All of us have had this experience at some point: you wake up, find out you’re late for a class or meeting, clean up, put on some nice clothes, and run. When you finally get to where you need to be, you’re sweating. You pull out a small deodorant bottle from your bag, give yourself a spray, and you’re set. Wasn’t that handy? The spray nozzle, also known as an atomiser, is a nifty piece of technology that creates a mist of particles from a liquid on demand. Liquids are easier to store whereas a spray spreads better. Thus some enterprising engineers invented the atomiser to allow you, and in fact many industries in the world, to make the best of both worlds.
What is an atomiser?
An atomiser is a device that creates a spray. A spray is in turn a collection of drops that disperses as gas. There are different kinds of atomisers based on the kind of spray required. Since there are many hundreds of scenarios where sprays are required — including injecting fuel into internal combustion engines, manufacturing steel, and to irrigate gardens and quench small fires — atomisers are also expected to have different abilities.
Some simple ways in which sprays differ are in the drop size, spray pattern, and angle of application.
There are at least two ways to measure spray drop sizes: by the drops’ average surface area or average volume. Some use a statistical figure called the Relative Span Factor (RSF). It denotes the distribution of drop sizes as a ratio of the size difference between the largest and smallest drops to the median size. If the RSF is close to 1, it means the spray is close to being very evenly sized.
There are also many ways to measure the drop sizes. For example, the greater the angle at which light is scattered by a drop, the smaller it is. So scientists can shine a laser light at a spray and assess drop sizes using a detector to record the scattered light.
Spray pattern refers to the distribution of the spray’s drops once they hit the target surface. While the spray on a deodorant may want to deliver drops to a wide area on skin, a spray in a coal mine may need to deliver a ring of drops spreading in a conical shape through the air to quickly trap as many coal-dust particles as possible (devices that can achieve the latter are good at preventing clogging and can create sprays at low pressure.)
Similarly, the angle of application matters to keep a spray from striking surfaces that shouldn’t be sprayed or, conversely, to cover a given area as efficiently as possible.
There are many more spray characteristics that matter.
How does an atomiser work?
There are many applications, so there are many atomisers. Perhaps the one mechanism they all share is that they create sprays by blowing up some liquid. In one simple implementation, liquid flowing through a wider channel is suddenly forced into a much narrower channel. A sufficiently high pressure drop will cause the liquid to break up into small drops. If the narrower channel has a notched opening at the other end, the spray emerges as a flat fan — of the kind used in spray painting.
If the narrower channel opens after a short distance to an upward ramp, the fluid hits the ramp in a sheet and then shatters into drops — an output that’s useful when a thin coating is required, like an insecticide on a plant.
Another design called a pressure-swirl atomiser works similarly to when you’re cradling a glass of chai in your hand. To help it cool, you might move the glass with your hand such that the liquid swirls inside, flowing more along the sides than in the centre. The atomiser does the same thing while allowing air to push through at the centre, keeping the fluid flowing along the walls. As gravity pulls the fluid down, a small opening allows it to flow out in a conical pattern.
More complicated designs cater to specific applications. For example, an atomiser can also deliver an aerosol — which is a spray where the drops are so small (typically 10 μm or smaller) that they can stay airborne for many hours instead of settling down. To do this the shear, or tearing, force acting on the liquid at the liquid-gas interface should be much higher than in, say, an atomiser used to spray cleaning liquid on a household surface.
Pressure-swirl atomisers can achieve this if the liquid is already at high pressure when entering the swirling chamber. Other techniques include ultrasonic nebulisation, where high-frequency vibrations induced on the liquid surface can cause small drops to break off, and air-assisted atomisers, where compressed air rips through the liquid as it flows out.
Where are atomisers used?
Aside from the applications mentioned thus far, atomisers are used everywhere where a liquid needs to be distributed in a specific and efficient way across a surface or through a space. In power plants, coolants are sprayed on spinning turbine blades and lubricants are often sprayed on machines with high-contact moving parts — in both cases to prevent heat build-up.
A method called spray drying is used to make milk powder by creating a spray and passing it through hot gas to quickly dry it. In the automobile and aerospace sectors, fuel injectors spray pressurised fuel into engines.
Firefighters’ only option for putting out fires involving flammable solids is often foam sprays.
In addition to pesticides and fertilizers, farmers use spray-based irrigation systems when planting in soils that have poor percolation.
Atomisers are ubiquitous in medicine: nasal sprays deliver drugs to the lungs, pain-relief sprays can quickly soothe aching muscles, antiseptics are sprayed on wounds, and disinfectants are used to keep air and hospital surfaces clean.
In the early days of COVID-19 pandemic, there was some confusion over how far the virus could spread by air, leaving many scientists trying to model the pathogen as an aerosol. Climate scientists also study aerosols because of their cooling effects in the atmosphere, to subtract them and estimate the actual level of warming.
Within a household itself, atomisers serve cooking oils, mirror cleaners, and fragrances for hair and perfumes. In the end, let’s not forget the humble deodorant itself that allows people to be around each other despite India’s increasingly hot summers without stuffing their noses.
Published – May 20, 2025 08:30 am IST