Comment on "An analytic solution of capillary rise restrained by gravity" by N. Fries and M. Dreyer.

The porous medium model of Green and Ampt, describing flow in porous media, appeared earlier than the capillary model of Washburn, although both lead to mathematically identical models. Here, the model of Green and Ampt was related to the Washburn model by an examination of the parameters involved in each. Fries et al. [N. Fries, M. Dreyer, J. Colloid Interface Sci. 320 (2008) 259-263] presented an explicit solution to this model. This solution is identical to the explicit solution of the Green and Ampt model presented earlier by Barry et al. [D.A. Barry, J.-Y. Parlange, G.C. Sander, M. Sivaplan, J. Hydrol. 142 (1993) 29-46].

Comment on "The effect of evaporation on the wicking of liquids into a metallic weave" by N. Fries, K. Odic, M. Conrath and M. Dreyer.

A recent paper reported capillary rise and evaporation experiments in metallic wicks, as well as a mathematical model. The authors found a consistent discrepancy between the model predictions and data: The model over-predicted the capillary height rise by about 20%. The model used assumes that the porous medium is either fully wet or dry, an assumption that is particularly unsuited to evaporation from the wick surface. An alternative variable-saturation model is proposed that provides a possible explanation for the 20% discrepancy reported by the authors.