Investigation and evaluation methods of shallow geothermal energy considering the influences of fracture water flow

Abstract The energy replenishment and heat convection induced by fracture water flowing through the rock mass impact the shallow geothermal energy occurrence, transfer and storage mechanisms in it. In this article, a suitability evaluation and categorization system is proposed by including judgement indexes that are more closely aligned with the actual hydrogeological conditions in fracture developed regions; an assessment approach of regional shallow geothermal energy is proposed by coupling the influences of fracture water into the calculation methods of geothermal capacity, thermal balance and heat transfer rate. Finally, by taking two typical fracture aperture distributions as examples, the impacts of fracture water on the investigation and evaluation of shallow geothermal energy are quantitatively analyzed. Although the fracture apertures only share 1.68% and 0.98% of the total length of a borehole, respectively, in the two examples, the fracture water convection contributes up to 11.01% and 6.81% of the total heat transfer rate; and the energy replenishment potential brought by the fracture water is equivalent to the total heat extraction of 262 boreholes. A single wide aperture fracture can dominate the aforementioned impacts. The research results can support more accurate evaluation and efficient recovery of shallow geothermal energy in fracture developed regions

Study on Calculation Method of Heat Exchange Capacity and Thermal Properties of Buried Pipes in the Fractured Rock Mass-Taking a Project in Carbonate Rock Area as an Example

Fractures are developed in carbonate rock areas, and the fracture water flow significantly influences the heat exchange between buried pipes and the rock mass by induing heat convection, providing the carbonate rock area a strong heat exchange capacity and preferable conditions for shallow geothermal development and utilization. In this paper, the calculation method of heat exchange capacity of buried pipes based on fracture distribution characteristics is proposed and deduced, featuring such advantages as quick speed and low cost. Taking an actual project in carbonate rock area as an example, the heat exchange capacity of buried pipes was obtained by the following two methods: in-situ thermal response test and calculation based on fracture distribution characteristics. In the thermal response test, the initial ground temperatures of the two test holes were 15.18 °C and 12.72 °C. By fitting the linear equation of time and average temperature with a linear thermal source model, the heat exchange capacities were 57.21 W/m and 58.22 W/m, the thermal conductivities were 3.56 W/(m·K) and 2.32 W/(m·K), the thermal diffusivities were 1.71 × 10−6 m2/s and 1.12 × 10−6 m2/s, and the volume specific heat capacity was 2.08 × 106 J (m3·K). The test results indicated that the thermal property parameters of rock and soil mass were higher than those of other areas, with obvious wide-range distribution characteristics. Through the statistical analysis of outcrop fracture characteristics, combined with the cube law to calculate the fracture water flow and convective heat transfer, an alternative method for the calculation and optimization of buried pipe heat transfer in fractured rock mass area is also proposed in this paper. According to the measured fracture distribution characteristics of the field outcrop, the heat exchange capacities of the two holes were 57.26 W/m and 58.56 W/m, which were basically consistent with the thermal response test values and verified the reliability of the calculation method of heat exchange capacity of buried pipes based on fracture distribution characteristics

An MPI parallel DEM-IMB-LBM framework for simulating fluid-solid interaction problems

The high-resolution DEM-IMB-LBM model can accurately describe pore-scale fluid-solid interactions, but its potential for use in geotechnical engineering analysis has not been fully unleashed due to its prohibitive computational costs. To overcome this limitation, a message passing interface (MPI) parallel DEM-IMB-LBM framework is proposed aimed at enhancing computation efficiency. This framework utilises a static domain decomposition scheme, with the entire computation domain being decomposed into multiple subdomains according to predefined processors. A detailed parallel strategy is employed for both contact detection and hydrodynamic force calculation. In particular, a particle ID re-numbering scheme is proposed to handle particle transitions across sub-domain interfaces. Two benchmarks are conducted to validate the accuracy and overall performance of the proposed framework. Subsequently, the framework is applied to simulate scenarios involving multi-particle sedimentation and submarine landslides. The numerical examples effectively demonstrate the robustness and applicability of the MPI parallel DEM-IMB-LBM framework

Development of Novel Perovskite-Like Oxide Photocatalyst LiCuTa3O9 with Dual Functions of Water Reduction and Oxidation under Visible Light Irradiation

Development of new visible-light-responsive materials is highly desirable in photocatalysis. Here, a novel oxide material LiCuTa3O9 (LCTO) with a characteristic perovskite-like structure, exhibiting a visible light absorption edge of approximate to 500 nm due to the hybridization of Cu 3d and O 2p orbitals, is reported. The structure of the as-obtained LCTO is experimentally characterized and theoretically simulated. UV-vis diffuse reflectance spectroscopy, Mott-Schottky, and density functional theory calculation results show that the LCTO is an n-type semiconductor with bandgap of approximate to 2.48 eV and exhibits suitable conduction band and valence band positions of approximate to-0.45 and 2.03 eV vs reversible hydrogen electrode, respectively. Based on initial optimization of preparative conditions and loading of cocatalysts, the as-modified LCTO sample can drive both water reduction and oxidation half reactions in the presence of corresponding sacrificial reagents under visible light irradiation (lambda >= 420 nm), demonstrating its promising application in solar water splitting. The dual functional features of LCTO render it a promising photocatalyst for one-step overall water splitting to produce hydrogen. In addition, the unobvious structural change of the LCTO photocatalyst during the reaction and repeated runs of the photocatalytic H-2 evolution reaction demonstrate its good photochemical stability

Intelligent Distribution Network Information Processing Based on Power Data Virtual Plane

Due to the diversity and complexity of distribution networks, the classical modular software development method may face the difficulty in modular division, data sharing and collaboration of different specialties. Inspired by the idea of separating the control plane from the data forwarding plane in software-defined networking (SDN), a method of power data virtual plane is proposed in this paper to improve software development efficiency. Layered processing of power data virtual plane is designed to meet the diversity characteristics of intelligent distribution network and the multi-source and heterogeneous characteristics of information. This paper introduces the design idea and implementation process of virtual plane in detail. The main component of the power data virtual plane, power data warehouse and application scheduling are presented. Finally, the performance of the proposed virtual plane method is verified by practical distribution network examples with different communication networks and information