agreement is found between the two methods. [ABSTRACT FROM AUTHOR]

The time of the onset of double-diffusive convection in time-dependent, nonlinear temperature fields is investigated theoretically. The initially quiescent horizontal fluid layer with a uniform solute gradient experiences ramp heating from below, but its stable solute concentration is to reduce thermal effects which invoke convective motion. The related stability analysis is conducted on the basis of the propagation theory. Under the linear stability theory the thermal penetration depth is used as a length scaling factor and the linearized perturbation equations of similarity transform are solved numerically. The resulting correlations of the critical time to mark the onset of regular cells are derived as a function of the thermal Rayleigh and the solute Rayleigh numbers. The predicted stability criteria are apparently consistent with existing experimental results for aqueous solution of sodium chloride. [ABSTRACT FROM AUTHOR]

We explore the physical influence of magnetic field on double-diffusive convection in complex biomimetic (peristaltic) propulsion of nanofluid through a two-dimensional divergent channel. Additionally, porosity effects along with rheological properties of the fluid are also retained in the analysis. The mathematical model is developed by equations of continuity, momentum, energy, and mass concentration. First, scaling analysis is introduced to simplify the rheological equations in the wave frame of reference and then get the final form of equations after applying the low Reynolds number and lubrication approach. The obtained equations are solved analytically by using integration method. Physical interpretation of velocity, pressure gradient, pumping phenomena, trapping phenomena, heat, and mass transfer mechanisms are discussed in detail under magnetic and porous environment. The magnitude of velocity profile is reduced by increasing Grashof parameter. The bolus circulations disappeared from trapping phenomena for larger strength of magnetic and porosity medium. The magnitude of temperature profile and mass concentration are increasing by enhancing the Brownian motion parameter. This study can be productive in manufacturing non-uniform and divergent shapes of micro-lab-chip devices for thermal engineering, industrial, and medical technologies., (© 2021. The Author(s), under exclusive licence to Springer Nature B.V.)

Solar stills are convenient, cheap and ambient friendly but has the drawback of low production of potable fresh water. To explore better the concept and make more attractive for use some more research is necessary to improve the productivity and thermal performance of these units. In this paper a numerical study on an inclined type solar still is performed to investigate the influence of the water film thickness on the heat transfer and fluid flow inside the device cavity. The solar still system temperatures are calculated for four film thicknesses, 0.14, 0.5, 1.0 and 3.0 mm, through the Runge-Kutta method for the ambient conditions of Campinas, southeast of Brazil. The temperatures of the film and the glass are input to the computational fluid dynamics investigation. The radiative transfer and double-diffusive convection of air and vapor mixture are simulated considering the nongray Spectral Line Based Weighted-Sum-of-Gray-Gases method. The results indicate that the use of film thickness δ w = 3.0 mm increased the temperature difference between the water film and the glass from 2.14 °C to 9.15 °C when compared to the film flowing over the bare plate, δ w = 0.14 mm, and increased the rate of fresh water yield more than 2.0 times, for summer conditions and peak insolation hours. The use of transparent gas approach slightly overpredicted radiative and convective heat transfer inside the solar still cavity. • An inclined solar still is numerically simulated considering nongray gas approach • Thick water films increase temperature and vapor concentration in the cavity core. • A film thickness of 3 mm is adequate for increased fresh water yield. • The moving water film does not induce a clockwise moving mixture. • The transparent gas approach results in errors up to 39% in temperature and vapor profiles. [ABSTRACT FROM AUTHOR]

We here analyse two models of double-diffusive convection in fluid layer when viscosity depends on temperature quadratically. However, to a linearized instability analysis, conditional and global (unconditional) nonlinear stability theories are applied. For the first model, we establish an unconditional nonlinear energy stability. Moreover, in the second model the standard energy method does not yield unconditional stability so a conditional energy analysis is employed to achieve nonlinear results. In addition, the nonlinear stability bounds is found to be independent of the salt field and a presentation of the region of possible subcritical instabilities is given. [ABSTRACT FROM AUTHOR]

Geothermal applications with waste water in abandoned mines are a sustainable way of recycling wastes in abandoned facilities for utilizing clean energy. Thermohaline stratification in mine water is significant to this energy application, because it dominates the heat and mass transport in the mine-water-geologic-formation system and consequently determines the efficiency and sustainability of geothermal energy systems. This study addresses six unresolved issues for understanding the formation and evolution of thermohaline stratification via multiphysics simulations, including effects of key transport parameters on thermohaline stratification; mechanisms underlying layer-merging; effects of the buoyancy ratio on thermohaline stratification, and predictions of the initial distributions of temperature and salinity for thermohaline stratification. Our results showed that the effective kinematic viscosity is the most dominant transport parameter to determine the layer-merging speed and layer number of thermohaline stratification, where seven more thermohaline stratification layers could be observed if two orders of magnitude of this parameter are increased. For layer-merging, relatively "weak" interfaces, which have a small buoyancy ratio across the neighboring layers, disappear and are eroded first. Our results also revealed that the buoyancy ratio determines the layer number, where increasing the buoyancy ratio from 2.16 to 4 can induce twenty more layers. The initially linear temperature and salinity distributions in mine water are needed for predicting the present and future thermohaline stratification, especially the energy recovery. To meet this need, an approach was proposed to accurately predict such initial distributions via back-calculating field measurements. This study provides insights into understanding the key energy transport mechanisms in mine water and recommendations for facilitating future implementations of geothermal energy recovery with mine water dominated by thermohaline stratification. Image 1 • Water transport parameters control layer conditions of thermohaline stratification. • "Weak" interfaces with low buoyancy ratios are eroded first. • A new method to predict initial distributions of layered temperature and salinity. • Expediting layer-merging in practice improves the energy application efficiency. [ABSTRACT FROM AUTHOR]

The Antarctic Ice Sheet loses about half its mass through ocean-driven melting of its fringing ice shelves. However, the ocean processes governing ice shelf melting are not well understood, contributing to uncertainty in projections of Antarctica's contribution to global sea level. We use high-resolution large-eddy simulation to examine ocean-driven melt, in a geophysical-scale model of the turbulent ice shelf-ocean boundary layer, focusing on the ocean conditions observed beneath the Ross Ice Shelf. We quantify the role of double-diffusive convection in determining ice shelf melt rates and oceanic mixed layer properties in relatively warm and low-velocity cavity environments. We demonstrate that double-diffusive convection is the first-order process controlling the melt rate and mixed layer evolution at these flow conditions, even more important than vertical shear due to a mean flow, and is responsible for the step-like temperature and salinity structure, or thermohaline staircase, observed beneath the ice. A robust feature of the multiday simulations is a growing saline diffusive sublayer that drives a time-dependent melt rate. This melt rate is lower than current ice-ocean parameterizations, which consider only shear-controlled turbulent melting, would predict. Our main finding is that double-diffusive convection is an important process beneath ice shelves, yet is currently neglected in ocean-climate models., Competing Interests: The authors declare no competing interest.

When fluid stratification is induced by the vertical gradients of two scalars with different diffusivities, double-diffusive convection (DDC) may occur and play a crucial role in mixing. Such a process exists in many natural and engineering environments. Especially in the ocean, DDC is omnipresent since the seawater density is affected by temperature and salinity. The most intriguing phenomenon caused by DDC is the thermohaline staircase, i.e., a stack of alternating well-mixed convection layers and sharp interfaces with very large gradients in both temperature and salinity. Here we investigate DDC and thermohaline staircases in the salt finger regime, which happens when warm saltier water lies above cold fresher water and is commonly observed in the (sub)tropic regions. By conducting direct numerical simulations over a large range of parameters, we reveal that multiple equilibrium states exist in fingering DDC and staircases even for the same control parameters. Different states can be established from different initial scalar distributions or different evolution histories of the flow parameters. Hysteresis appears during the transition from a staircase to a single salt finger interface. For the same local density ratio, salt finger interfaces in the single-layer state generate very different fluxes compared to those within staircases. However, the salinity flux for all salt finger interfaces follows the same dependence on the salinity Rayleigh number of the layer and can be described by an effective power law scaling. Our findings have direct applications to oceanic thermohaline staircases., Competing Interests: The authors declare no competing interest.

This work proposes that the mixed zones and haloclines in Lake Kivu are a result of the following changes: A drought triggered a limnic eruption around 4,000 yBP, which left behind a uniformly mixed lake. Increasing precipitation after the eruption generated the two upper zones by dilution, first by precipitation into the closed lake and subsequently by flushing when the lake overflowed to Lake Tanganyika. Sublacustrine and saline meteoric sources generated the first denser zone below the former holomictic zone from the eruption and later, magmatic CO 2 was added to the saline sources, generating a denser bottommost zone. The continuously inflowing sublacustrine sources caused upward movement of the mixed zones in the lake, movements that continue to this day. If not stopped, this movement will in the future bring the gases from the lower strata closer to the surface and thus to the point of preventing utilization of accumulated CH 4. If wanting to prevent future limnic eruptions, this would leave future generations with no other choice than venting the accumulating gases. Seven brown layers from the last 2,200 years in the sediments at Lake Kivu were thought to result from limnic eruptions. A re-evaluation of existing data indicates that these layers result from plumes of magmatic CO₂ emanating from fissures below the lake and entraining nutrient-laden bottom water to the mixolimnion, thus lowering the strata above the point of plume initiation. At unpredictable times and with unpredictable intensity, these plumes have thus for the last 2,000 to 3,000 years kept down the gas laden strata, thus contributing to preventing further abrupt limnic eruptions caused by gas accumulation. In addition, these CO₂ injections at varying depths and of varying intensities likely are a major contributor to onsets and disappearances of precipitating CaCO 3 from the mixolimnion reaching the bottom sediments. • A drought caused level reduction and likely the only limnic eruption of Lake Kivu. • Gas plumes were likely behind six other mixing events. • Saline inflows and CO₂ injections formed the two denser mixed zones deepest in lake. • Precipitation-induced dilution followed by flushing formed the two uppermost zones. • Droughts plus tectonic and volcanic events make forecasting the future uncertain. A review of sediment core data leads to proposing a drought-induced limnic eruption as being behind the formation of the 4–5 haloclines in Lake Kivu and that CO₂ plumes are not likely to cause catastrophic limnic eruptions, over years to decades they just cause emission of CO₂ from the resulting plumes. [ABSTRACT FROM AUTHOR]

To manage Lake Kivu in Central Africa to avoid its future eruption because of accumulated methane and carbon dioxide, a better understanding was required of the diffusive layering (DL) mode of double-diffusive convection (DDC) that governs the vertical transport mechanisms below the upper mixed layer (mixolimnion). Through emphasis on the physical mechanisms involved in this phenomenon, this work proposes a new understanding of which are the independent parameters in DL systems together with a hitherto missing explanation of the formation and long-term stability of subsea brine pools. Based on a review of observational data and of the basis for the existing hypothesis on the vertical transport of heat and mass in DL systems, a new hypothesis is proposed according to which the independent parameters are dβS 0 /dz, the solute density gradient, and geothermal heat flux, different from those hitherto believed (T and R ρ , the density ratio). Furthermore, diffusive and convective heat transport mechanisms balance to generate a constant heat flux in the DL systems. This causes an imbalance in the mass transport capacity that slowly causes some zones to mix and expand, thereby thinning the gradient zones. The steady state of this slow dynamic mechanism is the formation and maintaining of the completely mixed zones and the ultimately thinned gradient zones, that retain solutes below them and are found in deep brine pools, e.g. in the Mediterranean Sea and in the Red Sea. These results are of importance for understanding vertical transport phenomena in DL systems; all literature on this subject since 1965 likely needs to be revisited. Much theory likely will not hold and experimental results likely are insufficient if heat flux and the dimensions of the single ΔT and ΔS interfaces have not been measured. Furthermore, attempting to describe both the fingering and the DL modes of DDC by the same transport equations seems inappropriate. These conclusions probably also apply to DL systems in the Arctic Ocean, thus potentially influencing models of water circulation in the Atlantic Ocean. • Diffusive-layering mode of double-diffusive convection in quasi-steady state reviewed. • Independent parameters in such system are dβS 0 /dz and geothermal heat flux. • Mixed zones are generated and expanded by an instability in vertical mass flux. • Mixed zones eat into the gradients, which become thinner and thinner with time. • The ultimate steady state of such thinning are the sharp gradients over brine pools. A new understanding of governing parameters in diffusive layering leads to proposing the mechanism forming chemoclines and their ultimate steady-state thinness in Lake Kivu as well as over brine pools in the Mediterranean and in the Red Sea. [ABSTRACT FROM AUTHOR]

• Conceptual model with integrated extraction and crystal growth designed. • Double-diffusive convection identified as the mechanism for solute transport. • Correlation equation for convective transport proposed via CFD simulations. • Newly defined lower pseudocritical endpoints are desirable operating states. For a supercritical solvent–solute system, as a critical end point (CEP) is approached, the solubility becomes sensitive to temperature variations. By virtue of this phenomenon, a conceptual model is proposed to combine extraction and crystal growth. CO 2 –naphthalene is chosen as the reference system. Theoretical optimizations suggest that the newly defined pseudo-CEPs are favorable reference states, especially those close to the lower CEP. In each near-CEP region, the performance is promoted when the CEP is approached. The temperature at the bottom wall should be higher than that at the top one to offset the stabilizing concentration gradient due to gravity and initiate double-diffusive convection in the cooperative regime. Numerical simulations confirm that the performance of the current model operating at the optimized reference state is better than the previous experimental results in terms of crystal growth rates. The conceptual model provides an efficient configuration for coupled extraction and crystal growth apparatuses. [ABSTRACT FROM AUTHOR]

A theoretical study is presented to examine entropy generation in double-diffusive convection in an Electro-osmotic flow (EOF) of nanofluids via a peristaltic microchannel. Buoyancy effects due to change in temperature, solute concentration and nanoparticle volume fraction are also considered. This study was performed under lubrication and Debye-Hückel linearization approximation. The governing equations are solved exactly. The effect of dominant hydrodynamic parameters (thermophoresis, Brownian motion, Soret and Dufour), Grashof numbers (thermal, concentration and nanoparticle) and electro-osmotic parameters on double-diffusive convective flow are discussed. Moreover, trapping, pumping, entropy generation number, Bejan number and heat transfer rate were also examined under the influence of pertinent parameters such as the thermophoresis parameter, the Brownian motion parameter, the Soret parameter, the Dufour parameter, the thermal Grashof number, the solutal Grashof number, the nanoparticle Grashof number, the electro-osmotic parameter and Helmholtz–Smoluchowski velocity. The electro-osmotic parameter powerfully affected the velocity profile. The magnitude of total entropy generation increased as the thermophoresis parameter and Brownian motion parameter increased. Soret and the Dufour parameter had a strong tendency to control the temperature profile and Bejan number. The findings of the present analysis can be used in clinical purposes such as cell therapy, drug delivery systems, pharmaco-dynamic pumps and particles filtration. [ABSTRACT FROM AUTHOR]