FLOW RESTRICTOR AND SYSTEM FOR DELIVERING A FLOW OF LIQUID IN A MICROCAPILLARY

摘要

The present invention relates to apparatus for delivering a controlled or restricted flow of liquid and limiting bubble fragmentation at the inlet. This is achieved in flow restrictor with a flow channel having over most of its length a substantially constant, minimum hydraulic diameter D = 4A/W wherein A is the minimum local cross-sectional area of the channel and W is the minimum local wetting perimeter of the channel, by smoothly widening the channel at its inlet such that: at distances z from the inlet face with 0 < Z < Z1 the channel has a hydraulic diameter Dz >= k<*>D wherein k >= 1.3; at distances z from the inlet face with z1 < Z < Z2, the channel has a hydraulic diameter Dz with k<*>D >= Dz >= D; and at distances from the inlet face with z2 < z, the channel has a hydraulic diameter Dz with Dz <= 1.02D, except possibly for a similar widening of the channel at the outlet. It has been found that widening the flow channel at the inlet, such that its diameter increases smoothly and gradually, and preferably by a factor of at least 1.3 over a length of at least 3 channel diameters, significantly reduces the tendency towards bubble fragmentation in microcapillary flow restrictors, and also substantially increases the yield of devices which operate well.