Steady State Transport in Fluid and Pipe Permeator Wall

General Case Description

This verification case compares the TMAP8 solution with an independent analytical implementation of the steady state permeator against vacuum (PAV) transport model based on Fuerst et al. (2023). The model represents hydrogen isotope transport from flowing PbLi through a cylindrical vanadium membrane and into an ideal vacuum.

The transport process includes liquid mass transfer, jump between PbLi and vanadium surface, radial diffusion through the vanadium membrane, and recombination at the vacuum surface. The calculation is steady state and isothermal, and the hydrogen isotope partial pressure on the vacuum side is assumed to be zero.

TMAP8 represents the 5 m permeator with 20 axial control volumes. The outlet concentration of each control volume is used as the inlet concentration of the following control volume. The same radial transport model is applied within each control volume, as illustrated in Figure 1. The independent Python reference uses the same radial transport model but solves the corresponding continuous axial mass balance equation.

Schematic of the 20 axial control volumes and the radial transport model applied within each control volume.

Figure 1: Schematic of the 20 axial control volumes and the radial transport model applied within each control volume.

Case Setup

The geometry and operating parameters are summarized in Table 1.

Table 1: Geometry and operating parameters used for the PAV verification case.

ParameterDescriptionValueUnits
Temperature673.15K
Active permeator length5.00m
Inner tube radiusm
Outer tube radiusm
Number of TMAP8 axial control volumes20-
Inlet dissolved-isotope concentration1.0mol/m
PbLi velocity1.78m/s
Reynolds number-

The gas constant is J/(mol K), consistent with PhysicalConstants.

Material properties and liquid mass transfer

The PbLi hydrogen isotope diffusivity is (Fukada et al., 2013)

and the PbLi density is

The effective PbLi molar concentration is

where kg/mol.

The PbLi solubility coefficient is calculated using the model reported by Fuerst et al. (2023), based on Aiello et al. (2006):

with Pa.

For the vanadium membrane, the hydrogen isotope diffusivity is based on Völkl and Alefeld (1975),

and the hydrogen isotope solubility is based on Veleckis and Edwards (1969):

The hydraulic diameter is

Using the specified Reynolds number, the kinematic viscosity and Schmidt number are

and

The Sherwood number and liquid mass transfer coefficient are calculated using the correlation of Linton and Sherwood (1950):

and

The material property model parameters used in the reference implementation are summarized in Table 2. The corresponding material properties and transport quantities evaluated at 673.15 K are summarized in Table 3.

Table 2: Material-property parameters for the PAV verification case.

ParameterDescriptionValueUnitsBasis
PbLi diffusivity pre-exponential factorm/sFukada et al. (2013)
PbLi diffusivity activation energyJ/molFukada et al. (2013)
PbLi density constant10520.35kg/mFuerst et al. (2023)
PbLi density linear coefficient1.19051kg/(m K)Fuerst et al. (2023)
PbLi solubility coefficient factorPaFuerst et al. (2023)
Vanadium diffusivity pre-exponential factorm/sVölkl and Alefeld (1975)
Vanadium diffusivity activation energyJ/molVölkl and Alefeld (1975)
Vanadium solubility pre-exponential factor0.138mol/(m Pa)Veleckis and Edwards (1969)
Vanadium solubility exponential coefficientJ/molVeleckis and Edwards (1969)
Vanadium surface recombination coefficientm/(mol s)Fuerst et al. (2021)
Sherwood correlation coefficient0.023-Linton and Sherwood (1950)
Reynolds number exponent0.83-Linton and Sherwood (1950)
Schmidt number exponent-Linton and Sherwood (1950)
Schmidt number76.0233-Calculated
Sherwood number1376.29-Calculated

Table 3: Material properties and transport quantities evaluated at 673.15 K for the PAV verification case.

ParameterDescriptionValueUnitsBasis
Isotope diffusivity in PbLim/sCalculated
PbLi densitykg/mCalculated
PbLi solubility coefficientmol/(m Pa)Calculated
Isotope diffusivity in vanadiumm/sCalculated
Vanadium solubility coefficientmol/(m Pa)Calculated
Liquid mass transfer coefficientm/sCalculated

Analytical solution

The analytical solution is based on the analysis by Fuerst et al. (2023). For a local bulk PbLi concentration , the liquid mass transfer relation is

where is the PbLi concentration adjacent to the membrane. Equilibrium partitioning gives

Defining

radial diffusion through the cylindrical vanadium membrane is

The membrane resistance is therefore

At the vacuum surface, the model uses

Defining

and eliminating the intermediate interface concentrations gives

The positive root is

and the local permeation flux is

Continuous axial reference solution

TMAP8 applies the radial permeation relation in 20 axial control volumes. For the analytical calculation, the axial balance is instead treated continuously:

where

Let

From the radial solution,

Combining this relation with the continuous axial balance and integrating from the inlet to axial location gives

where

To compare TMAP8 predictions to the analytical solution, we solve this scalar analytical relation at the same axial locations used by the TMAP8 control volume model and recovers the bulk concentration from

The extraction efficiency is calculated as

Limiting case of negligible surface recombination resistance

The present formulation includes finite recombination kinetics at the vacuum surface through . The analytical model of Humrickhouse and Merrill (2015) instead assumes that the dissolved isotope concentration at the outer membrane surface is approximately zero because of the vacuum, . Within the present recombination boundary condition, this assumption is recovered in the limit

for which while the permeation flux remains finite. The membrane transport relation then reduces to

Combining this expression with the liquid mass transfer relation gives

where

Using , , and the solid permeability , this becomes

which is the dimensionless radial transport parameter defined by Humrickhouse and Merrill. Substituting the limiting flux into the continuous axial balance,

with gives

Integrating over the active permeator length yields

where

Therefore, in the limit of negligible surface recombination resistance,

which is the permeator efficiency expression derived by Humrickhouse and Merrill. Thus, the finite recombination model used here contains their ideal-vacuum analytical solution as the limiting case.

Results

Figure 2 compares the 20 segment TMAP8 solution with the continuous analytical reference. The concentration profile root mean square percentage error (RMSPE) is approximately 0.127 %, which signals good agreement. As shown in Figure 2, TMAP8 starts to slightly underestimate the analytical solution at higher axial positions, which can be alleviated by increasing the number of axial control volumes and therefore better approximate the continuous solution.

Comparison of the 20 segment TMAP8 bulk concentration profile with the continuous analytical PAV reference solution.

Figure 2: Comparison of the 20 segment TMAP8 bulk concentration profile with the continuous analytical PAV reference solution.

The numerical comparison is summarized in Table 4, which shows acceptable performance for this verification.

Table 4: Comparison of the TMAP8 solution with the analytical reference.

QuantityTMAP8AnalyticalRelative error
Outlet concentration, mol/m0.7592750.7609040.214 %
Extraction efficiency0.2407250.2390960.681 %
Average permeation flux, mol/(m s)0.681 %

Input files

The input file for this case can be found at (test/tests/ver-1p/ver-1p.i), which is used as a test in TMAP8 at (test/tests/ver-1p/tests). The independent analytical comparison and figure generation are implemented in (test/tests/ver-1p/comparison_ver-1p.py).

References

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  2. Thomas F. Fuerst, Matthew D. Eklund, John A. Leland, Adriaan A. Riet, and Chase N. Taylor. Parametric Study of the Vacuum Permeator for the Tritium Extraction eXperiment. Fusion Science and Technology, 79(8):1224–1234, 2023. URL: https://doi.org/10.1080/15361055.2023.2196237, doi:10.1080/15361055.2023.2196237.[Export]
  3. Thomas F. Fuerst, Paul W. Humrickhouse, Chase N. Taylor, and Masashi Shimada. Surface effects on deuterium permeation through vanadium membranes. Journal of Membrane Science, 620:118949, 2021. URL: https://doi.org/10.1016/j.memsci.2020.118949, doi:10.1016/j.memsci.2020.118949.[Export]
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  5. Paul W. Humrickhouse and Brad J. Merrill. Vacuum permeator analysis for extraction of tritium from DCLL blankets. Fusion Science and Technology, 68(2):295–302, 2015. doi:10.13182/FST14-941.[Export]
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  7. Ewald Veleckis and Russell Keith Edwards. Thermodynamic properties in the systems vanadium-hydrogen, niobium-hydrogen, and tantalum-hydrogen. The Journal of Physical Chemistry, 73(3):683–692, 03 1969. URL: https://doi.org/10.1021/j100723a033, doi:10.1021/j100723a033.[Export]
  8. J. Völkl and G. Alefeld. Hydrogen diffusion in metals. In A. S. Nowick and J. J. Burton, editors, Diffusion in Solids, pages 231–302. Academic Press, 1975. URL: https://doi.org/10.1016/B978-0-12-522660-8.50010-6, doi:10.1016/B978-0-12-522660-8.50010-6.[Export]