Dr.Nozzle

Dr. NOZZLE 

The selection of the spray nozzle depends especially on reaching the required target and several other criteria rather than application general conditions. Sometimes, the impact is taken into consideration, but a number of parameters such as spray width, particle size, pressure, flow rate, ambient temperature and similar ones are foregrounded in other cases. The choice and application of spray nozzles which look like a simple piece, are extremely complicated. Our team of experts will help you to make the right choice.

Below are some definitions and criteria for spray nozzles. The following subjects are mentioned for spraying liquids that are similar to water in terms of its viscosity or just water. In low or high viscosities, the behavior of the spray nozzle differs.

Spray nozzle is a unit which converts the fed liquid in to a spray form under certain pressure and flow rate according to spray orifice designed.
   

WHERE ARE THE SPRAY NOZZLES USED?

Tens of thousands of different types of spray nozzles are used in thousands of different applications, dozens of different industrial branches.

Some general applications can be summarized as follows; spray drying, mixing in tank, internal cleaning of storage tanks, fire extinguishing, odor suppression, essence spraying, decorative spraying, weed control, gas washing, particle suppression in gas, desulfurization, metal or marble cutting, quenching / quenching, roll cooling, descaling, food cleaning, food cooling...

 

 

WHAT ARE THE CRITERIA TO SELECT THE SPRAY NOZZLE?

There are many criteria to be considered when selecting a nozzle or designing a system. These can be briefly summarized as follows;

*flow rate

*working pressure and pressure losses 

*properties of the liquid (temperature, density, viscosity, pH value, conductivity, suspended solid rate, total hardness, TTS value etc.)

*material of the spray nozzle 

*spray angle 

*connection of the spray nozzle (with or without accessories)

*general arrangement of the nozzles

*spray height

*spray width

*spray thickness

*atomization degree and droplet size

*impact 

*spray geometry

*place of application (indoor, outdoor, high temperature, jigh humidity etc…) 

*.......

 

WHAT IS THE IMPORTANCE OF DROPLET SIZE?

Depending on the needs of the application, it may be desirable that the spray to be formed  is in the form of very fine droplets or coarse ones. Fine droplets are generated when more total surface-contact area is desired for the same amount of liquid per unit volume, while coarse droplets are preferred when the mechanical impact is requested. An ideal sphere water droplet can be commented as follows;

 

                                                         

** The volume of a 2D diameter droplet is the volume sum of 8 droplets with a diameter D.

**The surface area of a single 2D diameter droplet is 4 times larger than the surface area of a D diameter single droplet. However, in order to obtain the 2D volume, it is necessary to have 8 droplets of  D diameter, and the total surface area of 8 droplets with D diameter is 2 times larger than the surface area of one 2D droplet.

For this reason, it is desirable that spray droplets should be finer in applications where rapid heat transfer is required i.e. gas conditioning, humidification, ambient cooling is required

 

WHAT ARE THE CRITERIA OF THE NOZZLES ARRANGEMENT? 

Nozzle arrangement is a very important issue because of the fact that the sprayed liquid is not distributed evenly along the spray width. It is possible to spray a 1 m² area with one or 10 nozzles, but which one is correct or efficient? The following basic information will guide you through the nozzle arrangement and defining the number of the nozzle.

The spray nozzles do not homogeneously distribute the liquid throughout the entire width of the spray angle, therefore the overlapping and off-setting must be used in between the spray nozzles.

 

As a general rule;

For flat jet spray nozzles; The overlaying ratio is from 30% to 50% of the total spray width. An off-set angle between 5 ° and 15 ° relative to the pipe axis is recommended to avoid collision of the spray jets.

For spoon jet nozzles; Overlapping ratio of 50% and off-set angle of 15 ° are recommended.

For full or hollow cone nozzles; Overlapping ratio of 25% - 40% is recommended.

 

  

 

 

SPRAY WIDHT (D mm) IN RESPECT TO SPRAY ANGLE (ߺ) AND SPRAY HEIGHT (H mm) 

 

 

HOW IS SPRAY FORM AFFECTED BY THE PRESSURE INCREASE?

Increasing pressure results in a slight increase in spray angle for most of the spray nozzles. This happens as a reverse behavior for full or hollow cone spray nozzles. 

Flat jet nozzles tend to be more regular and sharp-edged by the increase of pressure while full and hollow cone nozzles tend to be more pulverized.

 

The following photographs were taken with three different types of spray nozzles operating at pressures of 0,5 - 3 and 10 bar.

FLAT JET SPRAY @ 0,5 - 3 - 10 bar

 

FULL CONE SPRAY @ 0,5 - 3 - 10 bar

SPIRAL JET SPRAY @ 0,5 - 3 - 10 bar

 

WHAT IS SPRAY IMPACT VALUE FOR A SPRAY NOZZLE?

The spray impact is requested at a higher value in some applications. 

The following formula for impact is indicative of giving an idea. 

 

Theoretical Impact value (kg/cm²) = 0,028 x flowrate (l/min) x (pressure kg/cm²) ½
(Note : 1 bar = 1,02 kg/cm²)

hesaplanan değerin aşağıdaki tablo ile tamamlanması gerekir;

Example; 
Accept that a hollow cone with 80° working @ 3 bar with 20 l/min flow rate; 

Theoretical Impact value (kg/cm²) = 0,028 x 20 x (3 x 1,02)½ = 0,979 kg/cm²
Since spray angle is 80°, the impact efficiency is 61%, so,

the total impact value close to reality = 0,61 x 0,979 = 0,597 kg/cm²
according to a/m table, the % per cm² is %0,2 in respect to total impact valuegöre, toplam vuruş etkisine göre cm² başına yüzdesi %0,2 'dir.

therefore, the impact value per cm² = 0,002 x 0,597 = 0,0011 kg

 

HOW IS CALCULATED FLOWRATE FOR A GIVEN PRESSURE?

The spray nozzles are listed in the catalogues for certain pressures and their flow rate outputs. In case intermediate values are needed, the following formulas can be used.

 

V₁ = the known flow rate at a certain pressure (from the catalogue table) (l/min)
V₂ = flow rate to be calculated (l/min)
P₁ = the known pressure (from the catalogue table) (bar)
P₂ = pressure to be calculated (bar)

V₂ = (P₂/P₁)½ x V₁   single fluid nozzles (except axial feed full cone nozzles)

P₂= (V₂/V₁)²  x P₁     single fluid nozzles (except axial feed full cone nozzles)

 

V₂ = (P₂/P₁)⅖ x V₁  for axial feed full cone nozzles
P₂ = (V₂/V₁)  x P₁   for axial feed full cone nozzles