The Effects of Simultaneous Heat and Mass Transport on Radionuclide Migration

1985 ◽  
Vol 50 ◽  
Author(s):  
Frank B. Walton ◽  
J. P. M. Ross ◽  
D. G. Juhnke
Keyword(s):  
Ionic Strength ◽  
Mass Transport ◽  
Thermal Convection ◽  
Thermal Gradient ◽  
Convective Transport ◽  
Radionuclide Migration ◽  
Cold Side ◽  
Heat And Mass Transport ◽  
Flow Channels ◽  
Simultaneous Heat

AbstractFive thermal-convection loops, constructed of granite, were operated for 350 d with a hot-side temperature of 60°C and a cold-side temperature of 20°C, to examine the effects of a thermal gradient on the convective transport of seven radionuclides. Radionuclide concentrations on the surface of the loop flow channels indicated that 125Sb, 60Co and 54Mn and precipitated iron oxyhydroxides were concentrated in the hot side of the loops. Concentrations of 144Ce and 99Tc were higher in the cold side of the loops. Both of these patterns were exhibited by 75Se. The concentration of 137Cs was not significantly affected by the thermal gradient. Radionuclide solubility and sorption were affected by variations in pH, Eh and ionic strength. Incorporation of the radionuclide into mineral lattices was found to play a key role in retarding the transport of all radionuclides tested.

scholarly journals Air and Water-Vapour Convection in Snow

1985 ◽  
Vol 6 ◽  
pp. 39-42 ◽  
Author(s):  
N. Klever
Keyword(s):  
Rayleigh Number ◽  
Mass Transport ◽  
Water Vapour ◽  
Thermal Convection ◽  
Critical Rayleigh Number ◽  
Conductive Heat ◽  
Heat And Mass Transport ◽  
Vapour Mixture ◽  
Small Change ◽  
Rayleigh Numbers

Heat and mass transport by an air and water-vapour mixture (pore air) in snow due to thermal convection has been computed. It can be shown theoretically that thermal convection is always occuring in newly fallen snow, but never occurs in snow with rounded grains. Rayleigh numbers of depth hoar and partly settled snow are close to the critical Rayleigh number, therefore a small change in one or more of the snow parameters will decide whether there is convective or conductive heat transport. The influence of thermal convection on the mass transport rates of water vapour in snow is computed based on the assumption of the ventilation approach. Although thermal convection occurs more often than previously assumed, its influence amounts only to about 2-3%.

scholarly journals Air and Water-Vapour Convection in Snow

1985 ◽  
Vol 6 ◽  
pp. 39-42
Author(s):  
N. Klever
Keyword(s):  
Rayleigh Number ◽  
Mass Transport ◽  
Water Vapour ◽  
Thermal Convection ◽  
Critical Rayleigh Number ◽  
Conductive Heat ◽  
Heat And Mass Transport ◽  
Vapour Mixture ◽  
Small Change ◽  
Rayleigh Numbers

Heat and mass transport by an air and water-vapour mixture (pore air) in snow due to thermal convection has been computed. It can be shown theoretically that thermal convection is always occuring in newly fallen snow, but never occurs in snow with rounded grains. Rayleigh numbers of depth hoar and partly settled snow are close to the critical Rayleigh number, therefore a small change in one or more of the snow parameters will decide whether there is convective or conductive heat transport.The influence of thermal convection on the mass transport rates of water vapour in snow is computed based on the assumption of the ventilation approach. Although thermal convection occurs more often than previously assumed, its influence amounts only to about 2-3%.

Mass Transport Modelling in Porous Media Using Delay Differential Equations

2006 ◽  
Vol 258-260 ◽  
pp. 586-591
Author(s):  
António Martins ◽  
Paulo Laranjeira ◽  
Madalena Dias ◽  
José Lopes
Keyword(s):  
Porous Media ◽  
Differential Equations ◽  
Mass Transport ◽  
Delay Differential Equations ◽  
Dispersion Model ◽  
Flow Characteristics ◽  
Convective Transport ◽  
Transport Modelling ◽  
Flow Field Characteristics ◽  
Delay Differential

In this work the application of delay differential equations to the modelling of mass transport in porous media, where the convective transport of mass, is presented and discussed. The differences and advantages when compared with the Dispersion Model are highlighted. Using simplified models of the local structure of a porous media, in particular a network model made up by combining two different types of network elements, channels and chambers, the mass transport under transient conditions is described and related to the local geometrical characteristics. The delay differential equations system that describe the flow, arise from the combination of the mass balance equations for both the network elements, and after taking into account their flow characteristics. The solution is obtained using a time marching method, and the results show that the model is capable of describing the qualitative behaviour observed experimentally, allowing the analysis of the influence of the local geometrical and flow field characteristics on the mass transport.

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