Exploring laser-induced cavitation for primary nucleation control

Abstract

Crystallization is one of the most sought after separation and purification technique in the process industries. However, the fundamental understanding on the formation of crystals poses quite a challenge due to the inherent complexity and stochasticity associated with the process. In the past, several attempts put forth to control crystal nucleation have been anything but successful. But, more recently, the use of lasers to control primary nucleation have led to promising prospects.

In the current study, efforts were made to explore the phenomena behind Non-Photochemical Laser Induced Nucleation (NPLIN). Experiments were carried out starting with a confined microfluidic system for both supersaturated aqueous potassium permanganate and potassium chloride solutions and later extended to unconfined geometry with potassium chloride solutions. A single nanosecond laser pulse of 532 nm wavelength was employed to create vapour bubbles and the resulting crystal formation was quantified.

To begin with, a quadratic relationship between the laser energy supplied and the maximum radius of the bubble formed was observed. By systematically varying both the supplied laser energy and the solution supersaturation, the probability of crystal formation for various energy–supersaturation combinations were studied. A minimum laser energy threshold for crystal formation was observed to be a function of solution supersaturation. The results obtained in this study will aid in developing a numerical model that can apriori predict the minimum necessary laser and supersaturation conditions required for any given salt to undergo NPLIN.