Spatially and Temporally Resolved Distributions of Liquid in an Effervescent Spray

Abstract

We employed Planar Laser-Induced Fluorescence (LIF) in combination with stereoscopic Particle Image Velocimetry for imaging of concentration and flux fields of liquid phase in an effervescent spray. Light heating oil (LHO) was continuously atomized with aid of pressurised air. The atomizer was operated at atomizing pressures of 0.1 – 0.5 MPa and Gas–to–Liquid–Ratio by mass (GLR) of 2 – 50%. Basic spectral and time-resolved LIF characteristics of natural fluorescence of LHO, used for LIF based concentration measurements, are detailed. Instant distributions of concentration and flux were processed into time-average radial profiles and into radial profiles of normalised root–mean–square (rms) fluctuations. Time-average concentration profiles are bell shaped with maximum concentration at the spray centreline and exponential decrease with radial distance. Liquid concentration based half-angles vary with operation conditions between 7.9 and 12.2 deg. GLR causes narrowing of the spray angle while inlet pressure has an indistinctive effect. Time-average flux profiles resemble the concentration profiles but are narrower, with half-angles of 4.6 – 6.4 deg. Radial profiles of rms fluctuations of concentration (and also flux) generally show low value near the spray axis, increase with increasing radial distance and maximum close to the spray edge. Overall values of the rms fluctuations are used as a measure of spray unsteadiness and correlated with internal two-phase flow patterns predicted by a published flow map. The spray unsteadiness is relatively low when operated in annular flow regime and increases with change to bubbly flow regime. It confirms a direct link between the spray and internal flow.

Použili jsme Planar Laser-Induced Fluorescence (LIF) v kombinaci s stereoscopic Particle Image Velocimetry (PIV) pro studium prostorově a časově rozlišeného rozložení kapaliny a plynu v "effervescent" spreji. V článku je popsána struktura spreje, hmotnostní toky a koncentrace kapaliny v effervescent spreji pro různá nastavení tlaku a GLR. Dále jsou posuzovány nestability spreje.