from Part III - Spray Formation and Impact onto Surfaces
Published online by Cambridge University Press: 13 July 2017
The process of atomization involves the generation of drops from bulk fluid, achieved using a wide variety of atomization concepts, depending on the desired local drop number, size and velocity flux densities, as well as on the bulk fluid and its properties, e.g. pure liquids, dispersions, suspensions, emulsions, etc. In the context of collision phenomena, atomization plays a key role in applications such as spray cooling, touchless cleaning and spray coating, whereby the latter can be understood in a very broad sense, encompassing applications such as spray painting, crop spraying, spray based encapsulation, domestic sprays (e.g. hair sprays, polishes) or even inhalators. Indeed, a majority of liquid collision phenomena involve atomization for the generation of individual drops and this fact motivates the present examination of the atomization process in more detail, with the aim of establishing an understanding between the atomization conditions and the resulting properties of the spray.
This chapter divides the atomization process into primary atomization (Section 8.1), i.e. overcoming the consolidating influence of surface tension by the action of internal and external forces (Lefebvre 1989), secondary atomization, and binary drop collisions in a spray, whereby several special modes of secondary atomization are treated in the final four sections. The causes of secondary atomization are manifold and can significantly alter the size distribution in a spray and are therefore important to consider. Typical causes of secondary atomization include aerodynamic forces whenever a drop is exposed to a relative air flow; covered in Section 8.2. Binary drop collisions can also lead to secondary atomization, as they occur in dense sprays, interacting sprays or when spray drops impinging onto a surface interact with drops ejected from the surface. Binary drop collisions are discussed in Section 8.3. Another cause of secondary atomization is when a drop impinges onto or is forced off a filament, for instance in a filter. This atomization scenario is the topic of Section 8.4. Finally, secondary atomization can also be electrically driven. In this case, evaporation in flight of electrified drops issued from electrostatic atomizers diminishes the drop surface area, while the electric charges they carry remain the same. As a result, the shrinking drop size can reach the so-called Rayleigh limit.
To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.