ISSN:
1089-7666
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Salt crystallization at surfaces is an important problem for buildings and monuments. We do not consider the formation of salt crystals as such, but focus on transport properties of ions in a drying porous medium. We deal with the first phase of the drying process, where the water is still uniformly distributed throughout the medium. An approximate model is presented, which accounts for both convection and diffusion. It is shown that the key parameter is the Peclet number at the evaporating surface, Pe≡hL/cursive-epsilonD, where h, L, cursive-epsilon, and D are the drying rate, sample size, porosity, and diffusion constant, respectively. When Pe(very-much-less-than)1 (diffusion dominates over convection) the ions remain uniformly distributed throughout the system. Strong accumulation at the evaporating surface occurs for Pe(very-much-greater-than)1 (convection dominates over diffusion). Crossover behavior is found for Pe(approximate)1. Therefore, it is likely that the first crystals will be formed both in the bulk and at the interfaces of the material when Pe(very-much-less-than)1. For high values of Pe the density peak at the evaporating surface will reach the saturation concentration long before it is reached in the bulk of the material. As a consequence, the salt starts to crystallize at the interfaces. © 2002 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1451081
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