Geothermics最新文献

In this study, we investigate the enhancement of horizontal geothermal heat exchangers equipped with helical fins on the pipe's exterior and internally ribbed turbulators. Our approach focuses on the interplay between geometry and thermal efficiency through innovative design modifications. Utilizing the finite element method, three-dimensional numerical simulations assessed the effects of varying geometric parameters such as the diameter and thickness of the fins. Our findings indicate significant increases in heat transfer efficiency with the addition of helical fins; specifically, increasing the fin diameter from 5 mm to 10 mm results in a 15 % increase in the heat transfer rate, while doubling the fin thickness from 2 mm to 4 mm enhances the rate by 10 %. These improvements are due to the expanded surface area facilitating greater heat exchange. Optimization using the desirability function approach yielded models with high performance, achieving desirability scores of 0.9879 for outlet temperature and 0.9534 for the heat transfer coefficient. This reflects the effective tuning of geometric parameters to maximize thermal performance. The study also introduces two predictive mathematical models for the outlet temperature and convective heat transfer coefficient of the U-shaped pipe equipped with these enhancements. These models, derived from extensive numerical data, provide practical tools for future design and operational applications of geothermal heat exchangers. This research advances the design and operational efficiency of geothermal heat exchange systems, establishing new benchmarks for thermal efficiency in the field with actionable insights and robust mathematical tools.

Effectively describing the heat transfer process of ground heat exchangers is crucial for fully utilizing geothermal energy. The current progress in heat transfer analysis models is to divide the soil into several non-isothermal soil layers based on the assumption of uniform borehole wall temperature and heat flux in traditional models, but the temperature and heat flux inside the layers are uniform. Rarely consider the non-uniformity of heat flux within the layer and the boundary problem of vertical heat flux at the ground level. This article adopts a composite medium method to modify the segmented model, considering the heat transfer problem between soil layers. The assumption of uniform temperature of the borehole wall was removed to improve the fluid analysis model. Afterwards, analyze the impact of the heat transfer process inside and outside the borehole on the heat flux of the borehole wall. Using the segmented trial-and-error technique to couple the fluid and soil heat transfer models, a new comprehensive model of the U-shaped grounded heat exchanger was established. Conducted initial underground soil temperature distribution and thermal response tests in different geomorphic units in Guanzhong, Shaanxi, and verified the model's reliability based on experimental data. Analyze three influencing factors, namely fluid mass flow rate, initial underground soil temperature considering variable temperature layer, and temperature difference between average initial underground soil temperature and inlet fluid temperature, to evaluate system performance. The results indicate that the recommended range of fluid mass flow rate in the Guanzhong region is 0.32–0.42 kg/s. It was found that the heat transfer capacity of the heat exchanger will be underestimated if it ignores the influence of the variable temperature layer. Furthermore, the determination of the heat extraction result is not due to the high inlet fluid temperature but rather to the high difference between the inlet fluid temperature and the initial underground soil temperature. This study can promote better system design and achieve higher system performance.

This study explores the Linyi geothermal field, located in Shandong Province, China, characterized by its non-magmatic, active fault-controlled geothermal system. Utilizing a combination of geochemical analyses, temperature measurements, and numerical simulations, a detailed genetic model of the geothermal system has been developed. The analysis included extensive water geochemical and isotopic characterization to determine reservoir temperature, depth, and origin of the geothermal waters. The thermal-hydro coupling model was integrated with these data to refine the thermal distribution and assess the evolutionary dynamics of the geothermal system. Our findings indicate that the geothermal anomalies in the Linyi field are predominantly controlled by hydrothermal convection within the Ordovician and Cambrian carbonate layers, facilitated by the high permeability of the Yishu Fault. The fault acts as a crucial conduit for meteoric water recharge, which undergoes significant heating due to the geothermal gradient in deeper rock formations. Isotopic analyses of hydrogen and oxygen revealed the meteoric origin of the geothermal waters, with recharge likely originating from the nearby Yimeng Mountains. Furthermore, the study established a conceptual evolutionary model to understand the mechanisms driving the geothermal resource development in the area. It was determined that the geothermal resources are typically fault-controlled, with significant potential for further exploration due to the identified hydrothermal anomalies at the fault's footwall. The model predicts the preservation of heated meteoric water in the reservoir rock for periods ranging from 10 to 50 thousand years, providing a sustainable source of geothermal energy. This comprehensive approach not only enhances the understanding of the heat accumulation mechanism but also highlights the potential for optimizing geothermal exploration strategies within fault-controlled geothermal systems.

This study examines the impact of polyphase tectonics on the development of structurally controlled hydrothermal fluid pathways in carbonate geothermal reservoirs. Our case study focuses on hydrothermal carbonate veins and vein-filled faults in Devonian carbonates from the North Rhine-Westphalia region in western Germany, currently being explored as a potential low-enthalpy geothermal reservoir at depths of 4–5 km. These veins, which can be up to 20 m thick, are subvertical and strike NNW, N, or ESE. They exhibit pinch-and-swell undulating geometries, faulted vein-wall contacts, and occasional fillings of hydrothermal breccias. Vein-filled normal faults show hybrid shear-dilatant openings, with fault tips characterized by horsetail vein terminations. The textures, orientations, and age of the veins suggest their formation at low confining pressures and at depths < 2 km during the Post-Variscan East-West extension. Orthogonal North- and East-striking strike slip faults, inherited from the Variscan orogeny, were likely reactivated during post-Variscan extension, with a significant dilatant component that formed the observed veins. In the Ruhr Basin, the dilation tendency analysis indicates that NNW-striking veins or joints are optimally oriented for re-opening under the current strike-slip stress regime, characterized by NNW-trending maximum horizontal stress. The intersections of fractures may currently create moderately SSE-plunging linear zones of enhanced fluid flow. The main uncertainty regards the presence of similar structures at geothermal reservoir depths of ∼4–5 km in the Middle Devonian carbonates underneath the Ruhr Basin. As the study veins are likely to have formed at depths <2 km, the existence of analogous dilatant conduits at greater depths remains speculative. Eventually, we propose that zones characterized by open discontinuities and channelized fluid flow in carbonate geothermal reservoir in strike-slip tectonic settings can be: (a) dilational jogs between overlapping strike-slip faults, (b) bends along faults, and (c) strike-slip fault terminations with horsetail extensional structures. These zones can also be prone to enhanced karstification.

This research focuses on the question of how geothermal energy public perception is formed within a national context where news media do not pay attention to geothermal energy, and there is no active opposition to geothermal energy. The research builds on theoretical underpinnings of heuristics in energy perceptions and highlights the importance of physical experiences and associations as sources of experiential learning. Through a survey conducted among members of the general public in Slovenia, the role of thermal water recreation in shaping public perception of geothermal energy is empirically tested. The results show that, in this context, geothermal energy is highly positively assessed compared to hydro energy and nuclear energy, and that there is a correlation between frequency of thermal recreation and certain aspects of public perception of geothermal energy. The policy implications go beyond the simple recommendation of including tourism in public awareness campaigns but point to the specific vulnerability of energy acceptance in this context, where perceptions are formed based on “thinking fast”, and where the media and the public discourse on geothermal energy have not (yet) considered the potential risks and opposition to geothermal projects.

Understanding stakeholders’ needs is crucial for promoting geothermal energy usage and gaining social acceptance. While local people are the key stakeholders in many geothermal projects, other groups have the potential to become directly or indirectly involved, even if they are initially unfamiliar with geothermal power generation. Variability in respondents’ knowledge and the uncertain and biased information associated with geothermal energy make it difficult to extract stakeholders’ needs when formulating a communication strategy. To evaluate stakeholders’ latent needs without providing respondents with detailed information of geothermal energy, this study develops a survey method using conjoint analysis. A web-based questionnaire survey conducted in Japan asked respondents to rank their preferences among seven power generation methods and various electricity supply conditions, which provided the factors necessary to evaluate the latent needs relating to each type of power generation. Subject knowledge is found to be lower for geothermal power generation than for the other power generation methods, although geothermal energy performs well in terms of both expressed and latent needs. Obvious differences in relative preferences among the other power generation methods are also revealed. The proposed method supports both local and outside stakeholders in identifying the various effects of geothermal projects and expressing their needs without undue burden. It is hoped that this approach will encourage stakeholders to understand each other, discuss which advantages/disadvantages of geothermal projects they can accept, and design a sustainable society that incorporates geothermal energy.

The Xianshuihe fault zone (XSFZ), which is characterized by intense tectonic activities, frequent earthquakes and great number of hot springs, has significant potential for exploiting geothermal resources. Previous studies primarily focus on certain hydrothermal systems in southeastern segment of XSFZ, such as Kangding hydrothermal system, but lack the synthetical comparison and systematic analysis of geothermal waters along the XSFZ. Based on detailed geological investigation, the XSFZ hydrothermal system has divided into six geothermal activity areas: Luhuo (LH), Daofu (DF), Qianning-Bamei (QB), Yalahe-Zhonggu (YZ), Kangding (KD) and Moxi (MX). According to the ⁸⁷Sr/⁸⁶Sr ratios and elements behaving in water-rock interactions, the dissolution of silicate minerals is the primarily source of the hydrogeochemical compositions in geothermal waters. The δ_D and δ¹⁸O composition indicate that geothermal waters primarily originated from meteoric waters, but also affected by deep fluids. However, the contribution of deep fluids to the southeastern geothermal areas (YZ, KD and MX) with high concentrations of Cl^- is greater than that of the northwestern (LH, DF and QB). The reservoir temperatures and chlorine-enthalpy model reveal that there are three distinct geothermal systems along the XSFZ: YZ and KD geothermal waters are originated from a common deep reservoir (R1), MX are from R3, and LH, DF, and QB are from R4. Due to the uneven thermal structural distribution along XSFZ, the southeastern segments generated stronger thermal stress and have more frequent earthquake occurrence. Thus, the study of geothermal waters along XSFZ can provide valuable insights into deep tectonic activities and geochemical indicators of earthquake monitoring in the region.

Understanding the temperature-dependent shear failure behavior of rock under compression-shear loads is significant for evaluating the stability of deep surrounding rock with high temperature. In this study, a series of variable angle shear (VAS) tests, were conducted on cubic granite specimens exposed to different high temperatures, observed by two-dimensional digital image correlation (2D-DIC) technique during the tests. The results show that the peak shear stress, the peak shear strain and shear modulus decrease with the shear angle α, regardless of the treatment temperature. The peak shear stress increases slightly as the high temperature rises to 400 °C, then decrease rapidly. Both the peak shear strain and shear modulus do not change significantly until 400 °C and 500 °C respectively, then reduce rapidly. The cohesion reduces and the internal friction angle increases with increasing temperature. Based on the principal strain field, the damage evolution and crack extension processes of typical specimen are analyzed. It shows that the cracks initiate from the upper and lower loading points, which further coalesce with each other at the middle part of shear band. The shear angle α has a significant effect on the compression-shear failure behavior of granite. The tension failures become less visible with increase of α and dominant failure patterns transform from mixed tension-shear failure to shear failure. The ratio of crack initiation force to peak load reduces obviously at 600 °C. In addition, the underlying failure mechanism of specimens under compression-shear load is explained by an established mechanical model in the paper.

Underground power cable systems (UPCSs) are generally buried close to the ground surface, exposing them to significant influences from ambient air and ground temperatures, which can affect heat dissipation and thermal efficiency. This study compares the heat transfer performance of UPCS with different cable bedding materials at critical current carrying capacity, considering the effects of ambient air and ground temperatures on system performance. The findings indicate that current carrying capacity decreases with higher ground temperatures, and that the critical ampacity leading to maximum cable temperature in UPCS is significantly influenced by actual ambient air and ground temperatures, rather than standard reference values like 20 °C. The newly developed cable bedding material, prepacked aggregate concrete (PAC), to enhance heat dissipation efficiency and prevent cable overheating is also proposed. Experimentally, PAC, with a higher thermal conductivity of 2.094 W/(m·K) versus 1.365 W/(m·K) for sand, lowers the maximum cable temperature to 70.6 °C, compared to 77.6 °C for sand under critical conditions. Moreover, the analytical solutions for ground temperature distribution models as boundary conditions are also highlighted, in which steady-state ground temperature analysis at the relevant depth may impact the accuracy of cable temperature predictions related to UPCS operation for both the system itself and the surrounding earth materials.

Internal flows (downflow and upflow) occur in geothermal wells because of different factors that affect the pressure and temperature measurements used to characterise a geothermal reservoir. In extreme cases, an internal flow can cool a hot reservoir if a sufficient flow at a low temperature is present. This work examines the internal flows, analysing two geothermal well tests from El Salvador that show downflow. We employed two approaches to model the downflow effect. Although the internal flows affect the pressure and temperature measurements, the model approaches can effectively simulate the downflow, capturing the complex interaction in the well and formation. The pressure response is more perceptible to detect a downflow because it generates instant perturbations. The temperature response experiences less noticeable perturbations because of downflows, being more appreciable by the end of the temperature derivative.