Spray nozzles for cooling systems

Engineering consideration 2 - Moving or static target?

Whether the object being cooled is moving or static will impact on the type of spray cooling system being deployed.

Moving target

If a conveyor of product requires cooling then a continual spray across a portion of the moving line can be deployed.  The heat removed will be in equilibrium with the heat brought in by the new hot target rolling into the cooling line.  For such dynamic cooling systems continuous steady spraying is required from the nozzle.  Variations in flow rate or spray consistency could result in poor cooling. 

Static target

If, however, the target is static there will be a timed period of spray required to achieve cooling.  As such, the cooling system will not be continuous - it will be start/stop or in some cases may require more sophisticated variations in spray properties over time.  This might mean that cooling is performed in several stages with different spray types, and hence nozzles, for each.  For example, when cooling very hot metals initial cooling needs to overcome the Leidenfrost effect*.  This means that initially a spray with some impact is required for optimum cooling but as the metal cools and the Leidenfrost effect lessens, optimum cooling will be produced by a spray with finer droplets and less impact.

*  A phenomenon in which a liquid, close to a solid surface that is hotter than the liquid's boiling point, produces an insulating vapour layer that stops the liquid from boiling rapidly.