Two-substance nozzles – also known as pneumatic atomisers – rely on a second medium (compressed air, gas or steam) to supply the energy required for atomisation.  The flow speed of the second medium breaks the liquid down into fine droplets. Consequently, the liquid that is being atomised only has to travel at a relatively low flow speed itself. This results in very fine atomisation even in the case of highly viscous liquids or suspensions.

Depending on its viscosity, density and surface tension, the liquid that is being atomised can be supplied using suction, a downward slope or pressure. Within certain limits, some two-substance nozzles can also act as injectors. Depending on their design, two-substance nozzles can be categorised as internal-mix or external-mix nozzles. This relates to whether the atomisation medium and the liquid are mixed inside or outside the nozzle.

External-mixing

The inbound liquid jet flows out through the central hole of the nozzle. Depending on the medium and the desired atomisation effect, pre-atomisation may be recommendable. It is generated through the use of a suitable swirl chamber. The liquid jet is subjected to shearing strain and broken up into fine drops by the compressed air exiting the annular gap.

The result: an outstandingly fine spraying pattern right up to atomisation.

Internal-mixing

The liquid flows through the central hole of the nozzle into an optimised mixing chamber. When it reaches the specially devised cone, it is distributed and broken down into single droplets by the swirled atomised air. The two-phase mix then leaves the air cap through the customer-specified bore holes.

The result: a very fine atomisation and a significantly greater area coverage than comparable external-mix models.

Two-substance nozzles with flat jet –
for intensive and even spray applications

External-mix two-substance nozzles with elliptical flat jet are often used for applications that require homogeneous fine droplets and wide coverage. This includes tablet coating in the pharmaceutical industry as well web or goods moistening in the textile, paper or wood industries. Depending on the model, the spray angle required for the application may be individually configured or preset.