Post 290 – by Gautam Shah
Spraying is a method of throwing or projecting atomized liquid by adding several times more volume of gas. Spraying was known to primitive humans as a way of adding air to water for gurgling the mouth, and to project it to a defined place with pressure. The technique was useful to ignite as well as douse the fires, with respectively, oil or water.
Spraying involves two processes, first atomization of liquid with a gas and secondly pushing through an orifice to exert pressure. The mouth with closing in lips, and caved or hollowed tongue formed a dynamic orifice, whereas the pressure was caused by breathed air. Primitive atomization was also caused by blowing air over a thin body of liquid. Vibrating bristles or shaking fingers dipped with liquid, also causes, the spread.
Spraying was used for many purposes. Oils were sprayed over fires and cooking foods. Colours were sprayed over body, ceramics, leather and clay floors. Colours were sprayed to achieve even mass tones and diffused edge effects. Colours were sprayed within marked boundaries or stencils.
One of the simplest ink spraying tool was an L bent tube, with a small aperture on the outer curve. The tube was thin enough to allow liquid to rise through capillary action, and the other tube was used to blow air. The blown air spayed the rising up liquid. A similar process is used in old style home-use insecticide pumps.
Spraying is used to create instant cooling and spread of oily substances (as carried with water or other solvents or through emulsification). Scents and medicines are sprayed to provide instant effect over a large area. Asthma sprays reach deep sections of throat to provide relief. Skin sprays create a thin coating over bleeding wound or painful muscle.
In India during the colour festival of Holi, coloured water is sprayed with a nozzle drum pump. This simple device is now being replaced with multi nozzle plastic guns. Home bath showers and garden sprinklers distribute the water into very fine strands or droplets.
Textile plants cotton spinning and weaving sections require high level of humidity. Similarly in very cold weather, chances of humidity being stripped out of the indoor air are very high. This requires addition of moisture in the air. Operation theatres need to be sterilized with formaldehyde vapour. All these spaces use water atomisation technology.
Spraying mechanisms are used in industrial burners and automobile combustion engines. By spraying fuels in burners, larger volume of oxygen is made available, which in turn minimizes the pollutants. Hot water spraying with heavy pressure is used for cleaning-washing without using any detergents or chemicals in many sensitive production areas like foods and pharmaceuticals. Water-sprays are used in chimney stacks to remove particulate and dissoluble matters. One of the most important uses of spray technology is in agriculture. Spray applications in agriculture include spread of herbicides, insecticides, pesticides and fertilizers.
Aerosol spray cans have become part of our life. These are used for spraying fluids like scents, deodorants, paints, waxes, hair-oils, whipped creams, food dressings, chemicals, medicines etc. These cans or packs have some form of propellant, ‘a general name for liquid chemicals that can readily be vaporized and so used for creating thrust or pressure. In 1939, American Julian S. Kahn received a patent for a disposable spray can, but its commercial success came much later.
It was found that chlorofluorocarbons (CFCs), used as propellants in aerosol sprays, depletes of Earth’s ozone layer. These were sought to be replaced with mixtures of volatile hydrocarbons, such as propane, n-butane and isobutane. Dimethyl and Methyl ethers. These replacement materials have a disadvantage of being flammable. Nitrous oxide and Carbon dioxide are also used as propellants to deliver foodstuffs (e.g. whipped cream, food dressings). Medicinal asthma inhalers use hydrofluoroalkanes (HFA).