Foam control nozzles - achieving the correct flow rate

Sprays used to control foam build up need to be carefully dosed. Too much spray being delivered can have an adverse effect as it may actually agitate the fluid below causing more foam to be created. Of course too little foam control spray will mean a failure to prevent foam build up.

The amount of fluid delivered per square meter will vary considerably depending on the rate at which foam is being created and the consistency of the foam. Very fine light foams required less fluid to counter them where as thick foams require more.

In general the very lightest foams will require about 4 liters of spray per square meter per minute for effective foam control and this rise to around 160 liters per minute per square meter for very aggressive foam forming situations. It should be noted that the upper limit of this range would be for an exceptionally fast forming foam.

So we can say that

Very light foams require 4-10 litres per minute per m2
Light foams require 11-20 litres per minute per m2
Medium foams require 21-50 litres per minute per m2
Heavy foams require 50+ litres per minute per m

The effect of spray angle and nozzle height

The nozzle size selected will determine it's absolute flow rate but, as illustrated below, the spray angle and distance from foam will affect the area that the fluid is delivered too. In many cases angle and distance from target will be as big an influence as nozzle selection and over all nozzle size.  

Relationship between height and spray angle

 
The spray angle of a nozzle and it height above the foam will determine the area over which its distributes its fluid. 

The area covered by a nozzle can be determine by the following formula

     Area covered = Pi(hTan(Ø/2))2

Where h is the height above the foam and Ø is the spray angle of the nozzle.

So the flow rate per m2 per minute can be determined as

     Flow rate/Pi(hTan(Ø/2))2 

Flow rate for individual nozzle can be seen by looking at relevant data sheets but the table below shows some examples of how this calculation might be applied in nozzle selection. 

Nozzle

Flow rate at 2 bar

Spray angle

Flow rate per m2 for nozzles at different heights above the foam 

0.1 m

0.25 m

0.5 m

0.75 m

1 m

TF20

53.2

90

1693.46

270.95

67.74

30.11

16.93

TF20

53.2

120

564.49

90.32

22.58

10.04

5.64

TF20

53.2

150

121.58

19.45

4.86

2.16

1.22

TF20

53.2

170

12.96

2.07

0.52

0.23

0.13

Nozzle

Flow rate at 0.5 bar

Spray angle

0.1

0.25

0.5

0.75

1

TF6

2.26

90

71.94

11.51

2.88

1.28

0.72

TF6

2.26

120

23.98

3.84

0.96

0.43

0.24

TF6

2.26

150

5.17

0.83

0.21

0.09

0.05

TF6

2.26

170

0.55

0.09

0.02

0.01

0.01

Nozzle

Flow rate at 1 bar

Spray angle

0.1

0.25

0.5

0.75

1

MP125

5.53

90

176.03

28.16

7.04

3.13

1.76

MP125

5.53

120

58.68

9.39

2.35

1.04

0.59

Nozzle

Flow rate at 0.5 bar

Spray angle

0.1

0.25

0.5

0.75

1

MPL

0.51

90

16.23

2.60

0.65

0.29

0.16

MPL

0.51

120

5.41

0.87

0.22

0.10

0.05


From the table above we can see that a TF14 nozzle could, in principle, be used light, medium or heavy foam control depending on the deployed spray angle and distance from the foam. Similar variations can be found in other nozzle types.

Foam Control Engineering Considerations:

Foam Control Nozzle Designs: