Cooling Tower Spray Nozzle Pressure Drop

Here is a clear, practical explanation of cooling tower spray nozzle pressure drop and how to estimate it for real systems.

 ✅ What Is Nozzle Pressure Drop?

Pressure drop across a cooling tower spray nozzle is the pressure required at the nozzle inlet to produce the correct flow rate and spray pattern (usually full-cone / umbrella).

Typical cooling tower nozzles operate at very low pressure, usually:

0.5 – 10 psi

(≈ 0.03 – 0.7 bar)

Crossflow towers often use even less:

1–2 psi is common.

Counterflow towers usually require:

2–6 psi depending on nozzle type.

Why Pressure Drop Matters

If pressure is too low:

* Spray pattern collapses

* Dry spots on fill

* Loss of tower capacity

If pressure is too high:

* Over-atomization

* Drift loss increases

* Erosion of ABS/PVC nozzles

Nozzle Pressure Drop Formula

Most cooling tower nozzles follow the standard nozzle equation:

Q = K \sqrt{P}

Where:

* Q = flow rate (GPM)

* P = pressure drop (psi)

* K = nozzle coefficient (depends on nozzle size)

Rearranged:

## [

P = \left(\frac{Q}{K}\right)^2

]

  Typical Pressure Drop Examples

1. Marley / BAC / EVAPCO Full-Cone Nozzles

Nozzle Type	Typical Pressure	Flow at Typical Pressure
Marley Spiral Nozzle	2–4 psi	20–60 GPM
BAC Spray Nozzle (counterflow)	3–6 psi	15–40 GPM
EVAPCO PP Nozzle	2–5 psi	10–50 GPM
Crossflow ABS target nozzle	1–2 psi	20–120 GPM

Pressure Requirements by Tower Type

Crossflow Cooling Tower

* Uses gravity + low-pressure nozzles

* 0.5–2 psi at nozzle inlet

* Larger orifices → less prone to clogging

Counterflow Cooling Tower

* Higher spray height

* Needs atomization for uniform fill wetting

* 3–6 psi typical

Example Calculation

Example: A nozzle with K = 10

Required flow = 30 GPM

P =(30/10)² = 9  psi

Higher K → needs less pressure

Lower K → needs more pressure

What Affects Nozzle Pressure Drop?

1. Nozzle orifice size

Smaller → higher pressure required.

2. Spray pattern (full cone vs flat fan)

Full cone = higher pressure.

3. Water quality

Scaling increases effective pressure.

4. Distribution piping layout

Improper design may starve nozzles.