When spraying into a hot gas flow over the limit of the coolant the greater part of the cooling is brought about by taking warmth from the gas to dissipate the liquid. The pace of vanishing will rely upon the normal droplet size of the spray. Sprays comprising of smaller drops will vanish undeniably more quickly that sprays containing bigger drops. In quick gas flows this can be vital as frequently cooling should be accomplished before the gas arrives at another point simultaneously. Right nozzle choice would thus be able to decrease the requirement for longer extinguish chambers.
In spray cooling applications for gas streams, it's not just about droplet size. Although sprays with smaller drops absorb heat faster, they are also more easily entrained within the gas flow. This means that if the spray is too fine, it may only cool a channel inside the gas flow instead of the entire gas volume. Therefore, there is often a balancing act between getting small enough droplets to achieve fast heat transfer and having enough larger drops to deliver the spray into the gas stream and disperse it evenly.
In many industrial applications, the amount of gas that needs to be cooled can vary depending on operating conditions. For example, pre-cooling of hot gases in a pipe before they enter a scrubber can vary significantly depending on what is happening further up the process line to produce the gases. Variable cooling loads present challenges for spray cooling because reducing the amount of coolant spray will typically mean reducing liquid pressure, which will increase the droplet size and therefore increase evaporation time. This means that in lower gas flow situations, cooling may not be achieved in time or may require a larger cooling chamber.
However, there are several ways in which proper nozzle selection can help overcome variable gas flow cooling issues. The use of spillback nozzle systems can help maintain a relatively constant droplet size even if the pressure and flow rate are reduced. Alternatively, air atomizing systems with variable air and liquid pressures can be used to maintain smaller droplets at reduced flows. Finally, deploying multi-nozzle arrays can provide stable droplet sizes for variable flows.
It's important to note that spray nozzle selection for gas cooling should be based on the specific application and operating conditions. Different types of nozzles have their own advantages and disadvantages.
For example, twisting TF nozzles are effective in producing a mix of small and larger drops to penetrate rapidly moving gases, while spillback spears are better suited for variable gas flows where drop size needs to be kept relatively constant. Spiral Air (SA) nozzles, on the other hand, are ideal for hot gas flows that require finely atomized sprays for quick extinguishing.
Ultimately, the best nozzle for a particular application will depend on factors such as the type of gas being cooled, the flow rate, and the desired cooling efficiency.
