How much temperature will increase the efficiency of electro-osmosis?

Abstract

Electro-osmosis is popularly used as a pump to dry soils or to reduce rising damp in buildings, but the literature results are contradictory. The basic formula of electro-osmosis has been analysed to point out its dependence on temperature, which is masked behind two coefficients, i.e. the dielectric ‘constant’ of water (that is not constant), and the coefficient of dynamic viscosity. These two physical quantities have been calculated with the accurate formulae by Malmberg and Maryott (the dielectric constant) and Voegel (the dynamic viscosity). The electro-osmosis formula includes the ratio between these two coefficients. Although the two formulae that represent them are formulated with equations having a formally different mathematical apparatus, their ratio strictly follows a straight line with values increasing with temperature. Dividing this equation by its initial value (i.e. considered at 0.1 °C) one obtains the Temperature Magnification Factor (TMF) that indicates how much the effectiveness of the system may vary with temperature. TMF is linearly increasing and has been calculated for the whole range of liquid water, i.e. from 0.1 to 99.9 °C. In the interval of the most common wall temperatures, from 0 to 50 °C, TMF increases from 1 to 2.5, showing that in summer, or in warm climate, the efficiency of this method is much higher (e.g. 2.5 times) than in winter or in cold regions. A comparison of the effectiveness of electro-osmotic interventions against rising damp can only be made for buildings under the same climate conditions. This explains the contradictory results found in the literature when case studies from different geographic areas, and different climates, are compared.