Fluid flow control in curved capillary channels

Abstract

A capillary pathway is dimensioned so that the driving force for the movement of liquid through the capillary pathway arises from capillary pressure. A plurality of groups of microstructures are fixed in the capillary pathway within discrete segments of the pathway for facilitating the transport of a liquid around curved portions of pathway. Capillary channels can be coupled between two adjacent groups of microstructures to either the inner and outer wall of the capillary pathway. The width of each capillary channel is generally smaller than the capillary pathway to which it is connected, and can be varied to achieve differences in fill initiation. The grouped microstructures are spaced from each other within each group on a nearest neighbor basis by less than that necessary to achieve capillary flow of liquid with each group. Each group of microstructures are spaced from any adjacent group by an inter-group space greater than the width of any adjacent capillary channels connected to the capillary pathway. Generally, the microstructures are centered on centers which are equally spaced from each other, and microstructures that are located closer to the inner wall of any curve in the capillary pathway are generally smaller than the microstructures located closer to the outer wall. This combination of structural features causes fluids to flow through the capillary pathway so that the rate of flow is somewhat non-uniform as the fluid travels around curved portions of the capillary pathway, the meniscus appearing to pause momentarily at each inter-group space, the flow being somewhat slower near the inner wall of a curved portion than near the outer wall.