Figure 3-53

Liquid in rectangular channel with square-grooved bottom.

The contact angle on all surfaces is 60 degrees, so Concus-Finn filaments do not form. The grooves in the bottom have high enough walls that the liquid advances in them. Note the outer grooves use the higher outside walls and thus have a greater capillary force and greater velocity. The bulk liquid above the grooves feels an effective bottom of ridge tops and perfectly wetting liquid tops, and so advances. For the particular dimensions of this model, If the channel had a flat bottom at the top of the grooves, the liquid would not advance. If the channel had a flat bottom at the base of the grooves, the liquid would advance, but slower.