Flow-concentrating supersonic gas/liquid nozzles have been invented for use in cleaning and in verifying the cleanliness of tanks, pipes, tubes, machine parts, and structures. The overall function of these nozzles is to generate concentrated two-phase flows, the mechanical action of which is highly effective in cleaning surfaces.

The Two-Phase Fluid flowing in from the supply tube becomes compressed between the flow-directing insert and the inner surface of the tubular section. After reaching maximum compression at the outermost diameter of the insert, the fluid expands to supersonic speed and converges upon itself, forming an intense jet that is highly effective for cleaning.

Previously, cleaning pro-cesses of the type to which these nozzles apply have involved flushing with solvents, spraying liquids at high pressure through nozzles, and the use of supersonic DeLaval nozzles. Solvent flushes use large volumes of chemicals to dissolve contaminants. High-pressure liquid sprays consume smaller quantities of solvents than solvent flushes, but the volumes are still substantial. Cleaning processes that involve supersonic DeLaval nozzles are the best of this type for minimum solvent usage, but the basic design and principle of operation of DeLaval nozzles leave room for improvement.

A nozzle of the present type includes a supply tube, a straight, precisely bored tubular section, and a flow-directing insert. The insert is placed inside the tubular section. The supply tube (omitted from the figure) is welded to the upstream end of the tubular section.

The gas/liquid mixture to be used for cleaning is pumped through the supply tube and into the tubular section; it is initially directed radially outward by the insert. The flow is thus compressed by the insert until it reaches the largest diameter of the insert, where it reaches the speed of sound. As the flow continues, it is allowed to expand and accelerate to supersonic speed. The flow leaves the nozzle with a radially inward component of velocity; in other words, the flow converges upon itself and thus becomes more concentrated. This concentration greatly increases the ability of the flow to remove contaminants.

A nozzle of this type operates with a much smaller volumetric rate of flow of solvent than does a comparable nozzle used in a high-pressure liquid spray. Unlike a solvent flush, it is not necessary to use a powerful solvent when cleaning with a nozzle of this type: instead, the cleaning process relies on the mechanical action of the jet generated by the nozzle.

In comparison with a DeLaval nozzle, a nozzle of this type is much more effective in removing contaminants. The flow from a nozzle of any of the types used previously (including high-pressure-liquid nozzles and DeLaval supersonic nozzles) spreads out and is weakened after it leaves the nozzle. In contrast, the flow from a nozzle of the present type reaches its greatest concentration a short distance downstream of the nozzle outlet, so that the intensity of the jet is greater than that from a DeLaval nozzle fed at the same pressure and flow rate. Yet another advantage of this design is that it eliminates the very difficult internal machining needed to fabricate a DeLaval nozzle.

This work was done by Raoul E. Caimi and Eric A. Thaxton of Kennedy Space Center. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp  under the Mechanics category. KSC-11883

NASA Tech Briefs Magazine

This article first appeared in the January, 2001 issue of NASA Tech Briefs Magazine.

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