Agitating – Stationary deflector in flow-through mixing chamber
Reexamination Certificate
1998-11-10
2001-02-20
Soohoo, Tony G. (Department: 1723)
Agitating
Stationary deflector in flow-through mixing chamber
C366S340000, C366S341000, C138S042000, C137S896000, C137S599120
Reexamination Certificate
active
06190034
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a micro-mixer having at least one mixing point which is connected to an inlet channel arrangement having at least two inlet channels and to an outlet channel arrangement. The invention relates furthermore to a mixing method for at least two fluids which are supplied from different directions.
Mixing of fluids is frequently required in order to initiate a chemical reaction. Such chemical reactions are necessary, for example, in an analysis in which the presence and/or concentration of a species in a fluid is to be determined. For that purpose the fluid has added to it a reagent (or several reagents), which form with the species a reaction product which can be detected in a detector. A controlled and homogeneous mixing of the fluid and the reagent, that is, between two or more fluids, is desirable here. The volume required for the mixing should be kept as small as possible, however, in order that the consumption of reagents does not become too great.
A static micro-mixer of the kind mentioned in the introduction has been proposed by the Technischer Universität Ilmenau, Faculty of Engineering, micro-systems engineering department in D-98684 Ilmenau. The base body of this micro-mixer consists of silicon. Micro-channels and openings are made in this base body. These channels are hermetically sealed by silicon or glass substrates. Mixing of two liquids is effected in that these two liquids are layered horizontally side by side in a mixing element and then separated vertically. The mixing element is in this case formed by a recess into which the two inlet channels open from opposite sides. Two part-flows are then extracted from this recess and are later mixed in the same manner in a following mixing element.
With this construction it is relatively difficult to predict the mixing behaviour of the liquids with sufficient accuracy. Predictions about the course of the reaction between the two fluids are therefore possible only to a limited extent. In a subsequent analysis of a reaction product there is therefore always the uncertainty as to whether the reaction, after complete mixing of the two fluids, has already finished or, if that is not the case, whether the individual reaction times are reproducible. This disadvantage can, of course, be mitigated by waiting for a certain time after bringing the two fluids together, but this waiting time slows down the analysis.
SUMMARY OF THE INVENTION
The invention is based on the problem of allowing a rapid and predeterminable mixing of fluids.
In a micro-mixer of the kind mentioned in the introduction, this problem is solved in that the inlet channels in the mixing point run parallel to one another in the same direction and that a separating element is provided which extends into a region of the mixing point in which the inlet channels run parallel to one another.
Using such a micro-mixer, the two fluid flows are, as it were, laminated onto one another. They meet in the mixing point having the same direction and the same speed. As soon as the separating element ends, each fluid flow lies smoothly on the other and a boundary surface is created, through which mixing by diffusion can take place. The diffusion behaviour of the two fluids is known or is determinable. By virtue of the construction of the micro-mixer, however, the diffusion area, which is an essential factor in the progression of the diffusion, is also known. The diffusion area corresponds to the area of the outlet channel in which also the separating element lies. A mixing of the two fluids which is effected by a mutual equalization of concentration can be observed.
It is also preferred for the inlet channels to be guided parallel to one another in offset planes at least in a section upstream of the mixing point. The inlet channels are here guided one above the other. In this manner arrangement of the two fluids in layers can be further influenced, for example, so that the individual layers are as wide and as thin as possible.
The inlet channels preferably have a width that is greater than their height. The width can be arranged substantially parallel to the planes. In this manner a really large diffusion area is produced when the two fluids are brought together. The larger is the diffusion area, the more quickly can mixing proceed. The diffusion surface is flat. The layer thickness or the height of the two fluids is constant over the width, so that the mixing behaviour can be predetermined relatively easily. With otherwise unchanged conditions, as the width increases the height decreases, so that the diffusion length shortens.
It is also preferred for the inlet channels to widen upstream of the mixing point. In this manner an even larger diffusion area and a smaller layer thickness can be created. Since at any rate a change in direction at least for a part of the fluid flow is associated with widening, after widening and before bringing the fluids together the same direction and optionally speed must first be restored.
In that case it is especially preferred for widening to effect a doubling of the width. At the same time the height of the inlet channels is halved, so that the cross-sectional area remains constant. There is no accompanying change in the speed of the flow.
The outlet channel arrangement is advantageously directed in the same direction as the inlet channels. The fluids therefore flow through the micro-mixer substantially in one main direction. Undue deviations can be avoided, because in that case there will always be the risk that it will not be possible to predict the diffusion area with sufficient accuracy. Relatively small changes in direction can be allowed, however.
In an especially preferred construction, provision is made for at least one outlet channel of the outlet channel arrangement to be divided into at least two sub-channels which form an inlet channel arrangement of a following mixing point. In this manner at each subsequent mixing point the number of layers doubles (in the case of two inlet channels of the mixing point) or even trebles (in the case of three inlet channels of a mixing point). The number of diffusion areas increases accordingly. The individual fluids are applied to one another in increasingly thinner layers. Apart from the enlargement of the diffusion areas, this has the added advantage that mutual penetration of the fluids can be effected considerably more quickly because the thickness that has to be penetrated by respective fluids is much smaller.
The sub-channels preferably lie in the same plane, which is defined by the width dimension. The division is therefore effected parallel to the narrow sides or to the height of the channels, whilst the application of the fluids to each other takes place parallel to the wide sides of the channel or at right angles to the lamination face of the preceding mixing point. This ensures that the greatest possible diffusion area is utilized.
The outlet channel arrangement preferably comprises a single outlet channel. Formation of the diffusion area between the individual fluids can be ensured in the best possible manner in this instance.
The separating element is preferably in the form of a flat plate. As each fluid lies on the other, no noticeable steps occur which could lead to disturbance during lamination of the two fluids onto one another.
It is in that case preferred for the separating element to have openings which are substantially smaller than the area of the separating element exposed to the inlet channels. Despite the openings, flow of the fluid is enforced and maintained until the fluids have the same direction and optionally the same flow speed. Manufacture of the micro-mixer is substantially simplified with the openings. For example, it is possible to reach right through the separating element to form an inlet channel by removing material.
One liquid path preferably has a course in one plane from at least one inlet channel to the outlet channel arrangement. This simplifies manufacture. Such a channel can be easily made in a surface of a
Branebjerg Jens Anders
Dyhr-Mikkelsen Poul
Gade Niels
Gravesen Peter
Nielsen Claus Rye
Danfoss A/S
Lee,Mann,Smith,McWilliams, Sweeney & Ohlson
Soohoo Tony G.
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