'Modeling of Gas Distribution in an Indoor Space' simulation project by pankajkumar979


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I created a new simulation project called 'Modeling of Gas Distribution in an Indoor Space':

Methane gas is a hazard in underground coal mining. It enters the mine ventilation system from tbe breakup of coal or from the face. This can lead to a explosion and injury to miners. This simulations aims to study the distribustion of methane concentration in a mining area and results are compared with a experimentals.


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#2

Description

Mining has been around for hundreds of years and it is considered as one of the most dangerous occupation. There are many problems faced during mining and one of them is the presence of methane. Many peoples have lost their lives because of explosions due to the accumulation of methane. Mine face ventilation systems were designed for ventilation to prevent its accumulation near the face areas of underground coal mines. The importance of ventilations for controlling underground methane levels was recognized in the 1920s.


The study related to the distribution of methane and airflow patterns under different ventilation conditions was conducted by Taylor, Chilton and Goodman. It was done for setting the guideline for the safety purpose.This study focused on validating CFD software using full-scale ventilation experimental data that assessed how curtain setback distance impacted airflow patterns and methane distributions at an empty mining face. Three CFD models of face ventilation with 4.6, 7.6 and 10.7 m are constructed and simulation results are validated with the data.



Geometry

Geometry was created by using Catia V5 with the dimensions as shown in the Figure 1.


Figure 1. Dimensions of the geometry with different sizes of face ventilation, Case A- 4.6m, Case B- 7.6m, Case C- 10.7m

Mesh

Tetra-dominant automatic Mesh with refinement for inflation was selected as it requires less computing time. Fine meshing was used at the mining face to bring out the features of methane inlet.


methane_inlet

Figure 2: Cross section of the mesh showing the inflation at the wall and methane inlet.

Boundary Condition

After mesh generation boundary conditions are defined for CFD domain. Custom boundary condition is used in simulations as it gives greater flexiblity and has the option of selecting the number of passive scalar and value can be assigned durung the simulation.

Geometry1


Figure 3: Boundary Conditions, STDR-Specific turbulence dissipation rate, PS1: passive scalar 1, TKE: Turbulence kinetic energy.

Zero Dirichlet boundary condition is used for velocity on all walls. Flow rate for air at the inlet is 2.80m^{3}/s and total methane flow rate at 8 inlets is 0.016m^{3}/s. Methane flow is divided equally at each inlets, i.e. 0.002m^{3}/s. k \omega SST model is used for accounting turbulence effects.

Grid Independence study

Three different meshes are used to study its effect on the simulation results. Velocity magnitude was calculated at the cross-section 1m from the mining face.

grid independence
Grid
From the figure we see clearly that the solution is grid independent although in case of Fine mesh, solution looks more smooth.

Results and discussion

By completion of all the test runs, velocity and methane concentration were studied and compared with the experiment results obtained by [3]. In case A, 16 locations in the geometry were used for measuring data as refered in the paper [3], similarly 24 locations in case B and 25 locations in case C. All the probe locations are at a height of 1.1m

face
Figure 4: Taken from [2], locations of probes.

Velocity


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Figure 5.1: Comparison of Velocity magnitude for 4.6m face ventilation with experimental data



Figure 5.2: Comparison of Velocity magnitude for 7.6m face ventilation with experimental data



Figure 5.3: Comparison of Velocity magnitude for 10.7m face ventilation with experimental data

From the above figure we see clearly that velocity magnitude obtained in simulation agrees well with the experimental data.

Methane Concentration


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Figure 6.1: Comparison of Methane Concentration for 4.6m face ventilation with experimental data


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Figure 6.2: Comparison of Methane Concentration for 7.6m face ventilation with experimental data


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Figure 6.3: Comparison of Methane Concentration for 10.7m face ventilation with experimental data

We notice from the above figure that methane concentration in simulation is higher than the experimental data. There is a parameter which determines whether the data is agreeable with the experimental data or not.

Coefficient of Determination R

The coefficient of determination is the square of the Pearson’s product-moment correlation coefficient and describes the proportion of the total variance in the observed data that can be explained by the model. It ranges from 0.0 to 1.0, with higher values indicating better agreement, and is given by

R^{2} = \frac{\sum{(X -\overline{X})(Y -\overline{Y})}}{\sqrt(\sum{(X -\overline{X})^{2}})\sqrt(\sum{(Y -\overline{Y})^{2}})}

Values greater than 0.5 considered acceptable [2]. Above table shows the coefficient of determination for each simulation and indicates better agreement between modeled and measured airflows than modeled and measured methane levels. These values for airflow range from 0.70–0.80 and 0.51–0.59 for methane.

References

[1] Luxner JV. Face ventilation in underground bituminous coal mines: airflow and
methane distribution patterns in immediate face area-line brattice. Washington DC: Bureau of Mines; 1969.

[2] Taylor CD, Chilton JE, Goodman GVR. Guidelines for the control and monitoring of methane gas on continuous mining operations. Depart Health Hum Serv, Inform Circulat 2010;3:322–40

[3] Zhou Lihong, Pritchard Christopher, Zheng Yi “CFD modeling of methane distribution at a continuous miner face with various curtain setback distances”
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