Modeling the impact of natural roughness of tension joints on heat transport

IF 3.5 2区 工程技术 Q3 ENERGY & FUELS Geothermics Pub Date : 2024-08-29 DOI:10.1016/j.geothermics.2024.103145
Benoit Nigon , Christophe Pascal , Andreas Englert
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Abstract

The understanding of heat transport in fractures is crucial for mining geothermal systems. Studies of heat transport in natural fractures at scales comprised between those of laboratory experiments and those of field tracer tests are seldom. To bridge the gap, a joint surface with characteristic plumose was scanned in the field using LiDAR technology. The scanned surface was used to build a numerical model of mode 1 fracture. Fluid flow and heat transport were modeled solving the steady-state Stokes equation and assuming Fourier transport, respectively. We considered three different fracture apertures and varied systematically roughness in order to investigate the impact of plumose on fluid and heat transport. The 3D velocity flow fields were characterized by mean hydraulic aperture and by statistics on the directional components of the velocity vector. The method of temporal moments was used to extract first and second moments from temperature breakthrough curves. Heat transport parameters (local and macroscopic) were calculated from first and second moments.

We show that hydraulic aperture and the longitudinal component of the velocity vector decrease with increasing roughness. The local variation of heat transport parameters is controlled by fracture roughness. For the macroscopic transport parameters, several transport regimes were identified. At low fracture aperture (i.e. 1 mm), conductive regime dominates heat transport in agreement with low Péclet numbers. In this case, fracture roughness affects the transport parameters via the loss of hydraulic aperture. With higher aperture (i.e. 3 mm) geometrical dispersion regime is dominant, roughness controlling the amplitude of transport parameters. At 5 mm aperture, transition from geometrical to Taylor dispersion occurs and the roughness tends to decrease dispersion and dispersivity according to the mean flow velocity.

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张力接头自然粗糙度对热传导影响的建模
了解裂缝中的热传输对于开采地热系统至关重要。在实验室实验和野外示踪试验之间,很少对天然裂缝中的热传输进行研究。为了弥补这一差距,我们在野外使用激光雷达技术扫描了具有梅花状特征的接合面。扫描表面用于建立模式 1 断裂的数值模型。流体流动和热量传输模型分别求解稳态斯托克斯方程和假设傅立叶传输。我们考虑了三种不同的断裂孔径,并系统地改变了粗糙度,以研究羽状纹对流体和热量传输的影响。三维速度流场以平均水力孔径和速度矢量方向分量统计为特征。采用时间矩法从温度突破曲线中提取第一和第二矩。我们发现,水力孔径和速度矢量的纵向分量随着粗糙度的增加而减小。热传输参数的局部变化受断裂粗糙度控制。对于宏观传输参数,我们确定了几种传输机制。在断裂孔径较小(即 1 毫米)的情况下,传导机制与低佩克莱特数一致,在热传输中占主导地位。在这种情况下,断裂粗糙度通过水力孔径的损失影响传输参数。随着孔径增大(即 3 毫米),几何弥散机制占主导地位,粗糙度控制着传输参数的振幅。当孔径为 5 毫米时,就会从几何分散过渡到泰勒分散,粗糙度会根据平均流速降低分散性。
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来源期刊
Geothermics
Geothermics 工程技术-地球科学综合
CiteScore
7.70
自引率
15.40%
发文量
237
审稿时长
4.5 months
期刊介绍: Geothermics is an international journal devoted to the research and development of geothermal energy. The International Board of Editors of Geothermics, which comprises specialists in the various aspects of geothermal resources, exploration and development, guarantees the balanced, comprehensive view of scientific and technological developments in this promising energy field. It promulgates the state of the art and science of geothermal energy, its exploration and exploitation through a regular exchange of information from all parts of the world. The journal publishes articles dealing with the theory, exploration techniques and all aspects of the utilization of geothermal resources. Geothermics serves as the scientific house, or exchange medium, through which the growing community of geothermal specialists can provide and receive information.
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