AHer a sLccessful app cation of tne phase Dopp er tecnnique to homogeneous transparent or opaqLe aspersed media, which are m a n y used for mode experiments. t was the aim to artain witn 1h.s methoo SimLllaneoJs size ana velocity measJrements of real process f d drop ets that are opt cal y aosorbent andlor inhomogeneous, in order to open tne way lo n-ne measurements for process contro Start ng with an oplical y aosoroent homogeneos iq. a (olack nk). phase Doppler measurements were tanen at on-axis angles o where either refracted I gnt or reflecteo light dominates. Vary:ng both the sizes of Ine monoo sperse orop ets and tneir opt.cal absorption showed tne I m'ts of the A@-d relation lor aom nant retract.on ano a transition to oom'nant ref ection at an OH-= s ang e (9 of 30'. On tne bass 01 previous experiments ann the idea of "s ng a largerwave engtn of 830 nm (sem.conductor .aser) nstead of 488 nm (Ar ion aser), ambiguos phase aifference-panicle diameter re ationsnips due to aosorpf'on were avoideo In a secono step the pnase Doppler techn que was applied to monooisperse oroplets of inhomogeneous I.qu:ds. Ls ng the arger wavelength the oroad size dslributions, experimental y ach ewed by employing the Ar ion laser, oecame mucn narrower. It was therefore concluoea tnat me Lse of sem condLctors for the pnase Doppler measurements can be advantageous for dealing witn aosorpt on ano innomogeneities proves to be an indispensable means for selecting the suitable PDA set-Lp parameters. For inhomogeneous iqLid droplets me Mie tneory and M e scatter ng computer programs can oe Lsed to descr oe an0 Jndersland their scattering behavio-r, if-as a preconoit on-:t is val o to ass gn to them an enect've complex refractive ndex. ThLs compJier aided PDh (CAPDA) measuements open the chance for n-ine process measurements 'n rea process liquid spraying.For opt'ca ly absorbent h0mogeneot.s I qLia orop.ers. the M.e theory alone
Real process fluids such as emulsions and suspensions are optically absorbent as well as inhomogeneous. Using phase-Doppler anemometry (PDA) for investigating the spray cone, the inhomogeneities have led to incomprehensible size distributions. In this paper, solutions of instant coffee and condensed milk, representing typical process fluids, were chosen for PDA measurements in comparison with PDA applied to water droplets with the same atomization process in order to clarify the reasons for the measured broad size distributions. By applying PDA to monodisperse droplets and to "monodisperse" and real polydisperse sprays consisting of such fluids, it is shown how the measured size distributions arise. Based on this knowledge, the real size distributions are reconstructed and compared with that of water atomization. Therefore, PDA can in future also be applied to real process fluids, and process control, based on the information provided by PDA, is coming nearer.
Phase‐Doppler experiments applied to optically absorbent (homogeneous and inhomogeneous) liquids are described. Simultaneous size and velocity measurements of single droplets were executed at three off‐axis angles ψ. These angles were found to be suitable for the evaluation of the phase‐Doppler technique by Mie theory. Both the sizes of the monodisperse droplets and their absorption properties were varied. At least with respect to homogeneous liquids, comparison of the droplet diameters obtained by phase‐Doppler measurement and by photography (reference technique) showed good agreement. Concerning the optical properties of inhomogeneous liquids, additional phase‐Doppler measurements were carried out using an alternative device based on a laser diode and photodiodes. The longer wavelength λ (830 nm instead of 488 nm) reduced the influence of the inhomogeneities on the droplets' scattering behaviour and thereby improved significantly the phase‐Doppler results. It is concluded that phase‐Doppler anemometry is suitable for the sizing of optically absorbent droplets of real process fluids. Such droplets result from atomization processes often used in various branches, such as the chemical, pharmaceutical and food industries (production of powders and granules, "spray drying"), automotive engineering (dispersing fuels for combustion) and agriculture (crop spraying). Mie scattering theory is a powerful aid for describing the scattering behaviour of dispersed droplets of real process fluids with more complicated optical properties compared with water, i.e. the behaviour of optically absorbent homogeneous liquids, and for determining the necessary parameters of the optical set‐up.
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