Numerical Investigation of Heat-Insulating Layers in a Cold Region Tunnel, Taking into Account Airflow and Heat Transfer
Abstract
:1. Introduction
2. Temperature Field Coupling Theory (Airflow to Lining/Heat-Insulating Layer to Surrounding Rock)
2.1. Theory of Airflow Temperature Field in Tunnel Based on Turbulence Equation
2.2. Analytical Theory for Temperature Fields of Tunnel Lining and Surrounding Rock
3. Field Test of the Dege Tunnel
4. Numerical Analysis of Dege Tunnel
4.1. Model Description
4.2. Model Validation
5. Parametric Study
5.1. Temperature Characteristics of Airflow inside Tunnel under Ventilation Condition
5.2. Temperature Characteristics of Tunnel Lining and Lane Plate under Ventilation Conditions
5.3. Temperature Characteristics of Surrounding Rock under Different Ventilation Conditions
6. Heat-Insulating Layer Design Considerations
6.1. Mechanical Ventilation Velocities (Using FLOLIC Material)
6.2. Heat-Insulating Materials (with Mechanical Ventilation Velocity of 5 m/s)
7. Conclusions
- (1)
- According to the field test results, the proposed design parameters of the heat-insulating layer for the Dege tunnel can meet the anti-freezing requirement. And the accuracy of the proposed numerical model is verified by using the field test data, with the numerical results showing consistency with the field test results in terms of the curve trend and the data magnitude.
- (2)
- The monthly average temperature contours of the airflow in the tunnel are parabolic curves, with the temperature gradient being larger in the near-wall regions while smaller in the tunnel center. The airflow outside the tunnel requires a longer time to reach the same airflow temperature after applying the heat-insulating layer, when compared with the case having no heat-insulating layer. Furthermore, the heat-insulating layer prevents the heat transferring from the surrounding rock to the airflow in cold months (from January to March and from October to December), which plays a role of heat preservation. On the other hand, the heat-insulating layer prevents the heat transfer from the airflow to the surrounding rock in warm months (from April to September), which plays a role of thermal insulating.
- (3)
- After applying the insulating layer made of the FLOLIC material, the monthly average temperatures above the lane plate are always positive even in the coldest month, and the temperature gradient becomes smaller. Attaching the insulating layer to the lining wall would not protect the lane plate and the tunnel springing from damages from frost. The surface temperatures at different locations in the same tunnel cross-section from the lowest to highest points are at the center of lane plate, the tunnel vault, the tunnel spandrel and the tunnel springing, respectively.
- (4)
- The monthly average temperature of the surrounding rock increases by increasing the depth towards into the surrounding rock, while the temperature gradient decreases by increasing the depth towards into the surrounding rock. The variation phase is delayed and the variation amplitude is reduced. After reaching a certain depth, there only appears to be a very small change in the temperature of the surrounding rock. The size of the negative temperature region and the range of the temperature variation in the surrounding rock were both reduced after applying the heat-insulating layer.
- (5)
- By increasing the thickness of the heat-insulating layer, the temperature at the end of the heat-insulating layer on the secondary lining surface drops more significantly which usually increases the length of the lining section of negative temperature region. However, the lining section with a negative temperature at the tunnel ends becomes longer when a thinner heat-insulating layer is applied. Thus, the design thickness of the heat-insulating layer needs to take into account the influence of tunnel ventilation. The temperature of the secondary lining surface drops slightly by increasing the mechanical ventilation velocity, but the design thickness is not affected with the mechanical ventilation condition.
- (6)
- After applying the heat-insulating layer, lining sections with a negative temperature are observed near the two ends of the heat-insulating layer. It means that the heat-insulating layer should be extended at the tunnel entrance and the exit. When considering tunnel ventilation, the design length of the heat-insulating layer should be more than 1.5 times longer than the length with negative temperature at the entrance/exit. When the velocity of mechanical ventilation is increased, the design length of heat-insulating layer should be increased accordingly.
- (7)
- The design thickness and length vary when using different heat-insulating materials. In the case with the same thickness, the material with better heat-insulating performance has to be of a longer length compared to the normal material. Thus, using a material with relatively poor thermal insulating performance to satisfy the anti-freezing requirement would be helpful to reduce construction budgets and receive better economic benefits.
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Material | Density (kg/m3) | Heat Capacity (Unfrozen Zone) (J/kg∙°C) | Heat Capacity (Frozen Zone) (J/kg∙°C) | Thermal Conductivity (Unfrozen Zone) (w/m∙°C) | Thermal Conductivity (Frozen Zone) (w/m∙°C) |
---|---|---|---|---|---|
Surrounding rock | 2450 | 1178 | 896 | 1.91 | 2.77 |
Concrete material | 2385 | 970 | 970 | 1 | 1 |
FLOLIC | 60 | 230 | 230 | 0.024 | 0.024 |
Material Type | Density (kg/m3) | Heat Capacity (Unfrozen Zone) (J/kg∙°C) | Heat Capacity (Frozen Zone) (J/kg∙°C) | Conductivity (Unfrozen Zone) (w/m∙°C) | Conductivity (Frozen Zone) (w/m∙°C) |
---|---|---|---|---|---|
Polyurethane | 45 | 185 | 185 | 0.027 | 0.027 |
Stem method aluminosilicate sheet | 188 | 320 | 320 | 0.038 | 0.038 |
Material Type | Covering Section | Different Thickness for Insulating Layer (cm) | Lining Length in Negative Temperature at Tunnel Ends (m) | Reasonable Thicknesses (cm) |
---|---|---|---|---|
FLOLIC | Entrance | 2 | 55 | 4 |
4 | 0 | |||
6 | 0 | |||
Exit | 2 | 31 | 4 | |
4 | 0 | |||
6 | 0 | |||
Polyurethane | Entrance | 2 | 78 | 6 |
4 | 21 | |||
6 | 0 | |||
Exit | 2 | 49 | 6 | |
4 | 18 | |||
6 | 0 | |||
Stem method aluminosilicate sheet | Entrance | 2 | 94 | 6 |
4 | 47 | |||
6 | 0 | |||
Exit | 2 | 52 | 6 | |
4 | 29 | |||
6 | 0 |
Material Type | Covering Section | Different Lengths (m) for Insulating Layer with Certain Thickness | Lining Length in Negative Temperature at the End of Insulating Layer (m) | Reasonable Lengths (m) |
---|---|---|---|---|
FLOLIC | Entrance | 500 (4 cm thickness) | 74 | 700 |
600 (4 cm thickness) | 25 | |||
700 (4 cm thickness) | 0 | |||
Exit | 500 (4 cm thickness) | 52 | 600 | |
600 (4 cm thickness) | 0 | |||
700 (4 cm thickness) | 0 | |||
Polyurethane | Entrance | 600 (6 cm thickness) | 85 | 800 |
700 (6 cm thickness) | 37 | |||
800 (6 cm thickness) | 0 | |||
Exit | 600 (6 cm thickness) | 48 | 700 | |
700 (6 cm thickness) | 0 | |||
800 (6 cm thickness) | 0 | |||
Stem method aluminosilicate sheet | Entrance | 600 (6 cm thickness) | 33 | 700 |
700 (6 cm thickness) | 0 | |||
800 (6 cm thickness) | 0 | |||
Exit | 600 (6 cm thickness) | 17 | 600 | |
700 (6 cm thickness) | 0 | |||
800 (6 cm thickness) | 0 |
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Yan, Q.; Li, B.; Zhang, Y.; Yan, J.; Zhang, C. Numerical Investigation of Heat-Insulating Layers in a Cold Region Tunnel, Taking into Account Airflow and Heat Transfer. Appl. Sci. 2017, 7, 679. https://doi.org/10.3390/app7070679
Yan Q, Li B, Zhang Y, Yan J, Zhang C. Numerical Investigation of Heat-Insulating Layers in a Cold Region Tunnel, Taking into Account Airflow and Heat Transfer. Applied Sciences. 2017; 7(7):679. https://doi.org/10.3390/app7070679
Chicago/Turabian StyleYan, Qixiang, Binjia Li, Yanyang Zhang, Jian Yan, and Chuan Zhang. 2017. "Numerical Investigation of Heat-Insulating Layers in a Cold Region Tunnel, Taking into Account Airflow and Heat Transfer" Applied Sciences 7, no. 7: 679. https://doi.org/10.3390/app7070679