Study on Air Cabin Ventilation System by Local Structural Optimization during Tunnel Construction
Abstract
:1. Introduction
2. Calculation of Air Demand and Energy Consumption
2.1. Air Demand for Driving Face
- (1)
- Air demand of workers breathing:
- (2)
- Air demand for blasting operation:
- (3)
- Air demand of the minimum air velocity:
- (4)
- Air demand for diluting mechanical exhaust gas:
2.2. Ventilation Energy Consumption
2.2.1. Calculation Principle
- (1)
- Air volume of the forced draft fan
- (2)
- Ventilation resistance
- (3)
- Power calculation:
2.2.2. Calculation of Ventilation Energy Consumption
3. Numerical Simulation of the Air Cabin
3.1. Numerical Computational Control Model
3.2. Physical Model
3.3. Mesh Independence
3.4. Boundary Conditions
- (1)
- The air cabin and duct wall were set as the wall, the roughness constant Re was 0.57, and the average roughness height Rh was 0.09.
- (2)
- The left and right fans in the air cabin outlets were set as the velocity inlet, with a wind speed of −15.6 m/s and −14.6 m/s, respectively, where “-” represents the direction, and in this paper, −15.6 m/s represents a velocity of 15.6 m/s in the negative direction of the X-axis.
- (3)
- The air supply outlet of the inclined shaft air duct was set as the velocity inlet, with a wind speed of 25 m/s.
- (4)
- The air inlet is set as the pressure inlet, and the inlet pressure (relative to atmospheric pressure) is defined as 0.
- (5)
- All walls were set as non-slip walls.
3.5. Field Test Verification
4. Results and Discussion
4.1. Effect of Length–Width Ratio R of Air Cabin on Fan Efficiency
4.2. Effect of Fan Spacing S on Fan Efficiency
4.3. Effect of Middle Diaphragm Length on Fan Efficiency
4.4. Effect of Angle of the Middle Diaphragm in “Y” Shape on Fan Efficiency
4.5. Effect Evaluation of Air Cabin Ventilation System
5. Conclusions
- (1)
- The air cabin ventilation system reduces the ventilation energy consumption and fully uses the inclined shaft’s clearance section. A numerical model was developed to simulate the air cabin ventilation system. The model’s simulation results are reliable, as verified by the actual measurement data in the field. The ventilation system has a good dust removal effect and ensures a healthy construction environment.
- (2)
- Increasing the length of the air cabin makes the wind flow develop more fully, which is the same as the results of other scholars. The pressure difference of the fan is the maximum when the length–width ratio R of the air cabin is 1:2, which satisfies the wind flow wind development demand.
- (3)
- The change of fan spacing has less effect on the pressure difference between the two fans arranged in axisymmetry. As the spacing between two fans on the same side increases, the vortex area increases, and the greater the impact on the differential pressure of the 2# fan. As S increases from 2 m to 4 m, the differential pressure of the 2# fan increases slightly by 0.2%. The fan spacing S is taken as 2−4 m to ensure the ventilation efficiency of the three fans.
- (4)
- When the difference in air demand between the two sides of the air cabin is large, the distribution of the flow field is not uniform, and the phenomenon of suction of fans occurs. The average wind speed on the left side was 53.28% higher than on the right. The middle diaphragm can reduce the phenomenon while generating a larger local pressure loss. The difference in wind speed between the left and right sides was reduced to 35.84%. A “Y”−shaped middle diaphragm with an angle can reduce local loss. When the angle is 30°, the local pressure loss sharply decreased by 59.40%.
- (5)
- This paper uses the control variable method to study each factor’s effect on the fan’s efficiency without considering the interaction between the factors. Therefore, subsequent research can design orthogonal experiments to improve the final combination of air cabin design parameters.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
Abbreviations
Symbols | Notes |
A | The sectional area of the driving face |
d | The equivalent diameter of the air passage section |
D | The width of the air cabin |
G | Total explosive mass |
hg | The friction resistance of the air duct |
hg11 | The local resistance of the air duct |
hv | The dynamic pressure loss at the air duct outlet |
H | The height of the air cabin |
Ht | The total pressure of the ventilation system |
The acceleration of gravity in direction i | |
The term for the generation of turbulent kinetic energy k due to the mean velocity gradient | |
k | The air demand per unit power of machinery |
k1 | The effective utilization coefficient of mechanical power |
k2 | The working coefficient of mechanical power |
L | Duct length |
L0 | Ventilation length |
The maximum number of people | |
Ni | The power of machinery operating |
Nt | The total power of the ventilation system |
P | The static pressure |
p1 | The ambient air pressure of the fan |
p0 | The standard atmospheric pressure |
pa | The total pressure of the air cabin inlet |
Pf | The total pressure of the fan inlet |
ptot | Fan full-pressure |
q | The air volume required per person per minute |
Q0 | Air demand |
Qa | Fan flow |
Qb | Air demand for discharging the dust produced by blasting |
Qf | The air volume of the forced draft fan |
Qs | The total air demand for diluting mechanical exhaust gas |
Qv | The total air demand to meet the minimum air velocity |
Air demand for workers’ breathing | |
R | The length–width ratio of an air cabin |
S | The fan spacing in the air cabin |
The turbulent momentum source term | |
SKW | The mechanical motor power |
t | Ventilation time |
T0 | Standard temperature |
T1 | Ambient temperature |
v | The minimum air velocity |
v1 | The wind speed of the air duct outlet |
The component of flow velocity in the direction | |
The right angle coordinates | |
The component mass fraction | |
ρ | Air density |
β | The average value of 100 m air leakage rate |
The Prandtl number of the K equation | |
The Prandtl number of the equation | |
The turbulent energy dissipation rate | |
The laminar viscosity coefficient | |
λ | Friction coefficient |
η | Fan efficiency |
Local resistance coefficient |
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Working Condition | Air Demand (m3/min) |
---|---|
The total air demand for breathing of workers | 180 |
The total air demand for discharging the dust produced by blasting | 1220 |
The total air demand to meet the minimum air velocity | 738 |
The total air demand for diluting mechanical exhaust gas | 878.4 |
1220 |
Item | Parameter | |
---|---|---|
100 m air leakage rate of air duct (%) | 1.5 | |
The friction coefficient of the air duct | 0.02 | |
Air demand of driving face (m3/min) | 1220 | |
Ventilation length of the inclined shaft (m) | 1030 | |
Left tunnel | Ventilation length of small mileage (m) | 1230 |
Right tunnel | Ventilation length of small mileage (m) | 1793 |
Ventilation length of large mileage (m) | 100 | |
Duct diameter (m) | 1.6 | |
Air density (kg/m3) | 1.004 |
Item | Calculated Value | |
---|---|---|
Air volume (m3/s) | Small mileage of left tunnel | 28.64 |
Small mileage of right tunnel | 31.28 | |
Large mileage of right tunnel | 24.12 | |
Resistance of air duct (Pa) | Resistance along the air duct | 2863.62 |
Local resistance at fan inlet | 82.99 | |
Local resistance at Three bends of air duct | 53.77 | |
Dynamic pressure loss at the air outlet of the air duct | 51.39 | |
Resistance at the inclined shaft (Pa) | Friction resistance of the inclined shaft | 99.96 |
Local resistance of inclined shaft air inlet | 1.03 | |
Local resistance of inclined shaft air outlet | 8.66 | |
Total resistance of ventilation system (Pa) | 3161.42 | |
Total power of ventilation system (kW) | 347 |
Item | Calculated Value | |
---|---|---|
Air volume (m3/s) | Small mileage of left tunnel | 23.76 |
Small mileage of right tunnel | 26.66 | |
Large mileage of right tunnel | 20.64 | |
Resistance of air duct (Pa) | Resistance along the air duct | 1528.92 |
Local resistance at two bends of the air duct | 35.85 | |
Dynamic pressure loss at the air outlet of the air duct | 51.39 | |
Resistance of diaphragm (Pa) | Friction resistance of the diaphragm | 552.28 |
Local resistance at the inlet of the inclined shaft fan | 79.09 | |
Local resistance at the outlet of the inclined shaft fan | 25.7 | |
Local resistance at the junction of the inclined shaft and tunnel diaphragm | 64.92 | |
Local resistance at the junction of the right tunnel and cross-passage diaphragm | 3.01 | |
Local resistance at the junction of tunnel diaphragm and fan | 24.15 | |
Resistance at the inclined shaft (Pa) | Friction resistance of the inclined shaft | 107.21 |
Local resistance of inclined shaft air inlet | 18.58 | |
Local resistance of inclined shaft air outlet | 9.29 | |
Total resistance of ventilation system (Pa) | 2500.39 | |
Total power of ventilation system(kW) | 275 |
Item | 1 | 2 | 3 | 4 | 5 |
---|---|---|---|---|---|
Length width ratio R | 1:1 | 1:1.5 | 1:2 | 1:3 | 1:4 |
Fan spacing S | 2 m | 4 m | 6 m | 8 m | ~ |
Length of the middle diaphragm | 1:1 D | 1:1.5 D | 1:2 D | 1:3 D | 1:4 D |
The angle of the middle diaphragm | 0° | 30° | 45° | 60° | 90° |
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Yang, S.; Ren, R.; Wang, Y.-Q. Study on Air Cabin Ventilation System by Local Structural Optimization during Tunnel Construction. Buildings 2022, 12, 2235. https://doi.org/10.3390/buildings12122235
Yang S, Ren R, Wang Y-Q. Study on Air Cabin Ventilation System by Local Structural Optimization during Tunnel Construction. Buildings. 2022; 12(12):2235. https://doi.org/10.3390/buildings12122235
Chicago/Turabian StyleYang, Shuai, Rui Ren, and Ya-Qiong Wang. 2022. "Study on Air Cabin Ventilation System by Local Structural Optimization during Tunnel Construction" Buildings 12, no. 12: 2235. https://doi.org/10.3390/buildings12122235
APA StyleYang, S., Ren, R., & Wang, Y.-Q. (2022). Study on Air Cabin Ventilation System by Local Structural Optimization during Tunnel Construction. Buildings, 12(12), 2235. https://doi.org/10.3390/buildings12122235