The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
Göran Hellström - One of the best experts on this subject based on the ideXlab platform.
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cfd modelling of natural convection in a groundwater filled Borehole heat exchanger
Applied Thermal Engineering, 2010Co-Authors: Annamaria Gustafsson, Lars Westerlund, Göran HellströmAbstract:In design of ground-source energy systems the thermal performance of the Borehole heat exchangers is important. In Scandinavia, Boreholes are usually not grouted but left with groundwater to fill the space between heat exchanger pipes and Borehole wall. The common U-pipe arrangement in a groundwater-filled BHE has been studied by a three-dimensional, steady-state CFD model. The model consists of a 3 m long Borehole containing a single U-pipe with surrounding bedrock. A constant temperature is imposed on the U-pipe wall and the outer bedrock wall is held at a lower constant temperature. The occurring temperature gradient induces a velocity flow in the groundwater-filled Borehole due to density differences. This increases the heat transfer compared to stagnant water. The numerical model agrees well with theoretical studies and laboratory experiments. The result shows that the induced natural convective heat flow significantly decreases the thermal resistance in the Borehole. The density gradient in the Borehole is a result of the heat transfer rate and the mean temperature level in the Borehole water. Therefore in calculations of the thermal resistance in groundwater-filled Boreholes convective heat flow should be included and the actual injection heat transfer rate and mean Borehole temperature should be considered.
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CFD-modelling of natural convection in a groundwater-filled Borehole heat exchanger
Applied Thermal Engineering, 2009Co-Authors: Anna M.k. Gustafsson, Lars Westerlund, Göran HellströmAbstract:In design of ground-source energy systems the thermal erformance of the Borehole heat exchangers is important. In Scandinavia, Boreholes are usually not grouted but left with groundwater to fill the space between heat exchanger pipes and Borehole wall. The common U-pipe arrangement in a groundwater-filled BHE has been studied by a three-dimensional, steady-state CFD model. The model consists of a three meter long Borehole containing a single U-pipe with surrounding bedrock. A constant temperature is imposed on the U-pipe wall and the outer bedrock wall is held at a lower constant temperature. The occurring temperature gradient induces a velocity flow in the groundwater-filled Borehole due to density differences. This increases the heat transfer compared to stagnant water. The numerical model agrees well with theoretical studies and laboratory experiments. The result shows that the induced natural convective heat flow significantly decreases the thermal resistance in the Borehole. The density gradient in the Borehole is a result of the heat transfer rate and the mean temperature level in the Borehole water. Therefore in calculations of the thermal resistance in groundwater filled Boreholes convective heat flow should be included and the actual injection heat transfer rate and mean Borehole temperature should be considered.
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Thermal Response Test – Current Status and World-Wide Application
Proceedings World Geothermal Congress, 2005Co-Authors: Burkhard Sanner, Jeff Spitler, Göran Hellström, Signhild GehlinAbstract:To design Borehole heat exchangers (BHE) for Ground Source Heat Pumps (GSHP) or Underground Thermal Energy Storage (UTES), the knowledge of underground thermal properties is paramount. In small plants (residential houses), these parameters usually are estimated. However, for larger plants (commercial GSHP or UTES) the thermal conductivity should be measured on site. A useful tool to do so is a thermal response test, carried out on a BHE in a pilot Borehole (later to be part of the Borehole field). For a thermal response test, basically a defined heat load is put into the hole and the resulting temperature changes of the circulating fluid are measured. Since late 1990s, this technology became more and more popular, and today is used routinely in many countries for the design of larger plants with BHEs, allowing sizing of the Boreholes based upon reliable underground data. The paper includes a short description of the basic concept and the theory behind the thermal response test, looks at the history of its development, and emphasizes on the worldwide experience with this technology.
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The influence of the thermosiphon effect on the thermal response test
Renewable Energy, 2003Co-Authors: Signhild Gehlin, Göran Hellström, Bo NordellAbstract:The issue of natural and forced groundwater movements, and its effect on the performance of ground heat exchangers is of great importance for the design and sizing of Borehole thermal energy systems (BTESs). In Scandinavia groundwater filled Boreholes in hard rock are commonly used. In such Boreholes one or more intersecting fractures provide a path for groundwater flow between the Borehole and the surrounding rock. An enhanced heat transport then occurs due to the induced convective water flow, driven by the volumetric expansion of heated water. Warm groundwater leaves through fractures in the upper part of the Borehole while groundwater of ambient temperature enters the Borehole through fractures at larger depths. This temperature driven flow is referred to as thermosiphon, and may cause considerable increase in the heat transport from groundwater filled Boreholes. The thermosiphon effect is connected to thermal response tests, where the effective ground thermal conductivity is enhanced by this convective transport. Strong thermosiphon effects have frequently been observed in field measurements. The character of this effect is similar to that of artesian flow through Boreholes.
Lars Westerlund - One of the best experts on this subject based on the ideXlab platform.
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cfd modelling of natural convection in a groundwater filled Borehole heat exchanger
Applied Thermal Engineering, 2010Co-Authors: Annamaria Gustafsson, Lars Westerlund, Göran HellströmAbstract:In design of ground-source energy systems the thermal performance of the Borehole heat exchangers is important. In Scandinavia, Boreholes are usually not grouted but left with groundwater to fill the space between heat exchanger pipes and Borehole wall. The common U-pipe arrangement in a groundwater-filled BHE has been studied by a three-dimensional, steady-state CFD model. The model consists of a 3 m long Borehole containing a single U-pipe with surrounding bedrock. A constant temperature is imposed on the U-pipe wall and the outer bedrock wall is held at a lower constant temperature. The occurring temperature gradient induces a velocity flow in the groundwater-filled Borehole due to density differences. This increases the heat transfer compared to stagnant water. The numerical model agrees well with theoretical studies and laboratory experiments. The result shows that the induced natural convective heat flow significantly decreases the thermal resistance in the Borehole. The density gradient in the Borehole is a result of the heat transfer rate and the mean temperature level in the Borehole water. Therefore in calculations of the thermal resistance in groundwater-filled Boreholes convective heat flow should be included and the actual injection heat transfer rate and mean Borehole temperature should be considered.
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CFD-modelling of natural convection in a groundwater-filled Borehole heat exchanger
Applied Thermal Engineering, 2009Co-Authors: Anna M.k. Gustafsson, Lars Westerlund, Göran HellströmAbstract:In design of ground-source energy systems the thermal erformance of the Borehole heat exchangers is important. In Scandinavia, Boreholes are usually not grouted but left with groundwater to fill the space between heat exchanger pipes and Borehole wall. The common U-pipe arrangement in a groundwater-filled BHE has been studied by a three-dimensional, steady-state CFD model. The model consists of a three meter long Borehole containing a single U-pipe with surrounding bedrock. A constant temperature is imposed on the U-pipe wall and the outer bedrock wall is held at a lower constant temperature. The occurring temperature gradient induces a velocity flow in the groundwater-filled Borehole due to density differences. This increases the heat transfer compared to stagnant water. The numerical model agrees well with theoretical studies and laboratory experiments. The result shows that the induced natural convective heat flow significantly decreases the thermal resistance in the Borehole. The density gradient in the Borehole is a result of the heat transfer rate and the mean temperature level in the Borehole water. Therefore in calculations of the thermal resistance in groundwater filled Boreholes convective heat flow should be included and the actual injection heat transfer rate and mean Borehole temperature should be considered.
Jeffrey D Spitler - One of the best experts on this subject based on the ideXlab platform.
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reference data sets for vertical Borehole ground heat exchanger models and thermal response test analysis
Geothermics, 2011Co-Authors: Richard A. Beier, Marvin D Smith, Jeffrey D SpitlerAbstract:Abstract Ground source heat pump systems often use vertical Boreholes to exchange heat with the ground. Two areas of active research are the development of models to predict the thermal performance of vertical Boreholes and improved procedures for analysis of in situ thermal conductivity tests, commonly known as thermal response tests (TRT). Both the models and analysis procedures ultimately need to be validated by comparing them to actual Borehole data sets. This paper describes reference data sets for researchers to test their Borehole models. The data sets are from a large laboratory “sandbox” containing a Borehole with a U-tube. The tests are made under more controlled conditions than can be obtained in field tests. Thermal response tests on the Borehole include temperature measurements on the Borehole wall and within the surrounding soil, which are not usually available in field tests. The test data provide independent values of soil thermal conductivity and Borehole thermal resistance for verifying Borehole models and TRT analysis procedures. As an illustration, several Borehole models are compared with one of the thermal response tests.
J. P. Greenhouse - One of the best experts on this subject based on the ideXlab platform.
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Improved resolution of ambient flow through fractured rock with temperature logs
Ground Water, 2010Co-Authors: P. E. Pehme, James A. Cherry, B. L. Parker, J. P. GreenhouseAbstract:In contaminant hydrogeology, investigations at fractured rock sites are typically undertaken to improve understanding of the fracture networks and associated groundwater flow that govern past and/or future contaminant transport. Conventional hydrogeologic, geophysical, and hydrophysical techniques used to develop a conceptual model are often implemented in open Boreholes under conditions of cross-connected flow. A new approach using high-resolution temperature (+/-0.001 degrees C) profiles measured within static water columns of Boreholes sealed using continuous, water-inflated, flexible liners (FLUTe) identifies hydraulically active fractures under ambient (natural) groundwater flow conditions. The value of this approach is assessed by comparisons of temperature profiles from holes (100 to 200 m deep) with and without liners at four contaminated sites with distinctly different hydrogeologic conditions. The results from the lined holes consistently show many more hydraulically active fractures than the open-hole profiles, in which the influence of vertical flow through the Borehole between a few fractures masks important intermediary flow zones. Temperature measurements in temporarily sealed Boreholes not only improve the sensitivity and accuracy of identifying hydraulically active fractures under ambient conditions but also offer new insights regarding previously unresolvable flow distributions in fractured rock systems, while leaving the Borehole available for other forms of testing and monitoring device installation.
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The active line source temperature logging technique and its application in fractured rock hydrogeology
Journal of Environmental & Engineering Geophysics, 2007Co-Authors: P. E. Pehme, J. P. Greenhouse, Beth L. ParkerAbstract:We present a technique for placing a Borehole into thermal dis-equilibrium, and thereby interpreting groundwater flow through fractures where it may have been previously undetected. Denoted as Active Line Source (ALS) logging, the method consists of temperature logging while a Borehole is heated by the cable and/or during cooling after the heating. With two or more logs collected during either heating or cooling, an estimate of thermal conductivity is obtained. The basic theory, widely used for such things as thermal conductivity probes, is shown to fit the recorded data well. The mechanics of ALS logging are described, and the practical challenges are outlined. In the absence of groundwater flow in or around the Borehole, variations in the thermal conductivity of the rock are largely due to variable water content and the ALS log provides a reasonable surrogate for the neutron log. When groundwater flow dominates the dissipation of thermal energy from the Borehole, however, the apparent thermal conductivity is increased. In open Boreholes this flow can be both ambient (within the formation itself) and connecting (vertical flow between fractures intersected by the Borehole). In cased or lined holes with no connecting flow, ALS logs are particularly useful as detectors of ambient groundwater flow. Alternative methods for flow detection, such as chemical dilution or flow-meters, require an open Borehole and either have poor vertical resolution or require multiple stationary' measurements, often with packers to minirrllze the effects of connecting flow. The ALS technique is a comparatively simple tool, useful in both open and cased or lined Boreholes, run continuously down the length of the Borehole, with fracture resolution on the order of a few centimeters. We describe ALS logging of a 75-meter section of a Borehole through fractured dolomite which has been lined with a FLUTe sleeve. The ALS results are compared to the geologic units encountered, conventional geophysical logging techniques, time-lapse passive temperature logging, heat pulse flowmeter data and packer testing.
Richard A. Beier - One of the best experts on this subject based on the ideXlab platform.
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Horizontal Borehole Study
2020Co-Authors: Richard A. Beier, William A. HollowayAbstract:Summary Ten horizontal Boreholes have been drilled to determine if thermal performance varies between Boreholes with bentonite grout and those without grout. If grout is not used, drilling mud and cuttings remain in the Borehole. All the Boreholes pass through clay soil at a site in Stillwater, Oklahoma. The thermal performance has been quantified by performing an in-situ thermal response test on each Borehole. The in-situ test provides estimates of Borehole resistance and soil thermal conductivity. Boreholes with bentonite grout have a mean Borehole resistance of 0.344 Btu/(hr-ft-°F), while Boreholes without grout have a mean resistance of 0.366 Btu/(hr-ft-°F). The difference in these values is too small to be statistically significant. Thus, as a group the Boreholes with grout perform about the same as the Boreholes without grout. Also, the average Borehole resistance in these horizontal Boreholes is slightly smaller than the value found in a comparably completed nearby vertical Borehole. We plan to retest the Boreholes after one year has passed to check for any changes with time.
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Vertical temperature profiles and Borehole resistance in a U-tube Borehole heat exchanger
Geothermics, 2012Co-Authors: Richard A. Beier, José Acuña, Palne Mogensen, Björn PalmAbstract:The design of ground source heat pump systems requires values for the ground thermal conductivity and the Borehole thermal resistance. In situ thermal response tests (TRT) are often performed on vertical Boreholes to determine these parameters. Most TRT analysis methods apply the mean of the inlet and outlet temperatures of the circulating fluid along the entire Borehole length. This assumption is convenient but not rigorous. To provide a more general approach, this paper develops an analytical model of the vertical temperature profile in the Borehole during the late-time period of the in situ test. The model also includes the vertical temperature profile of the undisturbed ground. The model is verified with distributed temperature measurements along a vertical Borehole using fiber optic cables inside a U-tube for the circulating fluid. The Borehole thermal resistance is calculated without the need for the mean temperature approximation. In the studied Borehole, the mean temperature approximation overestimates the Borehole resistance by more than 20%.
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reference data sets for vertical Borehole ground heat exchanger models and thermal response test analysis
Geothermics, 2011Co-Authors: Richard A. Beier, Marvin D Smith, Jeffrey D SpitlerAbstract:Abstract Ground source heat pump systems often use vertical Boreholes to exchange heat with the ground. Two areas of active research are the development of models to predict the thermal performance of vertical Boreholes and improved procedures for analysis of in situ thermal conductivity tests, commonly known as thermal response tests (TRT). Both the models and analysis procedures ultimately need to be validated by comparing them to actual Borehole data sets. This paper describes reference data sets for researchers to test their Borehole models. The data sets are from a large laboratory “sandbox” containing a Borehole with a U-tube. The tests are made under more controlled conditions than can be obtained in field tests. Thermal response tests on the Borehole include temperature measurements on the Borehole wall and within the surrounding soil, which are not usually available in field tests. The test data provide independent values of soil thermal conductivity and Borehole thermal resistance for verifying Borehole models and TRT analysis procedures. As an illustration, several Borehole models are compared with one of the thermal response tests.