TYPES OF NOZZLES - SKengineers

 

TYPES OF INDUSTRIAL NOZZLES -

A nozzle is a device designed to control the direction or characteristics of a fluid flow (especially to increase velocity) as it exits (or enters) an enclosed chamber or pipe.

A nozzle is often a pipe or tube of varying cross sectional area, and it can be used to direct or modify the flow of a fluid (liquid or gas). Nozzles are frequently used to control the rate of flow, speed, direction, mass, shape, and/or the pressure of the stream that emerges from them. In a nozzle, the velocity of fluid increases at the expense of its pressure energy.

Nozzle -

The nozzle performs four basic functions

Atomizes liquid into droplets.

Disperses the droplets in a specific pattern.

Meters liquid at a certain flow rate.

Provides hydraulic momentum.

The Nozzle Tip is one of the most important and least expensive part of a spraying system.

Types

Jet -

A gas jet, fluid jet, or hydro jet is a nozzle intended to eject gas or fluid in a coherent stream into a surrounding medium. Gas jets are commonly found in gas stoves, ovens, or barbecues. Gas jets were commonly used for light before the development of electric light. Other types of fluid jets are found in carburettors, where smooth calibrated orifices are used to regulate the flow of fuel into an engine, and in jacuzzis or spas.

Another specialized jet is the laminar jet. This is a water jet that contains devices to smooth out the pressure and flow, and gives laminar flow, as its name suggests. This gives better results for fountains.

The foam jet is another type of jet which uses foam instead of a gas or fluid.

Nozzles used for feeding hot blast into a blast furnace or forge are called tuyeres.

Jet nozzles are also used in large rooms where the distribution of air via ceiling diffusers is not possible or not practical. Diffusers that uses jet nozzles are called jet diffuser where it will be arranged in the side wall areas in order to distribute air. When the temperature difference between the supply air and the room air changes, the supply air stream is deflected upwards, to supply warm air, or downwards, to supply cold air.

High velocity -

A nozzle from the Ariane-5 rocket

Frequently, the goal of a nozzle is to increase the kinetic energy of the flowing medium at the expense of its pressure and internal energy.

Nozzles can be described as convergent (narrowing down from a wide diameter to a smaller diameter in the direction of the flow) or divergent (expanding from a smaller diameter to a larger one). A de Laval nozzle has a convergent section followed by a divergent section and is often called a convergent-divergent (CD) Nozzle ("con-di nozzle").

Convergent nozzles accelerate subsonic fluids. If the nozzle pressure ratio is high enough, then the flow will reach sonic velocity at the narrowest point (i.e. the nozzle throat). In this situation, the nozzle is said to be choked.

Increasing the nozzle pressure ratio further will not increase the throat Mach number above one. Downstream (i.e. external to the nozzle) the flow is free to expand to supersonic velocities; however, Mach 1 can be a very high speed for a hot gas because the speed of sound varies as the square root of absolute temperature. This fact is used extensively in rocketry where hypersonic flows are required and where propellant mixtures are deliberately chosen to further increase the sonic speed.

Divergent nozzles slow fluids if the flow is subsonic, but they accelerate sonic or supersonic fluids.

Convergent-divergent nozzles can therefore accelerate fluids that have choked in the convergent section to supersonic speeds. This CD process is more efficient than allowing a convergent nozzle to expand supersonically externally. The shape of the divergent section also ensures that the direction of the escaping gases is directly backwards, as any sideways component would not contribute to thrust.

Propelling -

A jet exhaust produces a net thrust from the energy obtained from combusting fuel which is added to the inducted air. This hot air passes through a high speed nozzle, a propelling nozzle, which enormously increases its kinetic energy.

Increasing exhaust velocity increases thrust for a given mass flow, but matching the exhaust velocity to the air speed provides the best energy efficiency. However, momentum considerations prevent jet aircraft from maintaining velocity while exceeding their exhaust jet speed. The engines of supersonic jet aircraft, such as those of fighters and SST aircraft (e.g. Concorde) almost always achieve the high exhaust speeds necessary for supersonic flight by using a CD nozzle despite weight and cost penalties; conversely, subsonic jet engines employ relatively low, subsonic, exhaust velocities and therefore employ simple convergent nozzle, or even bypass nozzles at even lower speeds.

Rocket motors maximise thrust and exhaust velocity by using convergent-divergent nozzles with very large area ratios and therefore extremely high pressure ratios. Mass flow is at a premium because all the propulsive mass is carried with vehicle, and very high exhaust speeds are desirable.

Magnetic -

Magnetic nozzles have also been proposed for some types of propulsion, such as VASIMR, in which the flow of plasma is directed by magnetic fields instead of walls made of solid matter.

Spray -

Many nozzles produce a very fine spray of liquids.

Atomizer nozzles are used for spray painting, perfumes, carburettors for internal combustion engines, spray on deodorants, antiperspirants and many other similar uses.

Air-Aspirating Nozzle uses an opening in the cone shaped nozzle to inject air into a stream of water based foam (CAFS/AFFF/FFFP) to make the concentrate "foam up". Most commonly found on foam extinguishers and foam handlines.

Swirl nozzles inject the liquid in tangentially, and it spirals into the centre and then exits through the central hole. Due to the vortexing this causes the spray to come out in a cone shape.

Vacuum -

Vacuum cleaner nozzles come in several different shapes. Vacuum Nozzles are used in vacuum cleaners.

Shaping -

Some nozzles are shaped to produce a stream that is of a particular shape. For example, extrusion moulding is a way of producing lengths of metals or plastics or other materials with a particular cross-section. This nozzle is typically referred to as a die.

Adjustable nozzle -

Most suitable for spraying targets which are not within the reach of a man.

Gives a wide angle hollow cone to a straight solid stream that is, it gives a jet to a cone type of spray pattern.

Difficult to calibrate as the flow and droplet sizes vary widely with the nozzle angle.

Double swirl spray nozzle

Used for spraying in two different directions simultaneously.

Nozzles can be fitted with different types of tips like hollow cone, solid cone or flat fan.

Suitable for high volume applications

The shape and size of Nozzle Tip orifice controls the spray angel, discharge rate and spray pattern. Spray angle influences the swath of a spray.

And also:-Droplet size increases as orifice size increases (for any given pressure). Droplet size decreases with an increase in fan angle (for any given nozzle size and pressure). When it is desired to spray with more than one nozzle with the help of a spray rig or a spray boom, care should be taken in mounting to avoid overlapping or gapping. Overlap causes double dose Higher dose is harmful to crop Gap leaves untreated area Poor biological efficacy.

Selecting a spray nozzle -

The proper selection and use of spray nozzle is the most important part of pesticide application.

The nozzle determines the amount of spray that is generated over a given area, the uniformity of the spray produced, the coverage obtained and the amount of drift that occurs.

The nozzle selected must optimize coverage application rate and pressure and minimize loss through drift. For each kind of application, dependent up-to the physical conditions prevailing, a different nozzle design is available.

Nozzle tips are usually available in brass, stainless steel, and engineering plastic. Steel tips are most resistant to corrosion and abrasion.

Brass tips are very commonly used, but ear out more easily and can be corroded by some chemicals. Engineering plastic is likely to become the most serviceable material for spray nozzles, being highly resistant to wear-and-tear and corrosion.

Hollow cone nozzles-Disc and core type -

These are used primarily where plant foliage penetration is essential for effective insect and disease control, and where drift is not a major consideration.

At pressures of 40 – 8- psi hollow cone nozzles give excellent spray coverage to the undersides of reduces penetration correspondingly.

Flat fan nozzles -

These are used largely for broadcast spraying, where foliar penetration and coverage are not essential.

The best operating pressure for flat fan nozzles is 15 – 30 psi, which produce coarser droplets that are not susceptible to drift.

Flood-jet nozzles –

These are ideal for high application rates and speeds, because they produce a wide-angle, flat fan pattern.

Operating flood-jet nozzles at 5-25 psi minimizes drift, but pressure changes critically affect the width of the spray pattern.

Generally, the spray generated by the flood-jet is not as uniform as the flat-fan type.

Adjustable nozzles -        

This model is capable of producing a cone spray in various angles, and also a solid or broken jet spray.

Single swivel nozzles -

Here the joint of the nozzle and extension rod is capable of swivelling without leakage, it can be locked for use at any angle between 0 – 180 degrees.

Double swivel nozzles -

This has two swivel nozzles instead of one, capable of independent movement.

Double fixed nozzle -

Double fixed nozzles are fixed on the ‘U’ bend, which is, in turn, coupled with the end of a straight extension rod.

NOTE: Single swivel, double swivel and double fixed nozzles come in both cones-spray and flat fan varieties.

Spray boom -

This design consists of several nozzles mounted on a rod, ideally suited to row crops, and can be operated with foot / rocker / knapsack / power operated sprayers.

Spray guns -

Spray guns consist of cut-of-value extension rod and nozzle and can be trigger or hand-operated.

The spray pattern is adjustable from solid jet to hollow cone, and are most widely used for tall trees.

Cut-off Valves   -     

These can be spring-activated (trigger control) or operated by means of a simple knob or trap.

A strainer can be built into the control valve handle, and in the trigger type a pressure regulating device can also be incorporated.

Every sprayer should have -

A discharge Line consisting of a delivery hose with couplings and a spray lance.

Every Spray Lance must have -

A cut-off valve

An extension rod-straight or goose-neck

An appropriate nozzle

Extension Rod -

Comes in varying lengths, according to customer requirements but lengths longer than 90 cms are difficult to handle.

For tree spraying, bamboo lances i.e. brass tubes inserted into a hollow bamboo are recommended.

The larger diameter of the bamboo helps to off-set the length of the lance (up to 2.5 meters, making it easier to handle).

General purpose nozzles

A spray nozzle is a device which makes use of the pressure energy of a liquid to increase its speed through an orifice and break it into drops.

Its performances can be identified and described precisely, so that the design engineer can specify exactly the spray nozzle required for a given process.

The relevant characteristics which identify the performances of a nozzle are the following:

The liquid flow delivered as a function of the nozzle feed pressure.

The opening angle of the produced spray.

The nozzle efficiency, as the ratio between the energy of the spray and the energy used by the nozzle.

The evenness of the flow distribution over the target.

The droplet size distribution of the spray.

Nozzle size -

Finding and selecting the right nozzle is one of the most important activities of a successful spray. It’s the combination of nozzle size along with nozzle pattern and shape that make for the most accurate sprays.

If you need to find the right nozzle size for your application, sometimes a simple chart is the easiest way to figure this out.

Nozzle size charts -

U.S. 15” spacings

U.S. 20” spacing

U.S. 30” spacing

Metric, 50 cm spacing

Selecting Your Nozzle Size

If you’re not using a chart, you’ll need to determine a few factors to determine the right size. You’ll want to determine the nozzle flow rate at gallons per minute (gpm). To find that, start with your application rate in gallons per acre (gpa).

Next, find an efficient and safe ground speed in miles per hour (mph). Then, determine the spray width per nozzle (W).

Different types of spray methods will require different spray width (W): 

Band spraying: W = band width in inches

Broadcast applications: W = nozzle spacing (distance between two nozzles on the boom) in inches

Directed spraying: W = row spacing in inches (or band width) divided by the number of nozzles per row (or band)

Now, you’ll be able to determine the flow rate (gpm), with the following equation³:

gallons per minute nozzle rate -

Finally, you’ll be able to select a nozzle size that will give the flow rate (gpm) determined above. If a specific nozzle size is not available, try changing the travel speed and determine the new flow rate needed.