Cooling Subgrade Effectiveness by L-Shaped Two-Phase Closed Thermosyphons with Different Inclination Angles and XPS Insulation Boards in Permafrost Regions
Abstract
:1. Introduction
2. Heat Transfer Model of the Subgrade with L-Shaped TPCTs
2.1. Heat Conduction Equation of Soil
2.2. Coupled Air Temperature—L-Shaped TPCT—Subgrade Soil Heat Transfer Model
- (1)
- Condenser section
- (2)
- Adiabatic section
- (3)
- Evaporator section
3. Finite Element Calculation Model and Verification
3.1. Model Establishment and Boundary Conditions
3.2. Model Validation
4. Influence of Evaporator Section Inclinations on the Cooling Effectiveness
4.1. Heat-Transfer Characteristics of L-Shaped TPCTs
4.2. Geotemperature Distribution in the Subgrade
5. Composite Subgrades with an L-Shaped TPCTs/Vertical TPCT/XPS Insulation Board System
6. Conclusions
- A coupled heat transfer calculation model of air temperature–L-shaped TPCT–subgrade soil, considering the changes in the evaporator section inclination angles of the L-shaped TPCT, was proposed. The comparison between the calculated results and the field-measured data showed that the model could simulate the thermal stability of a wide subgrade with L-shaped TPCTs in permafrost regions.
- In comparison to a vertical TPCT, the L-shaped TPCT had a relatively good cooling effect on the subgrade, as a whole, when the inclination angles of the evaporator section were 50° and 70°. However, in the 30th year, the thawing depth at the center of the subgrade with L-shaped TPCTs reached 9.0 m below the ground surface. When the evaporator section inclination angle of the TPCT was 50°, the corresponding heat flux was the largest, reaching a maximum value of 165.7 W·m−2 in January.
- The composite subgrade with L-Shaped TPCTs/vertical TPCT/XPS insulation board system is an effective method to protect the permafrost foundation and improve the long-term thermal stability of a wide subgrade. The maximum heat flux of evaporation section of the L-shaped TPCT and vertical TPCT of the composite subgrade was 196.8 W·m2 and 165.7 W·m2, respectively, throughout the working time, and the maximum heat flux of L-shaped TPCT was increased by 18.8%. However, this paper only studied the influence of L-shaped two-phase closed thermosyphons and XPS insulation boards on the subgrade temperature field, and more studies should be carried out on the deformation of the composite subgrade in the future.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Parameter | λa (W·m−1·°C−1) | ca (J·kg−1·°C−1) | ρa (kg·m−3) | μ (Pa·s) |
---|---|---|---|---|
Value | 0.023 | 10040 | 0.641 | 1.75 × 10−5 |
Parameter | λl (W·m−1·°C−1) | cpa (J·kg−1·°C−1) | ρl (kg·m−3) | ρva (kg·m−3) | μ (Pa·s) | Lr (kJ·kg−1) |
---|---|---|---|---|---|---|
Value | 0.298 | 2125 | 638.6 | 3.48 | 2.35 × 10−4 | 1263 |
Soil Layer | Soil Layer Thickness (m) | Dry Density (kg·m−3) | Thermal Conductivity (W·m−1·°C−1) | Specific Heat Capacity (J·kg−1·°C−1) | Latent Heat (J·m−3) | ||
---|---|---|---|---|---|---|---|
Frozen Soils | Unfrozen Soils | Frozen Soils | Unfrozen Soils | ||||
Subgrade fill | 3 | 2060 | 7128 | 6908 | 928 | 1081 | 2.04 × 107 |
Gravelly sand | 2 | 1900 | 5944 | 5220 | 960 | 1292 | 2.32 × 107 |
Clayey loam | 4 | 1600 | 4864 | 4050 | 1174 | 1473 | 6.03 × 107 |
Mudstone | 24 | 1800 | 6567 | 5306 | 1025 | 1166 | 3.77 × 107 |
Variable | T0 (°C) | A (°C) |
---|---|---|
Air temperature | −3.0 | 10.5 |
Asphalt pavement surfaces (CD) | 3.5 | 15 |
Slope surfaces (BC, DE) | 1.7 | 13 |
Natural ground surfaces (AB, EF) | −0.5 | 12 |
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Zhou, Y.; Wang, X.; Guo, C.; Hu, Y.; He, F.; Liu, D.; Jiang, D. Cooling Subgrade Effectiveness by L-Shaped Two-Phase Closed Thermosyphons with Different Inclination Angles and XPS Insulation Boards in Permafrost Regions. Materials 2022, 15, 8470. https://doi.org/10.3390/ma15238470
Zhou Y, Wang X, Guo C, Hu Y, He F, Liu D, Jiang D. Cooling Subgrade Effectiveness by L-Shaped Two-Phase Closed Thermosyphons with Different Inclination Angles and XPS Insulation Boards in Permafrost Regions. Materials. 2022; 15(23):8470. https://doi.org/10.3390/ma15238470
Chicago/Turabian StyleZhou, Yalong, Xu Wang, Chunxiang Guo, Yuan Hu, Fei He, Deren Liu, and Daijun Jiang. 2022. "Cooling Subgrade Effectiveness by L-Shaped Two-Phase Closed Thermosyphons with Different Inclination Angles and XPS Insulation Boards in Permafrost Regions" Materials 15, no. 23: 8470. https://doi.org/10.3390/ma15238470