图书馆订阅: Guest
Begell Digital Portal Begell 数字图书馆 电子图书 期刊 参考文献及会议录 研究收集
多孔介质期刊
影响因子: 1.49 5年影响因子: 1.159 SJR: 0.504 SNIP: 0.671 CiteScore™: 1.58

ISSN 打印: 1091-028X
ISSN 在线: 1934-0508

多孔介质期刊

DOI: 10.1615/JPorMedia.v8.i2.60
pages 175-191

Radon-222 Exhalation Rates from Phosphogypsum-Bearing Embankment Subjected to Constant Temperature and Fixed Activity Concentration

J. A. Rabi
Faculty of Zootechny and Food Engineering, University of Sao Paulo, Av. Duque de Caxias Norte, 225, Pirassununga, SP, 13635-900, Brazil

ABSTRACT

Stack or embankment disposal of phosphogypsum — a by-product from phosphate fertilizer industries-has given rise to environmental issues concerning 222Rn exhalation rates into the local atmosphere. Early models for radon transport in porous media have considered both diffusion and convection, although basically taking into account air flow driven by predefined pressure differences and Darcy's law. The present paper introduces buoyant effects and outlines a steady-state two-dimensional model for 222Rn transport through a phosphogypsum-bearing embankment, inside of which there are sources and sinks for this gaseous radionuclide. The embankment is treated as an open cavity filled with porous material and surrounded by isothermal and impermeable ground. Its top surface is subjected to fixed activity concentration and fixed lower temperature. Buoyancy-driven interstitial air flow is supposedly laminar and modeled according to Darcy-Brinkman-Boussinesq formulation. Governing equations are written in dimensionless form in order to account for concurrent effects of the various physical parameters involved, and three unconventional dimensionless groups are put forward apart from usual controlling parameters, such as Darcy, Grashof, Prandtl, and Schmidt numbers. An analytical solution regarding a strictly diffusive approach is inferred, whereas full model equations are solved numerically by adapting an existing finite-volume simulator. As a preliminary investigation, results are reported for Pr = 0.71 and Sc = 15, while Da and Gr are allowed to vary from 10−7 to 10−13 and from 107 to 109 , respectively. Results are also presented as a function of the modified Grashof number Grm = Gr·Da. For porous media with relatively low permeability (Da ≤ 10−9), 222Rn transport is diffusion dominated (i.e., natural convective effects play a minor role) and both Nusselt and Sherwood numbers prove to be insensitive to Grashof number. At approximately Grm ≈ 10, circulation cell splitting occurs within each embankment half, as the natural convective fluid flow increases its strength, which results in very low 222Rn concentration levels inside the porous matrix.


Articles with similar content:

MIXED CONVECTION HEAT TRANSFER IN A VENTILATED ENCLOSURE WITH AND WITHOUT A SATURATED POROUS MEDIUM
Journal of Porous Media, Vol.19, 2016, issue 4
Ali A. Mohammed, Amir S. Dawood
ANALYSIS OF CONVECTIVE HEAT TRANSFER IN A SQUARE CAVITY FILLED WITH A POROUS MEDIUM UNDER A MAGNETIC FIELD
Special Topics & Reviews in Porous Media: An International Journal, Vol.2, 2011, issue 3
M. Sathiyamoorthy
THREE-DIMENSIONAL SIMULATION OF DOUBLE DIFFUSIVE CONVECTION IN A POROUS MEDIUM: HEAT AND MASS TRANSFERS
ICHMT DIGITAL LIBRARY ONLINE, Vol.0, 2009, issue
D. Akrour, Djamel Kalache, M. Nacer
NUMERICAL SIMULATION OF DOUBLE-DIFFUSIVE MIXED CONVECTION IN A HORIZONTAL ANNULUS UNDER TANGENTIAL MAGNETIC FIELD, WITH A ROTATING OUTER CYLINDER
Heat Transfer Research, Vol.49, 2018, issue 14
Goodarz Ahmadi, Bengt Sunden, Mehdi Bidabadi, Alireza Khoeini Poorfar, Vahid Bordbar
Transient Natural Convection in Differentially Heated Porous Enclosures: Corrected Abstract
Journal of Porous Media, Vol.4, 2001, issue 2
A. A. Merrikh