Indoor Particulate Matter Transfer in CNC Machining Workshop and The Influence of Ventilation Strategies—A Case Study
Abstract
:1. Introduction
2. Materials and Methods
2.1. In-Situ Experiments
2.1.1. Investigated CNC Workshop
2.1.2. Particle Size Measurement
2.1.3. Particle Concentration Monitoring
2.1.4. Infiltration Rate of Enclosures
2.2. Numerical Simulation
2.2.1. Computational Domain
2.2.2. Boundary Conditions
2.2.3. Numerical Setup
2.2.4. Model Validation
2.3. Ventilation Strategies
3. Results
3.1. Monitored Results
3.1.1. Particle Size Distribution
3.1.2. Oil Mist Concentration in CNC Machining Workshop
3.1.3. Infiltration Rate of Enclosures
3.1.4. Oil Mist Concentration Inside the Enclosures
3.2. Ventilation Strategies
3.2.1. Particle Concentration Distribution
3.2.2. Airflow Patterns
3.2.3. Improved Ventilation Strategies
- (1)
- Average particle mass concentration in the working area at respiratory height was calculated as an evaluation index. In this study, the simulated particle size was 2.5 μm. The mass concentration in the working area was averaged for the comparisons.
- (2)
- Mean age of air is an index used to investigate the time when the air at a certain point or the whole space is renewed. A user-defined arbitrary scalar Φi represented the mean age of air in the commercial solver. The transport of scalar was solved by one additional convection-diffusion equation:
- (3)
- Ventilation efficiency is an index used to investigate the energy utilization effectiveness of a certain air distribution form. The higher the ventilation efficiency indicates, the better the system’s performance. The theoretical calculation formula of ventilation efficiency, ET, is calculated by Equation (6).
4. Discussion
4.1. Ventilation Strategies in Workshop
4.2. Limitation of this Study
5. Conclusions
- (1)
- The measurement results show that in the CNC workshop, the 99% cumulative mass concentration of particles was distributed within 2.5 μm, and the particle size distribution of particles at different heights in the workshop varied slightly. The infiltration rate of the fully closed enclosure was 1.117 ± 0.208 m3/s. The release rate of particles from the full enclosure was 6.545 ± 0.047 μg/s. The heat released from the enclosures can be neglected because the metalworking fluids take away most of the exclusive heat from the machining process.
- (2)
- This paper uses the RNG k-ε model and the Lagrange method to simulate the workshop’s velocity and particle field. The simulation results are consistent with the measured data in terms of velocity and particle mass concentration.
- (3)
- By comparing the simulation results of the five ventilation strategies with the same ventilation rates, the bilateral longitudinal ventilation strategy is superior to other methods in terms of average particle concentration and ventilation efficiency in the working area; Bilateral longitudinal ventilation strategy is only slightly higher than different strategies in terms of the age of air.
- (4)
- Bilateral longitudinal ventilation can make full use of the workshop corridor as the ventilation pathway. It can be further optimized by adding axial fans in the center of the workshop.
Author Contributions
Funding
Institutional Review Board Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
Abbreviations
CNC | Computer Numerical Control |
CFD | Computational Fluid Dynamics |
RNG | Renormalization group |
Nomenclature | |
R | Release rate of particles from the enclosure, μg/s |
I | Infiltration rate of the enclosure, m3/s |
P | Air change rate, 1/s |
t | Time, s |
V | Inner volume of enclosure, V = constant = 3.22 m3 |
Q | Ventilation rate, m3/s |
M | Total release rate of particles, μg/s |
Ci,p | Concentrations of particle matter inside the enclosure, μg/m3 |
Co,p | Concentrations of particle matter outside the enclosure, μg/m3 |
Ci,c | Concentrations of CO2 inside the enclosure, ppm |
Cy | Maximum allowable concentration of indoor particle matter, mg/m3 |
Cj | Concentration of pollutants entering the workshop room, mg/m3 |
ρ | Fluid density, kg m−3 |
v | Fluid velocity, m/s |
μeff | Effective viscosity of the air, Pa s |
Γi | Diffusion coefficient, m2/s |
ET | Ventilation efficiency |
Ce | Average particle concentration at outlets, μg/m3 |
Cb | Average particle concentration at respiratory height, μg/m3 |
Cs | Average particle concentration at air supply inlet, μg/m3 |
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Measuring Equipment | Parameters | Range | Accuracy |
---|---|---|---|
Testo 405i Hot-wire anemometer | Velocity (m/s) | 0–30 | ±0.015 |
Telaire 7001 | CO2 concentration (ppm) | 0–10,000 | ±50 |
HOBO Data logger | CO2 concentration (ppm) | 0–2500 | ±1 |
A4-CG Particulate sensor | Concentration of particle matters (μg/m3) | 0–6000 | ±10 |
Vario CAM Infrared imager | Surface temperature (°C) | 0–100 | ±1.5 |
APS 3321 | Particle size (μm) | 0.5–20 | ±0.02 (1 μm), ±0.03 (10 μm) |
Measuring Parameters | Boundary Conditions | Inputs |
---|---|---|
Air supply inlets | Air supply velocity (m/s) | 3.21 ± 0.10 |
Air supply angle (°) | 45 | |
Air temperature(°C) | 25 | |
Particles from enclosures | Mass concentration (μg/m3) | From A4-CG Particulate sensors |
The infiltration rate of fully enclosures (m3/s) | From tracer gas experiment | |
Number of machines (on) | Zone 1 | 16 |
Zone 2 | 11 | |
Zone 3 | 8 | |
Zone 4 | 0 | |
Zone 5 | 6 | |
Zone 6 | 6 | |
Thermal boundary | Enclosure Wall (°C) | 35.5 |
Meta-machining fluid (°C) | 25 | |
Other inner walls (°C) | 32 |
Enclosure Number | Rotation Speed of Spindle (1/min) | Travel Distance of Spindle (min) | Moving Speed of Spindle (mm/min) | Infiltration Rate (m3/s) |
---|---|---|---|---|
B1 | 0 | 0 | 0 | 1.472 |
B2 | 0 | 0 | 0 | 1.448 |
B4 | 0 | 0 | 0 | 1.523 |
B5 | 0 | 0 | 0 | 1.739 |
B6 | 0 | 0 | 0 | 0.603 |
B7 | 0 | 0 | 0 | 0.861 |
C1 | 2000 | 200 | 1000 | 1.307 |
2000 | 200 | 3000 | 0.758 | |
5000 | 100 | 1000 | 0.959 | |
5000 | 200 | 2000 | 0.980 | |
5000 | 200 | 3000 | 0.883 | |
5000 | 300 | 1000 | 1.204 | |
5000 | 300 | 3000 | 1.338 | |
8000 | 100 | 2000 | 1.078 | |
8000 | 200 | 1000 | 1.255 | |
8000 | 200 | 3000 | 1.106 | |
8000 | 300 | 2000 | 1.418 |
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Yao, H.; Qiu, S.; Lv, Y.; Wei, S.; Li, A.; Long, Z.; Wu, W.; Shen, X. Indoor Particulate Matter Transfer in CNC Machining Workshop and The Influence of Ventilation Strategies—A Case Study. Sustainability 2023, 15, 6227. https://doi.org/10.3390/su15076227
Yao H, Qiu S, Lv Y, Wei S, Li A, Long Z, Wu W, Shen X. Indoor Particulate Matter Transfer in CNC Machining Workshop and The Influence of Ventilation Strategies—A Case Study. Sustainability. 2023; 15(7):6227. https://doi.org/10.3390/su15076227
Chicago/Turabian StyleYao, Huimin, Shanshan Qiu, Yuling Lv, Shen Wei, Ang Li, Zhengwei Long, Wentao Wu, and Xiong Shen. 2023. "Indoor Particulate Matter Transfer in CNC Machining Workshop and The Influence of Ventilation Strategies—A Case Study" Sustainability 15, no. 7: 6227. https://doi.org/10.3390/su15076227