Research on Heat Exchange Law and Structural Design Optimization of Deep Buried Pipe Energy Piles
Abstract
:1. Introduction
2. Test Overview
2.1. Project Overview
2.2. Test Plan
3. Finite Element Numerical Simulation
3.1. Basic Assumptions
- (1)
- The fluid, heat exchange tube, concrete and soil are homogeneous, and their thermal performance is independent of temperature.
- (2)
- The self-weight of the fluid, the contact thermal resistance between the U-shaped pipe wall and pile foundation, the pile foundation and the surrounding soil are not considered.
- (3)
- Assuming that the initial temperatures of the soil and pile foundation are the same, the temperature at the far boundary of the soil remains unchanged.
- (4)
- The influence of groundwater on the heat exchange of energy pile is ignored.
- (5)
- The change of soil temperature along the depth direction is ignored.
- (6)
- The influence of environmental factors on shallow soil temperature is ignored.
3.2. Basic Assumptions
4. Result Analysis and Discussion
4.1. Well Depth
4.2. Pile Length
4.3. Inlet Water Temperature
4.4. Flow Rate
4.5. Comparison and Optimization
5. Conclusions
- (1)
- An increase in well depth can weaken the influence of pile length on the heat exchange effect of energy piles, so the pile well ratio is an important factor affecting the heat exchange effect of energy piles. Through analysis, it is found that the best benefit can be obtained when the pile-to-well ratio is approximately 0.3–0.4.
- (2)
- The inlet water temperature is the most significant factor affecting the heat exchange effect of energy piles. When the inlet water temperature is low, the heat exchange tube temperature rises evenly, and the time to reach the stable state is short. When the inlet water temperature is high, it shows the opposite trend; at the same time, the change in inlet water temperature has little effect on the heat exchange radius of the energy pile.
- (3)
- The flow rate has a significant impact on the heat exchange effect of the energy pile, but the pile-to-well ratio should be given priority when determining the operating parameters of the energy pile, and then the flow should be set reasonably. If only the lower outlet water temperature is considered in summer, the pile-to-well ratio can be reduced.
- (4)
- By exploring the heat exchange effect of deep buried pipe energy piles under different influencing factors, it is found that the influence of inlet water temperature, well depth, flow and pile length on the heat exchange efficiency of energy piles gradually weakens.
- (5)
- The long length of deep well and the spacing of heat exchange tubes will aggravate the thermal interference of pile foundation and the upper part of deep well, based on the pile well ratio and the selection of backfill materials, the thermal interference phenomenon can be appropriately reduced.
Author Contributions
Funding
Conflicts of Interest
References
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Test Number | Pile Length (m) | Drilling Depth (m) | Heating Power (kW) | Flow Velocity (m3/h) |
---|---|---|---|---|
1 | 23 | 100 | 3.5 | 1.0 |
2 | 5.5 | 1.0 | ||
3 | 5.5 | 0.6 | ||
4 | 18 | 100 | 5.5 | 1.0 |
5 | 0.6 |
Material | Thermal Conductivity (W/(m·°C)) | Thermal Capacity (J/(kg·°C)) | Density (kg/m3) |
---|---|---|---|
Heat exchange pipe | 0.45 | 2300 | 950 |
Concrete | 2.2 | 970 | 2500 |
Rock-soil mass | 1.98 | 2240 | 1970 |
Circulation medium | 0.6 | 4200 | 998 |
Backfill material | 0.58 | 966 | 2650 |
Test Number | Pile Length (m) | Drilling Depth (m) | Heating Power (kW) | Flow Velocity (m3/h) |
---|---|---|---|---|
6 | 23 | 50 | 30.2 | 1.0 |
7 | 75 | |||
8 | 100 | |||
9 | 125 | |||
10 | 50 | 27.2 | 1.0 | |
11 | 75 | |||
12 | 100 | |||
13 | 125 | |||
14 | 18 | 50 | 30.3 | 1.0 |
15 | 75 | |||
16 | 100 | |||
17 | 125 | |||
18 | 50 | 30.2 | 0.6 | |
19 | 75 | |||
20 | 100 | |||
21 | 125 |
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Chen, Z.; Wang, B.; Zheng, L.; Xiao, H.; Wang, J. Research on Heat Exchange Law and Structural Design Optimization of Deep Buried Pipe Energy Piles. Energies 2021, 14, 6449. https://doi.org/10.3390/en14206449
Chen Z, Wang B, Zheng L, Xiao H, Wang J. Research on Heat Exchange Law and Structural Design Optimization of Deep Buried Pipe Energy Piles. Energies. 2021; 14(20):6449. https://doi.org/10.3390/en14206449
Chicago/Turabian StyleChen, Zhi, Bo Wang, Lifei Zheng, Henglin Xiao, and Jingquan Wang. 2021. "Research on Heat Exchange Law and Structural Design Optimization of Deep Buried Pipe Energy Piles" Energies 14, no. 20: 6449. https://doi.org/10.3390/en14206449