Simulated liquid velocity and free surface height during the wicking of a parallelepiped of liquid over a single fin shaped channel, using the VOF. The top of each sub-figure documents the velocity, and just below we see liquid height distribution at z = 0.05 mm above channel bottom. Contact angle is 50°. The simulation domain consists of 6 elementary cells. The initial liquid parallelepiped is one elementary cell long. Dashed lines mark its limits. Just after t = 0 the liquid parallelepiped deforms quickly to smoother shape and wicks on channel bottom in the two directions x and − x. At t = 0.34 ms it has invaded the straight channel at the right, and is still progressing in the wider part at the left. However, at t = 0.64 ms the left front has compensated its delay. At t = 1.56 ms the left front has clearly covered more distance than the right front. At t = 1.94 ms the right front spreads a little further than before immediately receding because of surface tension that tends to decrease the free surface. Hereafter the right front remains pinned. On the other side, differently, we see that the flow suddenly accelerates in the fins since the time the left front touches at t = 1.56 ms. Between time instants t = 1.56 ms and t = 1.94 ms, the acceleration is caused by the tapered geometry of the fin that increases the wet solid surface over liquid volume ratio. At t = 1.94 ms, the liquid completely wets the fin surface but the kinetic energy is only partly dissipated. This results into reverse flow in the fins, converging to the middle of the channel. The volume increase in the center of the channel increases the free surface area: this transforms a fraction of the kinetic energy into surface energy. Relaxation then causes water to spread again, and to flood the next straight channel which acts as capillary.