Adjusting the Droplets Size
Controlling the droplet size in spraying system is a critical requirement in many industries and applications, with the main methods including adjustments the nozzle type, operating parameters, and liquid properties. Here are some of the main methods:
Choosing different nozzle types:
1. Hydraulic nozzles
Liquids are forced out of the nozzle opening to form mist droplets by a pump to pressurize them. Hollow cone nozzles such as Relab’s A Series, full cone nozzle as Relab’s B Series, flat fan nozzle as Relab’s C Series, and stream jet nozzles as Relab’s D Series are all hydraulic nozzles and can control the droplet size by adjusting the pressure. Larger droplets are produced at lower pressures, while smaller droplets are produced at higher pressures. Hollow cone nozzles produce a more uniform droplet distribution than solid nozzles.
AA Hollow Cone Nozzle
Model AA is a tangential-flow hollow cone nozzle with a male thread body, which is a combination of two pieces. The range of flow rate is from 0.32LPM to 78LPM at 2 bar. It delivers a standard spray angles of 55°~90° at 2 bar.
Read MoreBB Full Cone Nozzle
Model BB is the most commonly used full cone nozzle. It has a built-in X-style vane, which can better reduce clogging. If you want fast delivery, BB nozzle is the best choice.
Read MoreCB Small-flow Flat Fan Nozzle
Model CB is a small flow flat fan nozzle with a T-shaped design to be more convenient and accurate arrangement and better spray effect. The coverage area overlaps by 30% to obtain complementary and more uniform distribution.
Read MoreDA Standard Solid Stream Nozzle
DA solid stream nozzle is complete brass or stainless nozzle without any inserts. The model produces a precise, concentrated and high-velocity stream which is longer distances than flat fan nozzles to handle tough cleaning applications.
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2. Air atomizing nozzles
Compressed air is used to drive the liquid to form mist droplets, so both the liquid and air pressure are factors that affect the droplet size. For example, Relab’s J Series of air atomizing nozzles can achieve smaller droplet sizes than universal hydraulic nozzles. The average diameter can be from 40 microns to 200 microns.
JA Siphon Flat Air Atomizing Nozzle
Flat fan air atomizing nozzles are most used for coating and cooling applications when-ever a wide linear pattern is required. They are commonly used where products to be coated are moving on a conveyor.
Read MoreJB Pressure Flat Air Atomizing Nozzle
The pressure flat fan air cap is more suitable for assembling spray headers and using in large areas. Compared to the siphon fan air cap, the pressure fan air cap produces a larger spray angle, denser spray particles, and a longer delivery distance.
Read MoreJB Siphon Round Air Atomizing Nozzle
Full cone air atomizing nozzles are desirable for applications requiring a relatively narrow, long-reaching, circular pattern and are especially suited to gas cooling, gas conditioning and humidifying.
Read MoreJC Wide Round Air Atomizing Nozzle
The wide-angle round air cap produces a spray cluster combined from 6 round holes. The liquids are supplied by pressure. Compared with the round spray pattern, there is a bigger spray angle, a larger flow output and a faster liquid transfer speed.
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3. Ultrasonic nozzles
Liquids are dispersed into tiny droplets using high-frequency ultrasonic vibrations. The droplet diameter is inversely proportional to the ultrasonic frequency, and as the frequency increases from 20 kHz to 120 kHz, the average of the droplets can be reduced from about 120 microns to below 20 microns.
Adjusting operating parameters:
1. Flow rate and pressure
Flow rate and pressure are key factors affecting droplet size. Lower flow rates and higher pressures typically produce smaller droplet. For example, Relab’s F Series of fine mist nozzles, at a pressure of 60 bar, has a droplet size of 15-25 microns for a nozzle with a 0.2mm hole diameter, and at 80 bar pressure, the droplet size is 10-15 microns. For example, when the flow rate is controlled at ≤2 mL/min in ultrasonic spraying, the droplet size is small and evenly distributed.
Droplet Size Basics
The spray pattern of a nozzle is made up of many droplets of varying sizes. Droplet size is the diameter of an individual spray droplet and measured in microns (micrometers) often notated with the symbol µ. One micron equals 0.001 mm(0.0000394"); there are 25,400 microns in one inch. For example, the diameter of a human hair is about 100 microns. ...
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2. Adjusting speed and height
In the operation of agricultural UAVs, the flight speed and flow rate need to be adjusted in a coordinated manner. When the speed is increased from 5 meters/second 7 meters/second, if the dosage is kept constant, the system will automatically increase the nozzle flow rate. As the flight height increases, the flow rate needs to be adjusted to compensate for the loss of droplet drift.
In the indoor high-pressure misting/fogging system, when the installation height is increased from 2 meters to 3 meters and the direction is changed from downward to horizontal, the droplet size obtained on the ground becomes significantly smaller. The installation height and spray direction change the speed at which the droplets fall, the absorption of air also affects the size of the droplets.
Adjusting liquids:
Viscosity and surface tension
Liquids with high viscosity produce larger droplets, and reducing surface tension can promote the dispersion of liquids to form smaller droplets. For example, water with a of 1 mPa·s has a droplet diameter of about 50 microns, while a glycerol-water solution with a viscosity of 30 m·s has a droplet diameter increased to 70 microns.
Nozzle Coverage Calculation
The table demonstrates how the theoretical coverage from a spray nozzle of a specific included angle varies as a function of distance from the nozzle. ...
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Spray Impact
Impact is a measure of the force at which a spray liquid impinges on a surface. Its value depends on the six factors: liquid density, nozzle type, working pressure, flow rate, spray angle and installation distance. ...
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Droplet Size Basics
The spray pattern of a nozzle is made up of many droplets of varying sizes. Droplet size is the diameter of an individual spray droplet and measured in microns (micrometers) often notated with the symbol µ. One micron equals 0.001 mm(0.0000394"); there are 25,400 microns in one inch. For example, the diameter of a human hair is about 100 microns. ...
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Main Factors Affecting Spray
All the data relating to our nozzles contained in our catalog are based on spraying water at standard temperatures. When spraying liquids other than water, performance is likely to be different. The following presentation describes how various liquid properties and operating conditions affect performance. ...
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