Patternation is the specialized technical

art Art is a diverse range of human activity, and resulting product, that involves creative or imaginative talent expressive of technical proficiency, beauty, emotional power, or conceptual ideas. There is no generally agreed definition of wha ...

of performing quantitative measurements of specific properties of

particle In the physical sciences, a particle (or corpuscule in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass. They vary greatly in size or quantity, from ...

s within a spray and visualizing the patterns of this specific property within the spray. In order to understand patternation, we need to consider the role sprays play in our daily lives.

Uses of sprays

Sprays have a number of uses. In its natural form, sprays appear in

waterfall A waterfall is a point in a river or stream where water flows over a vertical drop or a series of steep drops. Waterfalls also occur where meltwater drops over the edge of a tabular iceberg or ice shelf. Waterfalls can be formed in severa ...

mists, rains and ocean sprays, according to Arthur Lefebvre, in his book, ''Atomization and Sprays''. Within the household sphere, sprays are used in

showers A shower is a place in which a person bathes under a spray of typically warm or hot water. Indoors, there is a drain in the floor. Most showers have temperature, spray pressure and adjustable showerhead nozzle. The simplest showers have a ...

garden hose A garden hose, hosepipe, or simply hose is a flexible tube used to convey water. There are a number of common attachments available for the end of the hose, such as sprayers and sprinklers (which are used to concentrate water at one point or ...

spray paint Aerosol paint (commonly spray paint) is paint that comes in a sealed, pressurized container and is released in an aerosol spray when a valve button is depressed. Aerosol painting is one form of spray painting; it leaves a smooth, even coat, unli ...

cans,

hair spray Hair spray (also hair lacquer or spritz) is a common cosmetic hairstyling product that is sprayed onto hair to protect against humidity and wind. Hair sprays typically consist of several components for the hair as well as a propellant. Ingr ...

, deodorant sprays and more. Industrial uses of sprays include

spray drying Spray drying is a method of changing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals, or materials which may requ ...

, coating, washing, and irrigating. Sprays are also used in many

internal combustion engines An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combust ...

to directly disperse the fuel into the combustion chamber and mix it with air so that either spontaneously ignite under high pressure and temperatures or they can be ignited using spark plugs.Lefebvre, Arthur, H. (1989) Atomization and Sprays, NY: Taylor & Francis.

Understanding the importance of spray patternation

Patternation of sprays is important in a variety of applications including IC engines,

turbines A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful Work (physics), work. The work produced by a turbine can be used ...

, spray coating, spray drying, agriculture, and consumer products. For example, asymmetries in patternation directly affect surface finish quality during painting and poor product quality during spray drying. Similarly, in gas turbines, variation in the spray pattern leads to fuel lean and fuel rich pockets resulting in excessive turbine wear and increased particulate emission. For

metered-dose inhaler A metered-dose inhaler (MDI) is a device that delivers a specific amount of medication to the lungs, in the form of a short burst of aerosolized medicine that is usually self-administered by the patient via inhalation. It is the most commonly used ...

s, the pattern of the spray is very important to ensure that the maximum amount of the drug goes through the throat passageways into the lungs. In agricultural nozzles the pattern of the spray is important so as to optimize the delivery of pesticides and fertilizers to the plants. Spray drying requires that the droplet sizes be closely controlled. In general, increasing the total drop surface area within the dryer will lead to higher evaporation rates and greater efficiency for the process. Similarly,

pharmaceutical A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy (pharmacotherapy) is an important part of the medical field an ...

tablets owe their thin film surface coating to an atomizer produced spray that needs to be perfect. The coating not only masks taste but also performs key functions such as sealing the tablet from moisture to improve shelf life, controlling drug release rates to get slow and extended release tablets.

How scientists study spray patterns

Spray patterns are studied using diagnostic tools known as patternators. A patternator quantifies the spatial location of the drops emitted from a sprayer and visualizes the patterns of sprays. There are different types of patternators, mechanical and

optical Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultravio ...

Mechanical patternators

Mechanical patternators are called intrusive patternators. They typically collect the mass flux of liquid in small containers or spray color onto papers to look at the pattern that are then weighed to provide local information. Mechanical patternators are not very accurate and suffer from a number of systematic and random errors In addition, they interfere with the spray pattern itself, and are generally not suitable for obtaining accurate data on spray patterns.

Optical patternators

To avoid the errors in mechanical patternation, it is generally accepted that the patternation technique has to be optical.

Optical patternators provide the distribution of drop surface areas rather than the mass flux. In many instances, this is advantageous as all local transfer phenomena, such as mass; momentum; energy and species are directly proportional to the surface area density of the droplets in the spray. There are three principal types of optical patternators: (a) those that use laser sheets, (b)those that use planar liquid laser induced fluorescence and (c) those that use laser extinction tomography.

Using a laser sheet

The first is based on using a laser sheet to illuminate a plane orthogonal to the spray direction or along the spray direction and capturing the image of the scattered light using an off-axis camera. It is assumed that the scattered intensity is proportional to the local drop surface area density.

Using planar liquid laser induced fluorescence

A second type of patternators are based on using planar liquid laser induced fluorescence. The liquid is mixed with some fluorescent material and illuminated with a high power laser sheet. The resulting fluorescence image is captured and analyzed to provide the local mass concentrations within the spray. Both these methods have significant errors due to laser extinction, signal

attenuation In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variabl ...

, and secondary emission

Using laser extinction tomography

The third set of optical patternators is based on laser extinction or laser extinction tomography. The laser extinction

tomography Tomography is imaging by sections or sectioning that uses any kind of penetrating wave. The method is used in radiology, archaeology, biology, atmospheric science, geophysics, oceanography, plasma physics, materials science, astrophysics, ...

system provides the local drop surface area density (number of drops per unit volume at a specific location multiplied by the surface area of the drops). This quantity is directly proportional to the evaporation of the drops and is very important in applications involving

combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combus ...

and spray drying. MultiplePlumes

The picture shows results from testing a Gasoline Direct Injector (GDI) using an optical patternator that is based on extinction tomography. This optical patternator can be used to analyze highly dense sprays.Yudaya Sivathanu and Jongmook Lim, Paul G. Hicks. (2007). Optical and Mechanical Patternation of an High Flow Rate Industrial Gas Turbine Nozzle, ILASS Americas, 20th Annual Conference on Liquid Atomization and Spray Systems, Chicago, IL, May 2007

References

{{reflist Aerosols Measurement