Pattern

Selecting a nozzle based on the pattern and other spray characteristics that are required generally yields good results.^[5] Since spray nozzles are designed to perform under many different spraying conditions, more than one nozzle may meet the requirements for a given application. Surfaces may be sprayed with any pattern shape. Results are fairly predictable, depending on the type of spray pattern specified. If the surface is stationary, the preferred nozzle is usually some type of full cone nozzle, since its pattern will cover a larger area than the other styles. Spatial applications, in which the objective is not primarily to spray onto a surface, are more likely to require specialized spray characteristics. Success in these applications is often completely dependent on factors such as drop size and spray velocity. Evaporation, cooling rates for gases and solids, and cleaning efficiency are examples of process characteristics that may depend largely on spray qualities.

Flat fan, solid cone and hollow cone spray patterns

Each spray pattern is described below with typical end use applications.

Flat spray

As the name implies, the spray pattern appears as a flat sheet of liquid. The pattern is formed by an elliptical or a round orifice on a deflective surface that is tangent to the exit orifice. The orifice has an external groove with a contoured internal cylindrical radius, or “cat's eye” shape. In the elliptical orifice design, the pattern sprays out of the orifice in line with the pipe. In the deflector design, the spray pattern is perpendicular to the pipe. There are two categories of flat spray, tapered and even, depending on the uniformity of the spray over the spray pattern. Flat spray patterns with tapering edges are produced by straight-through elliptical spray nozzles. This spray pattern is useful for overlapping patterns between multiple nozzle headers. The result is uniform distribution across the entire sprayed surface. Non-tapered flat spray nozzles are used in cleaning applications that require a uniform spray pattern without any overlap in spray area.

Multiple plume spray

Capacity

Spray nozzle manufacturers all tabulate capacity based on water. Since the specific gravity of a liquid affects its flow rate, the values must be adjusted using the equation below, where Qw is the water capacity and Spg is the specific gravity of the fluid used resulting the volumetric flow rate of the fluid used Qf.

${\displaystyle Q_{f}={Q_{w}}/{\sqrt {S{p_{g}}}}\ }$

Nozzle capacity varies with spraying pressure. In general, the relationship between capacity and pressure is as follows:

${\displaystyle {Q_{2}}={Q_{1}}{\sqrt {P_{2}/P_{1}}}}$

where Q1 is the known capacity at pressure P1, and Q2 is the capacity to be determined at pressure P2.

Spray impact

Impact of a spray onto the target surface is expressed as the force/area, N/m² or lb/in². This value depends on the spray pattern distribution and the spray angle. Generally, solid stream nozzles or narrow spray angle flat fan nozzles are used for applications in which high impact is desired, such as cleaning. When a nozzle is used for cleaning, the impact or pressure is called impingement. As with all spray patterns, the unit impact decreases as the distance from the nozzle increases, thereby increasing the impact area size.

The spray impact, ${\displaystyle F_{l}}$, depends on the volumetric flowrate Q and pressure drop according to the equation below. The nozzle type and distance between the nozzle and surface affect the constant C.

${\displaystyle {F_{l}}=CQ{\sqrt {\Delta P}}}$

Spray angle and coverage

The spray angle diverges or converges with respect to the vertical axis. As illustrated in the figure below, the spray angle tends to collapse or diverge with increasing distance from the orifice. Spray coverage varies with spray angle. The theoretical coverage, C, of spray patterns at various distances may be calculated with the equation below for spray angles less than 180 degrees. The spray angle is assumed to remain constant throughout the entire spray distance. Liquids more viscous than water form smaller spray angles, or solid streams, depending upon nozzle capacity, spray pressure, and viscosity. Liquids with surface tensions lower than water produce wider spray angles than those listed for water. Spray angles are typically measured using optical or mechanical methods. The optical methods include shadowgraphy, extinction tomography, and Mie Imaging.^[6] Sprays angles are important in coating applications to prevent overspraying of the coated materials, in combustion engines to prevent wetting of the cylinder walls, and in fire sprinklers to provide adequate coverage of the protected property.

Spray coverage

${\displaystyle {C}=2D\tan(\theta /2)}$

Spray drop size

The drop size is the size of the spray drops that make up the nozzle's spray pattern.^[7] The spray drops within a given spray are not all the same size. There are several ways to describe the drop sizes within a spray:

• Sauter Mean Diameter (SMD) or D32

• Fineness of spray expressed in terms of surface area produced by the spray.
• Diameter of a drop with the same volume-to-surface area ratio as the total volume of all the drops to the total surface area of all the drops .

• Volume Median Diameter (VMD) DV0.5 and Mass Median Diameter (MMD)

• Drop size expressed in terms of the volume of liquid sprayed.
• Drop size measured in terms of volume (or mass), with 50% of total volume of liquid sprayed drops with diameters larger than median value and 50% with smaller diameter.

Drop sizes are stated in micrometers (µm). One micrometer equals 1/25,400 inch.

Drop size distribution

The size and/or volume distribution of drops in a spray is typically expressed by the size versus the cumulative volume percent.

Cumulative drop size distribution graph

Practical considerations

Drop size data depend on many variables, and are always subject to interpretation. The following guidelines are suggested to facilitate understanding and effective use of the drop size data.

Data collection repeatability and accuracy

an average value drop size test result is repeatable if the data from individual tests do not deviate by more than ±10%; however, this may be larger or smaller depending on several factors. Accuracy requires a primary standard which is not available for spray measurements.

Instrumentation and reporting bias

to make valid data comparisons, particularly from different sources, it is extremely important to know the type of instrument and range used, the sampling technique, and the percent volume for each size class. Instrumentation and reporting bias directly affect drop size data.

Consider the Application

select the drop size mean and diameter of interest that is best suited for the application. If the object is simply to compare the drop size of alternate nozzles, then the VMD or SMD report are sufficient. Additional information such as RSF, DV90, DV10, and others should be used when appropriate.

Fuel sprays

Sprays of hydrocarbon liquids are among the most economically significant applications of sprays. Examples include fuel injectors for gasoline and diesel engines, atomizers for jet engines (gas turbines),^[12] atomizers for injecting heavy fuel oil into combustion air in steam boiler injectors, and rocket engine injectors. Drop size is critical because the large surface area of a finely atomized spray enhances fuel evaporation rate. Dispersion of the fuel into the combustion air is critical to maximize the efficiency of these systems and minimize emissions of pollutants (soot, NOx, CO).^[13]

Electrical power generation

Limestone slurry is sprayed with single fluid spray nozzles to control acid gas emissions especially sulfur dioxide (SO2) emissions from coal-fired power plants with liquid scrubbers. Calcium hydroxide (lime) is atomized into a spray dryer absorber to remove acid gases (SO2 and HCl) from coal-fired power plants. Water is sprayed to remove particulate solids using a spray tower or a cyclonic spray scrubber^[14] Cooling towers use spray nozzles to distribute water.

Food and beverage

• Sprays are used to wash fruits and vegetables.
• Spray drying^[15][16] is used to produce hundreds of food products, including instant coffee, powdered soups, and flavor concentrates.
• Coating of food products with flavorings and surface additives.
• Cleaning and sanitizing storage tanks, and process equipment single fluid nozzles are used to rinse and wash away materials. These specialized tank-cleaning nozzles often have a fluid powered rotary motion to increase cleaning effectiveness.

Manufacturing

Sprays are used extensively in manufacturing.^[17] Some typical applications are applying adhesive, lubricating bearings, and cooling tools in machining operations.

• Cleaning components with sprays of hot water and detergent sprays for degreasing, electric motor rebuilding, diesel engine rebuilding, plant maintenance, steel mill bearings, railroad bearings and engine rebuilding.^[18]
• High pressure sprays are used to de-burr machined parts.
• Spray painting is broadly used in many manufacturing processes; for example, for automobiles, appliances, office furniture.

Paper making

• High pressure debarking
• Coating paper
• Cleaning rolls
• Trimming paper

Electronics

• Spraying etching chemicals and printed circuit boards flux agents

Fire protection

• Spraying water from fixed sprinklers
• High pressure water misting systems for expensive and delicate equipment, for example, marine engine rooms.
• Deluge systems for protecting assets or keeping potentially explosive materials cool in the event of fire (e.g. gas canisters)
• Water tunnel systems designed to ensure a safe "cool" corridor to allow people to escape in the event of fire.

Mining

• Water sprays are critical to reducing coal dust during mining^[19]
• Water is sprayed to control dust emission produced during grinding; spray nozzles are also used for washing gravel in screening plants.

Lime and cement

• Suppressing dust from raw materials.
• Feeding fuel to high temperature calcining rotary kilns.
• Cooling and conditioning gas.

Steel industry

• High pressure water is used to remove scale (iron oxide) from red hot steel during the process of rolling into sheet or strip forms.
• Sprays are used in the continuous casting process and quenching of hot gases.
• Quenching coke from coke-ovens
• Cooling metal extrusions
• Pickling solutions and rinsing pickling solutions

Chemical, petrochemical, and pharmaceutical

• Spraying reagents to enhance dispersion and to increase liquid-gas mass transfer. Many systems are used, including spray towers.
• Spray drying fluid cracking catalyst for oil refining
• Washing and rinsing solids in filters and centrifuges
• Applying coating to many pharmaceutical tablets

Waste treatment

• Single fluid nozzles are used to break foam in activated sludge wastewater aeration basins and to apply antifoams.
• Water is spray mixed with material being composted.
• Liquid waste is injected into high temperature incinerators.

Agricultural applications

Knapsack sprayer used to sulfate on vegetables. Valencian Museum of Ethnology.

Spray application of herbicides, insecticides, and pesticides is essential to distribute these materials over the intended target surface.^[20] Pre-emergent herbicides are sprayed onto soil, but many materials are applied to the plant leaf surface. Agricultural sprays include the spraying of cropland, forest, turf grass, and orchards. The sprayer may be a hand nozzle, on a ground vehicle, or on an aircraft. Herbicides, insecticides and pesticides are spray applied to soil or plant foliage to distribute and disperse these materials. See aerial application, pesticide application, sprayer. The control of spray characteristics is critical to provide the coverage of foliage and to minimize off target drifting of the spray to adjacent areas. (pesticide drift). Spray drift is managed by applying only in appropriate wind conditions and humidity, and by controlling drop size and drop size distribution. Minimizing the height of the spray boom above the crop reduces drift. The spray nozzle type and size and the operating pressure provide the correct application rate of the material and control the amount of driftable fines. Spays, single fluid nozzles, are also used to cool animals

Consumer products

Atomizers are used with pump-operated sprays of household cleaning products. The function of these nozzles is to distribute the product over an area. See aerosol spray and spray can

• Water and detergent sprays for the car washing