Fog Droplet Vaporization and Fragmentation by a 106-μm Laser Pulse

Abstract

A pulsed CO(2) laser is used to irradiate single fog droplets. The droplets are photographed before, during, and after irradiation by a high speed back-illuminated photomicrograph system. The laser pulse has an energy of about 0.5 J, and the pulse width is about 300 nsec (full width at half-maximum); the power density in the region of the water droplet is about 10 MW/cm(2). In the larger droplets (~20-,microm radius) front surface vaporization is observed; this is accompanied by spallation of the droplet at its back surface. Presumably, a shock wave is produced within the droplet in reaction to the rapid blowoff of the vapor at the front surface, and the spallation is produced when the shock wave is reflected from the back surface of the droplet. Smaller droplets (<12-,microm radius) undergo volume heating rather than front-surface heating. The photographs are taken with a 20-nsec exposure, and the interval between photographs can be varied in steps of 10 nsec, a typical interval being ~1 microsec.

Denaturation of lysozyme and myoglobin in laser spray

“…When the liquid beam had a diameter of Յ20 m, the laser-generated plume became nondirectional, and the droplets formed became much finer. These results are in good agreement with the study of Kafalas and Ferdinand [3].…”

“…The resulting explosive process is known as a vapor explosion [2]. Kafalas and Ferdinand studied vaporization and fragmentation of water (fog) droplets at atmospheric pressure by irradiation with a 10.6 m, CO 2 laser pulse [3]. In the larger droplets (Ͼ ϳ40 m diameter), front surface vaporization, accompanied by spallation of the droplet at its back surface, was observed.…”

Cavitation in water: a review

“…CO 2 lasers have been used to warm up small size droplets [41,42] or the surface of a liquid water bath [43]. It was found that vapor explosion of the droplet occurs only above a threshold in the laser fluence [42,43].…”

Modeling and Simulation of Turbulent Non-Reacting and Reacting Spray Flows

“…Another study of vaporization of laser irradiated droplets was done in [9,10,11]. Experimental studies of vaporization of droplets by irradiation with a pulsed laser can be found in [11,12,14]. In the case considered here, the vaporization of a large droplet by irradiation with a long-time laser pulse of low energy, the vaporization process is governed by the processes of heat conduction and diffusion of the vapor [10].…”

“…The boundary conditions for the liquid phase equations (17)(18)(19)(20) are The source terms, Sy, Sm, and Se, for the mass, momentum, and energy equations, respectively, needed in Eqs. (11)(12)(13)(14) are given in [20].…”