Evaporation during Liquid Imbibition into Micro-Channels

Imbibition of liquids into porous materials is of relevance for many fields and applications such as filtration, geology, heat pipe design, etc. The one-dimensional absorption process is well described for isothermal conditions using the Lucas-Washburn model, considering surface tension, permeability, and gravity. The present study expands on this existing work by studying the effect of evaporation on imbibition of liquids into capillaries with smaller dimensions. A gradual change in behavior during imbibition depending on temperature is observed and presented. Starting at low channel temperature with isothermal imbibition which is well-described using the Lucas-Washburn model, the effect of evaporation increases with increasing temperature until the liquid no longer contacts the capillary due to the Leidenforst effect. Using a temperature controlled capillary channel the relevance of evaporation and its effect on the imbibition velocity is examined for varying channel dimensions. In particular, the current knowledge will be extended to capillary channels with very small dimensions down to a depth of the order of 10 μm, which are more comparable to the pore and channel sizes found in relevant porous materials.