Spray nozzles are used to cool numerous industrial processes from stamping presses to freshly forged steel and from gas turbine inlets to power plant exhaust streams. But what is it about spray nozzles that make them an attractive cooling solution? It comes down to momentum, surface area and vaporisation.

Importance of vaporisation

Vaporising liquids takes a lot of energy. For water, it takes about five times more energy to vaporise water (transition from liquid to gas) than it would take to heat it from just-melted ice (at 0 °C) to just-about-to-boil liquid (at 100 °C). Of course, even if a liquid does not vaporise it can still cool a surface. Spraying lubricating oil on a stamping press is going to cool it. But we can cool things far more effectively if we allow the liquid to vaporise. So why do spray nozzles help with vaporisation? By making the spray, we have created a lot more surface area between the liquid and the medium we are trying to cool.

Surface area & heat transfer (cooling) 

Why not just flood surfaces with water to cool them? There is a limit to how much heat transfer (cooling) one can achieve with just a pool of boiling liquid. As water boils (vaporises) it expands into a gas. If there is enough of this expansion at the hot surface, we reach a point where the liquid never touches the surface directly. We now have a layer of gas insulating the hot surface. Spray droplets fly through the air with some momentum. Even if there is a gas layer insulating the surface, momentum can carry droplets through.

Cooling hot gas flow

Of course, spray nozzles are not only used to cool surfaces. They can be used to cool gas flows as well. In many industrial applications such as power plant exhausts, a hot gas flow must be cooled before it can enter other equipment or is released into the atmosphere. Spray nozzles are a great choice for these sorts of applications. Because sprays have their own velocity, you can have just a few at strategic locations that still fill the duct with droplets – cooling all the gas. Strategic positioning of sprays in gas flows is key to preventing liquid droplets from hitting hot equipment causing fast evaporation. Droplet surface area in a gas flow is key to effective gas cooling.  

Finally, one does not have to go above the boiling point of water to benefit from spray cooling. Outdoor misters rely on vaporisation to cool desert air while staying well below boiling. This principle is used to increase the power output of power generation gas turbines. Cooler air is denser. Therefore, there is more oxygen that can enter the inlet and hence more fuel can be burned.  

Spray cooling technology 

Cooling plays a critical role in a wide range of applications across many industries. Spray technology is used and many of our spray nozzles provide the necessary spray cooling.  

• WhirlJet hollow cone spray nozzles – evaporative cooling in spray ponds and cooling towers, gas scrubbing, washing and cooling, water aerating and water cooling.
• VeeJet flat spray nozzles – cooling and quenching, fire suppression/prevention, gas washing, washing/rinsing and water cooling. 
• FullJet Full Cone and CasterJet spray nozzles – heat transfer cooling in steel mill operations. 
• FloMax Air Atomising and HP FogJet spray nozzles – gas cooling and conditioning operations. 
• Lances and Precision Spray Injectors – gas cooling.

Cooling applications – sustainable solutions

Solid objects are typically cooled using spray nozzles and headers, especially in food processing and metalworking. Examples include cooling jam and jelly jars after steam sterilisation, cooling and curing concrete blocks, and poultry grow-out house cooling. Here are some examples of products that require cooling to optimise coverage and minimise waste. 

• Case study 1 solution: Cast iron pipe manufacturer eliminates rework and saves $40 000 pm with new spray system
• Product feature: HHX FullJet full cone nozzles provide consistent spray distribution to ensure uniform cooling and high heat transfer in the steel industry. They are ideal for secondary cooling operations such as billets, blooms, rounds and slabs.
• Case study 2 solution: New spray nozzles save 2.7million gallons of water for beef processor.
• Product feature: Quick FloodJet flat spray nozzles form a flat spray pattern that is evenly distributed from the centre of the spray. The deflector surface enables wider spray angles compared to other flat spray nozzles.

Gas cooling

Gas cooling can be complicated and challenging owing to high temperatures and extreme environments. It is highly imperative to determine the exact drop size required to achieve the desired cooling effect without wetting. The process stream and operating conditions have a big impact on spray performance, so computational fluid dynamics (CFD) is often used to identify the best spray nozzle type, drop size, placement in the gas stream and spray direction. 

Gas cooling is widely used in refineries, power plants and chemical processing. Typical applications include in-duct cooling, pollution abatement, emergency quench and more.  

There are many other spray cooling applications we test and give solutions to our customers who run into challenges:

• Cooling steel in continuous casters 
• Quenching metals after heat treating 
• Roll cooling in steel mills 
• Cooling food jars after processing 
• Zoned cooling of roofing materials 
• Evaporative cooling for livestock and poultry 
• Cooling extruded PVC pipe 
• Spray ponds to cool water from heat exchanger

If you would like to learn more about our spray nozzles for cooling applications or want to discuss a specific application please contact us for your no-charge plant audits.

grant@monitorspray.co.za

www.spray-nozzles.co.za