Effect of Freeze Pipe Eccentricity in Selective Artificial Ground Freezing Applications

Abstract Building concentric tubes is one of biggest practical challenges in the construction of freeze-pipes of selective artificial ground freezing (S-AGF) applications for underground mines. In this study, the influence of tubes eccentricity on phase-front expansion (i.e., expansion of the frozen body) and energy consumption of S-AGF systems is analyzed. A 1+1D semi-conjugate model that solves two-phase transient energy conservation equation is derived based on the enthalpy method. The 1+1D model is firstly validated against experimental data and then verified with a fully-conjugate model from our previous work. After that, the 1+1D model is extended to a field-scale of typical underground mines to examine the effect of freeze-pipe eccentricity. The results show that concentric freeze-pipes form the desired frozen ground volume 15% faster than eccentric freeze-pipes. Also, the geometrical profile of the phase-transition-front of the frozen ground is found to be significantly influenced by the freeze-pipe eccentricity. Furthermore, in the passive zone, where S-AGF coolants are isolated from the ground to reduce energy consumption, freeze pipe eccentricity can increase the coolant heat gain by 20%. This percentage can increase up to 200 % if radiation heat transfer is minimized.

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Effect of Freeze Pipe Eccentricity in Artificial Ground Freezing Applications

Volume 11: Heat Transfer and Thermal Engineering ◽

10.1115/imece2020-23417 ◽

2020 ◽

Author(s):

Ahmad F. Zueter ◽

Minghan Xu ◽

Mahmoud A. Alzoubi ◽

Agus P. Sasmito

Keyword(s):

Energy Consumption ◽

Radiation Heat Transfer ◽

Conservation Equation ◽

Underground Mines ◽

Phase Front ◽

Two Phase ◽

Ground Freezing ◽

Deep Underground ◽

Artificial Ground Freezing ◽

Conjugate Model

Abstract Building concentric tubes is one of biggest practical challenges in the construction of freeze-pipes of artificial ground freezing (AGF) applications for deep underground mines. In this study, the influence of tubes eccentricity on phase-front expansion (i.e., expansion of the frozen body) and energy consumption of AGF systems is analyzed. A 1+1D semi-conjugate model that solves two-phase transient energy conservation equation is derived. The model is firstly validated against experimental data and then verified with a fully-conjugate model from the literature. After that, the model is extended to a field scale of typical deep underground mines to study freeze-pipe eccentricity. The results show that an eccentric freeze pipe can reduce the phase-front expansion by around 25%, as compared with a concentric one. Also, the geometrical profile of the phase-front is significantly influenced by the freeze-pipe eccentricity. Furthermore, in the passive zone, where AGF coolants are isolated from the ground to reduce energy consumption, freeze pipe eccentricity can increase the coolant heat gain by 10%. This percentage can increase up to 200% if radiation heat transfer is minimized.

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Artificial ground freezing using solar-powered thermosyphons

10.21079/11681/42421 ◽

2021 ◽

Author(s):

Anna Wagner ◽

Jon Maakestad ◽

Edward Yarmak ◽

Thomas Douglas

Keyword(s):

Solar Array ◽

Freeze Ground ◽

Passive Mode ◽

Frozen Ground ◽

Air Temperatures ◽

Ground Freezing ◽

Refrigeration Unit ◽

Artificial Ground Freezing ◽

Solar Powered ◽

The 1960S

Thermosyphons are an artificial ground-freezing technique that has been used to stabilize permafrost since the 1960s. The largest engineered structure that uses thermosyphons to maintain frozen ground is the Trans Alaska Pipeline, and it has over 124,000 thermosyphons along its approximately 1300 km route. In passive mode, thermosyphons extract heat from the soil and transfer it to the environment when the air temperature is colder than the ground temperature. This passive technology can promote ground cooling during cold winter months. To address the growing need for maintaining frozen ground as air temperatures increase, we investigated a solar-powered refrigeration unit that could operate a thermosyphon (nonpassive) during temperatures above freezing. Our tests showed that energy generated from the solar array can operate the refrigeration unit and activate the hybrid thermosyphon to artificially cool the soil when air temperatures are above freezing. This technology can be used to expand the application of thermosyphon technology to freeze ground or maintain permafrost, particularly in locations with limited access to line power.

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Development of Analytical Solution for a Two-Phase Stefan Problem in Artificial Ground Freezing Using Singular Perturbation Theory

Journal of Heat Transfer ◽

10.1115/1.4048137 ◽

2020 ◽

Vol 142 (12) ◽

Cited By ~ 1

Author(s):

Minghan Xu ◽

Saad Akhtar ◽

Ahmad F. Zueter ◽

Victor Auger ◽

Mahmoud A. Alzoubi ◽

...

Keyword(s):

Analytical Solution ◽

Singular Perturbation ◽

Stefan Problem ◽

Underground Structure ◽

Computational Cost ◽

Singular Perturbation Theory ◽

Singular Perturbation Method ◽

Two Phase ◽

Ground Freezing ◽

Artificial Ground Freezing

Abstract Artificial ground freezing (AGF) has historically been used to stabilize underground structure. Numerical methods generally require high computational power to be applicable in practice. Therefore, it is of interest to develop accurate and reliable analytical frameworks for minimizing computational cost. This paper proposes a singular perturbation solution for a two-phase Stefan problem that describes outward solidification in AGF. Specifically, the singular perturbation method separates two distinct temporal scales to capture the subcooling and freezing stages in the ground. The ground was considered as a porous medium with volume-averaged thermophysical properties. Further, Stefan number was assumed to be small, and effects of a few site-dependent parameters were investigated. The analytical solution was verified by numerical results and found to have similar conclusions yet with much lesser computational cost. Keywords: artificial ground freezing, Stefan-like problems, singular perturbation, porous media, outward solidification.

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