The novel designs for increasing heat transfer in ground heat exchangers to improve geothermal heat pump efficiency

Saeidi, Reza; Karimi, Amir; Noorollahi, Younes

doi:10.1016/j.geothermics.2023.102844

Cited by 14 publications

(2 citation statements)

References 33 publications

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“…The basic connecting feature is the effort to increase the heat flux while minimising the negative effects on the operating parameters, for example, in the form of an increase in the pressure drop, an increase in external work, or a change in the strength characteristics of the structural parts, as well as parameters related to the economics of operation and its environmental parameters. These principles are applied in the whole spectrum of technologies in terms of the size of their spatial differences, heat flux, or the range of industrial-scale applications [6,7].…”

Section: Introductionmentioning

confidence: 99%

Numerical Study of Fluid Flow in a Gyroid-Shaped Heat Transfer Element

Beer,

Rybár

2024

Energies

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This paper deals with the design of porous geometry of a heat transfer element. The proposed geometry combines a gyroid triply periodic minimal surface with the recursive principle of geometric body creation. The designed geometry is based on an attempt to increase the heat transfer surface while eliminating negative impacts on the fluid characteristics in the form of pressure loss or increase of the friction coefficient. The proposed geometry of the heat transfer element was compared with a pair of geometries based on the basic gyroid shape but with different channel size parameters. A numerical simulation was performed in Ansys Fluent 2020 R1 using the SST k-omega turbulence model for flow velocities in the range of 0.01 m.s−1 to 0.5 m.s−1, which covered a wide range of the Reynolds number and thus also flow forms in terms of the turbulence intensity. The presented results clearly show lower values of pressure loss and friction coefficient of the proposed geometry compared to the evaluated porous structures. Also, at the same time, they describe the factors positively influencing the mixing process of the liquid in the proposed element, which leads to an increase in the efficiency of the heat transfer process.

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Section: Introductionmentioning

confidence: 99%

Numerical Study of Fluid Flow in a Gyroid-Shaped Heat Transfer Element

Beer,

Rybár

2024

Energies

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“…As an important heat-exchange device for GSHPs, the heat-transfer performance of buried ground heat exchangers (GHEs) directly affects their efficiency. Vertical GHEs buried in boreholes with long depths are widely adopted, and single U, double U, W, and spiral shapes are common types that are used to fully extract hot or cold energy from the ground [4][5][6]. Many researchers have attempted to improve the performance of GSHPs by different methods, such as increasing the length of the borehole [7], enlarging the space for GHEs [8], optimizing the geometric dimensions of buried pipes [9], or using backfill materials of high thermal conductivity [10,11].…”

Section: Introductionmentioning

confidence: 99%

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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