Abstract
The immersion liquid sampling method is widely used to determine spray droplet sizes for its simple principle and easy sampling technique, but the method has some problems unsettled which we should be cautious of when we adopt it. The coalescence of droplets in the immersion liquid is one of them and is liable to cause an unexpected increase of measured diameter.
By considering a simplified model for sampling of droplets, theoretical formulas for possibility of the coalescence and for increase rate of mean diameter due to the coalescence have been derived. The calculated values were compared with measured ones under various spraying and sampling conditions. While quantitative agreement between them was not acheaved, it was confirmed the calculated values agree quite well with measured ones qualitatively and the formulas are applicable to analyse the effects of various factors on the coalescence and on the increase of mean diameter.
The following items have been revealed by this theory and the related experiments.
1. The increasing number of droplet, the higher viscosity of immersion liquid, the larger nozzle hole and the smaller droplet diameter have tendency to increase the mean diameter due to the droplet coalescence.
2. It should be avoided to bring the sampling position too close to the noz-zle.
3. Discharge velocity of the jet does not affect on the droplet coalescence and on the increase of mean diameter remarkably.
