Fluid handling – Flow affected by fluid contact – energy field or coanda effect
Patent
1996-10-16
1998-03-24
Chambers, A. Michael
Fluid handling
Flow affected by fluid contact, energy field or coanda effect
137833, 137896, 417151, F15C 100
Patent
active
057301875
DESCRIPTION:
BRIEF SUMMARY
The present invention pertains to a fluid microdiode permeable to fluids in only one direction for directionally incorporating submicroliter quantities of a fluid medium into another stationary or flowing target fluid contained in a closed system. Corresponding requirements exist in the dosing, mixing and injecting of fluids in the submicroliter range for applications especially in the fields of biomedical engineering and chemical microsensor technology.
The incorporation of a liquid into another liquid contained in a closed system is a wide-spread procedure in the fields of medical engineering and flow-injection analysis. As is generally known, such incorporation is Luque de Castro et al., Analyst 109 (1984) 413! or based on hydrodynamic currently commercially available devices using these techniques are exclusively based on expensive fine-mechanical manufacturing technologies. There are further known development projects dealing with piezo-electrically driven micromechanical valves based on Silicon et al., A Silicon Integrated Miniature Chemical Analysis System, Sensors and Actuators B6 (1992) 57-60!. The problems arising here are not yet fully understood, the development being still in its infancy. The following problems can be seen presently. Mechanical valves are not capable of completely shutting, which puts restrictions on the accuracy of dosing. A second problem is the large space requirements of such micromechanical members. A third problem is the complicated manufacturing technology since valve structures are complex.
It is the object of the invention, while avoiding the problems encountered with micromechanical valves, to provide a technical solution to the problem of incorporating a dosed fluid into a stationary or flowing target fluid with a high dosing accuracy in the submicroliter range, offering a maximum reliability in preventing the target fluid from flowing into the dosed fluid.
This object is achieved according to the invention by a fluid microdiode which is permeable to fluids in one direction only consisting of one or a system of several microcapillaries open on both sides which are in direct contact with the target fluid on the outlet side and whose inlet side facing towards the dosed fluid is separated from the dosed fluid by an air or gas cushion in such a way that the target fluid spreading upwards in the capillaries is prevented from getting further due to the surface tension and forms a meniscus. The dosed fluid is brought onto this meniscus discontinuously, preferably as a self-supporting fluid jet, and incorporated into the target fluid by diffusion and convection processes.
The fluid microdiode according to the invention is preferably intergrated into a microtechnical flow channel, reliably preventing an outflow of the liquid standing or flowing in the flow channel (target fluid) while ensuring the entry of a second liquid which is to be brought onto said fluid microdiode from the outside (dosed fluid). In the arrangement of a grid-like structure of microcapillaries adjacent to a flow channel, according to the invention, a coupling surface for the incorporation of microdroplets of a dosed fluid is formed by the large number of outwardly oriented open capillaries. The gas/liquid interface at the end of each microcapillary for maintaining the function of the fluid microdiode at any moment is a sine qua non for the functions of the building elements and thus is a part of the building element.
The microcapillaries have dimensions in the .mu.m three-dimensional range and, due to the high accuracy requirements on their geometries, are preferably manufactured by anisotropic etching of <100> or <110> silicon substrates. The length of each individual microcapillary is to be selected such that the target fluid will spread up to the capillary ends and there will form a defined liquid/gas interface in the form of a meniscus at the end of each microcapillary under the action of the surface tension and the fluidic gravitational pressures. The formation of the menisci terminates
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Howitz Steffen
Pham Minh Tan
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