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.

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>

Failure Analysis of Heat Exchangers

2021 ◽  
pp. 3-19
Author(s):  
Dusan P. Sekulic
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Failure Analysis ◽  
Thermal Energy ◽  
Solid Surface ◽  
Heat Exchangers ◽  
Heat Transfer Surface ◽  
Tubular Heat Exchanger ◽  
Erosion Corrosion ◽  
Different Temperatures

Abstract Heat exchangers are devices used to transfer thermal energy between two or more fluids, between a solid surface and a fluid, or between a solid particulate and a fluid at different temperatures. This article first addresses the causes of failures in heat exchangers. It then provides a description of heat-transfer surface area, discussing the design of the tubular heat exchanger. Next, the article discusses the processes involved in the examination of failed parts. Finally, it describes the most important types of corrosion, including uniform, galvanic, pitting, stress, and erosion corrosion.

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.

Numerical simulation of flow distribution in the header of plate-fin heat exchanger

2020 ◽  
Vol 34 (14n16) ◽  
pp. 2040111
Author(s):  
Shu-Ling Tian ◽  
Ying-Ying Shen ◽  
Yao Li ◽  
Hai-Bo Wang ◽  
Sheryar Muhammad ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Fluid Flow ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Optimization Design ◽  
High Efficiency ◽  
Flow Distribution ◽  
Optimal Number ◽  
Compact Structure ◽  
Flow Maldistribution

Plate-fin heat exchangers are widely used in industry at present due to their compact structure and high efficiency. However, there is a problem of flow maldistribution, resulting in poor performance of heat exchangers. The influence of the header configuration on fluid flow distribution is studied by using CFD software FLUENT. The numerical results show that the fluid flow inside the header is seriously uneven. The reliability of the numerical simulation is validated against the published results. They are found to be basically consistent within considerable error. The optimal number of the punch baffle is investigated. Various header configuration with different opening ratios have been studied under the same boundary conditions. The gross flow maldistribution parameter (S) is used to evaluate flow nonuniformity, and the flow maldistribution parameters of different schemes under different Reynolds numbers are listed and compared. The optimal header with minimum flow maldistribution parameter is obtained through the performance analysis of headers. It is found that the flow maldistribution of the improved header is significantly smaller compared with the conventional header. Hence, the efficiency of the heat exchanger is effectively enhanced. The conclusion provides a reference for the optimization design of plate-fin heat exchanger.

scholarly journals Seasonal High Temperature Heat Storage with Medium Deep Borehole Heat Exchangers

2015 ◽  
Vol 76 ◽  
pp. 351-360 ◽  
Author(s):  
Kristian Bär ◽  
Wolfram Rühaak ◽  
Bastian Welsch ◽  
Daniel Schulte ◽  
Sebastian Homuth ◽  
...  
Keyword(s):  
High Temperature ◽  
Heat Exchangers ◽  
Heat Storage ◽  
Deep Borehole ◽  
Temperature Heat ◽  
Borehole Heat Exchangers

scholarly journals The influence of main parameters of regenerative heat exchanger on its energy efficiency

2020 ◽  
Vol 178 ◽  
pp. 01024
Author(s):  
Nikolay Monarkin ◽  
Anton Sinitsyn ◽  
Mikhail Pavlov ◽  
Timur Akhmetov
Keyword(s):  
Energy Efficiency ◽  
Heat Capacity ◽  
Heat Exchanger ◽  
Wall Thickness ◽  
Thermal Energy ◽  
Thermal Efficiency ◽  
Heat Exchangers ◽  
Regenerative Heat ◽  
Flow Through ◽  
Geometric Length

The influence of various parameters of stationary switching regenerative heat exchangers used for ventilation on its thermal efficiency was studied. Considered are the geometric (length, diameter and wall thickness of a single equivalent nozzle channel), thermophysical (density and heat capacity of the nozzle material) and operation (air flow through the regenerator and the time of one stage of accumulation/regeneration of thermal energy) parameters.

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