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.

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.

Onset of Natural Convection from a Suddenly Heated Horizontal Cylinder

1980 ◽  
Vol 102 (4) ◽  
pp. 636-639 ◽  
Author(s):  
J. R. Parsons ◽  
J. C. Mulligan
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Stability ◽  
Heat Capacity ◽  
Natural Convection ◽  
Stability Analysis ◽  
Horizontal Cylinder ◽  
Finite Cylinder ◽  
Global Motion ◽  
Experimental Apparatus

A study of the onset of transient natural convection from a suddenly heated, horizontal cylinder of finite diameter is presented. The termination of the initial conductive and “locally” conuectiue heat transfer regime which precedes the onset of global natural convection is treated as a thermal stability phenomenon. An analysis is presented wherein the effects of finite cylinder diameter, cylinder heat capacity, and cylinder thermal conductivity are included in calculations of the convective delay time. A simple experimental apparatus is described and data presented. The thermal stability analysis is confirmed experimentally and data is presented which indicates localized natural convection prior to global motion.

Experimental and Numerical Analysis of Mixing Process of Two Component Gases in a Vertical Fluid Layer in a VHTR

2019 ◽  
Vol 5 (2) ◽  
Author(s):  
Tetsuaki Takeda
Keyword(s):  
High Temperature ◽  
Natural Convection ◽  
Numerical Analysis ◽  
Pressure Vessel ◽  
Storage Tank ◽  
Molecular Diffusion ◽  
Flow Characteristics ◽  
Mixing Process ◽  
Two Component ◽  
Air Ingress

When a depressurization accident of a very-high-temperature reactor (VHTR) occurs, air is expected to enter into the reactor pressure vessel from the breach and oxidize in-core graphite structures. Therefore, in order to predict or analyze the air ingress phenomena during a depressurization accident, it is important to develop a method for the prevention of air ingress during an accident. In particular, it is also important to examine the influence of localized natural convection and molecular diffusion on the mixing process from a safety viewpoint. Experiment and numerical analysis using a three-dimensional (3D) computational fluid dynamics code have been carried out to obtain the mixing process of two-component gases and the flow characteristics of localized natural convection. The numerical model consists of a storage tank and a reverse U-shaped vertical rectangular passage. One sidewall of the high-temperature side vertical passage is heated, and the other sidewall is cooled. The low-temperature vertical passage is cooled by ambient air. The storage tank is filled with heavy gas and the reverse U-shaped vertical passage is filled with a light gas. The result obtained from the 3D numerical analysis was in agreement with the experimental result quantitatively. The two component gases were mixed via molecular diffusion and natural convection. After some time elapsed, natural circulation occurred through the reverse U-shaped vertical passage. These flow characteristics are the same as those of phenomena generated in the passage between a permanent reflector and a pressure vessel wall of the VHTR.

Natural Convection from a Horizontal Cylinder—Laminar Regime

1981 ◽  
Vol 103 (3) ◽  
pp. 522-527 ◽  
Author(s):  
B. Farouk ◽  
S. I˙. Gu¨c¸eri
Keyword(s):  
Natural Convection ◽  
Horizontal Cylinder ◽  
Heat Transfer Characteristics ◽  
Convective Flows ◽  
Finite Difference Numerical Method ◽  
Temperature Boundary ◽  
Recirculation Zones ◽  
Boussinesq Fluid ◽  
Temperature Boundary Condition ◽  
Good Agreement

A finite-difference numerical method has been adopted to generate flow patterns and heat transfer characteristics for laminar, steady-state, two-dimensional natural convection around a circular cylinder submerged in an unbounded Boussinesq fluid. The approach allows the use of nonuniform as well as uniform specified temperature and heat flux distributions over the cylindrical surface. Part of the results are generated for reverse convective flows with recirculation zones which occur when part of the cylinder is below the ambient temperature while the remaining part is above. The results for uniform temperature boundary condition are in good agreement with the experimental data and other solutions available in literature.

Flow characteristics of aqueous salt solutions for applications in supercritical water oxidation

2007 ◽  
Vol 42 (2) ◽  
pp. 241-254 ◽  
Author(s):  
Shin-Ichiro Kawasaki ◽  
Taro Oe ◽  
Shinji Itoh ◽  
Akira Suzuki ◽  
Kiwamu Sue ◽  
...  
Keyword(s):  
Supercritical Water ◽  
Water Oxidation ◽  
Flow Characteristics ◽  
Supercritical Water Oxidation ◽  
Salt Solutions ◽  
Aqueous Salt Solutions
Sign in / Sign up

Export Citation Format

Share Document