Hydraulic nozzles operate on the principle of driving a liquid under pressure through an orifice considerably smaller than the diameter of the feed line. The change from large to small diameter results in a large increase in the liquid’s velocity, which in turn causes the stream of liquid exiting the nozzle to become unstable and to break up into small drops. Nozzles operating on this principle are the most commonly used type because of their inherent simplicity.
A full-cone spray is one in which the drops are distributed uniformly throughout a conically-shaped volume with its origin atthe orifice exit. Depending on the shape of the exit orifice, the cross-sectional shape of the spray envelope can be circular,square, rectangular, or oval.
Such a spray pattern is commonly used since it provides an even distribution of liquid on a surface. Another reason for usinga full-cone spray is to distribute drops uniformly within a given volume, for example, distributing water drops inside a coolingtower.
The range of processes utilizing full-cone nozzles is large. As a result, many different types of designs have been developed toaccommodate the requirements of specific applications.
Standard Full Cone: These nozzles use a specially shaped vane placed at the nozzle inlet to impart a rotational component to the fluid flowing through it. This causes the liquid exiting the nozzle orifice to open up into a full-cone shape. The cone angle is a function of both exit speed (therefore, inlet pressure) and the internal design of the nozzle. Cone angles can vary from 0° to 130°.
Spiral full cone (impact nozzle): This type of device does not technically produce a full-cone, but rather it generates a continuous liquid curtain that develops in the shape of a spiral inside a conical volume. The distribution of liquid within the cone is not as uniform as that from conventional fullcone nozzles. However, this is offset by exceptionally good resistance to clogging, making it a good choice in those applications where clogging can not be tolerated.
Multiple full cone This configuration is employed in applications where very small drops are required to be distributed over a wide area and where relatively high flow rates are needed. Small drops are usually associated with air-assisted nozzles. However, that type of nozzle is limited both in its capability to produce a wide-angle spray and to operate at high flow rates.
In this design, several nozzles are clustered together, each pointed in a different direction.
The resulting spray pattern comes from the addition of the patterns from each of the nozzles in the cluster.
FLAT SPRAY NOZZLES
A flat spray is one in which the liquid drops are formed into a long, narrow pattern. The thickness of the narrow dimension of the spray varies according to the design of the device and the flow rate.
The principal use of flat spray nozzles is to produce a well-defined spray pattern on a surface as the surface (or the nozzle) moves transversely with respect to the wide dimension of the spray. A typical example would be nozzles used in a car washing tunnel. The majority of flat-spray nozzles used in industry operate according to one of the following principles:
In-line flat spray (Pressure nozzle) This is the general purpose flat spray nozzle. Liquid enters the
nozzle in-line with its length axis and is fed into a pressure chamber, from where it is ejected through the nozzle orifice. Flow rate and spray angle are determined by the cross- section
and profile of the orifice.
In-line straight spray (Pressure nozzle) This can be considered a special type of flat spray nozzle, with 0o spray angle. It produces a sharp, stable stream with powerful, uniform impact.
Typical examples of their use is in washing or gas cooling applications.
Spoon flat spray (Impact nozzle) For this type of nozzle, the liquid is fed under pressure into a
round outlet orifice and then forced to impact onto a smooth surface causing it to assume a flat spray shape.
This design has the advantage of producing a stronger impact
than in-line flat spray nozzles at the same feed pressures. The higher impact velocity results from the increased efficiency of the design.
A hollow-cone spray pattern consists of drops concentrated on the outer surface of a conically shaped volume, with very little spray within the interior of the spray envelope. Typical examples of their use are in washing or gas cooling applications.
Hollow cone (Turbulence nozzle) These nozzles use a tangential injection of liquid into a whirling chamber to generate centrifugal forces that break up the liquid stream as soon as it leaves the orifice.
Precisely designed orifice profiles, which use the Coanda effect (a phenomenon in which liquid, moving at high velocity, tends to hug the walls of a chamber), allows very large spray angles to be developed.
Hollow cone (Impact nozzle) This type of hollow-cone nozzle relies on having the liquid
stream impact onto a specially designed surface in order to break the liquid into drops and distribute them into a hollow-cone spray pattern.