Geotechnical Considerations in the Design of Borehole Heat Exchangers

2020 ◽  
Author(s):  
Despina Maria Zymnis ◽  
Andrew J. Whittle
Keyword(s):  
Heat Exchanger ◽  
Parametric Study ◽  
Heat Exchangers ◽  
Design Parameters ◽  
Ground Source Heat Pumps ◽  
Heat Exchanger Design ◽  
Heating And Cooling ◽  
Adjacent Structures ◽  
Borehole Heat Exchangers

The use of ground source heat pumps to transfer heat to and from the ground via borehole heat exchangers (BHE) is among the most energy efficient techniques for space heating and cooling. Broader applications in urban environments require more careful evaluation of hydro-mechanical behavior of soil to ensure their reliable long-term performance and to minimize adverse effects on adjacent structures. An advanced soil model has been integrated within a finite difference (FD) framework, to solve coupled thermo-hydro-mechanical (THM) problems in an axisymmetric space. The FD simulator is applied to a prototype project and the ground conditions represent typical stress history profiles found in Geneva, Switzerland. An extensive parametric study is undertaken to study the long-term THM response of clay for a broad range of heat exchanger design parameters. The results show that significant settlements can be induced due to the long-term operation of BHEs (i.e., over periods from 10–50 years). The parametric study gives useful guidelines for heat exchanger design and identifies a design space of optimum solutions that meet pre-specified foundation settlement criteria. The study provides a qualitative investigation and a systematic framework for analyzing the long-term THM response of clay to seasonal heating and cooling.

The Concept of Irreversibility in Heat Exchanger Design: Counterflow Heat Exchangers for Gas-to-Gas Applications

1977 ◽  
Vol 99 (3) ◽  
pp. 374-380 ◽  
Author(s):  
A. Bejan
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Design Method ◽  
Thermal Design ◽  
Design Parameters ◽  
Regenerative Heat ◽  
Pressure Drops ◽  
Heat Exchanger Design ◽  
Thermodynamic Irreversibility ◽  
Useful Power

The thermal design of counterflow heat exchangers for gas-to-gas applications is based on the thermodynamic irreversibility rate or useful power no longer available as a result of heat exchanger frictional pressure drops and stream-to-stream temperature differences. The irreversibility (entropy production) concept establishes a direct relationship between the heat exchanger design parameters and the useful power wasted due to heat exchanger nonideality. The paper presents a heat exchanger design method for fixed or for minimum irreversibility (number of entropy generation units NS). In contrast with traditional design procedures, the amount of heat transferred between streams and the pumping power for each side become outputs of the NS design approach. To illustrate the use of this method, the paper develops the design of regenerative heat exchangers with minimum heat transfer surface and with fixed irreversibility NS.

Deformations and permeability variations in fine sediments induced by freezing-thawing cycles caused by borehole heat exchangers

2021 ◽  
Author(s):  
Giorgia Dalla Santa ◽  
Simonetta Cola ◽  
Antonio Galgaro
Keyword(s):  
Heat Exchanger ◽  
Pore Size ◽  
Heat Exchangers ◽  
Heat Extraction ◽  
Water Salinity ◽  
Cohesive Sediments ◽  
Borehole Heat Exchanger ◽  
Freeze Thaw ◽  
Vertical Permeability ◽  
Borehole Heat Exchangers

<p>In closed-loop Ground Source Heat Pump system, the circulation of a heat-carrier fluid into the heat exchanger provides the thermal exchange with the underground.</p><p>In order to improve the heat extraction from the ground, the fluid temperature is often lowered down to subzero temperatures; as a consequence, the thermal alteration induced in the ground is more intense and can cause freezing processes in the surroundings. In sediments with significant clay fraction, the inner structure and the pore size distribution are irreversibly altered by freezing-thawing cycles.</p><p>A wide laboratory program has been performed in order to measure the induced deformations and the permeability variations under different conditions of mechanical loads/depth [1], interstitial water salinity [2] and soil plasticity [3]. In addition, vertical deformations and permeability variations induced by freeze-thaw cycles have been measured also in Over-Consolidated silty clays at different OCR [4].</p><p>The results suggest that, despite the induced frozen condition is quite confined close to the borehole [5], in Normal-Consolidated silty clay layers the freezing-thawing-cycles induce an irreversible settlement up to 16%, gathered cycle-after cycle depending on sediment plasticity, pore fluid salinity and applied load. In addition, despite the overall contraction of the soil, the vertical hydraulic conductivity may increase by about 8 times due to a remarkable modification of the soil fabric with increases in pore size, pores connectivity and orientation [6].</p><p>The OC silty-clays show an opposite behavior. Experimental results point out that, in case of OC deposits, higher the OCR lower the freeze-thaw induced settlement. In case of OCR > 15, the settlement turns to a slight expansion. Conversely, the observed augment in vertical permeability increases with the OCR degree [4].</p><p>These occurrences are significant and irreversible and could affect the functionality of the system as well as lead to environmental effects such as local settlements, negative friction on the borehole heat exchangers or interconnection among aquifers in the probe surroundings.</p><ul><li>[1]. Dalla Santa G*, Galgaro A, Tateo F, Cola S (2016). Modified compressibility of cohesive sediments induced by thermal anomalies due to a borehole heat exchanger. <strong>Engineering Geology</strong> 202, 143-152.</li> <li>[2]. Dalla Santa G*, Galgaro A, Tateo F, Cola S (2016). Induced thermal compaction in cohesive sediments around a borehole heat exchanger: laboratory tests on the effect of pore water salinity. <strong>Environmental Earth Sciences</strong>, 75(3), 1-11.</li> <li>[3]. Cola S, Dalla Santa G, Galgaro A (2020). Geotechnical hazards caused by freezing-thawing processes induced by borehole heat exchangers. <strong>Lecture Notes in Civil Engineering</strong>, 40, pp. 529–536</li> <li>[4]. Dalla Santa G, Cola S, Galgaro A (2021). Deformation and Vertical Permeability Variations Induced by Freeze-Thaw Cycles in Over-Consolidated Silty Clays. <strong>Challenges and Innovations in Geomechanics</strong>, 117</li> <li>[5]. Dalla Santa G*, Farina Z, Anbergen H, Rühaak W, Galgaro A (2019). A Comparative Study on the Relevance of Computing Freeze-Thaw Effects for Borehole Heat Exchanger Modelling. <strong>Geothermics</strong> 79, 164-175.</li> <li>[6]. Dalla Santa G*, Cola S, Secco M, Tateo F, Sassi R, Galgaro A (2019). Multiscale analysis of freeze-thaw effects induced by ground heat exchangers on permeability of silty-clays. <strong>Geotechnique</strong> 2019, 69(2).</li> </ul>

scholarly journals Simulation of the effectiveness of longitudinal rectangular fins on the efficiency of the double pipe heat exchanger

2019 ◽  
Vol 21 (4) ◽  
pp. 48-57
Author(s):  
N. F. Timerbaev ◽  
A. K. Ali ◽  
Omar Abdulhadi Mustafa Almohamed ◽  
A. R. Koryakin
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Cold Water ◽  
Tube Diameter ◽  
Hot Water ◽  
Outer Tube ◽  
Design Parameters ◽  
Double Pipe ◽  
Central Pipe ◽  
Pipe Heat

In this article, a mathematical simulation of a double pipe heat exchanger is carried out, having the longitudinal rectangular fins with the dimension of (2*3*1000) mm, mounted on the outer surface of the inner tube of the heat exchanger. In this paper, the advantage of using of that type of fins and its effect on the effectiveness of the heat exchanger are studied with the help of the computer program. The carried out research allowsmaking the calculation to find the optimum design parameters of heat exchangers. The outer tube diameter is (34.1mm) while the inner tube diameter is (16.05mm). The tubes wall thickness is (1.5mm) and the model length was (1 m). The hot water is flowing through the inner tube in parallel with the cold water that passing the outer tube. The hot and cold water temperature at the inlet is (75°C & 30°C) respectively. The mass flow rate inside the central pipe is (0.1 kg/s) while the annular pipe carrying (0.3 kg/s). In the present work, the program ANSYS Workbench 15.0 was used to find out the results of heat transfer as well as the behavior of liquids inside the heat exchangers.

Basis of the Tubesheet Heat Exchanger Design Rules Used in the French Pressure Vessel Code

1992 ◽  
Vol 114 (1) ◽  
pp. 124-131 ◽  
Author(s):  
F. Osweiller
Keyword(s):  
Heat Exchanger ◽  
Pressure Vessel ◽  
Heat Exchangers ◽  
Tube Bundle ◽  
Outer Edge ◽  
Design Rules ◽  
Effective Elastic Constants ◽  
Heat Exchanger Design ◽  
Solid Plate ◽  
Main Basis

For about 40 years most tubesheet exchangers have been designed according to the standards of TEMA. Partly due to their simplicity, these rules do not assure a safe heat-exchanger design in all cases. This is the main reason why new tubesheet design rules were developed in 1981 in France for the French pressure vessel code CODAP. For fixed tubesheet heat exchangers, the new rules account for the “elastic rotational restraint” of the shell and channel at the outer edge of the tubesheet, as proposed in 1959 by Galletly. For floating-head and U-tube heat exchangers, the approach developed by Gardner in 1969 was selected with some modifications. In both cases, the tubesheet is replaced by an equivalent solid plate with adequate effective elastic constants, and the tube bundle is simulated by an elastic foundation. The elastic restraint at the edge of the tubesheet due the shell and channel is accounted for in different ways in the two types of heat exchangers. The purpose of the paper is to present the main basis of these rules and to compare them to TEMA rules.

A Heuristic for Designing Hybrid Compact Heat Exchangers for Nuclear Applications

2021 ◽  
Author(s):  
Venkata Rajesh Saranam ◽  
Peter Carter ◽  
Kyle Rozman ◽  
Ömer Dogan ◽  
Brian K. Paul
Keyword(s):  
Heat Exchanger ◽  
Diffusion Bonding ◽  
Heat Exchangers ◽  
Nuclear Power ◽  
Nuclear Industry ◽  
Compact Heat Exchangers ◽  
Bonding Parameters ◽  
Heat Exchanger Design ◽  
Creep Fatigue ◽  
Gen Iv

Abstract Hybrid compact heat exchangers (HCHEs) are a potential source of innovation for intermediate heat exchangers in nuclear industry, with HCHEs being designed for Gen-IV nuclear power applications. Compact heat exchangers are commonly fabricated using diffusion bonding, which can provide challenges for HCHEs due to resultant non-uniform stress distributions across hybrid structures during bonding, leading to variations in joint properties that can compromise performance and safety. In this paper, we introduce and evaluate a heuristic for determining whether a feasible set of diffusion bonding conditions exist for producing HCHE designs capable of meeting regulatory requirements under nuclear boiler and pressure vessel codes. A diffusion bonding model for predicting pore elimination and structural analyses are used to inform the heuristic and a heat exchanger design for 316 stainless steel is used to evaluate the efficacy of the heuristic to develop acceptable diffusion bonding parameters. A set of diffusion bonding conditions were identified and validated experimentally by producing various test coupons for evaluating bond strength, ductility, porosity, grain size, creep rupture, creep fatigue and channel deviation. A five-layer hybrid compact heat exchanger structure was fabricated and tensile tested demonstrating that the bonding parameters satisfy all criteria in this paper for diffusion bonding HCHEs with application to the nuclear industry.

The Deeper the Better? A Thermogeological Analysis of Medium-deep Borehole Heat Exchanger Efficiency in Crystalline Rocks

2022 ◽  
Author(s):  
Kaiu Piipponen ◽  
Annu Martinkauppi ◽  
Sami Vallin ◽  
Teppo Arola ◽  
Nina Leppäharju ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Heat Exchanger ◽  
Thermal Energy ◽  
Heat Production ◽  
Heat Exchangers ◽  
Energy Production ◽  
Crystalline Rocks ◽  
Deep Borehole ◽  
Deep Well ◽  
Borehole Heat Exchangers

Abstract The energy sector is undergoing a fundamental transformation, with significant investment in low-carbon technologies to replace fossil-based systems. In densely populated urban areas, deep boreholes offer an alternative over shallow geothermal systems, which demand extensive surface area to attain large-scale heat production. This paper presents numerical calculations of the thermal energy that can be extracted from the medium-deep borehole heat exchangers of depths ranging from 600-3000 m. We applied the thermogeological parameters of three locations across Finland and tested two types of coaxial borehole heat exchangers to understand better the variables that affect heat production in low permeability crystalline rocks. For each depth, location, and heat collector type, we used a range of fluid flow rates to examine the correlation between thermal energy production and resulting outlet temperature. Our results indicate a trade-off between thermal energy production and outlet fluid temperature depending on the fluid flow rate, and that the vacuum-insulated tubing outperforms high-density polyethylene pipe in energy and temperature production. In addition, the results suggest that the local thermogeological factors impact heat production. Maximum energy production from a 600-m-deep well achieved 170 MWh/a, increasing to 330 MWh/a from a 1000-m-deep well, 980 MWh/a from a 2-km-deep well, and up to 1880 MWh/a from a 3-km-deep well. We demonstrate that understanding the interplay of the local geology, heat exchanger materials, and fluid circulation rates is necessary to maximize the potential of medium-deep geothermal boreholes as a reliable long-term baseload energy source.

scholarly journals Method of Averaging the Effective Thermal Conductivity Based on Thermal Response Tests of Borehole Heat Exchangers

Energies ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3737
Author(s):  
Aneta Sapińska-Śliwa ◽  
Tomasz Sliwa ◽  
Kazimierz Twardowski ◽  
Krzysztof Szymski ◽  
Andrzej Gonet ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Exchanger ◽  
Effective Thermal Conductivity ◽  
Heat Exchangers ◽  
Thermal Response ◽  
Method Of Averaging ◽  
Thermal Response Test ◽  
Borehole Heat Exchanger ◽  
Measurement Results ◽  
Borehole Heat Exchangers

This work concerns borehole heat exchangers and their testing using apparatus for thermal response tests. In the theoretical part of the article, an equation was derived from the known equation of heat flow, on which the interpretation of the thermal response test was based. The practical part presents the results of several measurements taken in the AGH Laboratory of Geoenergetics. They were aimed at examining the potential heat exchange capacity between the heat carrier and rock mass. Measurement results in the form of graphs are shown in relation to the examined, briefly described wells. Result analysis made it possible to draw conclusions regarding the interpretation of the thermal response test. The method of averaging the measurement results was subjected to further study. The measuring apparatus recorded data at a frequency of one second, however such accuracy was too large to be analyzed efficiently. Therefore, an average of every 1 min, every 10 min, and every 60 min was proposed. The conclusions stemming from the differences in the values of effective thermal conductivity in the borehole heat exchanger, resulting from different data averaging, were described. In the case of three borehole heat exchangers, ground properties were identical. The effective thermal conductivity λeff was shown to depend on various borehole heat exchanger (BHE) designs, heat carrier flow geometry, and grout parameters. It is important to consider the position of the pipes relative to each other. As shown in the charts, the best (the highest) effective thermal conductivity λeff occurred in BHE-1 with a coaxial construction. At the same time, this value was closest to the theoretical value of thermal conductivity of rocks λ, determined on the basis of literature. The standard deviation and the coefficient of variation confirmed that the effective thermal conductivity λeff, calculated for different time intervals, showed little variation in value. The values of effective thermal conductivity λeff for each time interval for the same borehole exchanger were similar in value. The lowest values of effective thermal conductivity λeff most often appeared for analysis with averaging every 60 min, and the highest—for analysis with averaging every 1 min. For safety reasons, when designing (number of BHEs), safer values should be taken for analysis, i.e., lower, averaging every 60 min.

scholarly journals Finite element modeling of geothermal source of heat pump in long-term operation

2020 ◽  
Vol 154 ◽  
pp. 04003
Author(s):  
Elżbieta Hałaj
Keyword(s):  
Finite Element ◽  
Heat Source ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Transport Model ◽  
Heat Pumps ◽  
Initial Temperature Distribution ◽  
Term Operation ◽  
Borehole Heat Exchangers

Heat pumps become more and more popular heat source. They can be an alternative choice for obsolete coal fired boilers which are emissive and not ecological. During heat pump installation designing process, especially for heat pumps with higher heating capacity (for example those suppling larger buildings), a simulation of heat balance of ground heat source must be provided. A 3D heat transport model and groundwater flow in the geothermal heat source for heat pump (GSHP) installation was developed in FEFLOW according to Finite Element Modelling Method. The model consists of 25 borehole heat exchangers, arranged with spacing recommended by heat pump branch guidelines. The model consists of both a homogeneous, non-layered domain and a layered domain, which reflected differences in thermal properties of the ground and hydrogeological factors. The initial temperature distribution in the ground was simulating according to conditions typical for Europe in steady state heat flow. Optimal mesh refinement for nodes around borehole heat exchangers were calculated according to Nillert method. The aim of this work is to present influence of geological, hydrogeological factors and borehole arrangement in the energy balance and long term sustainability of the ground source. The thermal changes in the subsurface have been determined for a long term operation (30 years of operation period). Some thermal energy storage applications have also been considered.

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