Method and apparatus for controlling the mixing of two fluids

DETAILED DESCRIPTION According to a broad aspect of the present invention, there is provided a method of controlling the mixing of two fluids of the same state or of substantially the same state in a mixing region having a flow axis, in which method at least one of the fluids in directed to flow into direct contact with the other fluid at the beginning of the mixing region; characterized in that an active element is driven to induce, in the vicinity of the beginning of the mixing region, oscillations of the two fluids about an axis substantially normal to said mixing region flow axis so as to produce, at the boundaries of said mixing region, small flow fluctuations substantially perpendicular to the flow axis.
The active element may move up and down in translation, or may change its angle of attack (i.
e.
, the inclination angle between the fluid stream and the chord of the element).
In any case, the active element induces, at the boundaries of the mixing region small fluctuations in the flow which are generally normal to the flow axis, or direction of streaming, through the mixing region.
It is these normal (perpendicular) fluctuations, or small velocity perturbations, which contribute to the inherent instability of the flow and enhance (or otherwise control) the mixing.
In most of the preferred embodiments of the invention described below, the active element is driven by an external drive.
One form of active element which has been found particularly useful for inducing the oscillations is a pivotable flap which is driven by an external drive about a pivot axis substantially at the beginning of the mixing region, i.
e.
the point at which the two fluids first meet.
The drive for oscillating the active element, e.
g.
the pivotable flat, may be externally driven by mechanical, electrical or hydraulic devices.
It has been found, as will be shown below, that both the frequency and amplitude of oscillation influence the mixing of the two fluids in the mixing region.
The introduction of small velocity perturbations or oscillations in the flow substantially normal to the direction of streaming, may be implemented by other active elements, for example by a rotated flap, a reciprocating ribbon, or a rotating nozzle which injects small quantities of a fluid normal to the direction of streaming