The concept of a +spray is known to all, but many would struggle to describe a spray precisely. A suitable definition for a spray is a mist scattered within a gas. A familiar example would be what is produced by spraying a can of underarm +deodorant . The liquid inside the can is turned into a mist, which is of course dispensed into the air. It can easily be understood how this ties in with the definition.

In the above example, the air was the gas that that the drops of deodorant were dispersed in. However, the definition of a spray allows for liquid to be sprayed into any gas, for example when various liquids are sprayed into the emissions of power plants, to help strip out harmful chemicals.

The process of creating a spray is sometimes called atomization. In practice, the liquids are not literally split down into individual atoms, but rather, small liquid droplets. The significance of changing liquids into this state can be seen by looking at some examples of how sprays are used. Since liquid sprays are used in so many applications, only a selection will be considered.

Sprays are used extensively by companies producing foods and drinks. Spray washers are used to clean fruit and vegetables, while many flavorings and additives are sprayed onto foods. Sprays are very controllable, which helps manufacturers to ensure the correct amount of ingredient is added, for example a little too much spice will make food inedible for some people, so reasonable precision is required. Another advantage of sprays is that they can help ensure a uniform distribution of ingredient is applied over a food product.

Staying with food and drink, many commonplace foods are created using a technique called spray drying. Here, liquid products are turned into a fine spray, which is dried out in hot air. Instant coffee, milk powder, colorings and spice powders are made with this process.

While spray drying is perhaps not familiar to the lay person, spray painting is far more widely known. As well as the mundane spray paint can known to all, there are other more advanced forms of spray painting. An interesting variation is electrostatic spray painting, where the paint spray is given an electric charge, and the item to be painted is given an opposite charge so that it will attract the paint. This has clear advantages over brush painting, where it can be very hard to paint into awkward areas.

Perhaps the most important use of sprays is where they are used in engines. Fuel sprays inject the fuel into many types of engine, including petrol, diesel, jet and rocket engines, and also in steam boilers. The injection of fuel in this manner is highly significant, because turning it into a spray creates a very high surface area, while also dispersing it through the air, which allows it to be ignited very efficiently.

Although many people do not have a full understanding of what a spray is, the fact that sprays are used in power generation, familiar items such as deodorants and spray paint, food production, and in running some of our most important forms of transportation, shows how important they can be.