Effect of gradation on the thermal conductivities of backfill materials of ground source heat pump based on loess and iron tailings

Kong, Dequan; Wan, Rong; Chen, Jianxun; Kang, Jiayuan; Jiao, Xintong

doi:10.1016/j.applthermaleng.2020.115814

Cited by 20 publications

(4 citation statements)

References 25 publications

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“…This is strong to the physical properties of loess, such as water content, particle composition and microstructure, and mechanical properties such as compressibility, collapsibility and shear strength. Among these physical and mechanical properties, the particle size distribution (PSD) is crucial and directly affects the compressibility, permeability, thermal conductivity and other engineering properties of loess (Kong et al, 2020; Ren et al, 2020; Xu, Gao, et al, 2020). The number and distribution of clay particles in loess determine the size of cohesion and plastic limits.…”

Section: Introductionmentioning

confidence: 99%

A new method for determining loess particle size distribution based on ‘core + clothes’ structure

Zhou

et al. 2023

Earth Surf Processes Landf

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The particle size distribution (PSD) of loess particles and agglomerates is the key factor determining the microstructure of loess. The PSD largely determines many physical and mechanical properties such as mechanical strength, deformation characteristics and permeability of loess. In this paper, we combined image processing, geometric measurements and statistical methods to quantitatively characterize the scanning electron microscopy (SEM) images of loess. A new method based on the ‘core + clothes’ structure is proposed to determine the PSD. The developed Gaussian mixture model is applicable to describe the overall distribution of the image pixel density. Determining pixel density distribution and particle boundary allows for the measurement of various geometric parameters. The comparison analyses suggest that the sieve‐hydrometer method has a well‐developed test procedure; however, the measured particle size is limited to 0.075 mm. The laser diffraction method is simple and fast, yet only weak agglomerates can be dispersed, and very fine particles are influenced by size data conversion theory and light source parameters. X‐ray microtomography has the advantage of a non‐destructive sample preparation and intuitive process. However, the results are greatly affected by the parameter settings and segmentation algorithm, and the segmentation effect is poor for particles with a size smaller than 12 μm. The new image processing technique developed in this study improves the limitation of the measurement results via changes in the loess state (water content, stress level). Moreover, different PSDs can be determined according to the variation of functional units. This work is of great significance for the study of numerous properties related to the loess state.

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Section: Introductionmentioning

confidence: 99%

A new method for determining loess particle size distribution based on ‘core + clothes’ structure

Zhou

et al. 2023

Earth Surf Processes Landf

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“…Therefore, the comprehensive utilization and treatment of IT have attracted much attention from lots of scientists. At present, IT is mainly used for backfilling the mining area, road base materials, construction materials, soil improver, trace element fertilizer, and so forth 14–17 . However, the low utilization rate of IT leads to a large number of IT still cannot being effectively utilized.…”

Section: Introductionmentioning

confidence: 99%

“…At present, IT is mainly used for backfilling the mining area, road base materials, construction materials, soil improver, trace element fertilizer, and so forth. [14][15][16][17] However, the low utilization rate of IT leads to a large number of IT still cannot being effectively utilized. Therefore, exploring a new utilization strategy of IT is helpful to realize the high-value utilization of IT resources.…”

mentioning

confidence: 99%

Thermoplastic polyurethane composites based on aluminum hypophosphite/modified iron tailings system with outstanding fire performance

Liu

Sun

et al. 2022

J of Applied Polymer Sci

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Iron tailings (IT) is the remaining industrial solid waste after beneficiation. The accumulation of billion tons of tailings not only occupies valuable land resources but also causes serious environmental pollution and human harm. This work aims to explore the potential application of IT in flame retardant field. The modified iron tailings (MIT) were combined with aluminum hypophosphite (AHP) to prepare a series of TPU/AHP/MIT composites by melt blending method. Thermogravimetric (TGA) test indicated that MIT and AHP significantly improved the thermal stability of the composites. The char residue of TPU/AHP22.5/MIT2.5 was enhanced to 29.60 wt% compared with 27.51 wt% of TPU/AHP25. Cone calorimetry test (CCT) confirmed that PHRR and THR of TPU/AHP15/MIT10 were decreased by 88.4% and 55.2% compared with those of pure TPU. Adding 2.5 wt% MIT could reduce the gas production of the TPU/AHP system by 32.82%. Scanning electron microscopy (SEM) and Raman spectroscopy tests confirmed that AHP/MIT system could increase the thickness and graphitization degree of char residue for the TPU composites, and thus increase the thermal stability and fire resistance of the composites. Lastly, the possible fire retarding mechanism of TPU/AHP/MIT composites was illustrated. This work provided a novel strategy for utilization of IT.

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“…Common issues with GSHPs include a thermal imbalance, the depletion of the heat exchange capacity of the borehole, and a decrease in the system efficiency. As the direct contact medium between the U pipe and the stratum, the backfill material (BM) in the heat exchange borehole determines the heat exchange performance between the buried pipe and the surrounding rock and soil, and prevents the penetration of the surface water into the ground through the heat exchange borehole [4,5]. There are two approaches to enhance the ability of the thermal transfer for backfill materials.…”

Section: Introductionmentioning

confidence: 99%

Improvements in the Water Retention Characteristics and Thermophysical Parameters of Backfill Material in Ground Source Heat Pumps by a Molecular Sieve

et al. 2022

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The thermophysical properties of backfill material (BM) in a heat exchange borehole significantly influence the heat exchange effect of ground source heat pumps (GSHPs). Several treatments such as compaction and adding bentonite, cement, and fine sands are often used to improve the thermophysical properties. In this study, a 3A molecular sieve (3A-MS), a type of porous material, was added to the BM to enhance its water maintaining capacity. Three types of backfill materials with different additive contents, named as BM-0, BM-1, and BM-2, were examined. The variation of the BM properties such as the soil–water characteristic curve (SWCC), thermal conductivity, specific heat capacity, and thermal diffusivity with the groundwater content were investigated through a series of experiments and simulations. A scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and the BET method for specific surface area pore size analysis were used to characterize the material. The results indicated that the specific heat capacity improved with the water content whereas the thermal conductivity and thermal diffusivity decreased with the water content. The variation of the buried pipe outlet temperature with the change of the thermal physical parameters of the BM were researched by a numerical simulation and theoretical calculations; the results showed that BM-2 could raise the heat transfer rate per meter by 45.9% in summer and 118.4% in winter compared with the backfill materials without groundwater (NW). The research results provide theoretical support for the improvement of BM for ground source heat pump projects where abundant groundwater is available.

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Effect of gradation on the thermal conductivities of backfill materials of ground source heat pump based on loess and iron tailings

Cited by 20 publications

References 25 publications

A new method for determining loess particle size distribution based on ‘core + clothes’ structure

A new method for determining loess particle size distribution based on ‘core + clothes’ structure

Thermoplastic polyurethane composites based on aluminum hypophosphite/modified iron tailings system with outstanding fire performance

Improvements in the Water Retention Characteristics and Thermophysical Parameters of Backfill Material in Ground Source Heat Pumps by a Molecular Sieve

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