Droplets and Sprays by Saptarshi Basu Avinash Kumar Agarwal Achintya Mukhopadhyay & Chetankumar Patel

Author:Saptarshi Basu, Avinash Kumar Agarwal, Achintya Mukhopadhyay & Chetankumar Patel
Language: eng
Format: epub
Publisher: Springer Singapore, Singapore

The resultant droplet size is usually scaled with length scale of the capillary waves (Eq. 9, Lang 1962)

(8)

where is surface tension; F is excited sound frequency in Hz. Studies have reported the promising nature of ultrasonic atomizer in achieving droplets size in the range of ≤10 µm. For instance, nebulizers adopted this technique to generate ultrafine droplets. However, like electrostatic technique, this atomizer suffers from the limitation of low flow rate.

8.5 Hybrid Atomizers

The comprehensive discussion presented in the previous section clearly shows, besides advantages, the limitation associated with each atomization technique limiting their practical usage in high-speed combustors.

Conventionally used atomizers in combustion systems like airblast and pressure jet offer high momentum, but for the several reasons, the minimum droplet size is limited to ~40–50 µm (Lefebvre 1980, 1990). To meet the size requirements, studies have been carried out to promote atomization in these atomizers by supplementing with other additional techniques. For instance, flash boiling is realized in pressure atomizers by preheating the fuel above its boiling point, before it leaves the orifice. Likewise, airblast atomizer is mated with electrostatic/ultrasonic techniques to reduce the droplet size. Among these, flash-boiling and effervescent atomizer show potential in combustion applications.

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