Capillary flows are commonly encountered in microfluidic devices. For example, in bio chip designs lengthy micro channels are often used to deliver liquid solution from one place to another. An inlet channel is connected to a liquid reservoir and surface tension forces pull the liquid into the micro channel (provided the liquid is “wetting” to the chip surface). This page covers some specific applications for FLOW-3D in the analysis of such capillary flows: filling, absorption and switching.
Marangoni flow in a dish of water that is heated at its center. Flow generated by non-uniform surface tension is demonstrated by a shallow 8.0 cm diameter dish of water of depth 0.75 cm at an initial temperature of 20º C. Placed at the center of the circular dish is a cylindrical rod of diameter 0.5 cm, which is heated to a temperature of 80 Cº and is submerged into the water surface to a depth of 0.05 cm. As the water near the hot rod is heated its surface tension is reduced by an amount of 0.1678 dyne/cm/ºC causing the surface to retract toward the outer rim of the dish. The retraction is shown by massless marker particles initially sprinkled over the surface.