Laboratory experimental investigation  of heat transport in fractured media

Abstract. Low enthalpy geothermal energy is a renewable resource that is still underexploited nowadays in relation to its potential for development in society worldwide. Most of its applications have already been investigated, such as heating and cooling of private and public buildings, road defrosting, cooling of industrial processes, food drying systems or desalination. Geothermal power development is a long, risky and expensive process. It basically consists of successive development stages aimed at locating the resources (exploration), confirming the power generating capacity of the reservoir (confirmation) and building the power plant and associated structures (site development). Different factors intervene in influencing the length, difficulty and materials required for these phases, thereby affecting their cost. One of the major limitations related to the installation of low enthalpy geothermal power plants regards the initial development steps that are risky and the upfront capital costs that are huge. Most of the total cost of geothermal power is related to the reimbursement of invested capital and associated returns. In order to increase the optimal efficiency of installations which use groundwater as a geothermal resource, flow and heat transport dynamics in aquifers need to be well characterized. Especially in fractured rock aquifers these processes represent critical elements that are not well known. Therefore there is a tendency to oversize geothermal plants. In the literature there are very few studies on heat transport, especially on fractured media. This study is aimed at deepening the understanding of this topic through heat transport experiments in fractured networks and their interpretation. Heat transfer tests have been carried out on the experimental apparatus previously employed to perform flow and tracer transport experiments, which has been modified in order to analyze heat transport dynamics in a network of fractures. In order to model the obtained thermal breakthrough curves, the Explicit Network Model (ENM) has been used, which is based on an adaptation of Tang's solution for the transport of the solutes in a semi-infinite single fracture embedded in a porous matrix. Parameter estimation, time moment analysis, tailing character and other dimensionless parameters have permitted a better understanding of the dynamics of heat transport and the efficiency of heat exchange between the fractures and the matrix. The results have been compared with the previous experimental studies on solute transport.

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Laboratory experimental investigation of heat transport in fractured media

10.5194/npg-2016-54 ◽

2016 ◽

Author(s):

Claudia Cherubini ◽

Nicola Pastore ◽

Concetta I. Giasi ◽

Nicoletta Maria Allegretti

Keyword(s):

Heat Transport ◽

Power Plants ◽

Time Moment ◽

Experimental Studies ◽

Renewable Resource ◽

Fractured Media ◽

Single Fracture ◽

Tracer Transport ◽

Transport Dynamics ◽

Experimental Apparatus

Abstract. Low enthalpy geothermal energy is a renewable resource that is still underexploited nowadays, in relation to its potential for development in the society worldwide. Most of its applicabilities have already been investigated, such as: heating and cooling of private and public buildings, roads defrost, cooling of industrial processes, food drying systems, desalination. One of the major limitations related to the choice of installing low enthalpy geothermal power plants regards the initial investment costs. In order to increase the optimal efficiency of installations which use groundwater as geothermal resource, flow and heat transport dynamics in aquifers need to be well characterized. Especially in fractured rock aquifers these processes represent critical elements that are not well known. Therefore there is a tendency to oversize geothermal plants. In literature there are very few studies on heat transport especially in fractured media. This study is aimed to deepen the understanding of this topic through heat transport experiments in fractured network and their interpretation. The heat transfer tests have been carried out on the experimental apparatus previously employed to perform flow and tracer transport experiments, which has been modified in order to analyze heat transport dynamics in a network of fractures. In order to model the obtained thermal breakthrough curves, the Explicit Network Model (ENM) has been used, which is based on an adaptation of a Tang's solution for the transport of the solutes in a semi-infinite single fracture embedded in a porous matrix. Parameter estimation, time moment analysis, tailing character and other dimensionless parameters have permitted to better understand the dynamics of heat transport and the efficiency of heat exchange between the fractures and matrix. The results have been compared with the previous experimental studies on solute transport.

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Evidence of non-Darcy flow and non-Fickian transport in fractured media at laboratory scale

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-10-221-2013 ◽

2013 ◽

Vol 10 (1) ◽

pp. 221-254 ◽

Cited By ~ 1

Author(s):

C. Cherubini ◽

C. I. Giasi ◽

N. Pastore

Keyword(s):

Solute Transport ◽

Rock Sample ◽

Breakthrough Curves ◽

Fractured Media ◽

Hydraulic Loss ◽

Assessment Procedure ◽

Tracer Transport ◽

Flow And Transport ◽

Experimental Apparatus ◽

Study Laboratory

Abstract. Accurate predictions of solute propagation in fractured rocks are of particular importance when assessing exposure pathways through which contaminants reach receptors during a risk assessment procedure, as well as when dealing with cleanup and monitoring strategies. The difficulty in modeling fractured media leads to the application of simplified analytical solutions that fail to reproduce flow and transport patterns in such complex geological formations. A way for understanding and quantifying the migration of contaminants in groundwater systems is that of analyzing tracer transport. Experimental data obtained under controlled conditions such as in a laboratory allow to increase the understanding of the fundamental physics of fluid flow and solute transport in fractures. In this study laboratory hydraulic and tracer tests have been carried out on an artificially created fractured rock sample. The tests regard the analysis of the hydraulic loss and the measurement of breakthrough curves for saline tracer pulse inside a rock sample of parallelepiped (0.60 × 0.40 × 0.8 m) shape. The effect of the experimental apparatus on flow and transport tests has been estimated. In particular the convolution theory has been applied in order to remove the effect of acquisition apparatus on tracer experiment. The experimental results have shown evidence of a non-Darcy relationship between flow rate and hydraulic loss that is best described by Forchheimer's law. The observed experimental breakthrough curves of solute transport have been modeled by the classical one-dimensional analytical solution for advection–dispersion equation (ADE) and the single rate mobile–immobile model (MIM). The former model does not fit properly the first arrival and the tail while the latter provides a very decent fit.

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Channeling Flow and Solute Transport in a Single Fracture

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.316-317.632 ◽

2013 ◽

Vol 316-317 ◽

pp. 632-635

Author(s):

Ye Fei Tan ◽

Zhi Fang Zhou ◽

Shi Qiang Wu ◽

Xing Hua Xie ◽

Bo Ning

Keyword(s):

Finite Element Method ◽

Drinking Water ◽

Breakthrough Curve ◽

Laboratory Experiments ◽

Fractured Media ◽

Single Fracture ◽

The Finite Element Method ◽

Dispersive Equation ◽

One Dimensional ◽

Channeling Flow

Groundwater in fractured media plays an important role in drinking water supply, and the understanding of its principle mechanisms is essential for securing the groundwater exploring and utilization. In this paper, a novel conceptual fracture model was presented on the basis of the reality of channeling flow in natural fractures and laboratory experiments were conducted for the purpose of getting a better understanding of the step-like breakthrough curve (BTC). Experimental results were fitted with convective dispersive equation (CDE) and compared with those of the finite element method (FEM) models. Results showed that the traditional one-dimensional CDE was invalid in the fitting of a step-like BTC and needed to be improved.

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Comment on “Flow and tracer transport in a single fracture: A stochastic model and its relation to some field observations” by L. Moreno et al.

Water Resources Research ◽

10.1029/90wr02310 ◽

1991 ◽

Vol 27 (1) ◽

pp. 129-131 ◽

Cited By ~ 4

Author(s):

Daniel J. Goode ◽

Allen M. Shapiro

Keyword(s):

Stochastic Model ◽

Single Fracture ◽

Field Observations ◽

Tracer Transport

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A SINGULAR PERTURBATION PROBLEM IN FRACTURED MEDIA WITH PARALLEL DIFFUSION

Mathematical Models and Methods in Applied Sciences ◽

10.1142/s0218202598000299 ◽

1998 ◽

Vol 08 (04) ◽

pp. 645-655 ◽

Cited By ~ 1

Author(s):

J. DAVID LOGAN ◽

GLENN LEDDER ◽

MICHELLE REEB HOMP

Keyword(s):

Boundary Condition ◽

Singular Perturbation ◽

Porous Matrix ◽

Fractured Media ◽

Singular Perturbation Problem ◽

Single Fracture ◽

Direction Parallel ◽

Flux Boundary Condition ◽

Perturbation Problem ◽

Parallel Diffusion

We study differential equations that model contaminant flow in a semi-infinite, fractured, porous medium consisting of a single fracture channel bounded by a porous matrix. Models in the literature usually do not incorporate diffusion in the porous matrix in the direction parallel to the fracture, and therefore they must omit a no-flux boundary condition at the edge, which, in some problems, may be unphysical. Herein we show that the problem usually treated in the literature is the outer problem for a correctly posed singular perturbation problem which includes diffusion in both directions as well as the no-flux boundary condition.

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