On the Potential for Homogeneous Nucleation in Aqueous Salt Solutions at Elevated Temperatures and Pressures

2000 ◽  
Author(s):  
Kenneth A. Smith ◽  
Marc Hodes ◽  
Peter Griffith
Keyword(s):  
Boundary Layer ◽  
Water Oxidation ◽  
Homogeneous Nucleation ◽  
Elevated Temperatures ◽  
Lewis Number ◽  
Operating Conditions ◽  
Convective Boundary ◽  
Solution Interface ◽  
Salt Layer ◽  
Aqueous Salt Solutions

Abstract Recent studies have experimentally and theoretically examined the rate of salt deposition by natural convection on a cylinder heated above the solubility temperature corresponding to the concentration of salt in the surrounding solution at conditions typical of the Supercritical Water Oxidation (SCWO) process (Hodes et al., 2000A; Hodes, 1998). The total deposition rate of salt on the cylinder is the sum of the rates of deposition at the salt layer-solution interface (SLSI) formed on the cylinder and within the porous salt layer. The rate of deposition at the SLSI can not be accurately computed without determining whether or not salt nucleates homogeneously in the adjacent (natural convective) boundary layer. A methodology to determine whether or not homogeneous nucleation in the boundary layer is possible is presented here. This is accomplished by computing the temperature and concentration profiles in the boundary layer under the assumption that homogeneous nucleation does not occur. If, under this assumption, supersaturation does not occur, homogeneous nucleation is impossible. If supersaturation is present, homogeneous nucleation may or may not occur depending on the amount of metastability the solution can tolerate. It is shown that the Lewis number is the critical property in determining whether or not homogeneous nucleation is possible and a simple formula is developed to predict the Lewis number below which homogeneous nucleation is impossible for a given solubility boundary and set of operating conditions.

On the Potential for Homogeneous Nucleation of Salt From Aqueous Solution in a Natural Convection Boundary Layer

2002 ◽  
Vol 124 (5) ◽  
pp. 930-937 ◽  
Author(s):  
Kenneth A. Smith ◽  
Marc Hodes ◽  
Peter Griffith
Keyword(s):  
Boundary Layer ◽  
Natural Convection ◽  
Water Oxidation ◽  
Homogeneous Nucleation ◽  
Lewis Number ◽  
Operating Conditions ◽  
Convection Boundary Layer ◽  
Solution Property ◽  
Salt Layer ◽  
Convection Boundary

Recent studies have examined the rate of salt deposition by natural convection on a cylinder heated above the solubility temperature corresponding to the concentration of salt in the surrounding solution at conditions typical of the Supercritical Water Oxidation (SCWO) process (Hodes et al. [1,2], Hodes [3]). The total deposition rate of salt on the cylinder is the sum of the rate of deposition at the salt layer-solution interface (SLSI) formed on the cylinder and that within the porous salt layer. The rate of deposition at the SLSI cannot be computed without determining whether or not salt nucleates homogeneously in the adjacent (natural convection) boundary layer. A methodology to determine whether or not homogeneous nucleation in the boundary layer is possible is presented here. Temperature and concentration profiles in the boundary layer are computed under the assumption that homogeneous nucleation does not occur. If, under this assumption, supersaturation does not occur, homogeneous nucleation is impossible. If supersaturation is present, homogeneous nucleation may or may not occur depending on the amount of metastability the solution can tolerate. It is shown that the Lewis number is the critical solution property in determining whether or not homogeneous nucleation is possible and a simple formula is developed to predict the Lewis number below which homogeneous nucleation is impossible for a given solubility boundary and set of operating conditions. Finally, the theory is shown to be consistent with experimental observations for which homogeneous nucleation is absent or present.

A Natural Convection Model for the Rate of Salt Deposition From Near-Supercritical, Aqueous Solutions

2003 ◽  
Vol 125 (6) ◽  
pp. 1027-1037 ◽  
Author(s):  
Marc Hodes ◽  
Kenneth A. Smith ◽  
Peter Griffith
Keyword(s):  
Natural Convection ◽  
Deposition Rate ◽  
Water Oxidation ◽  
Molecular Diffusion ◽  
Horizontal Cylinder ◽  
Salt Deposition ◽  
Solution Interface ◽  
Salt Layer ◽  
Aqueous Salt Solutions ◽  
Convection Model

A model is developed for the rate of salt deposition by natural convection from aqueous salt solutions onto a horizontal cylinder heated beyond the solubility temperature for the dissolved salt. The model accounts for the deposition rate at the salt layer-solution interface (SLSI) formed on the cylinder, but it does not account for deposition which may occur inside the porous salt layer (PSL). Dissolved salt is transported to the SLSI by molecular diffusion (with advection) and subsequently nucleates heterogeneously there. The model is applied to the experimental deposition rate data acquired by Hodes et al. (1998, 2002) at conditions pertinent to Supercritical Water Oxidation (SWCO). The ratio of the predicted deposition rate to the measured one ranges from roughly 0.5 to 2 indicating that deposition inside the PSL can be considerable.

scholarly journals Finite Element Study for Magnetohydrodynamic (MHD) Tangent Hyperbolic Nanofluid Flow over a Faster/Slower Stretching Wedge with Activation Energy

Mathematics ◽  
2020 ◽  
Vol 9 (1) ◽  
pp. 25
Author(s):  
Bagh Ali ◽  
Rizwan Ali Naqvi ◽  
Amna Mariam ◽  
Liaqat Ali ◽  
Omar M. Aldossary
Keyword(s):  
Activation Energy ◽  
Finite Element ◽  
Volume Fraction ◽  
Wedge Angle ◽  
Energy Parameter ◽  
Reliability And Validity ◽  
Lewis Number ◽  
Convergence Criteria ◽  
Convective Boundary ◽  
Differential Formulation

The below work comprises the unsteady flow and enhanced thermal transportation for Carreau nanofluids across a stretching wedge. In addition, heat source, magnetic field, thermal radiation, activation energy, and convective boundary conditions are considered. Suitable similarity functions use to transmuted partial differential formulation into the ordinary differential form, which is solved numerically by the finite element method and coded in Matlab script. Parametric computations are made for faster stretch and slowly stretch to the surface of the wedge. The progressing value of parameter A (unsteadiness), material law index ϵ, and wedge angle reduce the flow velocity. The temperature in the boundary layer region rises directly with exceeding values of thermophoresis parameter Nt, Hartman number, Brownian motion parameter Nb, ϵ, Biot number Bi and radiation parameter Rd. The volume fraction of nanoparticles rises with activation energy parameter EE, but it receded against chemical reaction parameter Ω, and Lewis number Le. The reliability and validity of the current numerical solution are ascertained by establishing convergence criteria and agreement with existing specific solutions.

scholarly journals Numerical study of bio-convection flow of magneto-cross nanofluid containing gyrotactic microorganisms with activation energy

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Qiu-Hong Shi ◽  
Aamir Hamid ◽  
M. Ijaz Khan ◽  
R. Naveen Kumar ◽  
R. J. Punith Gowda ◽  
...  
Keyword(s):  
Radiation Effects ◽  
Numerical Study ◽  
Source Parameters ◽  
Lewis Number ◽  
Convective Boundary Condition ◽  
Convection Flow ◽  
Convective Boundary ◽  
Similarity Transformations ◽  
Cross Nanoliquid ◽  
Source Sink

AbstractIn this study, a mathematical model is developed to scrutinize the transient magnetic flow of Cross nanoliquid past a stretching sheet with thermal radiation effects. Binary chemical reactions and heat source/sink effects along with convective boundary condition are also taken into the consideration. Appropriate similarity transformations are utilized to transform partial differential equations (PDE’s) into ordinary ones and then numerically tackled by shooting method. The impacts of different emerging parameters on the thermal, concentration, velocity, and micro-rotation profiles are incorporated and discussed in detail by means of graphs. Results reveal that, the escalation in magnetic parameter and Rayleigh number slowdowns the velocity and momentum of the fluid. The increase in Biot number, radiation and heat sink/source parameters upsurges the thermal boundary but, converse trend is seen for escalating Prandtl number. The density number of motile microorganisms acts as a growing function of bioconvection Lewis number and declining function of bioconvection Peclet number.

scholarly journals Design of Molecular Water Oxidation Catalysts Stabilized by Ultrathin Inorganic Overlayers—Is Active Site Protection Necessary?

Inorganics ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 105 ◽  
Author(s):  
Laurent Sévery ◽  
Sebastian Siol ◽  
S. Tilley
Keyword(s):  
Water Oxidation ◽  
Atomic Layer ◽  
Deposition Process ◽  
Operating Conditions ◽  
Molecular Water ◽  
Side Reactions ◽  
Aqueous Environment ◽  
Oxidation Catalysts ◽  
Initial Onset ◽  
Anchoring Groups

Anchored molecular catalysts provide a good step towards bridging the gap between homogeneous and heterogeneous catalysis. However, applications in an aqueous environment pose a serious challenge to anchoring groups in terms of stability. Ultrathin overlayers embedding these catalysts on the surface using atomic layer deposition (ALD) are an elegant solution to tackle the anchoring group instability. The propensity of ALD precursors to react with water leads to the question whether molecules containing aqua ligands, such as most water oxidation complexes, can be protected without side reactions and deactivation during the deposition process. We synthesized two iridium and two ruthenium-based water oxidation catalysts, which contained an aqua ligand (Ir–OH2 and Ru–OH2) or a chloride (Ir–Cl and Ru–Cl) that served as a protecting group for the former. Using a ligand exchange reaction on the anchored and partially embedded Ru–Cl, the optimal overlayer thickness was determined to be 1.6 nm. An electrochemical test of the protected catalysts on meso-ITO showed different behaviors for the Ru and the Ir catalysts. The former showed no onset difference between protected and non-protected versions, but limited stability. Ir–Cl displayed excellent stability, whilst the unprotected catalyst Ir–OH2 showed a later initial onset. Self-regeneration of the catalytic activity of Ir–OH2 under operating conditions was observed. We propose chloride ligands as generally applicable protecting groups for catalysts that are to be stabilized on surfaces using ALD.

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