M3TC Technical Report UG Mine Ventilation 2

March 22, 2018 | Author: Mc Hunt | Category: Natural Gas, Computational Fluid Dynamics, Viscosity, Turbulence, Mining
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M3TC Technical ReportM3TC/TPR/2012/03 A Technical report on COAL MINE DESIGN AND MODELLING A STUDY OF FLOW PATTERNS IN DIFFERENT MINING CONFIGURATIONS OF A HORSESHOE MINE TUNNEL Prepared by: Lee Cheow Beng Kenny, Dr. Agus P. Sasmito, Dr. Erik Birgersson and Prof. Arun Sadashiv Mujumdar Minerals, Metals and Materials Technology Centre (M3TC) National University of Singapore Report No. M3TC TN-12-03 May 2012 Not for general distribution Foreword As a part of its mission, M3TC is involved in providing appropriate manpower training in the areas of minerals, metals and materials sector. One of our ongoing research programs that analyzes the underground mine ventilation system in coal mines to design an efficient, intelligent and low cost mining ventilation system is tied up with this mission of training young engineers for possible careers in the resources industrial sector. This is accomplished by guiding final year undergraduate students in various engineering departments at NUS. This M3TC report is a report prepared by a Final Year student as part of his B.Eng. degree requirements. This study involved analysis of an underground mining ventilation system through the use of mathematical modeling. The goal is to enhance efficiency of the system so as to reduce the carbon footprint of the ventilation system which is crucial to the security and safety of the coal mining operation. Director of Research M3TC 2 Acknowledgements The author Kenny wishes to acknowledge the assistance of the following people/organisations: 1. Professor Mujumdar, Arun Director M3TC, Mechanical Engineering National University of Singapore. Firstly, l would like to thank Professor Mujumdar for the opportunity to work on this research project. The mentorship, advice and encouragement given throughout the duration of this research project and dissertation is highly appreciated. 2. Assistant Professor Birgersson, Erik Engineering Science Department of Chemical Engineering For the continual assessment of this research report and making me a personal communicator and person. Special Thanks to 3. Sasmito, Pulung Agus Department of Mechanical Engineering For his patience, advice and help during the length of this entire research project. Most especially for his advice and technical expertise in assisting in ANSYS FLUENT Computational Fluid Dynamics (CFD) Software. 3 TABLE OF CONTENTS 1. List of Figures .................................................................................................................... 5 2. List of Tables ..................................................................................................................... 5 3. List of Symbols .................................................................................................................. 6 4. List Of Appendix ............................................................................................................... 6 Summary .................................................................................................................................... 7 1. Introduction ........................................................................................................................ 8 1.1 Types of Mines ............................................................................................................ 8 1.1.1 Longwall Mining ................................................................................................. 8 1.1.2 Room and Pillar Mining....................................................................................... 9 1.2 Aims and Objectives ................................................................................................. 10 2. Basic Concepts ................................................................................................................. 12 2.1 Introduction to Mining Gases .................................................................................... 12 2.1.1 Methane.............................................................................................................. 12 2.2 Coal Mining Ventilation Systems ............................................................................. 13 2.3 Numerical methodology ............................................................................................ 15 2.4 Turbulent Models ...................................................................................................... 15 3. Literature Review............................................................................................................. 17 4. Coal Mine Design, Modelling and Simulation ................................................................ 21 4.1 Introduction ............................................................................................................... 21 4.2 Aim and Objectives ................................................................................................... 21 4.3 Model Development .................................................................................................. 21 4.4 Numerics ................................................................................................................... 22 4.5 Assumptions .............................................................................................................. 23 4.6 Choosing A Turbulence Model ................................................................................. 23 4.6.1 Comparisons Of Spalart Allmaras, Rsm, k-ε and k-ω Turbulent Models ....... 23 5. Results and Discussion .................................................................................................... 27 5.1 Analysis Of Molar Concentration Of Methane At Z-Iso Surfaces And For Y Iso- Surface @ Y=0 Metres ........................................................................................................ 27 5.1.1 Discussion: Methane Distribution in Z Iso-surfaces .......................................... 28 5.1.2 Discussion: Methane Distribution for Y=0 Iso Surface [51] ............................. 29 5.2 Analysis Of Velocity Distribution Of Z-Iso Surface at 4, 8, 12, 16 Metres And Velocity Distribution at Y=0 ............................................................................................... 30 4 5.2.1 Discussion: Velocity Distribution for Z iso-surfaces ......................................... 31 5.2.2 Discussion: Velocity distribution for Y=0 surface ............................................ 32 5.3 Analysis of Pumping Power and ventilation effectiveness ....................................... 33 6. Conclusion ....................................................................................................................... 35 7. Recommendations for Future Work................................................................................. 36 5 1. List of Figures Figure 1: Longwall Mining ........................................................................................................ 9 Figure 2: Longwall Mining ........................................................................................................ 9 Figure 3: Room and Pillar Mining ........................................................................................... 10 Figure 4: Room and Pillar Mining ........................................................................................... 10 Figure 5: Coward Diagram showing the relationship between Oxygen and Methane Content .................................................................................................................................................. 13 Figure 6: Iso-surfaces ............................................................................................................... 38 Figure 7: Case 1: Tunnel Configuration with the ventilation duct placed at an angle of 45 from the center of the cross section as shown in figure A ....................................................... 39 Figure 8: Case 2: Tunnel Configuration with the ventilation duct placed on the left side of the tunnel........................................................................................................................................ 40 Figure 9: Case 3: Tunnel Configuration with circular ventilation duct placed on the right side of the horseshoe tunnel ............................................................................................................ 41 Figure 10: Case 4: Tunnel Configuration whereby circular duct is placed directly above the center of the z-cross section of the tunnel ................................................................................ 42 Figure 11: Case 5: Tunnel configuration with an overhead ventilation duct with 2 sets of holes. Each set consists of two holes at an angle of 45° away from one another. Total number of 4 holes. ................................................................................................................................. 43 Figure 12: Case 6: Tunnel Configuration where the overhead ventilation duct has two downward holes angled at 90° and are at a spacing of 10m. ................................................... 44 Figure 13: Case 7: Tunnel Configuration where the overhead ventilation duct has five downward holes angled at 90° and are at a spacing of 5m ...................................................... 45 Figure 14: Case 8: Tunnel Configuration with a square ventilation duct placed at an angle of 45° from the center of the cross section [compare with Case 1] ............................................. 46 Figure 15: Case 9: Tunnel Configuration whereby square duct is placed directly above the center of the z-cross section of the tunnel ................................................................................ 47 Figure 16:Case 10: Tunnel with an overhead duct with a ―U-shaped‖ splitter Add-on .......... 48 Figure 17: Case 11: Tunnel with an overhead duct with a ―Y-shaped‖ Add on. ..................... 49 2. List of Tables Table 1: Ways to improve mining ventilation ......................................................................... 11 Table 2: Literature Review Table ............................................................................................ 20 Table 3: Number of Cells in Tunnel Layouts .......................................................................... 22 Table 4: Pumping Power, Mass flow rate of Methane ............................................................. 33 6 3. List of Symbols m/s Speed, Metres per second m Length, Metres k-ω Turbulence model, k-omega k-ε Turbulence model, k-epsilon RSM Turbulence model, Reynolds Stress Model ° Angle, in degrees T Temperature, in Kelvins V Volume, in m 3 x, y, z axis @ Abbreviation, ‗at‘ kmol Amount of substance, kilomole m 3 Volume, Metre cube 4. List Of Appendix APPENDIX A: ISO- SURFACES ........................................................................................... 38 APPENDIX B: TUNNEL CONFIGURATIONS .................................................................... 39 APPENDIX C: CONCENTRATION OF METHANE (CH4) FOR Z-ISO SURFACE AT 4M .................................................................................................................................................. 50 APPENDIX D: MOLAR CONCENTRATION OF METHANE(CH4) FOR Z-ISO SURFACE AT 8M ................................................................................................................... 52 APPENDIX E: MOLAR CONCENTRATION OF METHANE(CH4) FOR Z-ISO SURFACE AT 12M ................................................................................................................. 54 APPENDIX F: MOLAR CONCENTRATION OF METHANE(CH4) FOR Z-ISO SURFACE AT 16M ................................................................................................................. 56 APPENDIX G: MOLAR CONCENTRATION OF METHANE(CH4) FOR Y-ISO SURFACE AT Y=0 ................................................................................................................. 58 APPENDIX H: VELOCITY DISTRIBUTION FOR Z-ISO SURFACE AT Z=4M .............. 60 APPENDIX I: VELOCITY DISTRIBUTION FOR Z=8M ISO-SURFACE ......................... 62 APPENDIX J: VELOCITY DISTRIBUTION FOR Z=12M ISO SURFACE ........................ 64 APPENDIX K: VELOCITY DISTRIBUTION FOR Z=16M ISO-SURFACE ...................... 66 APPENDIX L: VELOCITY DISTRIBUTION FOR Y=0 ISO-SURFACE ........................... 68 APPENDIX M: INCLUSION OF A BRATTICE TO AID GENERAL AIRFLOW IN A CROSSCUT REGION IN ROOM-AND-PILLAR MINING ................................................. 70 APPENDIX N: CHOICE OF TURBULENT MODEL ........................................................... 86 7 Summary This final year research project covers the aspect of mining ventilation related specifically to the - horseshoe shaped tunnel found in underground coal mines. This horseshoe shaped tunnel is made specifically for a coal mining method known as longwall mining. The main objective of this final year report is to understand the flow patterns that take place inside such a tunnel. The underlying flow will be compared to other theoretical designs for analysis. The scope of this final year research project will include modeling work for 11 different ventilation layouts for the horseshoe shape tunnel configuration. After a thorough analysis, this review will offer recommendations of how better designs can be built and applied to walkways and covered areas so as to make the underground structure a safer place for the miners. A mine without proper ventilation controls will be prone to methane buildups and explosions. The modelling work for this review was carried out by a powerful, yet easy to use software known as ANSYS Fluent. 8 1. Introduction Coal, a combustible fossil fuel, is an important resource for electricity generation. It is mined from underneath the ground where coal strata is present. Coal originates from terrestrial land plants buried under increased heat and pressure from millions of years ago. The land plants decompose to become an organic chemical compound known as Type III kerogen, which eventually becomes coal after further heating in a process known as diagenesis 1 . The extraction of coal from an underground coal mine is extremely dangerous. The coal mining industry has claimed 2631 coal miners in 2009 2 , with the possibility of many more being unreported. The casualty rate in coal mines is attributed to a high number of explosions, occurring due to heavy buildup of dangerous mining gases such as methane and accumulations of dust which causes dust explosions. Improving the amount of air ventilation would improve the level of safety in coal mines. An efficient and adequate ventilation would reduce the possibility of explosion by mitigating the amount of dangerous gases present by aiding airflow and preventing recirculation. This final year report will serve with an aim to achieve better airflow in underground coal mines. 1.1 Types of Mines 1.1.1 Longwall Mining Longwall mining is a form of underground coal mining where a stretches of coal are mined in a single slice, resulting in straight and long sections. The longwall panel (the block of coal that is being mined) is typically 3–4 km long and 250–400 m wide. To mine the coal surface, miners use a equipment called the shearer as shown in figure 2. Subsequently, modern equipment known as hydraulic jacks, are used to support the roof of the mined tunnel. 1 http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B8G3P-4SH7GNY- B&_user=10&_coverDate=12%2F31%2F1967&_rdoc=1&_fmt=high&_orig=gateway&_origin=gateway&_sort=d&_docan chor=&view=c&_searchStrId=1701756537&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_use rid=10&md5=6fbb8b997244c9fe50dd7d7bde77c30e&searchtype=a 2 http://www.chinadaily.com.cn/regional/2010-10/20/content_11436191.htm) 9 Figure 1: Longwall Mining Figure 2: Longwall Mining 1.1.2 Room and Pillar Mining Room and pillar (also called bord and pillar) is a mining process in which square shaped rooms of coal are cut, leaving "pillars" of untouched material to support the roof overburden. The rooms are generally 6-8m wide and the pillars can be up to 30m wide. As the mine is formed, the general layout of the mine would have a grid-like pattern. Room and pillar mining is usually used for relatively flat-lying deposits. 10 Figure 3: Room and Pillar Mining Figure 4: Room and Pillar Mining 1.2 Aims and Objectives In this final year report, the conventional ventilation layout and design of a horseshoe shaped coal mine tunnel [Figure 7] will be simulated and evaluated by CFD analysis. The analysis of the results will provide new answers for the ventilation ducts position, size and suitability of use. The results of this final year report will conclude if it is the most ideal configuration for having in a ventilation network. The original tunnel configuration was first identified in Parra (2009). According to Parra, traditional ventilation tunnels are placed overhead, at an 45° angle from the center of the tunnel [Figure 7]. Through this review, 11 different tunnel configurations will be drawn and analyzed. This analysis could present an integrated engineering design in the future to improve existing mine ventilation and air conditioning. 11 Generally, a coal mine with an extensive coal ventilation system will be able to prevent explosions, save lives, and minimize any additional costs through extensive repair and injury claims by the mine-workers. This project addresses the ventilation of mines from a modelling and simulation point of view. The models will be drawn and meshed on GAMBIT software, and subsequent Computational Fluid Dynamics (CFD) analysis will be implemented using FLUENT 6.3 Software. This final year project will begin with some of the basic concepts of methane and ventilation networks. Subsequently, there will be the description of the modelling simulation of 11 different tunnel layouts that can be found in chapter 4 [21]. The results will be discussed after. Coal mining ventilation is a broad subject. While this final year project covers a specific section, there are other ways to improve safety in a working coal mine. The ideal method will be to implement control of the quality, quantity and temperature humidity of the underground atmospheric environment. More often than not, dangers in a coal mine will increase when the overall temperature increases due to the increased presence of gases and dust. Secondly, increased size of a coal mine, most probably to increase business output, will give rise to higher complexity, increased manpower and mechanization needs. Increasing the design and subsequently airflow of a coal mine is only one way of improved mining ventilation. The others are listed in Table 1 (Hartmann, nd). For the purpose of this review, the focus will be the design of specific tunnel configurations catered to a certain tunnel shape. Other factors that can lead to improved ventilation in tunnel networks Ways to improve mining ventilation 1. Systems approach which optimizes complex industrial operations, permitting personnel, materials and methods to be coordinated in the most efficient manner 2. Incorporated on Hi-tech and monitoring devices 3. Extensive federal legislation to impose strict checks and fines to those that do not abide by rules 4. Application of technology with consideration to the Political, social and environmental consequences of any inclusion of device/process. Table 1: Ways to improve mining ventilation 12 2. Basic Concepts 2.1 Introduction to Mining Gases 2.1.1 Methane Methane, commonly referred to as natural gas, is an odourless, colourless and tasteless gas. It is one the by-products of high rank coal seams found in coal mines. Methane is a highly diffusive gas, and translates by moving from high to low pressure zones, and/or from higher to lower concentrations. Methane is emitted when fissures and underlying pores in the coalbed are exposed when the coal seam is extracted 3 . Fundamentally, it is a type of hydrocarbon which consists of one atom of carbon and 4 atoms of hydrogen (CH4). It is one of the most common and dangerous gases found in coal mines. Current requirements by government regulatory boards state a maximum level of 1% in most coal mines. It is thus our topic of interest to remove methane from underground coal mines to a level below 1%. This will make breathing underground sustainable for the mine workers and prevent explosions. When coal is mined, other dangerous or contamination gases such as carbon dioxide, higher hydrocarbons and dust are produced as well. To note, the volume of by-product gases increases with the rank of coal, where, for every ton of coal formed, nearly 20 000 (565 of carbon dioxide and 27000 (765 of methane is produced. In events where output is ramped up due to increased demand or higher coal prices, increased mining activity would lead to the increase of internal temperature and pressure and the depletion/total elimination of oxygen (Hargrave, 1973). Methane is an asphyxiant, capable of driving out oxygen and causing death by suffocation. When air of high concentration of methane is combined with oxygen, explosions will occur. Methane gas has been the culprit for tens of thousands of death among coal miners worldwide. It is undoubtedly one of the most feared gases in the mining industry. In addition, methane is also a relatively potent greenhouse gas, residing in the Earth‘s atmosphere for approximately 10 years. An atmospheric methane concentration between 5 and 15% can ignite and explode at standard pressure and temperature. According to Figure 5, the most powerful explosive 3 http://www.erc.uct.ac.za/Research/publications/05Lloyd-Cook%20Methane%20release.pdf 13 methane/air mixture is where there is 9.5% methane, as the combustion process consumes all methane (CH4) and oxygen (O2), producing carbon dioxide (CO2) and water (H2O), (Eltschlager et al. 2001). The reaction between the methane and oxygen can be depicted as: CH4 + 2O2 → CO2 + 2H2O Figure 5: Coward Diagram showing the relationship between Oxygen and Methane Content From the diagram above, the dangerous combination of methane and oxygen is found on at the top side of the diagram. As such, ventilation systems in coal mines have to keep methane concentrations low and increase airflow such that oxygen content is readily available. 2.2 Coal Mining Ventilation Systems The mine ventilation system consists of fans, airways, and control devices for conducting airflow. These ventilation equipment are typically used to reduce the high amount of goaf gas (CO2 and methane) in mines. In addition, the ventilation system works in tandem with the 14 selection of an optimal number of openings to surface to improve overall performance. In coal mining ventilations, the shape, size, and number of airways, location of control devices and fans, result in different types of airflows. The aim of this final year report is to aim for quality airflows; one with high air velocity in reference to the inlet velocity of the ventilation and low concentrations of methane. The most important consideration for choosing the ventilation system for a mine is that the ventilation system must complement the mining method, and vice versa. A carefully engineered and chosen ventilation system can also give rise to better contingency, emergency and evacuation plans in times of emergencies (Hartmann, n.d). The mine airflow distribution is completely defined by (1) the physical parameters of the airways including shape, area, length and characteristics of the airway surface; (2) the layout of the mine openings; (3) the pressure sources (eg fans) in the system, their location and characteristics; and (4) the interconnections between the airways, mine openings and pressure sources (Hartmann, n.d) A mining ventilation system is akin to a human body, where a passageway of necessary operating supply (air) is needed to be supplied to working areas of the body(in this case, the mine) . There is also a need to remove a variety of waste products generated in the mining process as well. In coal mining, the primary pollutant to be removed is methane gas. The goal is to keep methane concentration levels to safe and low levels. To provide adequate ventilation to a coal mine, it would require excellent primary ventilation channels such as a blowing ventilation duct to ensure good air distribution and adequate fan capabilities. A good and safe coal mine should have various control devices such as stoppings 4 , overcasts 5 , regulators 6 , line brattices 7 and fans so that the arranged airflow can be managed in a desired manner in the desired quantities. Control devices in mine ventilation serve to 1) separate the intake and return airstreams in adjacent airways 2)allow the crossing of the intake and return streams without mixing(overcasts) and 3) regulate the flow of air 4 Stoppings are physical barriers erected between intake and return airways to prevent air flowing in them from mixing with each other. Stoppings can be temporary or permanent. 5 Overcasts or crossings are air bridges that allow the intake and return airflows to cross on another without mixing. 6 Regulators are used to control and redistribute the quantity of flow in each split of air. The regulator is an opening in a stopping in an airway and may be equipped with an adjustable or sliding door 7 Brattices are partition placed in the opening to divide it into intake and return airways 15 through the various airways in the desired manner when the quantity has to be split between the airways (regulators) (Hartmann, nd). 2.3 Numerical methodology The models in this final year research paper (APPENDIX B) were drawn in the GAMBIT pre-processor software. This software has the capability to draw various geometries ranging from 1-D to 3-D. In addition, the meshes for the models in Appendix B were meshed in GAMBIT. GAMBIT software provides a variety of mesh structures – triangular, tetrahedral, hexahedral and polyhedral. Generally a model that contains a finer and more delicate (less skewed) mesh would obtain a more accurate and precise result. The meshes drawn on GAMBIT for the 11 tunnel configurations have undergone a rigorous grid independence test. Results were compared among mesh of different sizes. In addition, GAMBIT also has the capability to have boundary layer meshes and size function meshes for complex geometries and flows. Subsequently, after the models were meshed, it was transferred to the ANSYS FLUENT Computational Fluid Dynamics (CFD) software. FLUENT software makes use of the finite volume method to solve for the transport equations found in the meshes of GAMBIT. The results were calculated and the summations of flows are presented in methane or velocity contours found in Appendix C-K. 2.4 Turbulent Models Turbulent flows in fluids consist of fluctuating velocity fields. These fluctuations are caused by the interaction of energy, momentum, transported entities and species concentration in the fluid. These fluctuations occur in high frequency and small scale, making it computationally costly to replicate in practical engineering calculations. Hence, a time-averaged, otherwise manipulated equation can be chosen to cancel out these small fluctuations. The disadvantage is that these equations might add unknown variables and the turbulence models are needed to determine the variables in terms of known quantities. FLUENT provides the following choices of turbulence models: 16 1. Spalart Allmaras model 2. k-ε models - Standard k-ε model - Renormalization-group (RNG) k-ε model - Realizable k-ε model 3. k-ω models - Standard k-ω model - Shear-stress transport (SST) k-ω model 4. Reynolds stress model (RSM) - Linear pressure-strain RSM model - Quadratic pressure-strain RSM model - Low-Re stress-omega RSM model 5. Detached eddy simulation (DES) model - Spalart-Allmaras RANS model - Realisable k-ε RANS model - SST k-ω RANS model 6. Large eddy simulation (LES) model - Smargotinsky-Lilly subgrid-scale model - WALE subgrid-scale model - Kinetic-energy transport subgrid-scale model 17 3. Literature Review This chapter provides a background and summary of published literature related to this study. While the individual topics on coal degasification and coal mining equipment are diverse and in abundance, specific studies into the effectiveness of tunnel ventilation configurations are few and far between. The final year project has been largely inspired by the work Parra [92] on the study of ventilation systems working in the cul-de-sac of a coal mine as well as Torano [21], on the use of CFD to understand flow behaviour in coal mines. Studies conducted by Kissell, Aminnossadati [92], provided early investigation of a coal mining equipment known as a line brattice for the brief initial starting stages of this study [APPENDIX M]. Parra [92] Numerical and experimental analysis of different ventilation systems in deep mines A study of ventilation systems working in the cul-de-sac of a coal mine. Parra conducted a simulation with different turbulent models and compared results with experimental data. Torano, Torno, Menendez, Gent, Velasco[20] Models of methane behaviour in auxiliary ventilation of underground coal mining Use of CFD to understand flow behaviour in coal mines. Torano compared how the distance of a blowing ventilation duct from a dead end would affect airflow behaviour. Su, Chen, Teakle, Sheng [19] Characteristics of coal mine ventilation Analysis of equipment and analytical techniques used in coal mines. Contains information of some coal mines (depth, height etc). Yuan, Liming, Smith Alex [93] Numerical Study on Spontaneous Combustion of Coal in Longwall Gob Areas. A study of a comparison between a bleeder and bleederless ventilation System. Yuan concludes that a bleederless ventilation system is better. Overall, this journal is a study to identify the methods of spontaneous combustion. Kissell F and Matta J. [8] Face Ventilation in Coal Investigated use of line brattice 18 Mines in coal mines. It was found the line brattice aids airflow into dead-zones. Aminossadati, S.M [92] Numerical Workings of ventilation air flow in underground mine workings Use of CFD to understand flow in cross cut regions. Aminossadati advocates the use of line brattices as it brings airflow into dead zones. Investigated effectiveness of line brattices by varying the length of line brattices into the channel. Likar J [9] Ventilation design of enclosed underground structures Use of mathematical equations to solve for flow inside an enclosed space. Ting Ren, Rao Balusu [15] The use of CDF modelling as a tool for solving mining health and safety problems. Goal management and drainage, goaf inertisation for heating control, and longwall dust control strategies is summarized. Somers, Schultz [93] Thermal oxidation of coal mine ventilation air methane Understanding oxidation of coal and use of underground coal mining equipment. Torano, Torno [21] Auxiliary ventilation in mining roadways driven with roadheaders CFD modelling of dust particles in Coal Mines. Su [19] An assessment of mine methane mitigation and utilisation technologies Coal Mining equipment used in a Queensland mine for methane mitigation purposes Franz,B [5] Integrated planning of partially automated Banji Coal Mine Network equipment found in coal mines Hargreaves, L [12] The computational modelling of the ventilation flows within a rapid development drivage (Karacan, 2006) Use of CFD inside a longwall tunnel to understand airflow patterns with a longwall machine. Hargreaves incorporated a longwall mining machine into his simulation due to the theory that there are increased drivage in recent times. He compared his results with experimental data and concluded that CFD models may be successfully used to identify ventilation characteristics Karacan C.O[6] Development and A study of mine optimization 19 application of reservoir models and artificial neural networks for optimizing ventilation air requirements in development mining of coal seams in longwall mining. Advocate of reservoir simulation and ANN modelling. Karacan C.O[7] Modeling and prediction of ventilation methane emissions of U.S longwall mines using supervised artificial neural networks Use of ANN modelling to predict mine emission rates. The author obtained data from 63 mines to compare his model successfully. Noack K[13] Control of gas emissions in underground coal mines A study on a method to predict gas emission in coal mines. According to the author, there is a formula to calculate an air requirement. Also proposed a few ventilation solutions such as introducing an auxiliary fan as well as using a gas drainage borehole to reduce emissions. Diego et al[4] A practical use of CFD for ventilation of underground works A study on the losses occurred inside a length of a coal mine. The author claims that CFD modelling is inaccurate as its values are consistently below values derived from conventional means. Subsequently provides guidance on the use of the numerical method. Lowndes et al[11] The ventilation and climate modelling of rapid development tunnel drivages A study of how climate change can affect the safety of workers in a coal mine. With a validated model, the author simulated the design and operation of a coal mine ventilation system. Author proposes an optimum cooling strategy for increased drivages conditions. Bridgewood E[3] Mathematical approximation processes applied to mine ventilation problems Author provides a solution for solving booster fan network found in underground coal mines. Also provides a non- iterative mathematical model. Liu et al[10] Investigation of the ventilation simulation model in mine based on multiphase flow CFD to understand heat exchange flow in a ventilation pipeline. 20 Amano et al[1] A Calculation System using a personal computer for the design of underground verntilation and air conditioning Author proposes a new method for calculating underground air moisture. As there are problems associated with obtaining specific resistance and elapsed time factor for each airway, such as estimating these factors, author has came out with a system to calculate the underground air moisture using a personal computer. Table 2: Literature Review Table 21 4. Coal Mine Design, Modelling and Simulation 4.1 Introduction This coal mine simulation will attempt to compare how some theoretical coal mining tunnel layouts will fare against a conventional horseshoe shaped tunnel (APPENDIX B). A tunnel with adequate airflow will help to reduce dust formation, increase productivity in coal mines, as well as reduce the threat of an explosion due to the buildup of methane. 4.2 Aim and Objectives The aim of the simulation will be to collect data from the simulation of theoretical tunnels in attempt to recommend future designs of coal mining layouts. This simulation will aid to provide information of possible cut-off zones, and regions of high/low air velocity. In addition, the data collection for the molar concentration of methane will also be amassed and analyzed. The information will also be broken down into section-by-section analysis for a critical analysis of a coal mine tunnel. 4.3 Model Development The original main tunnel layout is shown in Case 1 under Appendix B [39]. It measures 36 m in length and 2.9 m in total height. It contains a ventilation duct inside that has a radius of 0.6 m. This particular tunnel layout is a scaled down model of a coal tunnel that can be found in longwall mining. Inside this tunnel, it contains a ventilation duct that is located at a coordinate of (1.2, 0.8, 0) from the center of the tunnel. It is a blowing ventilation duct blowing oxygen at a rate of 12m/s from the inlet located as indicated in Case 1 in Appendix B. The flow of oxygen will flow from inlet along the ventilation duct walls and finally out of the duct end. Subsequently, it will flow towards the dead end of the tunnel, reverse, and travel along the length to the tunnel. The purpose of the ventilation system is to eradicate slow moving air or methane emission caused from the mining operation. Throughout the simulation, the mining walls in Case1 will be emitting methane at a rate of 0.03m/s (Parra). The results can be found in from Appendix C-K [50]. 22 4.4 Numerics A total of 11 cases of different tunnel layouts were drawn on GAMBIT software. Its dimensions and be found in Appendix B. The number of cells for the each case is found in the following table. Case Number of Cells Computational Time Per Run/Simulation(hrs) Number of iterations Number of Simulations Case 1 300,813 3.5 1000 4 Case 2 300,252 4.0 1000 4 Case 3 300,146 3.25 1000 4 Case 4 300,547 3.0 1000 4 Case 5 310,945 4.5 1000 4 Case 6 305,953 2.5 1000 4 Case 7 307,595 3.75 1000 4 Case 8 266,684 1.75 1000 4 Case 9 287,294 2.25 1000 4 Case 10 234,116 1.75 1000 4 Case 11 242,816 2.0 1000 4 Table 3: Number of Cells in Tunnel Layouts For each case, a total of 4 runs were conducted. The first 2 runs for each case excluded methane emission. This was to analyze the general flow behavior of the ventilation. Subsequently, the next 2 runs included methane emission to simulate a real-time scenario. All 4 simulations were subjected to a grid independence test. Skewed meshes are subjected to changes but in accordance with computing power and the time factor. Generally, most cases required an optimum mesh size of 0.02. A mesh size of 0.01 would require double the computing time but similar results. A mesh size of 0.25-0.03 would leave large pockets of areas unaccountable for. As such, a grid size of 0.02 is ideal. The Spalart Allmaras viscous model is selected to be the turbulent model of choice for this simulation. The reason for choosing this particular model has been validated by comparing a simulation of a coal mine with experimental data found in APPENDIX N. Repeated testing and checks were carried out to make sure the boundary conditions were intact and general flow was accurate. Process: 1. Obtained fundamental data and information. 2. Proper construction of CFD model geometry and computational mesh/grids. 3. Refinement of meshing and mesh quality. Conduct a grid independence test. 4. Initial model simulation. Compare with experimental data. 23 4.5 Assumptions Certain assumptions were made in this final year report. Firstly, it is assumed that the tunnel were to be free of other obstructions that may derail a flow. Secondly, it is assumed the flow from the inlet at 12m/s remains constant. It is also assumed the mine ventilation is a steady- state process, which means none of the variables of flow changes with time. It is also assumed that air is an incompressible Newtonian fluid. 4.6 Choosing A Turbulence Model Among turbulent models in FLUENT, there is no single turbulent model that is considered to be superior to the rest. Each turbulent model is known to have it advantages and disadvantages. The choice of turbulent depends very much upon factors such as level of accuracy required, complexity of mesh and drawings, the problem to be solved as well as considerations for available computational time required for the simulation. For this experiment and final year project, choice of turbulent model depended much on the accuracy as well as the CPU time required. 4.6.1 Comparisons Of Spalart Allmaras, Rsm, k-ε, k-ω Turbulent Models Among the four turbulent models, Spalart Allmaras is the least expensive turbulent model, as it only requires one turbulence transport equation to be solved. k-ε and k-ω turbulent models require more computational effort and time as they contain additional transport equations. As both k-ε and k-ω are two-equation models, they require the same computational effort. Among the k-ε models, the least expensive is the standard k-ε model, followed by the realizable k-ε model and subsequently the RNG k-ε model. Compared with the k-ε and k-ω models, the RSM requires additional memory and CPU time due to the increased number of the transport equations for Reynolds stresses. In addition, 24 15—20% more memory is needed for the increase in computional requirement associated with the RSM. Under Appendix N [86], it will show in detail how the Spalart Allmaras turbulent model was selected for this report. A Spalart Allmaras model can also be used via a personal computer as it required less computational power and time. In Appendix N, Spalart Allmaras was chosen among 4 other models as simulation tests were run to compare drawn models against experimental data. After these tests, it was found that Spalart Allmaras was most accurate. Since the purpose of this final year project is to understand general flow in coal mines, the least complicated Spalart Allmaras turbulent model would be the ideal turbulent model chosen for FLUENT 6.3. Governing Equations for Mathematical Model: In the above instantaneous Navier Stokes equations, the solution variables are decomposed into mean (ensemble-averaged or time-averaged ) and fluctuating components. For the velocity components: _ ' u u u = + Where _ u and ' u are the mean and fluctuating velocity components. Similarly, for pressure and other scalar quantities, _ ' | | | = + . 25 Spalart-Allmaras: The following equations represent the commonly used Spalart-Allmaras equations. It is a relatively simple one-equation model that solves a modeled transport equation for the kinematic eddy (turbulent) viscosity. The ―~‖ or tilde symbol represents the turbulence field variable. The transport equation is given by the following equation: ~ ~ ~ 2 1 ( ) .( ) .( ( ) v b v v v vu G v C v Y t µ µ µ µ µ o c ( +V ÷ + V + + V ÷ ( c ¸ ¸ In the above equation, Y v is the destruction of turbulent viscosity and G v is the production of turbulent viscosity and that occurs in the near-wall region due to wall blocking and viscous damping. σ v and C b2 are constants and ν is the molecular kinematic viscosity given by μ/ρ. The destruction term, Y v , is modeled as 2 ~ 1 v w w v Y C f d µ | | | = | \ . Where C w1, C w2 and C w3 are constants And 1/6 6 3 6 6 3 6 2 ~ 2 2 1 ( ) w w w w C f g g C g r C r r v r S d k . ( + = ( + ¸ ¸ = + ÷ = The turbulent viscosity, μ t is computed from ~ 1 t v v f µ µ = Where the viscous damping function, f v1 , is given by 26 And ~ v v _ = The additional equations, the production term, G v, is modeled as ~ ~ 1 v b G C S v µ = Where ~ ~ 2 2 2 v v S f d k = O+ To avoid possible numerical problems, the term ~ S must never be allowed to reach zero or go negative. Also, 2 1 1 1 v v f f _ _ = ÷ + S is a scalar measure of the deformation tensor which is based on the magnitude of the vorticity, where C b1 and κ are constants and d is the distance from the wall. ~ ~ 2 2 2 v v S f d k = O+ Where 2 ij ij W W O = is the magnitude of the vorticity, d is the distance to the nearest wall. 1 ( ) 2 j i ij j i u u W x x c c = ÷ c c The model constants have the following values 1 0.1355 b c = 2 3 o = 2 0.622 b c = 0.41 k = 2 0.3 w c = 3 2 w c = 1 7.1 v c = 1 2 1 2 1 b b w c c c k o + = + 27 5. Results and Discussion In the simulation of 11 different cases, iso-surfaces were drawn on 5 surfaces. There are 4 on the Z iso-surface, namely Z=4m, 8m, 12m and 16m. There is also one on the Y iso-surface at Y=0. These iso-surfaces will provide information on both the methane distribution [Section 5.1] as well as the velocity distributions [Section 5.2]. The Z and Y iso surfaces were drawn to give a comprehensive understanding of methane and airflow speeds throughout the tunnel. Having different Z iso-surfaces at Z=4m, 8m, 12m and 16m gives a section-by-section analysis of the tunnel to observe any changes within the range of 4m. By incorporating an additional Y iso-surface, it would give an analysis of the thickness of a particular region or type of airflow inside the underground structure. 5.1 Analysis Of Molar Concentration Of Methane At Z-Iso Surfaces And For Y Iso-Surface @ Y=0 Metres Tunnel Configuration Reference Table Case 1 Original tunnel configuration by Parra 2009 [Figure 7]. Case 2 Tunnel configuration with circular ventilation duct directly left of center [Figure 8]. Case 3 Tunnel configuration with circular ventilation duct directly right of center [Figure 9] Case 4 Tunnel configuration with circular ventilation duct directly above center [Figure 10]. Case 5 Tunnel configuration with circular ventilation duct with outlets located at 10m intervals. Each outlet consist of two sub-outlets that allow air to flow out. Sub- outlets are angled at an angle of 45° from the bottom [Figure 11] Case 6 Tunnel configuration with outlets located at 10 metre intervals. Circular ventilation duct consists of 2 outlets [Figure 12]. Case 7 Tunnel configuration with outlets located at 6 metre intervals. Circular ventilation duct consists of 5 outlets [Figure 13]. Case 8 Similar to case 1, circular ventilation duct is replaced by a square ventilation duct [Figure 14]. Case 9 Similar to case 4, circular ventilation duct is replaced by a square ventilation duct. Square ventilation duct lies directly above center [Figure 15]. Case 10 Tunnel configuration in case 4 has been added with a ―U-splitter‖ [Figure 16]. Case 11 Tunnel configuration in case 4 has been added with a ―Y-splitter‖[Figure 17]. 28 5.1.1 Discussion: Methane Distribution in Z Iso-surfaces Methane Distribution @ Z=4m [50] From Appendix C @ Z=4m, comparatively high levels of methane concentration occurred in cases 3, 5 and 7. The ventilation ducts in these cases have failed to regulate flow at Z=4m. At a distance of 4m, being the closest to the dead-zone, it is expected that most ventilation designs would provide a safe level of ventilation. However, this is not the case for these 3 cases and the results depict a highly dangerous scenario. This is inferred from the red zoned areas in Appendix C [50]. In Appendix C, the red zone areas have a methane concentration of 0.024 kmol/m 3 . Moderate levels of methane occur in cases 1,2,4,6. The ideal cases for z=4m lies in cases 8, 9, 10 and 11. In cases 8, 9, 10, 11, methane concentrations are as low as 0.009 kmol/m 3 . Methane Distribution @ Z=8m [52] At another iso-surface is taken at Z=8m, it is expected that the methane levels will build up as flow slows. In a comparison with Z=4m, case 3 remains unchanged with the highest levels of methane. Cases 3, 5, 7 once again display high levels of methane concentration. It is concluded that having holes along a ventilation duct is not an ideal scenario as it would increase the levels of methane concentration at iso-surfaces closer to the dead zones. This is due to the early release of air into underground structure. In Z=8m, generally most cases display similar levels of methane buildup. The outlier would be case 9, a square duct located at the top position of the coal mine. The methane level for case 9 is the lowest for all cases at 0.012kmol/m 3 . The use of a square duct has resulted in satisfactory flow results at a distance of 8m from a dead zone. Methane Distribution @ Z=12m [54] The change of iso-surface from Z=8m to Z=12m has encountered more drastic changes. This is seen from the increase in the number of red zones. In fact, several regions in case 5 have deteriorated completely. It is thus a highly unsatisfactory, not to mention, a highly dangerous scenario for workers in the coal mine. Case 5 is a ventilation duct with angled outlets at 45° from each other (43). They are located in sets at intervals of 10m from the inlet. Each set would contain 2 outlets. The most favourable cases for Z=12m are cases 6, 9,10 and 11. This is due to these cases having the largest areas of blue/green zones. From the results of the iso- 29 surfaces at Z=12m, it is concluded that most of the conventional ventilation designs would be unable to support ventilation areas at a third of the tunnel length. According to Torano (93, 20), the distance of the ventilation duct outlet from the dead-zone plays a critical part of the airflow characteristic. In most of the cases, namely from cases 1-9, the ventilation duct remains at a distance of 6m from the dead-end zone. However, it is seen that at Z=12m, most ventilation systems would not be able to maintain safe levels until this distance. There is a need to 1) increase velocity of airflow at this juncture or 2) introduce boreholes and fans to maintain safety levels. Methane Distribution @ Z=16m [56] In iso-surface z=16m, cases 5 and 7 has become regions of high methane concentration. The cases that show comparatively lower methane concentrations include cases 4, 8, 9, 10 and 11. It is also noticed that as methane build up, regions on the outer contours would first be exposed to the methane, subsequently making way towards the center of the coal mine. In conclusion, cases 4, 8, 9, 10 and 11 fare better compared to the conventional layout shown in case 1. However, from Z=12m onwards, most of the ventilation systems, regardless of design, would have little impact on the safety of the coal mine. 5.1.2 Discussion: Methane Distribution for Y=0 Iso Surface [58] From Appendix G, the favourable tunnel layouts are cases 4, 8, 9, 10 and 11. Cases 8 and 9 both have a square ventilation duct as compared to a circular one. While cases 10 and 11 have good distribution, bottom areas near the inlet tend to have high concentrations of methane. If such designs are to be used, it is advisable to include fans and brattices near the pressure outlet regions to aid in mitigation of the buildup of gases and dusts in these areas. In cases 2 and 3, it is noticed that by having the ventilation ducts to either extreme case is unfavourable as it would leave the extreme end isolated. From 5.1.1, it is known that from 12m from the dead-zone, most ventilation designs will fail to maintain adequate airflow. The Y iso-surface confirms our inference. In most cases, the levels of methane concentrate increase from 0.02kmol/m 3 from a distance of 10m onwards. 30 5.2 Analysis Of Velocity Distribution Of Z-Iso Surface @ 4, 8, 12, 16 Metres And Velocity Distribution @Y-0 Tunnel Configuration Reference Table Case 1 Original tunnel configuration by Parra 2009. Case 2 Tunnel configuration with circular ventilation duct directly left of center. Case 3 Tunnel configuration with circular ventilation duct directly right of center. Case 4 Tunnel configuration with circular ventilation duct directly above center. Case 5 Tunnel configuration with circular ventilation duct with outlets located at 10m intervals. Each outlet consist of two sub-outlets that allow air to flow out. Sub- outlets are angled at an angle of 45° from the bottom. Case 6 Tunnel configuration with outlets located at 10 metre intervals. Circular ventilation duct consists of 2 outlets. Case 7 Tunnel configuration with outlets located at 6 metre intervals. Circular ventilation duct consists of 5 outlets Case 8 Similar to case 1, circular ventilation duct is replaced by a square ventilation duct. Case 9 Similar to case 4, circular ventilation duct is replaced by a square ventilation duct. Square ventilation duct lies directly above center. Case 10 Tunnel configuration in case 4 has been added with a ―U-splitter‖ Case 11 Tunnel configuration in case 4 has been added with a ―Y-splitter‖ 31 5.2.1 Discussion: Velocity Distribution for Z iso-surfaces Velocity Distribution @ Z=4m [60] Regions of low velocity in coal mines are prone to dust-buildup. Proper ventilated areas, however, lead to oxygen renewal and a better working environment for safety and productivity. At 4m from the dead zone, the speed of air (0.21% oxygen), has been reduced from an initial speed of 12m/s to a region of approximately 3 m/s. The reduction of speed is approximately 75%. Also, with reference to Appendix H, in case 1, while there is a region with airflow of 2 m/s, it is observed that the bottom right corner tends to be isolated with no or little airflow. The bulk of air will flow towards the region opposite of the ventilation duct. In addition, it is also observed from cases 4 and 6 that an overhead ventilation duct is most suitable as the velocity distribution is spread over the floor area. The disadvantage of cases 4 and 6 would be the low velocities near the roof of the coal mine. In Z=4m, it is also surprising that cases 10 and 11 did not fare as well as expected. Hence, while cases 10 and 11 have low methane concentration levels, they might not be effective in dust removal. Velocity Distribution @Z=8m [64] As expected, the maximum velocities at Z=8m iso-surface has dropped to 1.75m/s from 3m/s in Z=4m. The reduction of velocity has increased to 90%. Among the 11 cases in Appendix I, Case 9 has the most favourable flow condition. Most of the cases exhibit similar flow characteristics with the center of the tunnel approximately having a velocity flow of 1 m/s. Velocity Distribution @Z=12m [64] In Appendix J, velocities in Case 1 have deteriorated severely. Most of the air at iso-surface Z=12m stands at 0.25 m/s. Case 5 performs badly at this iso-surface. There is little flow is this iso-surface. Velocity Distribution @Z=16m [66] In Z=16m, it is seen that Case 1 and Case 5 have increased velocities as compared with the iso-surface @Z=12m. Cases 8-11 are the best performers. Overall observation 32 The observation of case 1 in its velocity distribution show that while in some regions it has good velocity distribution, it is often sporadic. Also, the current ventilation layout in case 1 show that there are too many regions isolated, which makes it dangerous for use, The best cases for the simulation are cases 4, 8, 9, 10 and 11. Case 10 and 11, however, do not fare well in iso-surfaces @ Z=4m. 5.2.2 Discussion: Velocity distribution for Y-0 Surface [68] In case 1, it would be ideal if the mixture of velocity magnitudes would contain more red zones. This is not to be confused with Appendix C as red zones in this scenario depict high velocity zones as compared to the former where red zones were used to depict regions of high methane. From the analysis of this iso-surface, it can be seen that the distribution of air for case 1 is poor as compared to other designs. In case 2, there is a large red zone on the left. It is the ventilation duct located at the side of the mine tunnel. The resulting velocity magnitude is satisfactory. For the velocity distribution of the Y=0 iso-surface, most cases show similar signs of velocity distribution. Cases 1, 5, 6 and 7, however, show poor distribution of velocities. These cases contain pockets where velocity magnitudes are low; prone to form cut-off areas 33 5.3 Analysis of Pumping Power and ventilation effectiveness (i) Case (ii) Configuration (iii) Pressure Difference (Pa) (iv) Volume Flow Rate at the inlet (m 3 /s) (v) Pumping Power (W) (vi) Mass flow rate of Methane at outlet (kg/s) (vii) Average Molar Concentration (kmol/m 3 ) (viii) Star Rating 1 Tunnel Original 143.8 3.2 608.5 8.29 0.025 0.014 2 Tunnel Left 165.2 3.2 699.0 8.27 0.026 0.012 3 Tunnel Top 141.3 3.2 597.8 8.10 0.025 0.014 4 Tunnel Right 71.3 3.2 301.7 8.31 0.028 0.028 5 Tunnel Top with 2 holes @ 45 degrees 66.2 3.2 280.0 8.11 0.026 0.029 6 Tunnel Top with 2 holes 74.7 3.2 316.0 8.11 0.029 0.026 7 Tunnel Top with 5 holes 22.3 3.2 94.3 8.25 0.023 0.087 8 Tunnel Original with Square Duct 83.3 4.3 480.0 8.30 0.023 0.017 9 Tunnel Top with Square Duct 80.0 4.3 461.1 8.30 0.021 0.018 10 U-Splitter Add-on 178.2 3.2 754.2 8.28 0.026 0.011 11 Y-Splitter Add-on 68.0 3.2 287.9 8.28 0.026 0.029 Table 4: Pumping Power, Mass flow rate of Methane 34 Table 4 gives the pumping power required in the coal mine tunnels, the average molar concentration of methane as well as the mass flow rate of methane at the outlet. The equations for Table 4 are as follows: 1. Pressure Difference (pa) = Pressure at inlet – Pressure at the Outlet in out p p p A = ÷ ------------------------------------- (1.1) 2. Volume flow rate (m 3 /s) = Area at inlet x Velocity at inlet . Q Au - = -----------------------------------------------(1.2) 3. Pumping Power (W)= Pressure Difference(1) x Volume flow rate(2) . pump pump p Q P q = A ------------------------------------------ (1.3) 4. Mass Flow Rate (kg/s)= Mass fraction of methane x Volume flow rate 4 . CH m w m - - = ------------------------------------------- (1.4) 5. Star Rating = Mass flow rate / Pumping Power 4 CH pump m P c - = --------------------------------------------(1.5) Like any system, power is required to drive the ventilation system. The higher the power, the greater the need for electricity, and thus the higher the costs. Among the 11 cases, Case 10 and Case 7 has the highest pumping power and the least pumping power respectively. However, the unsatisfactory results from 5.1 show that case 7 is a less than ideal design for having in an underground mine. Hence, while it may offer some economic savings, the long term use of case 7 is not recommend as there would be risks of explosions. From the results of methane concentration, analysis of pumping power from case 8 to case 11 will be of high importance. This is so as case 8 to case 11 has better airflow and low methane characteristics 35 compared to other cases found in earlier studies. Case 11 is a good choice of ventilation duct as it has high star rating and low pumping power. From table 4, it is seen that both the mass flow rate and the average molar concentration of methane for the 11 cases have similar magnitudes. This implies that there is no one case that is superior than the rest. This is due to the fact that most of the designs are unable to support low methane concentrations levels for the entire length of the tunnel using current specifications.As such, results in the intermediaries of the tunnel are different. For example, at regions of Z=4m and Z=8m, the tunnel layout at case 11 will have better airflow characteristics than case 5. To enhance the airflow of the 11 tunnel configurations, it is thus recommended to include additional suction fans or ducts to remove additional methane near the entrance of the tunnel. 6. Conclusion This final year study has provided the results and analysis of 11 different mining configurations. From the results, it is seen that cases 8 to cases 11 present the best results. They are the use of square ducts in overhead as well as original positions and the use of splitter add-ons. From the iso-surfaces that measure methane distribution, it is seen that certain designs are truly unfavourable for mine tunnelling. The velocity iso-surfaces have also provided insight to tunnel designs whereby there are possible cut-off zones. It is interesting that minor changes in design for the tunnels have resulted in completely different sets of patterns of airflow. In this final study report, it is understood that a blowing ventilation duct would be unable to provide airflow for the entire length of the channel on its own independently. It is observed in the breakdown or drastic increase in methane levels from 10- 12m from the dead-end. However, cases 8-cases 11 show under a section-by-section analysis that square ducts and splitters offer a good intermediate solution for areas near the dead-end. From the results in Table 4, it can be seen that as the 11 tunnel configuration offer the same methane removal at the pressure outlet, additional ventilation systems can be incorporated to aid in airflow. This final year study concludes that the conventional design of the ventilation duct in a horseshoe tunnel requires more design testing and modifications. 36 7. Recommendations for Future Work This final year research paper has provided theoretical designs for longwall mining. Upon analysis, it is observed that by having a square duct or add-ons, it would increase ventilation airflow and provide a safe working environment. For future work, l suggest the following - Most of the cases involve having a ventilation duct at a distance of 6m from a dead- zone. From the results obtained, it is concluded that in a 36m tunnel with current size specifications, the blowing ventilation network will hold only to a distance of 12m from the dead-end zone. Future analysis can be done on a blowing ventilation system with various distances away from the dead-end zone. - Future modeling work can involve tunnels of different shapes. Square, oval etc. - This final year research has provided 10 theoretical designs as a trial and error basis for improving airflow. Future work can involve more innovative designs. - Since this modeling work involves mines which are longwall mined, modeling work can be applied to room-and-pillar mining for more in-depth comparisons. - Present modelling work involve a ventilation duct with a blowing exhaust system. A future analysis can be done incorporating a blowing ventilation duct with an exhaust one to improve efficiency. The results from this study can be used toward the study of the placement of the exhaust duct. - The coal mining simulation takes place in an empty tunnel. However, it is often not the case in an actual scenario. It would be good that information regarding the use of passageways can be provided. - Obtain more boundary conditions regarding ventilation in coal mines. There is a lack of information regarding ventilation speeds on the internet. This can be done by establishing links with mining companies in Australia and Indonesia. A collaboration can be done such as ideas can be shared and more research can be conducted. - Engineering solutions has to be always balanced with cost. Implementing safety measures, buying of safety equipment, installing ventilation systems can be a costly affair. A research can be done on the economics of airflow and the relative costs of purchasing/installing some equipment. Research could also go into the depth of 37 available technologies in the market or investigate technologies that can be introduced or improved. - This final year project was conducted on ANSYS FLUENT software. Subsequent simulations can be conducted on other commercial software to determine the effectiveness of this particular software. A similar study of this final year research can be conducted to compare with the results shown in (APPENDIX C-K) 38 APPENDIX A: ISO- SURFACES Z=4 m from dead zone Z = 8m from dead zone Z = 12m from dead zone Z=16 m from dead zone Y=0 Iso-surface Tunnel Layout Figure 6: Iso-surfaces 39 APPENDIX B: TUNNEL CONFIGURATIONS Case 1: Tunnel Configuration with the ventilation duct placed at an angle of 45° from the center of the cross section as shown in Figure A metres Figure 7: Case 1: Tunnel Configuration with the ventilation duct placed at an angle of 45 from the center of the cross section as shown in figure A (Parra, 2009) 40 Case 2: Tunnel Configuration with the ventilation duct placed on the left side of the tunnel 2.9m 1.8m 1.1m 0.6m 3.6m metres Figure 8: Case 2: Tunnel Configuration with the ventilation duct placed on the left side of the tunnel 41 Case 3: Tunnel Configuration with circular ventilation duct placed on the right side of the horseshoe tunnel 0.6m 1.8m 1.1m 3.6m 2.9m Figure 9: Case 3: Tunnel Configuration with circular ventilation duct placed on the right side of the horseshoe tunnel 42 Case 4: Tunnel Configuration whereby circular duct is placed directly above the center of the z-cross section of the tunnel Figure 10: Case 4: Tunnel Configuration whereby circular duct is placed directly above the center of the z-cross section of the tunnel 43 Case 5: Tunnel configuration with an overhead ventilation duct with 2 sets of holes. Each set consists of two holes at an angle of 45° away from one another. Total number of 4 holes. Figure 11: Case 5: Tunnel configuration with an overhead ventilation duct with 2 sets of holes. Each set consists of two holes at an angle of 45° away from one another. Total number of 4 holes. 44 Case 6: Tunnel Configuration where the overhead ventilation duct has two downward holes angled at 90° and are at a spacing of 10m. Figure 12: Case 6: Tunnel Configuration where the overhead ventilation duct has two downward holes angled at 90° and are at a spacing of 10m. 45 Case 7: Tunnel Configuration where the overhead ventilation duct has five downward holes angled at 90° and are at a spacing of 5m. Figure 13: Case 7: Tunnel Configuration where the overhead ventilation duct has five downward holes angled at 90° and are at a spacing of 5m 46 Case 8: Tunnel Configuration with a square ventilation duct placed at an angle of 45° from the center of the cross section [compare with Case 1] Figure 14: Case 8: Tunnel Configuration with a square ventilation duct placed at an angle of 45° from the center of the cross section [compare with Case 1] 47 Case 9: Tunnel Configuration whereby square duct is placed directly above the center of the z-cross section of the tunnel Figure 15: Case 9: Tunnel Configuration whereby square duct is placed directly above the center of the z-cross section of the tunnel 36m 48 Case 10: Tunnel with an overhead duct with a U-shaped splitter ‗Add-on‘ Figure 16:Case 10: Tunnel with an overhead duct with a ―U-shaped‖ splitter add-on 49 Case 11: Tunnel with an overhead duct with a ―Y-shaped‖ add on. Figure 17: Case 11: Tunnel with an overhead duct with a ―Y-shaped‖ add on. 50 APPENDIX C: CONCENTRATION OF METHANE (CH4) FOR Z-ISO SURFACE @ 4M CASE1 TO 6 Case 1 Case 2 Case 3 ase 4 Case 5 Case 6 (kmol/m 3 ) 51 CASE 7 TO 11 Case 7 Case 8 Case 9 Case 10 Case 11 MOLAR CONCENTRATION OF METHANE(CH4) FOR Z-ISO SURFACE @ 4M (kmol/m 3 ) 52 APPENDIX D: MOLAR CONCENTRATION OF METHANE(CH4) FOR Z-ISO SURFACE @ 8M CASE1 TO 6 Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 (kmol/m 3 ) 53 MOLAR CONCENTRATION OF METHANE(CH4) FOR Z-ISO SURFACE @ 8M CASE 7 TO 11 Case 7 Case 8 Case 9 Case 10 Case 11 (kmol/m 3 ) 54 APPENDIX E: MOLAR CONCENTRATION OF METHANE(CH4) FOR Z-ISO SURFACE @ 12M CASE 1 TO 6 Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 (kmol/m 3 ) 55 MOLAR CONCENTRATION OF METHANE(CH4) FOR Z-ISO SURFACE @ 12M CASE 7 TO 11 Case 7 Case 8 Case 9 Case 10 Case 11 (kmol/m 3 ) 56 APPENDIX F: MOLAR CONCENTRATION OF METHANE(CH4) FOR Z-ISO SURFACE @ 16M CASE1 TO 6 Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 (kmol/m 3 ) 57 MOLAR CONCENTRATION OF METHANE(CH4) FOR Z-ISO SURFACE @ 16M CASE 7 TO 11 Case 7 Case 8 Case 9 Case 10 Case 11 (kmol/m 3 ) 58 APPENDIX G: MOLAR CONCENTRATION OF METHANE(CH4) FOR Y-ISO SURFACE @ Y=0 CASE 1 TO 6 Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 (kmol/m 3 ) 59 MOLAR CONCENTRATION OF METHANE(CH4) FOR Y-ISO SURFACE @ Y=0 CASE 7 TO 11 Case 7 Case 8 Case 9 Case 10 Case 11 60 APPENDIX H: VELOCITY DISTRIBUTION FOR Z-ISO SURFACE AT Z=4M CASE 1 TO 6 Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 0.5 2 2 2 . 0 1. 5 61 VELOCITY DISTRIBUTION FOR Z-ISO SURFACE AT Z=4M CASE 7 TO 11 Case 7 Case 8 Case 9 Case 10 Case 11 1. 5 1. 5 3 0.5 55 62 APPENDIX I: VELOCITY DISTRIBUTION FOR Z=8M ISO-SURFACE Case 1 to 6 Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 (m/s) 63 Velocity Distribution for Z=8m Iso-surface Case 7 to 11 Case 7 Case 8 Case 9 Case 10 Case 11 (m/s) 64 APPENDIX J: VELOCITY DISTRIBUTION FOR Z=12M ISO SURFACE Case 1 to 6 Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 65 Velocity Distribution for Z=12m Iso-surface Case 7 to 11 Case 7 Case 8 Case 9 Case 10 Case 11 66 APPENDIX K: VELOCITY DISTRIBUTION FOR Z=16M ISO-SURFACE Case 1 to 6 Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 67 Velocity Distribution for Z=16m Iso-surface Case 7 to 11 Case 7 Case 8 Case 9 Case 10 Case 11 68 APPENDIX L: VELOCITY DISTRIBUTION FOR Y=0 ISO-SURFACE Case 1 to Case 6 Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 69 Velocity Distribution of Y=0 Iso-surface Case 7 to 11 Case 7 Case 8 Case 9 Case 10 Case 11 70 APPENDIX M: INCLUSION OF A BRATTICE TO AID GENERAL AIRFLOW IN A CROSSCUT REGION IN ROOM-AND-PILLAR MINING ABSTRACT This chapter will review the inclusion of brattice sails in underground cross-cut regions to aid flow. Brattice sails are cost effective ventilation control devices used in underground mining areas to deflect air into unventilated areas. A cross-cut region in a coal mine is a region whereby one opening is open to the airway while another is sealed. Computational Fluid Dynamic (CFD) software, will be used to model various types of air flows in underground mining structures. In this chapter, the general airflow in a section of a coal mine with a crosscut region will be examined using ANSYS Fluent software. The aim of this experiment is to design and install a brattice which will maintain a sufficient supply of fresh air and achieve contaminant removal as well as air circulation in a cross-cut region. Comparisons will be carried out between crosscut regions with and without a brattice inclusion to compare the relative effectiveness of a brattice. Brattice sails are usually fire resistant cloths and have thin and lightweight properties. Coal mines are abound with crosscuts regions and the following illustrations will serve to demonstrate the effectiveness of a simple brattice structure. INTRODUCTION In underground mining, it is of particular importance to maintain fresh and cool air in unventilated areas to maintain safe working environments for workers inside a coal mine. The underground mining environment is subjected to the dangers of heating due to excess oxygen as well as presence of dangerous gases such as methane. As a result, air is injected into underground mines as a way to ventilate the surrounding air. This serves to dilute as well as reduce the air temperature in the mine. By hanging as simple a device as a brattice sail, as air is injected into a mine, brattice sails can be aid the airflow into unventilated areas and bring contaminants out of the region. Numerous mine companies have been continuously innovating over the years to try to bring a best range of ventilation variations of a brattice into 71 the market. It is with the aim to make brattice sails more cost effective durable and resistant to mechanical wear and tear. In this experiment, we would analyse the effectiveness of designing a brattice sail inside a crosscut region to aid in airflow using fluent, a CFD program. We will also be comparing literature reviews as well as results from our own simulations. According to a similar study done by Aminossadi 2009, brattice sails would enable better airflow as cool air would reach unventilated areas for a safer working environment. A study by Tien (1988) and Potts and Jankowski(1988) have analyzed the airflow pattern in working faces and concluded that the usage of a brattice is mandatory in preventing recirculation and to control respiratory dust in the face area. For this review, we would want to study if an inclusion of a brattice sail would successfully dispose unwanted contaminants out of these regions. Cross cut regions in coal mines typically house mining equipment, various machineries and electrical equipment such as transformers. Most miners will not frequent such areas, but it is important that we analyse these regions so as to make them save for those that do. The following simulations will be basic tests on the fluid flow behavior with brattice sails. It will present a few scenarios to allow a more varied analysis. In the review by Aminossadati et al, he compared the different lengths of brattices and their effectiveness with regard to their length into the crosscut region. In his study, it is noted that with brattices with lengths up to entire length of the cross-cut region proved to be most effective. For his study, however, the brattice lengths were only confined to a simple cross-cut region. This proves to be a limitation as a coal mine is filled with many rooms and pillars. For our experiment, we will use a longer brattice for a variety of added scenarios. We would also vary the thickness of brattice and height of a few brattice arrangements. In subsequent chapters, changes to the modelling structure will be implemented to improve the accuracy of the experiment. Figure 1.1 shows a sketch of a room and pillar enclosure in a coal mine. The remaining structural pillars are coloured black and the emptied coal strata is colored white. The emptied coal strata would form a passageway for further coal to be mined. Figure 1.2 shows how the flow will behave as it flows from left to right. 72 A cross-cut region in a coal mine is defined as a region whereby one opening is open to the airway while the other is sealed. Its shape is shown in figure 1.2. In figure 1.2, there are numerous cross cut regions that are sealed off and have low ventilations. These areas would be prone to methane and dust buildup which are extremely dangerous for miners. The cross-cut region shown in figure 1.2 will be mapped and used for Part I simulation. An enlarged cross-cut region is shown in figure 1.3. MODEL DEVELOPMENT Figure 1 shows a cross-cut region inside a two dimensional mine airway. For our review, we will be using the k-ε turbulence model to simulate air flow behavior. To aid general flow in cross cut region, a brattice is introduced as shown in figure 1.3. A test velocity of 5m/s flows from left to right in figures A and B to show the differences of airflow with the addition of a brattice. A brattice is usually a fire resistant cloth and has thin and lightweight properties. From figure B, it is seen that the inclusion of the brattice has resulted in improved circulation in a previously static region. The experiment was conducted under a k-epsilon turbulent model with approximately 21500 cells. A study on the different lengths of brattices was also carried out. It was found the longer the brattice length into a cross-cut region, it would be easier and more efficient for the fluid wash out the cross-cut region. The most effective length is found in figure 1.4(approximately 2.75 of depth of cross-cut region) Figure 1.1 Figure 1.2 Speed Scale 11 m/s 6-8m/s 4-6m/s 3-4m/s 0-2m/s Cross-cut region 73 In our experiment, it is assumed that air is considered an incompressible fluid. The opening width(H) and the fluid velocity( ) are used as the length and velocity scale respectively. The flow filed consists of an entrance and exit section, each of which is 2H length, with the crosscut of width H and depth L=3H. The wall brattice distance is W=H/10 Figure 1.3 MODEL FORMATION To display better understanding of airflow with/without a brattice, there will be five figures in this review each with a different scenario. The flowing simulations were carried out in 2-D at an airflow flowing from left to right at 5m/s for all tests. ASSUMPTIONS We first assume a ―T‖ shaped cross cut region for a coal mine and the walls of the crosscut regions are assumed to be smooth. The Reynolds number calculated based on R , where 74 v= kinematic viscosity and d=H. D=5 and the air is assumed to be at room temperature. For room temperature, kinematic viscosity of air is 15.11 x 10 -6 . Hence, Reynolds number calculated is 17 x 10 5 . The cross-cut region is comprised of a top horizontal rectangular section measuring 5 units x 1 unit and resting on a vertical rectangular section measuring 1 unit x 3 units. The governing equation for this experiment is: ( ) (( ) t t t t t t t t v grad S t u u µu µ u u c +V ÷V I = c Where represents the variable of interest, is the instantaneous air density, is the diffusive coefficient and is the source rate per unit volume. From left to right these terms are the transient term(which is absent in our study for the steady state condition), the convective term, the diffusive term, and the source term. The results show that all values of Re, installation of a brattice increases the magnitude of stream function within the crosscut function. NUMERICAL DETAILS Ansys Computational Fluid Dynamics Software 6.3 was used for this study to handle velocity distribution in the ―T‖ section as shown in figure 1. The software was also used to support mass continuity, momentum, and two additional transport equations for turbulent kinetic energy, k and its dissipation, ε. 75 RESULTS AND SIMULATION Simulation 1: No Brattice Figure: A RESULTS AND DISCUSSION (1) Figure A depicts three consecutive crosscut regions in a coal mine. The fluid is initialized from the left hand corner of the picture with a test velocity of 5m/s. From this illustration, it is seen that the fluid moves unperturbed from left to right, maintaining the mean velocity at approximately 5 m/s. It is seen here that the fluid velocity inside the cross-cut regions remains between 0.02 to 1.37 m/s. This would represent a drop of approximately >95%. As air flow is approximately 0.02m/s, it would also mean air is stagnant and at a highly unacceptable level. The dust contaminants would not be washed out of the cross-cut region and it would be endanger the safety of personnel inside it. Percentage of Speed in cross-cut region to main air flow = ( / )x100% 76 = (0.02/5)X100% = 0.4% where and are the velocities for the cross cut region and the test velocity respectively. With the percentage of speed in cross cut region to main flow at 0.4%, dust contamininants and old air would not be replaced in that region, and it might lead to build up of gases such as methane as the air is not replenished. For safer levels, we aim to increase this value with help of a brattice in following simulations. 77 SIMULATION 2: NORMAL BRATTICE WITH NO FILLETED EDGE Figure B RESULTS AND DISCUSSION (2) With an inclusion of a brattice structure in the first crosscut region, it can be seen that the flow in the main airway has increased. This is due to the reduction in the area of the main airway. The same streamlines of air are ―forced‖ upwards of the brattice and made to flow over a smaller area, speeding up the flow. We also see a few positive changes. Firstly, the flow is no longer stagnant as shown in Figure A. The flow has began to circulate inside the cross-cut region. With deeper observation, some of the flow slides in beneath the brattice and travels down to the bottom of the crosscut region. The airflow subsequently travels along the side walls of the cross-cut region and rejoins the 78 main airflow. For this section, the speed of air along the side walls of the cross-cut region is approximately 2m/s. Percentage of Speed in Cross-cut region to main air flow = (speed in cross-cut region/test velocity)x100% = (2/5)X100% =40% The reduction of speed of air in the cross-cut region has increased from 0.4% in Simulation to 40% with the aid of the brattice. However, while the inclusion of this brattice has resulted in some airflow entering and exiting the cross-cut region, the first cross-cut region still appears to have heavy recirculation. Recirculation in a coal mine has to be avoided as the main purpose of airflow is to flush out air that is filled with methane and other gases. A consortium old gases will be unsafe for a mine worker as only fresher air can ensure easier breathing and hence better productivity. 79 SIMULATION 3: BRATTICE WITH FILLETED EDGE Figure C RESULTS AND DISCUSSION (3) To try to bring more airflow into the cross cut region, we would include a filleted brattice in the airway as shown. As compared with figure B, the new brattice sail in figure C has a filleted edge. This addition would be to study if an edge would aid in more flow entering the cross-cut region from the upper side of the brattice. With a new filleted edge, the airflow near the fillet region is driven downward, joining the airflow that is flowing out from the right edge of the crosscut region. This is beneficial as air from both regions will be able to carry the contaminants out of the cross-cut region. The airflow in the cross-cut region also appears more rotational. There are also regions on the edge of the crosscut regions where the speed of the flow reaches approximate 2-2.73m/s. A slight increase over results from figure 2 albeit with more rotational flow. However, there is a region in the bottom section where it appears that the flow remains in a circular anti-clockwise rotation. This would not aid in bringing the contaminants out of the crosscut region. Filleted Edge 80 SIMULATION 4: Thin Brattice Figure D RESULTS AND DISCUSSION (4) With the inclusion of the thin brattice, the amount of circulation inside the cross-cut region has increased, evident from the increase in the number of colours and number of vector arrows in figure D. However, there is still recirculation of flow inside the cross–cut regions. Hence, it would be ideal case such that the brattice is used together with another device, such as a fan, to aid in bringing the flow inside the cross-cut region out into the main walkway. However, it is concluded that the airflow using a brattice in figure D is superior to cases found in B and C. 81 SIMULATION 5: 3 BRATTICES ALONG 3 CROSS CUT REGIONS (SAME HEIGHT) Figure E RESULTS AND DISCUSSION (5) Figure E will show how an addition of three brattices over three crosscut sections will be useful. Notice that the brattices are at the same levels. From figure E, it is seen that all three crosscut regions are experiencing some sort of rotational flow. Flow is directed underneath the brattice and made to flow along the sides of the cross-cut regions. The flow along the side walls is roughly 2.3m/s. For contaminants located at the wall of the cross-cut regions, the brattice will have some effect of be able to wash them out. 82 SIMULATION 6: 3 BRATTICES ALONG 3 CROSS CUT REGIONS (DIFFERENT HEIGHT) Figure F RESULTS AND DISCUSSION (6) In figure F, a variation with regards to the location of the brattice is implemented. From the first brattice on the left to the second highest brattice, the increment is half the thickness of the brattice. From the above figure, it can be seen that the walls of the crosscut regions flow with an average of 2.6m/s. Comparing figure e and f, the airflow in figure 5 is marginally faster. 83 SIMULATION 7: USE OF A THIN BRATTICE FOR THREE CROSS-CUT REGIONS FIGURE G RESULTS AND DISCUSSION (7) In comparison with simulation 4, thin brattice is applied to three cross-cut regions as shown. It is observed that with the thin brattice additions, velocity at the walls tend to have increased, denoted by the red zones. Overall, there is increased circulation of air inside the cross-cut region. 84 SIMULATION 8: COMPARISON OF DIFFERENT THIN BRATTICE LENGTHS FIGURE H RESULTS AND DISCUSSION (8) In figure h, it is seen that with increased brattice length, the flow inside the cross-cut region increases. From figure h, it is seen that the optimum length would be 0.9 of the cross cut region. If the brattice is sufficiently shorter than 0.5 of the length, it is observed that there would be heavy recirculation. Recirculation is highly undesired in underground ventilation. 85 CONCLUSION In all the cases, the thin brattice is the most effective for simulating the dead zones inside the cross-cut region. A thin brattice would effectively direct air into a cross-cut region as opposed to thicker brattice. A thin brattice is also more space efficient. An inclusion of a brattice aids in diverting part of the air flow into the crosscut region. The resulting air flow out of the cross-cut region is roughly 35-40% of the original test airflow of 5m/s. The success of driving the contaminants out of a cross-cut region hence depends on the amount and size of constituents in contaminants such as dust particles. If airflow were to be slow, the resulting 60-65% reduction in speed may not be successful in bringing the contaminants out of the cross-cut regions. From most of the simulations, there is still a rotational section that remains in each cross-cut section. It is not helpful for the air to continue to re-circulate within this confinement as the buildup of unsafe gases may be unable to be vented out of the coal mine. While the brattice is somewhat effective, a brattice is best used with another device to bring dust contaminants out of a dead zone. 86 APPENDIX N: CHOICE OF TURBULENT MODEL ABSTRACT The choice of turbulent model for use for the 11 tunnel configurations will be Spalart Allmaras. The Spalart Allmaras turbulent model was chosen among the Reynolds Stress Model(RSM), k-ω and k-ε models. The tunnel configuration chosen for the selection of turbulent model was taken from Parra(2009). Over a few experiments, the choice of selection of Spalart Allmaras will be explained. MODEL DEVELOPMENT Figure X 87 The model for use is shown in figure X. It is a ‗horseshoe‘ shaped tunnel measuring 36 metres in length and 2.9 metres at it highest point. Such a tunnel is common among longwall mining structures. Coal mines may have different sizes, but the main purpose of this particular model is used to analyze and compare data from a literatary source which contains experimental data. According to Parra(2009), several anemometers were used in a tunnel and their experimental data was recorded over a course of a few days. Each set of anemometers consists 5 sets of readings and are placed at intervals Z=4, 12 and 18metres respectively. The layout is found in the experimental setup. Using Ansys Fluent CFD 6.3 program, Z iso surfaces will be displayed. This experiment will be conducted in FLUENT 6.3 and the results of simulation will be compared to those in the literature review by Parra. NUMERICS AND MATHEMATICAL DEVELOPMENT For the model shown in figure X, Fluent 6.3 will be used to support the following equations along with the choice of turbulent model. Mass: Momentum: EXPERIMENTAL SETUP (LOCATION OF ANEMOMETERS) Z=4m Z=12m Z=18m 88 RESULTS AND DISCUSSION From results from figure Y1, Y2 and Y3, among the 4 turbulent models (Spalart- Allmaras(SA), k-epsilon(k-ε), k-omega (k-ω) and Reynolds Stress(RSM)), SA comes closest to the numerical experimental data. At each point of the simulation, a percentage error for each measurement point was taken and compared with the experimental value. According to Parra, it is noted that the deviation for experimental data is provided at 10% for iso-surfaces located at the z-axis Z=4m and Z=12m. The deviation for Z=18m will be 20%. In total, the difference obtained by SA was the least. From figures Y1, Y2, Y3, it is observed that at iso-surface Z=4m, the 4 turbulent models give a similar shape and pattern. However, at Z=12m and Z =18m, there is a divergence is each of the turbulent model used. It is also inferred that the airflow velocity is reduced as the air moves toward the end of the tunnel. Airflow velocity and patterns is harder to measure and predict when the velocity slows. CONCLUSION As the main aim is to understand general flow, the satisfactory results shown by spalart allmaras would be it the ideal choice for selection. In addition, since spalart allmaras is an one equation model, computational time would be lesser and it would aid in the computational processing of 11 different tunnel configurations for the purpose of the this research project. Z=4 89 Figure Y1 **Contains 10% experimental error. For example, value 2.2 at Point 1 may contain a value range from 1.98 m/s to 2.42 m/s. Error can be attributed to experimental errors found in experiment. 90 Z=12m Figure Y2 **Contains 10% experimental error. 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