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Sources of radon and its measurement techniques in underground uranium mines – an overview

Sahu P., Panigrahi D. C., Mishra D. P.

Journal of Sustainable Mining

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2014

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Vol. 13, iss. 3

11--18

EN

Purpose This study aims to identify the potential sources of radon exhalation and its measurement in underground uranium mines to control the radiation levels within safe limits and protect miners from radiation hazards. Methods An extensive literature review on radon exhalation in underground uranium mines from various sources such as uranium ore, backfill tailings and mine water has been carried out. The influence of different important factors, viz. ore grade, porosity, grain size and moisture content on radon exhalation has been discussed in depth. Different methods for the measurement of radon exhalation from various sources in mines have also been presented in this paper. Results The review of literature revealed that the radon exhalation rate in porous uranium bearing rocks is less affected by the ore grade than in non-porous rocks. The exhalation of radon from backfill tailings is quantitatively more significant than from the uranium ore itself due to higher bulk porosity and enhanced surface area. Thus, porosity is the dominant factor that affects the rate of radon exhalation from rock surfaces into mine openings. Practical implications The knowledge of the sources of radon and quantitative estimation of radon from various sources will be very much useful in the planning and designing of ventilation systems in underground uranium mines. The accurate measurement of radon exhalation in underground uranium mines can be made by choosing the optimum size of accumulation chamber and a suitable radon build-up period in the chamber. Originality/ value The study portrays the important sources of radon and its measurement techniques in underground uranium mines based on an extensive literature review. The methods of measurement of radon exhalation from the ore body and backfill tailings in underground uranium mines, used by the authors of this paper, comparatively give more accurate results than previously used methods. Furthermore, the methods are more effective in terms of portability, cost and time for measuring the average radon exhalation across a large.

2

CFD simulations for selection of appropriate blade profile for improving energy efficiency in axial flow mine ventilation fans

Panigrahi D. C., Mishra D. P.

Journal of Sustainable Mining

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2014

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Vol. 13, iss. 1

15--21

EN

Purpose This study focuses on one of the key design aspects of mine ventilation fans, i.e. the selection of an appropriate aerofoil blade profile for the fan blades in order to enhance the energy efficiency of axial flow mine ventilation fans, using CFD simulations. Methods Computational simulations were performed on six selected typical aerofoil sections using CFD code ANSYS Fluent 6.3.26 at angles of attack varying from 0 to 21 at an interval of 3 and at Reynolds number Re = 3 × 106, and various aerody-namic parameters, viz. coefficients of lift (Cl) and drag (Cd) as a function of angle of attack (α) were determined to assess the efficiency of the aerofoils. Results The study revealed that the angle of attack has a significant effect on the lift and drag coefficients and stall condition oc-curred at α values of 12 and 15 in most of the aerofoils. Based on the criterion of higher lift to drag ratio (Cl/Cd), a blade profile was chosen as the most efficient one for mine ventilation fans. Practical implications This study forms a basis for selecting appropriate blade profiles for the axial flow fans used for ventilation in mining industry. Originality/ value The application of an appropriate aerofoil blade profile will impart energy efficiency to the mine ventilation fans and thereby result in energy saving in mine ventilation.

3

Productivity improvement in underground coal mines – a case study

Mishra D. P., Sugla M., Singha P.

Journal of Sustainable Mining

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2013

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Vol. 12, iss. 3

48--53

EN

Improvement of productivity has become an important goal for today’s coal industry in the race to increase price competitiveness. The challenge now lying ahead for the coal industry is to identify areas of waste, meet the market price and maintain a healthy profit. The only way to achieve this is to reduce production costs by improving productivity, efficiency and the effectiveness of the equipment. This paper aims to identify the various factors and problems affecting the productivity of underground coal mines adopting the bord and pillar method of mining and to propose suitable measures for improving them. The various key factors affecting productivity, namely the cycle of operations, manpower deployment, machine efficiency, material handling and management of manpower are discussed. In addition, the problem of side discharge loader (SDL) cable handling resulting in the wastage of precious manpower resources and SDL breakdown have also been identified and resolved in this paper.

4

Experimental investigation of n-heptane droplet combustion at high pressure conditions

Mishra D. P., Rukmangadhan G.

Archivum Combustionis

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2011

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Vol. 31 nr 1-2

17-27

EN

An experimental study was carried out on the combustion of n-heptane droplets at atmospheric and higher pressure under normal gravity condition. Suspended droplet technique was adopted to investigate the isolated droplets. The burning rate constants were determined for each pressure and the dependence of burning rate constant on pressure was analyzed. The D2 law for droplet combustion was experimentally established. The burning rate constant was found to increase monotonically with pressure. Using back light photography and image processing techniques the flame shape and its dependence on pressure was also analyzed.

5

Numerical Studies of Bluff-Body Stabilized Lean Premixed Flame Based Combustor

Mishra D. P., Singh H. J.

Archivum Combustionis

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2010

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Vol. 30 nr 1-2

63-85

EN

The present research deals with numerical simulation of premixed flow inside the bluff body flame stabilized combustor. The effect of variation of co-flow velocity on important flow quantities such as radial velocity, static pressure, static temperature, turbulent kinetic energy, turbulence and dissipation rate have been studied thoroughly for reacting flow. Besides this, flame shape is identified with the help of temperature contours which indicates that the flame length becomes short with high co-flow velocities. It was found out that re-circulation length reduces significantly by 21.73 % as the co-flow velocity was increased. A comparison between turbulent kinetic energy for the co-flow velocity of 1.25 and 2.5 m/s shows that re-circulation zone becomes more compact and strengthened for higher co-flow velocities leading to more dissipation. Comparison between isothermal and reacting flow has been carried out for all the flow properties.

6

Study of Downward Smoldering Combustion in Polyurethane Foams

Mishra D. P., Verma A.

Archivum Combustionis

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2009

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Vol. 29 nr 3-4

73-81

EN

A study of downward smoldering combustion in polyurethane foams is carried out in a realistic experimental model with a terrycot cloth wrapped around the foam material which is widely used in household upholstered furniture. Measurements are performed for the smolder reaction temperature and velocity as a function of time and location of the smolder zone in the sample. Three distinct zones in terms of smoldering velocity are identified during the smoldering process. The first one is the low smoldering velocity zone occurring at the top followed by the middle velocity zone and the last is the high velocity zone. Based on the observations made on the smoldering velocity the parameters responsible for the self propagation of the smoldering reaction have been explored. A comparison has also been made between the temperature profiles of the smoldering zone between thin and thick cloth wrapping foam cases. Interestingly it was found that the smoldering rate in the thin cloth wrapped foam case was higher as compared to the thick cloth wrapped foam.

7

An Experimental Study of Flame Spread over an Inclined Thin Fuel Surface

Mishra D. P., Maheshwari M.

Archivum Combustionis

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2009

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Vol. 29 nr 3-4

101-109

EN

An experimental study was carried out to analyze the downward flame spread rate over thin solid fuel (paper) in its dry state as well as when it is soaked with a combustible liquid fuels. The downward flame spread rate is estimated for different inclination angles varying from 0° to 90°. The flame spread rate is found out to be enhanced in the range of 0° to 30° while it remains almost constant over the other part of the range. The downward flame spread rate also decreases with increase in the thickness of the fuel. As the boiling point of the combustible liquid increases, the flame spread rate is found to get decreased. When the boiling point of the combustible liquid is less than the pyrolysis temperature of the paper, the flame spread rate is observed to be higher than that of the dry paper. However, the downward flame spread rate decreases with increase in orientation and thickness of the paper.

8

Numerical Studies of Combustion of Single n-Heptane Droplet

Mishra D. P., Majee A.

Archivum Combustionis

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2007

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Vol. 27 nr 1-2

45-54

EN

Numerical simulations of single fuel droplet combustion have been carried out using transient finite difference method with finite rate chemistry and variable transport properties under the assumptions of spherical symmetry. The present predicted burning rate matches well with experimental data in the initial burning phase. The slope of the et law curve remains almost constant for droplet burning. The transient variations of droplet center temperature, droplet surface temperature and flame temperature are analyzed in details. The present result predicts the experimental data of flame diameter qualitatively, which can be improved further in future. The analysis of detailed structure of the droplet combustion flame simulation indicates that the thin flame approximation assumed by earlier analytical works is valid.