Thermal performance analysis and assessment of PCM backfilled precast high-strength concrete energy pile under heating and cooling modes of building

Cao, Ziming; Zhang, Guozhu; Liu, Yiping; Zhao, Xu

doi:10.1016/j.applthermaleng.2022.119144

Cited by 38 publications

(6 citation statements)

References 46 publications

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“…Heat conduction in solid materials and heat convection of the circulating fluid were adopted in the model, as these are the main heat-transfer processes in the GHEs system. Considering that heat transfer between the buried pipe and the ground is a complex, unsteady process, some hypotheses are needed: (1) Backfill material and the surrounding soil are considered to be homogenous and isotropic [26,27]; (2) the backfill material in the borehole has been fully backfilled [26]; (3) All the contacting boundaries satisfy the continuity condition, in which the thermal resistance is ignored [27]. As the influences of groundwater seepage and a lack of groundwater seepage on heat transfer are considered separately in this paper, more hypotheses are proposed as the groundwater seepage is taken into consideration: (1) The flow state of groundwater in porous media conforms to Darcy's law; (2) The entire soil around the borehole is assumed to be a porous medium composed of three phases: solid, liquid, and gas; (3) The initial groundwater temperature in the model is set to be the same as the stratum temperature; (4) The velocity of the groundwater seepage is constant.…”

Section: Methodsmentioning

confidence: 99%

“…The heat-transfer process of solid mass in the GHEs system is controlled by the following equation [26,28]:…”

Section: Governing Equationsmentioning

confidence: 99%

“…where the circulating fluid within the buried pipe is considered to be incompressible and the turbulent flow is based on the Reynolds number. The equation of continuity, momentum, and energy could be expressed as follows [25,26]:…”

Section: Governing Equationsmentioning

confidence: 99%

“…In Equation ( 2)-( 4), f D represents the Darcy friction factor of circulating fluid based on Churchill's friction model [29,30]. Meanwhile, q wall denotes the source term defined as follows [26,28,31]:…”

Section: Governing Equationsmentioning

confidence: 99%

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Investigation of the Long-Term Performance of Waste Backfill Materials of High Thermal Conductivity in Vertical Ground Heat Exchangers

Wu,

Chen,

Liu

et al. 2024

Buildings

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Backfill material used as a heat-transfer medium in boreholes of ground heat exchangers (GHEs) has a great influence on heat-transfer efficiency. Abandoned waste material causing environmental pollution has become a key issue around the world. To make full use of solid waste, backfill material made of waste fly ash in combination with graphite of high thermal conductivity was proposed. First, the thermal properties of cement/fly ash blended with different mass ratio of graphite were tested through laboratory tests. Then, a numerical model was established, in which the accuracy was validated based on a field test. Finally, an investigation of the long-term performance (over a period of 90 days) for four boreholes backfilled with natural sand, cement/fly ash, and cement/fly ash combined with different proportions of graphite was conducted through this numerical model, and the heat-transfer rates under constant inlet temperature in four boreholes decreased from 13.31, 44.97, 45.95, and 46.73 W/m to 14.18, 14.96, 15.66, and 16.19 W/m after the 90-day operation. Considering the influence of groundwater seepage, the horizontal groundwater flow had a positive impact, improving the long-term heat-transfer performance. The heat-transfer rates of four testing boreholes decreased from 44.46, 46.38, 47.22, and 47.68 W/m to 21.18, 21.93, 22.62, and 23.13 W/m. However, long-term groundwater seepage in a vertical direction caused a sharp decrease in the heat-transfer rate, and the values after 90 days were 10.44, 10.62, 10.78, and 10.81 W/m, which were the lowest of all the working conditions. The feasibility of using fly ash blended with graphite as backfill material was further validated through a comprehensive perspective, including indoor laboratory, field testing, and numerical simulation, which has rarely been conducted in previous research.

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Section: Methodsmentioning

confidence: 99%

“…The heat-transfer process of solid mass in the GHEs system is controlled by the following equation [26,28]:…”

Section: Governing Equationsmentioning

confidence: 99%

Section: Governing Equationsmentioning

confidence: 99%

Section: Governing Equationsmentioning

confidence: 99%

See 2 more Smart Citations

Investigation of the Long-Term Performance of Waste Backfill Materials of High Thermal Conductivity in Vertical Ground Heat Exchangers

Wu,

Chen,

Liu

et al. 2024

Buildings

Self Cite

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“…It was found that the addition of PCM to C50 phase-change concrete specimens significantly reduced the compressive strength of concrete, and the thermal conductivity and heat capacity of the specimens decreased with the increase in the mass fraction of the phase-change material. Cao Ziming et al [32] established a threedimensional heat transfer model of prefabricated high-strength concrete (PHC) energy piles with PCM backfill (PCMB) and studied the thermal response of PCMB-PHC energy piles in building heating and cooling modes. The improvement of the thermal conductivity of PCMB is beneficial to the enhancement of the heat transfer capacity of PCMB-PHC energy piles, and the presence of phase-change materials reduces the temperature fluctuation of the soil around the pile.…”

Section: Introductionmentioning

confidence: 99%

Study on Thermodynamic Properties of Spiral Tube-Encapsulated Phase-Change Material Energy Pile

Liu,

Zhang,

Yang

et al. 2024

Buildings

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Based on the research status of phase-change material (PCM) energy piles, this paper proposes a new type of PCM energy pile-spiral tube-encapsulated PCM energy pile. In order to study the related properties of the energy pile, this study designed and processed the relevant test equipment and built an indoor scale model experimental system. The thermodynamic performance of the spiral tube-encapsulated phase-change energy pile under summer conditions was studied by the test system. Through the indoor scale model test, it is found that compared with the traditional energy pile, the spiral tube-encapsulated PCM energy pile improves the heat exchange capacity of the unit pile body in the early and middle stages of operation, and reduces the surface temperature of the pile body and the heating rate of the surface temperature of the pile body. The upward displacement of the energy pile top is reduced. The heat exchange capacity of the unit pile depth is increased by 6.52 W/m, the maximum pile surface temperature difference is 0.62 °C, and the maximum pile top displacement difference is 0.005 mm. In addition, the total heat transfer of the spiral tube-encapsulated PCM energy pile during the whole operation period is 3.38% higher than that of the traditional energy pile. However, during the whole operation period, the surface stress value of the spiral tube encapsulated PCM energy pile is higher than that of the traditional energy pile. The maximum difference between the two is 9.84 kPa and the maximum difference is 10.8%. The difference between the two is finally stabilized at 1.4 kPa with an increase in time, and the final difference is only 8.8%.

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Sustainable thermal energy storage concrete incorporated with phase change materials

Liu,

Pan,

et al. 2024

Sustainable Concrete Materials and Structures

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Thermal performance analysis and assessment of PCM backfilled precast high-strength concrete energy pile under heating and cooling modes of building

Cited by 38 publications

References 46 publications

Investigation of the Long-Term Performance of Waste Backfill Materials of High Thermal Conductivity in Vertical Ground Heat Exchangers

Investigation of the Long-Term Performance of Waste Backfill Materials of High Thermal Conductivity in Vertical Ground Heat Exchangers

Study on Thermodynamic Properties of Spiral Tube-Encapsulated Phase-Change Material Energy Pile

Sustainable thermal energy storage concrete incorporated with phase change materials

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