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By L. Zhou, J. P. Rider, T. W. Beck, J. A. Organiscak, Y. Zheng

The National Institute for Occupational Safety and Health’s Office of Mine Safety and Health Research recently developed a series of models using computational fluid dynamics (CFD) to study the gas distribution around a continuous mining machine with various fan-powered flooded bed scrubber discharge configurations. CFD models using Species Transport Model without reactions in FLUENT were constructed to evaluate the redirection of scrubber discharge toward the mining face rather than behind the return curtain. The following scenarios are considered in this study: 100 percent of the discharge redirected back toward the face on the off-curtain side of the continuous miner; 100 percent of the discharge redirected back toward the face, but divided equally to both sides of the machine; and 15 percent of the discharge redirected toward the face on the off-curtain side of the machine, with 85 percent directed into the return. These models were compared against a model with a conventional scrubber discharge, where air is directed away from the face into the return. The CFD models were calibrated and validated based on experimental data and accurately predicted sulfur hexafluoride (SF6) gas levels at four gas monitoring locations. One additional prediction model was simulated to consider a different scrubber discharge angle for the 100 percent redirected, equally divided case. These models identified relatively high gassy areas around the continuous miner, which may not warrant their use in coal mines with medium to high methane liberation rates. This paper describes the methodology used to develop the CFD models, and the validation of the models based on experimental data.

Jan 1, 2015

By L. Zhou, J. P. Rider, T. W. Beck, J. A. Organiscak, Y. Zheng

The U.S. National Institute for Occupational Safety and Health (NIOSH)’s Pittsburgh Mining Research Division (PMRD) recently developed a series of models using computational fluid dynamics (CFD) to study gas distribution around a continuous mining machine with various fan-powered flooded bed scrubber discharge configurations in an exhaust curtain working face. CFD models utilizing species transport model without reactions in FLUENT were constructed to evaluate the redirection of scrubber discharge toward the mining face rather than behind the return curtain. The study illustrates the gas distribution in the slab (second) cut. The following scenarios are considered in this study: 100 percent of the discharge redirected back toward the face on the off-curtain side; 100 percent of the discharge redirected back toward the face, but divided equally to both sides; and 15 percent of the discharge redirected toward the face on the off-curtain side, with 85 percent directed toward the return curtain. These models are compared against a model with a conventional scrubber discharge where air is directed away from the face into the return. The models were validated against experimental data, proving to accurately predict sulfur hexafluoride (SF6 ) gas levels at four gas monitoring locations. This study includes a predictive simulation examining a 45° scrubber angle compared with the 23° angle for the 100 percent redirected, equally divided case. This paper describes the validation of the CFD models based on experimental data of the gas distribution results.

Jan 1, 2017

By L. Zhou, J. P. Rider, T. W. Beck, J. A. Organiscak, Y. Zheng

The U.S. National Institute for Occupational Safety and Health (NIOSH)’s Pittsburgh Mining Research Division (PMRD) recently developed a series of models using computational fluid dynamics (CFD) to study gas distribution around a continuous mining machine with various fan-powered flooded bed scrubber discharge configurations in an exhaust curtain working face. CFD models utilizing species transport model without reactions in FLUENT were constructed to evaluate the redirection of scrubber discharge toward the mining face rather than behind the return curtain. The study illustrates the gas distribution in the slab (second) cut. The following scenarios are considered in this study: 100 percent of the discharge redirected back toward the face on the off-curtain side; 100 percent of the discharge redirected back toward the face, but divided equally to both sides; and 15 percent of the discharge redirected toward the face on the off-curtain side, with 85 percent directed toward the return curtain. These models are compared against a model with a conventional scrubber discharge where air is directed away from the face into the return. The models were validated against experimental data, proving to accurately predict sulfur hexafluoride (SF6 ) gas levels at four gas monitoring locations. This study includes a predictive simulation examining a 45° scrubber angle compared with the 23° angle for the 100 percent redirected, equally divided case. This paper describes the validation of the CFD models based on experimental data of the gas distribution results.

Jan 1, 2018

By Ying Mao, Zhancheng Guo, Long Ma, Huiqing Tang

"A new 2D computational fluid dynamic (CFD) model was developed for the gaseous reduction of iron ore fines in an innovative reactor-multilayer moving-fluidized bed. The solution of the proposed model was performed by integration of FLUENT and PHOENICS. Numerical results of cold state were compared with the experimental data and the agreement between them was good. A hot case-gaseous reduction of iron ore fines using syngas with this reactor was simulated using the present CFD mode. Results indicate that under the given simulation conditions, total pressure drop is 90 Pa less than that under cold state though the gas supply rate is increased about 4m3 under hot state. Gas temperature decreases from 1073 K at the bottom to 500 K at the top, Utilization efficiency of the gas reduction potential is about 27 %. For ore fines reduction, the final reduction fraction could reach 0. 70 and solid temperature 900 K.IntroductionWith the development of coal gasification technology, various coals could be converted to Syngas with air or steam. Therefore gaseous reduction of iron ore fmes becomes an acceptable alternative process for iron making besides blast furnace route[!] and moreover it still has some advantages in processing low grade iron ore fines[2]. Gaseous reduction using fluidized bed technologies is the most competitive in all direct reduction iron-making processes up to now. It has the advantage that ore fines can be directly charged to the process without prior treatment while its disadvantages are particle agglomeration and high gas/solid ratio[3]. To avoid these advantages, a new reactor, multilayer moving-fluidized bed reactor has been developed for carrying out the gaseous reduction. Hydrodynamic behaviors of gas and fines in the reactor were studied and the results were satisfying[4]. However, due to its unique structure of the multilayer moving-fluidized bed and unique gas-solid flow pattern, models of multiphase flow as IPSA, DPM and Eulerian Model could not give a satisfying solution. The current paper is developed a new CFD model and a new solution approach for simulation of the reactive gas-solid flow in the multilayer moving-fluidized bed for its optimization, design improvement and future scale-up."

Jan 1, 2013

By D. J. Englund, R. A. Davis

"A three-dimensional CFD model of a straight grate furnace for indurating iron-oxide pellets was developed for exploring conditions of furnace operation for fluid flow, heat transfer and reactions. The model includes reactions for natural gas combustion in the gas phase and calcination and magnetite oxidation as well as drying in the pellet bed. The performance of the model was investigated with a series of pellet production rates that included adjustments to the fuel rates to achieve proper induration temperatures in the pellet bed. The model may be used to discover opportunities for process improvement.IntroductionIron oxide pellets are a feedstock to blast furnaces for iron making. Pellets require physical strength characteristics needed to maintain their integrity during storage, handling, transportation and smelting. Pellets are produced from iron ore in a series of mineral processing operations that form wet green balls from slurries of iron-ore concentrate with binders, such as bentonite, and possibly fluxing-agents such as limestone and dolomite. The green balls are dried, fired at high temperature, and then cooled in an induration furnace to achieve the strength and chemical composition required for efficient reduction and slag separation in blast furnaces. Induration furnaces are generally straight grates or grate-kilncooler configurations. These furnaces operate with pellet beds passing through a series of temperature zones to control drying and chemical reactions in the bed.Process air passes through the zones in an overall counter flow direction to the pellets for efficient heat transfer and energy recovery from the cooling stage. Consequently, the zone conditions and the overall furnace performance are highly coupled. Thus, it becomes challenging to predict how changes to any single zone may affect the rest of the furnace. To gain a better understanding of machine performance and coupling, a three-dimensional, steady-state model of a complete straight grate induration furnace was created using computational fluid dynamics (CFD)."

Jan 1, 2015

By K. V. Raj

"The development and advancement of computational fluid dynamics (CFD) has made it possible to better understand pollutant flow and distribution in deep open pit mines. Open pits located at higher latitudes, especially in the Arctic and sub-Arctic, face a unique problem due to atmospheric temperature inversion, which is prevalent during much of the winter. A three-dimensional CFD model of an actual open pit mine in the Arctic was developed to analyze the problem of pollutant growth during inversion, and mitigation of the pollutants through improved ventilation schemes. Due to the availability of mine-specific data, such as contaminant concentrations and coordinates of sampling locations, the actual 2013 pit geometry was used for model validation Concentrations predicted by the selected realizable ?-e turbulent model are compared to measured pollutant concentrations at the open pit. Pollutant concentrations at selected locations showed differences, but remained within the same order of magnitude in most cases. INTRODUCTION Computational fluid dynamics (CFD) has emerged as a useful tool for ventilation modeling in underground mines (Edwards and Hwang 1999, Purushotham and Bandopadhyay 2009, Wala et al. 1998, Xu et al. 2011). Application of CFD in open pit mines has been limited, however, since most open pit mines located at lower latitudes do not encounter considerable ventilation problems. Open pits located at higher latitudes, especially the Arctic and sub-Arctic, face a unique problem due to atmospheric temperature inversion, which is prevalent during winter. A number of Russian researchers have tried to understand the air inversion and resulting pollutant transport problem by modeling air flow phenomena in open pit mines (Baklanov and Burman 1996, Baklanov 1984, Baklanov 1995, Belousov 1985, 1989, 1995). Much of their work, however, was based on numerical models and methods of finite difference. Baklanov (2000) applied a modified ?-e and a ?-l CFD model to air flow phenomena on various terrains. More recently, Choudhury (2011) used the COMSOL CFD package for modeling pollutant transport for an idealized open pit mine. Collingwood et al. (2012a, 2012b) used a two-dimensional model for fluid flow and contaminant transport at an Arctic open pit mine. The authors have also previously presented work on CFD modeling of an actual open pit mine at high latitude (Bandopadhyay et al. 2014, Raj et al. 2015a). However, the CFD work done by the above-cited researchers lacked model validation with field-measured data. Validation of a developed model is important in assessing the quality and accuracy of the predicted results. In general, experiments are done numerous times in controlled environments to assess the validity of collected data. There are two types of assessments used in CFD simulations: (1) verification and (2) validation. Model verification is checking the accuracy of the computer codes during the implementation phase of a real-world problem, within the specific limits of accuracy (Oberkampf and Trucano 2002). Since, the pollution transport model presented in this paper used the commercial ANSYS-FLUENT CFD package, verification is not needed as the program has been tested widely, and verified numerous times."

Jan 1, 2016

By Ernie M. Crist, Laurentiu Nastac, Frank Spadafora

"This paper describes the modeling techniques and the experimental and computer results for two casting processes that are under development and optimization. These processes are described as follows:1) Electromagnetic stirring (EMS) during casting of Ti-6Al-4V round ingots using the plasma arc cold hearth melting (PAM) process: The purpose of EMS is to establish a singlemelt PAM process capable of consistently producing as-cast ingots without helium porosity and also having no need for surface conditioning prior to secondary processing.. The modeling approach is based on the numerical solution of Maxwell's equations, fluid flow, and heat transfer equations, and mesoscopic modeling of the grain structure.2) Casting of Ti-6Al-4V slabs using the single-melt PAM process: The purpose of slab casting is to improve yield by eliminating an intermediate blooming step for converting round ingots to slabs. The modeling approach is based on the numerical solution of fluid flow and heat transfer equations. The effects of pouring and mold temperatures on the pool and temperature profiles were studied. Also, the torch effects (such as the torch standoff and its traversing path) on the pool and temperature profiles were investigated and the best-case scenario was used in the experiments. Evaluation results at RMI Titanium Company showed that the plates made from the slabs met the mechanical properties and microstructure requirements.Acknowledgment. This work was conducted by the National Center for Excellence in Metalworking Technology (NCEMT) operated by Concurrent Technologies Corporation (CTC) under contract No. N00014-00-C-0544 to the US. Navy as part of the US. Navy Manufacturing Technology Program. Dr. K. b. Yu from RMI and my colleagues from CTC are acknowledged for their comments on this work."

Jan 1, 2004

"Controlling dust generation and keeping it below permissible limits at the working face of a room and pillar mine is a challenge for mine operators. With the recent changes in the respirable-dust regulation, it has become increasingly difficult. The current most effective practice of dust control at a continuous miner face in an underground mine is the use of a flooded-bed scrubber. A study carried out by the National Institute for Occupational Safety and Health (NIOSH) stated that a flooded-bed scrubber, under its optimum condition, can achieve cleaning efficiencies between 58 and 90 percent. The performance of such a system can be maintenance intensive. Other industries face similar dust control issues. The University of Kentucky partnered with Toyota Motor Manufacturing for the development of a novel wet scrubber for capturing paint overspray, with capture efficiencies in excess of 98 percent and minimal maintenance. The aim of this study is to assess the ability of this novel wet scrubber to capture respirable dust in an underground coal mine. This paper presents the conceptual design and the computational fluid dynamics (CFD) modeling of this novel wet scrubber. It discusses the results of the CFD simulation performed on the novel wet dust scrubber. INTRODUCTION Dust generation from underground coal mining is an inescapable phenomenon. No matter the practices employed, it inevitably occurs. Elevated concentrations of coal dust are potential health and safety hazards. Although dust in an underground coal mine cannot be completely avoided, its influence can be mitigated through good engineering practices. The effect of dust on the health of mining personnel has had a significant impact. The prolonged exposure of airborne respirable dust (< 5 µm) can cause coal workers’ pneumoconiosis (CWP), silicosis, emphysema, and chronic bronchitis, collectively known as black lung (U.S. Department of Labor, 2014). According to the National Institute for Occupational Safety and Health, black lung has killed more than 10,000 miners between 1995 and 2004 (NIOSH, 2008). In addition to being a health issue, coal dust is also a safety issue to the underground coal miners. The generated dust, if not captured, is dispersed into the mine air through the ventilating air and deposited downwind on the return entries’ surfaces. In the event of a methane explosion, the coal dust, if insufficiently diluted with rock dust, triggers a coal dust explosion which is much more severe than a methane explosion and causes more damage (Kenneth et al, 2006). The Jim Walters No. 5 Mine and the Upper Big Branch Mine disasters which together killed 42 people and resulted in damage worth millions of dollars in property are the examples of coal dust explosions (U.S. Department of Labor, 2001 & 2010)."

Jan 1, 2016

By W. Collingwood

As openpit mines continue to grow deeper and productivity continues to increase, the management of respirable dust and noxious gases can become a challenge. The natural wind flow in openpit mines is often recirculatory. This recirculation traps dust and gases in deep openpit mines. This problem is particularly acute in high-latitude openpit mines, due to a phenomenon known as atmospheric inversion. In the winter, arctic and subarctic regions experience short days and long nights. This deficit of solar radiation creates a situation in which cold, still air accumulates near the bottom of the pit. In openpit mines, this can result in unhealthy accumulations of gases and other contaminants. In this study, the natural wind flow patterns in and around openpit mines were investigated using a computational fluid dynamics (CfD) program. Two-dimensional models were created for a variety of pit geometries. The effect of depth, slope angle and wind speed on the recirculation pattern in the pit was examined.

Jan 1, 2012

By K. V. Raj

"Air inversion is a meteorological phenomenon generally occurs during winter times. Release of pollutants below the inversion height in an open-pit mine during periods of weak winds and consequently weak vertical mixing may result in very high concentrations of primary and secondary pollutants, causing serious consequences for health and safety of miners. Mine operations cease if the concentration of NOx or CO exceeds the threshold limit value (TLV) of the pollutants. Artificial ventilation is required to dilute the pollutants to an extent that mine workers can safely resume work. Studies of the turbulence parameters suggest that effective ventilation of the pit and removal of pollutants can be accomplished if a large enough mixing length in the open pit can be created. Turbulent mixing by eddies of different length scales under an inversion layer is product of wind shear, thermal gradient and buoyancy. The main result of turbulence is mixing of the atmospheric profile and transport of momentum. Computational fluid dynamics (CFD) Simulation results of a novel mitigation approach using cloud cover will be presented in this paper. INTRODUCTION In extreme climatic conditions, deep open-pit mines tend to trap pollutants at the pit bottom due to air inversions. Keeping open pits adequately ventilated is a considerable challenge for the mining community. Mine operators in cold regions are very familiar with this problem, the severity of which can be judged from Figures 1 and 2. The top portion of the figures show clear sky and snow covered benches. The brown haze, containing various contaminants accumulated over time in the pit under the air inversion, can be seen in the bottom portion of the figures. Several Arctic or subarctic mines have reported air inversions. Even Rio Tinto’s Bingham Canyon pit in Utah has reported local air inversions from time to time [1].Mitigation of pollutants in deep open-pit mines in the Arctic is a challenging task. Release of pollutants below the inversion height in an open-pit mine during periods of weak winds and consequently weak vertical mixing may result in very high concentrations of primary and secondary pollutants, causing serious consequences for human health. Mine operations cease if the concentration of any one of the pollutants (NOx or CO) exceeds the TLV. Sustained cessation of a mine operation has serious economic consequences. For continued mining operation, the levels of pollutants must be below the TLVs. If no significant synoptic meteorological situation changes during an inversion, a warm air mass sits over the cold air mass within the open pit. Artificial ventilation is required to dilute the pollutants to an extent that mine workers can safely resume work. Some of the early approaches in artificially ventilating open pits were attempted in the USSR. Most of the studies by Soviet researchers suggested the use of turbojets and turbo-propeller engines, airscrews, axial pit fans, and meteotrons [2, 3]. However, the majority of these studies were only theoretical in nature, with no evidence of an approach that really worked in practice."

Jan 1, 2017

By J. C. Edwards, C. C. Hwang

A computational fluid dynamics (CFD) program was applied to fire spread along combustibles in a ventilated mine entry. The rate of flame spread was evaluated for the ribs and roof of a coal mine entry; timber sets; and a conveyor belt. The CFD program models char forming materials with temperature dependent thermal properties. The program solves three dimensional time dependent flow equations with a mixture fraction model for the gas phase reactions. Radiant heat exchange is evaluated for non-scattering gas. The CFD program predicted a flame spread rate of 0.0145 m / s for an actual coal mine fire in which the estimated flame spread rate was 0.0086 m / s. This overestimated flame spread rate was a possible consequence of the presence of inert materials in the mine entry’s roof and ribs. CFD fire spread rate predictions of 0.043 m / s and 0.73 m / s bounded the measured value of 0.27 m / s for fire spread along Douglas Fir timber sets in a tunnel.

Jan 1, 2006

By Haibin Wang, Kaile Tang, Chenn Q. Zhou, Guangwu Tang, Zhixiang Cui, Ping Zhou, Armin K. Silaen, Hongjie Yan, Zhi Wang

The submerged lance smelting furnace (SLS) for copper smelting has been developed and used by Dongying Fangyuan Nonferrous Metals Co., Ltd. The technology has shown advantages such as high oxygen enrichment, good feed adaptability, short processing time, high SO2 concentration for acid plant, and auto-thermal operation. In this study, computational fluid dynamics (CFD) was used to investigate the gas/matte two-phase flow characteristics and the chemical reactions in the SLS during typical operational conditions. The Eulerian-Eulerian approach was employed to model the phase interactions. The chemical reactions were modeled by calculating the mass transfer coef ficients and using the eddy-dissipation model. The simulation was conducted using the commercial software ANSYS Fluent®. The developed CFD model is able to predict the flow, temperature, and species distributions inside the SLS under various operating conditions.

Mar 1, 2018

By G. E. Bogin, C. Strebinger, J. F. Brune

"Evidence shows that methane gas emanates from the mined-out area or gob of a longwall coal mine and can travel towards the working face, posing an explosion risk. Since the gob consists of varying levels of compacted rock, many researchers have modeled fluid flow through the gob as a Darcy-type porous media with a specified porosity and permeability. When studying methane gas explosions near the gob fringe, the Darcy flow assumption may not be applicable to describe the methane flame interaction with the gob. Computational fluid dynamic studies were performed modeling methane flame propagation across a simulated gob which was modeled as both a Darcy porous medium and as discrete rock objects with varying sphericity. Modeling the gob as a Darcy porous medium results in unrealistic methane flame propagation since the porous media assumption does not consider any differences in rock size and/or distribution. Additionally, the porous media model does not allow for ignition within and subsequent flame propagation through the porous medium, which must be modeled to understand the potential for methane gas explosions in the gob area. Modeling the gob as discrete rock objects produces more realistic methane flame dynamics and agrees with experimental observations. Modeling results show flame propagation across circles, hexagons, and squares, meant to represent rock rubble in the gob, produce different levels of turbulence which affects methane flame propagation velocity. This research demonstrates that modeling methane gas explosions in a longwall coal mine environment, specifically near the gob area, requires modeling obstacles, such as rock rubble, as discrete physical objects to capture the complex coupling of fluid dynamics, thermodynamics, and heat transfer. INTRODUCTION Although there are methods to mitigating methane accumulations in a longwall coal mine, explosive gas zones (EGZs) of methane and air may exist and pose an explosion risk to nearby miners and equipment (Brune, 2014) (Karacan, Ruiz, Cote, & Phipps, 2011). In the event of an explosion, the resulting methane flame and pressure wave can be catastrophic as evidenced by the Upper Big Branch explosion in 2010 that killed 29 miners (Page, et al., 2011). Since the mining process is transient, it is difficult to determine exactly where these EGZs exist, but investigative reports show in many cases, these EGZs can be near the working face, behind the shields, or within the gob area (Brune, 2014) (McKinney, et al., 2001). Additionally, miners have recounted seeing flames moving back and forth within the gob and under the roof supports (McKinney, et al., 2001) and in other cases, anecdotal evidence of hearing small pressure pops deep within the gob area (Brune, 2014)."

Jan 1, 2019

By Dieter Neuschiitz, Pengfu Tan

"In order to understand the sintering phenomena during iron ore sintering process, a CFD model of iron ore sintering has been developed, combining with the kinetics of 15 relevant chemical reactions with the aim of describing the temperature fields and the gas flow patterns in the sintering bed. This CFD model can be used to simulate the concentrations of the gaseous and solid species, temperatures of the gas and solid, melting and molten fractions of the mixture, gas velocities, temperature zones and residence times of the gas in each temperature zone. IntroductionThe off-gas analyses clearly revealed that the off-gas of a sinter strand does not have a composition corresponding to thermodynamic equilibrium, for example, the CO, CO2 and O2 concentrations are not the mutually consistent equilibrium values. Apparently the chemical reactions in the sinter bed are controlled kinetically. Therefore kinetic modeling of sintering reactions combined with CFD modeling is necessary to understand the sintering phenomena during iron ore sintering process.Several models of iron ore sintering have been developed since 1970 [l-l 4l, each being more refined than its predecessor. The models were formulated as a series of differential equations to describe chemical and physical changes occurring at a point in the bed. These equations were solved numerically in a vertical plane along the strand. The present CFD model, based on the Nath's model [14], has been published in the reference [15]. In this work, some new chemical kinetic models of gas-solid reactions are incorporated in the present CFD model. The concentrations of gaseous and solid species, temperatures of gas and solid, melting and molten fractions of solid, velocity of gas, and residence time of gas in each combustion zone can be calculated by this model."

Jan 1, 2004

By Q. Cao, A. Pitts, L. Nastac

Accurate prediction of the desulfurization behavior of steel is of great importance for process control during ladle metallurgical furnace (LMF) steel refining. A CFD model capable of simulating multiphase flow with bulk and free surface turbulence phenomena and desulfurization behavior in the gas-stirred ladle has been developed. The fluid flow behavior shows that slag and metal try to entrap each other, forming a two-phase mixing zone. The resulting substantial contact area between the two phases will provide very favorable kinetic conditions for chemical reactions. For reaction kinetics model, the reactions at the metal/slag bath interface as well as the entrapped droplet surface are included. Predicted results show that the sulfur content changing with time in the ladle agrees well with the industrial-scale experimental measurements.

Mar 1, 2017

By Lanre M. Oshinowo, André Bakker

"An understanding of the parameters that govern the just-suspended impeller speed, Njs, and the distribution of solids, is critical to the efficient operation of hydrometallurgical and other processes involving solid-liquid suspensions. In this paper, the distribution of solids in stirred tanks under a range of solids loadings (0.5 to 50 vol%) was predicted using CFD and validated against experimental data obtained from the literature. The multiphase flow is modeled using the Eulerian Granular Multiphase model. This paper will also review the established design parameter Njs in the context of scale-up and compare it to the quality of solids dispersion as a means of assessing correct scale-up in suspension tank design. The results of this study will describe a straightforward procedure to obtaining comprehensive information about reactor behavior with complex CFD models.The performance of hydrofoil impellers and a 45° pitched-blade turbine at suspending solids under different agitation speeds was studied. Both single and dual impeller operation have been evaluated. The settled solids fraction for speeds below N js, and the cloud height for impeller speeds above Njs were predicted. The CFD predictions are in good agreement with experimental literature data on velocity distribution and cloud height."

Jan 1, 2001

By Liming Yuan

Three-dimensional computational fluid dynamics (CFD) modeling is conducted to simulate spontaneous heating in a large-scale coal chamber with a forced ventilation system. Spontaneous heating is modeled as the low-temperature oxidation of coal using kinetic data obtained from previous laboratory-scale spontaneous heating studies. Heat generated from coal oxidation is dissipated by convection and conduction, while oxygen and oxidation products are transported by convection and diffusion. The water vapor transfer and the effect of heat of wetting are not modeled. The CFD model is validated by comparing simulation results with test results from U.S. Bureau of Mines experiments conducted in the coal chamber. The model predicts lower temperatures in the early stage but agrees well on the induction time for spontaneous heating. The effects of airflow rate and order of reaction on the spontaneous heating process are also examined. The calibrated CFD model is found to be useful for predicting the induction time for spontaneous heating in underground coal mines.

Jan 1, 2009

By Nathanael Hudson, Ruel A. Overfelt, Sushil H. Bhavnani

"In the aerospace and automotive industries, complex shapes exist which require casting. The problem with these cast parts is the empiricism required to develop the casting process and the accompanying time and expense to develop that process.There has been an interest in using fluidized beds to allow molding sand to better encapsulate the complicated surface geometries of lost foam patterns. Fluidization coupled with a mixing jet helps to homogenize the sand through stirring and may improve the integrity of the casting.At issue is the hydrodynamics of the sand and air around the foam pattern. The commercial package PHOENlCSTM is used to simulate the flow around the pre-casting foam geometry. Employing a two fluid approach, each component is considered a fluid that interpenetrates the other phase. To this end, the kinetic theory of granular 'flow for the sand phase was incorporated into the re-compilable PHOENlCSTM code.The results of this study consist of time-averaged void fraction patterns, with voidage being defined as the fraction of air in the mixture, around the foam pattern submerged in a two-dimensional fluidized bed. The model was benchmarked against past fluidized bed experiments. In order to better understand the dependence of the void fraction pattern around the lost foam pattern, certain physical parameters are varied and the resultant void fraction maps are predicted with the model. Physical parameters such as the aspect ratio of length to width, the placement of the mixing jet, and different mixing jet velocities are varied to illustrate the dependence of the time-averaged void fraction on those variables.Results consistently indicate the presence of channeling around the lost foam pattern, with the extent of the channeling and void formation reliant to a greater degree upon the placement of the mixing jet, and to a lesser degree on mixing jet velocity and aspect ratio.The increase in radial position of the mixing jet from the bed centerline had the desirable effect of granting the churning benefits of a penetrating jet, while at the same time minimizing the formation of excess void fraction at the top of the pattern."

Jan 1, 2001

By S. Mohanty, K. Sarangi, S. Dash, P. P. Patra

Industrial effluent from various industries contains heavy metals that are a serious threat to humans, flora and fauna in water bodies, and the environment. The heavy metals are dumped after precipitation, which has serious environmental consequences. In this paper, a 2D axi-symmetry CFD model has been developed to study the extraction of chromium ion from industrial effluent, in a hollow fibre membrane, using Alamine 336 as the carrier and kerosene as the diluent. The Navier Stokes equation was used to predict the velocity profile of the aqueous and organic phases, and species transport equation, which considers both convective and diffusive mass transfer, was used to predict the concentration profile of the chromium ion in the computational domain. The distribution coefficient was experimentally determined at a pH 4, which was found to be the optimum pH. Numerical simulations were performed considering 11.11 mol/m3 of initial feed concentration for chromium ions and extractant concentration of 0.2 M. Simulations were carried out with various aqueous and organic flow rates, and validated with experimental data. Keywords: CFD, metal extraction, hollow fibre membrane, heavy metals

Jan 1, 2020

By A. Juganda, Jr. Bogin, J. Brune, J. Grubb, S. Lolon

"Face ignitions at the longwall face are a serious hazard in underground coal operation that can lead to a major mine explosion. Despite having methane monitoring system mounted on the shearer and at various locations on the longwall face, undetected accumulations of methane can still occur and result in face ignitions. With the use of Computational Fluid Dynamics (CFD), the interaction between the air flow at the longwall face and factors that contribute to the accumulation of methane around the longwall face can be modeled and visualized in great detail. The results confirm that the tailgate corner of longwall face is a critical area that is prone to face ignitions and needs to be properly monitored. The occurrence of roof falls on the tailgate entry inby the face and/or poor caving conditions behind the shields can pose a safety risk in the longwall operation. Poor gob caving can lead to insufficient face air quantity to dilute methane at the tailgate corner, while blocking of tailgate by a roof fall can carry methane contaminated air from behind the shields back into the face near the tailgate corner and pull the explosive gas zones (EGZs) inside the gob closer to the face. INTRODUCTION Ignitions of accumulated methane gas at longwall faces are well known to be among the major causes of methane explosion in underground coal longwall mining operations. Some of these ignitions can lead to major mine explosions, such as the Upper Big Branch mine disaster in 2010, in which methane migrated from the gob to the shearer cutting drum where it was ignited, resulting in a major mine disaster (Phillips, 2012). History has shown that, despite having methane monitoring systems mounted on the shearer and various locations at the longwall face and alarms set to 1% CH4 (Mine Safety & Health Administration, 2012), undetected accumulations of explosive methane-air-mixtures can still occur and result in face ignitions. Recent study by Verma and Brune (2016) state that frictional ignitions on longwall faces contributed to 379 incidents or 23% of the total 1,637 cases of face ignitions recorded from 1983 to 2014. The common cause of mine explosions usually involves poorly designed ventilation systems, insufficient ventilation, and inadequate monitoring in critical areas that are prone to methane accumulations. In longwall operation, the tailgate corner of the longwall face can be considered as one such critical area. On-site studies by Krog et al (2006) and Thakur (2008) show that increasing the longwall panel width may also increase cumulative methane emissions at the tailgate. There are also indications that increasing longwall face lengths can result in an increase of the void space behind the face under certain roof conditions (Schatzel et al, 2006). This may cause higher leakage rates from the face to the gob, thus reducing the amount of fresh air available at the tailgate."

Jan 1, 2017