A spray is a dynamic collection of drops dispersed in a gas. The process of forming a spray is known as atomization. A spray nozzle is the device used to generate a spray. The two main uses of sprays are to distribute material over a cross-section and to generate liquid surface area. There are thousands of applications in which sprays allow material to be used most efficiently. The spray characteristics required must be understood in order to select the most appropriate technology, optimal device and size.
Spray atomization can be formed by several methods. The most common method is through a spray nozzle which typically has a fluid passage that is acted upon by different mechanical forces that atomize the liquid. The first atomization nozzle was invented by Thomas A. DeVilbiss of Toledo, Ohio in the late 1800s His invention was bulb atomizer that used pressure to impinge upon a liquid, breaking the liquid into a fine mist. Spray formation has taken on several forms, the most common being, pressure sprayers, centrifugal, electrostatic and ultrasonic nozzle.
Sprays of hydrocarbon liquids (fossil fuels) are among the most economically significant applications of sprays. Examples include fuel injectors for gasoline and diesel engines, atomizers for jet engines (gas turbines), 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).
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 Cooling towers use spray nozzles to distribute water.
Sprays are used extensively in manufacturing. Some typical applications are applying adhesive, lubricating bearings, and cooling tools in machining operations.
Spray application of herbicides, insecticides, and pesticides is essential to distribute these materials over the intended target surface. 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
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