Design and performance of a variable gap system for thermal conductivity measurements of high temperature, corrosive, and reactive fluids

Gallagher, Ryan; Birri, Anthony; Russell, Nick; Ezell, N. Dianne Bull

doi:10.1016/j.ijheatmasstransfer.2022.122763

Cited by 7 publications

(6 citation statements)

References 95 publications

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“…The specimen itself has three heat transfer mechanisms; therefore, it should have three resistances in parallel (radiation R th,rad , conduction R th,cond , convection). However, convection is considered negligible for the small gap sizes measured, proven based on an assessment of the Rayleigh number in Gallagher et al [18].…”

Section: Principles Of Operationmentioning

confidence: 97%

“…Thermal conductivity measurements of molten salts at ORNL are performed using the variable gap technique. This technique was developed in 1973 by Cooke [13] and adapted by Gallagher [18,19]; the system developed by Gallagher is considered herein. The variable gap technique is a steady-state technique involving careful measurement of temperature difference across a gap with a fluid specimen with unknown thermal conductivity while driving a known heat flux across.…”

Section: Principles Of Operationmentioning

confidence: 99%

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FY23 Progress Report on Viscosity and Thermal Conductivity Measurements of Molten Salts

Birri,

Termini,

Garland

et al. 2023

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As presented in this report, thermal conductivity and viscosity measurements were performed on key chloride pseudo-binary molten salt systems of relevance to molten salt reactor developers. Thermal conductivity measurements were conducted with a variable gap technique, in which a known heat flux is driven across a molten salt specimen and the temperature difference is measured, allowing calculation of the thermal conductivity. This is achieved by establishing a small gap between the bottom of a cylindrical inner containment, which houses electrical heating elements, and an outer containment, which houses cooling channels; the gap size can be varied by compression of a formed bellows. A new calibration scheme was developed herein, involving a correction factor to the heat flux based on He measurements at various temperatures. Furthermore, the data processing methodology was improved to minimize the impact of radiative heat transfer in the calculation of salt specimen thermal conductivity from the temperature difference measurements. Viscosity measurements were conducted with a rolling ball viscometer, in which a ball rolls some known distance in an angled tubular crucible, and the terminal velocity can be used to calculate the viscosity of the salt. The measurement can be performed in a quartz crucible, with which a standard camera can be used to track the ball, or in a metal crucible, with which x-ray radiography is required to track the ball. A new custom x-ray system was made and dedicated to the rolling ball viscometer to enable high throughput automated measurements with salts which require containment with metal. Both systems have been integrated with a ventilation stack which allows for off-gassing of radioactive material, enabling future measurements with U-bearing salts.The thermal conductivity measurements performed herein were with NaCl-KCl (44 mol% NaCl). This salt system was measured in the previous fiscal year, however the thermal conductivity values obtained were comparatively low, and so the system was remeasured with the aforementioned calibration scheme and improved post-processing techniques. The newly obtained thermal conductivity values for NaCl-KCl (44 mol% NaCl) indicate good agreement with kinetic theory and ab-initio models (within 5-10 %). The viscosity measurements performed herein were with three different compositions of NaCl-KCl: 75, 50, and 25 mol% NaCl; a new calibration scheme was applied to account for variable flow effects in the laminar regime. The results show reasonable agreement with literature (5-20 %, depending on the temperature, composition, and study); however, literature values are likely higher than true values based on pure end-member measurements performed in the comparative studies. The measurements conducted herein do show a trend such that viscosity increases with increasing NaCl concentration, which agrees well with one of two comparative studies. In general, the measurements conducted herein gives confidence in the capability to use these systems to accurately m...

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Section: Principles Of Operationmentioning

confidence: 97%

Section: Principles Of Operationmentioning

confidence: 99%

FY23 Progress Report on Viscosity and Thermal Conductivity Measurements of Molten Salts

Birri,

Termini,

Garland

et al. 2023

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“…The model was recently improved by accounting for thermal radiation. The experimental design, though originally prone to axial heat losses, was modified with guard heaters to prevent this [36].…”

Section: Variable Gap Apparatusmentioning

confidence: 99%

Use of a Needle Probe to Measure the Thermal Conductivity of Electrically Conductive Liquids at High Temperatures

Ruth,

Merritt,

Munro

2024

Preprint

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This paper considers the necessary conditions for using a derivative of a transient hot wire (termed a needle probe) approach to measure electrically conducting fluids at high temperatures, especially molten halide salts. The focus is on the development of a new theory based on a multi-layer system necessary to ensure electrical isolation of electrical wires from the surrounding fluid. This includes the use of a thin annulus of fluid to minimize convective heat transfer modes within the fluid of interest, which was inspired by the concentric cylinder method. Good measurements require the following considerations: concentricity of the probe and surrounding crucible to ensure a consistent fluid gap, accounting for corrections for deviation of the model at early times, and modeling radiation heat transfer through transparent fluids. Uncertainties are larger than transient hot wire methods because of the deviations from experimental conditions that can easily match an analytical approximation. An appropriate estimation of the measurement uncertainty can be obtained through careful design of the instrumentation, thorough uncertainty analysis, and limiting the measurements to only the applicable thermal property ranges of the approach. The 1D model used to interpret measured temperature data has been shown to be reliable for thermal conductivity measurements ranging from at least 0.39 W/mK to 0.92 W/mK and for temperatures from 293-1023 K. The approach is used to present thermal conductivity data of the molten salts NaCl-KCl (51-49 mol%) and LiCl-NaCl (28-72 mol%).

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“…Measuring the salt temperature can be difficult because temperature gradients in the experiment can cause the salt to be several degrees hotter than the gas above the salt. This effect can be minimized by applying additional heaters, like the guard heaters used in thermal conductivity measurements (Gallagher et al, 2022), as well as thermal insulation, well-calibrated systems, and long equilibration times.…”

Section: Conclusion and Conceptual Design Of Solubility Measurement A...mentioning

confidence: 99%

The effect of interfacial phenomena on gas solubility measurements in molten salts

et al. 2023

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The behavior of fission gases in molten fuel salt reactors governs activity transport from the reactor and can also affect the performance of the reactor itself. The gas solubility can be described thermodynamically by Henry’s law. However, the coupling of the condensed and gas phases depends on the interfacial area, which is difficult to measure or even to estimate. Surfaces of materials in the reactor will include disperse phases in the salt and porosity within the structural materials, covering a range of compositions and sizes. These attributes can affect measurements of fundamental properties such as gas solubility. Methods to obtain gas solubility, surface tension, interfacial energies, and bubble gas transport are reviewed. Recent data from manometric experiments are interpreted based on xenon sorption onto salt-wetted quartz.

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Design and performance of a variable gap system for thermal conductivity measurements of high temperature, corrosive, and reactive fluids

Cited by 7 publications

References 95 publications

FY23 Progress Report on Viscosity and Thermal Conductivity Measurements of Molten Salts

FY23 Progress Report on Viscosity and Thermal Conductivity Measurements of Molten Salts

Use of a Needle Probe to Measure the Thermal Conductivity of Electrically Conductive Liquids at High Temperatures

The effect of interfacial phenomena on gas solubility measurements in molten salts

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