Iterative inversion of phase-Doppler-anemometry size distributions from sprays of optically inhomogeneous liquids

Köser, Ole; Wriedt, Thomas

doi:10.1364/ao.35.002537

Cited by 11 publications

(4 citation statements)

References 6 publications

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“…Therefore, special algorithms have to be applied to compute the unknown diameter distribution q(d). The transfer function has to be known; it can be found by measuring a larger number of monodispersed droplets [11].…”

Section: Mathematical Inversion Algorithmmentioning

confidence: 99%

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Standard PDA for measuring the size of inhomogeneous droplets

Mitschke¹,

Wriedt²,

Bauckhage³

1998

Meas. Sci. Technol.

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A method to obtain the diameter of inhomogeneous droplets by using phase-Doppler anemometry (PDA) is described. Inhomogeneities included in a fluid droplet disturb light scattered by the droplet. Consequently the phase difference measured between two Doppler bursts deviates from the value calculated by geometrical optics theory for a droplet of diameter d . Because evaluation of the measured phase differences is based on a linear relationship between phase difference and particle diameter the accuracy of PDA is deteriorated. The difference between the real and the measured diameters of such droplets can be characterized by convolution with a Gaussian probability function. For monodisperse droplets and for a given type of inhomogeneity the standard deviation of the Gaussian function increases linearly with increasing mass concentration of these inhomogeneity. Applying infrared laser-PDA (IR-PDA) with a wavelength of 1312 nm, the measuring range to investigate droplets of, for instance, water-latex suspensions containing 450 nm polystyrene spheres can be extended to suspensions with six times the measurable concentration standard PDA using a He-Ne laser at λ = 632.8 nm. The relative improvement obtained by applying IR-PDA (in comparison with a standard PDA system equipped with a 632.8 nm laser) can be estimated by the decrease of the extinction efficiency Q ext of the inclusions with laser wavelength. The linear relation between extinction E and standard deviation σ can be used by a blind deconvolution algorithm. Starting from the measured diameter distribution of the inhomogeneous droplets the real diameter distribution and the standard deviation of each size class of the particles can be calculated by the algorithm. From this standard deviation it is possible to determine the extinction E and the mass concentration of the inhomogeneities.

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Section: Mathematical Inversion Algorithmmentioning

confidence: 99%

“…Thus, with the found 'real distribution', simulations were performed to optimize the number of iteration steps. Details about this optimization process can be found in [11]. For our application this optimization was further improved by distributing the random numbers according to the supposed diameter distribution.…”

Section: Mathematical Inversion Algorithmmentioning

confidence: 99%

Standard PDA for measuring the size of inhomogeneous droplets

Mitschke¹,

Wriedt²,

Bauckhage³

1998

Meas. Sci. Technol.

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“…Domnick et al (1994) measured a paint spray with metal flakes in the droplets and found that PDA retains reasonably good linearity between the measured phase and the diameter even with flakes in droplets, although this is apparently not consistent with the experimental results of Wriedt et al (1993). The work done by Wriedt et al has been complemented by introducing a scheme for correction of the size distribution, based on deconvolution (Wriedt et al 1993, Köser andWriedt 1996) which worked well with certain presumed size distribution functions. In addition, Schneider and Hirleman (1994) investigated PDA sizing for particles with symmetrical refractive index gradients within the spherical particles and Onofri et al (1996) have also evaluated the response of PDA to multi-layered droplets.…”

Section: Introductionmentioning

confidence: 98%

Application of shadow Doppler velocimetry to paint spray: potential and limitations in sizing optically inhomogeneous droplets

Morikita

Taylor

1998

Meas. Sci. Technol.

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This paper reports size measurement of droplets with optically inhomogeneous media by shadow Doppler velocimetry (SDV), which can provide spatially and temporally precise in situ readings of the size and velocity of a single particle with irregular shape and with arbitrary optical properties of the particle medium. In this work, water, instant coffee solution and water-based paint with various solid contents were measured to evaluate the capability and limitations of the measurement. The experiment with instant coffee solutions of 2 and 5% (wt:wt), which contained 10 µm discrete particles, atomized by a standard paint spray gun, demonstrated that the accuracy of sizing was not affected by the optical properties of the medium. Insensitivity to the optical properties is one of the primary advantages of SDV over the other optical, single-particle sizing methods. As a further demonstration, paint samples atomized by the same gun containing solid flakes of nominal diameter 25 µm were also measured. The results revealed a spatially uniform arithmetic mean diameter of 30 µm and suggested that the atomization characteristics were influenced in the highest flake volume fraction case (red paint containing mica, 1.5%) with the result that the mean diameter was 20% larger than that of a similar paint with a smaller flake volume fraction (green paint containing aluminium, 0.4%). It was also found that the measurable number density is limited to no more than 1000 droplets cm −3 in the case of droplets with an average size of 20 µm.

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“…Dual-mode PDA permits measurements under such severe conditions, but at the possible expense of a reduced acceptance rate. Another approach is based on a mathematical correction of measured polydisperse size distributions by a deconvolution technique [4]. This method was later verified experimentally [5] by investigating suspension droplets.…”

Section: Introductionmentioning

confidence: 99%

Working Principle and Experimental Results for a Differential Phase-Doppler Technique

Wriedt

Bauckhage

1998

Part. Part. Syst. Charact.

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By replacing the two detectors of a standard phase-Doppler anemometer (PDA) with a charge coupled device (CCD) line scan sensor, the scattered light can be measured not only with high temporal but also with improved spatial resolution. Thereby, the quantity to be measured by PDA, the phase difference D, can be determined as function of the elevation angle . This allows a statistical evaluation of the received signal and permits precise measurements of the size and velocity even of non-ideal solid particles with inhomogeneous composition, aspherical shape or rough surface. In this paper, the basis of data acquisition and evaluation is described. This is followed by experimental results for glass spheres with intact and defect surfaces and, for comparison, for water droplets. These results demonstrate the potential of this measuring device, described as a differential phase-Doppler anemometer (DPDA).

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Iterative inversion of phase-Doppler-anemometry size distributions from sprays of optically inhomogeneous liquids

Cited by 11 publications

References 6 publications

Standard PDA for measuring the size of inhomogeneous droplets

Standard PDA for measuring the size of inhomogeneous droplets

Application of shadow Doppler velocimetry to paint spray: potential and limitations in sizing optically inhomogeneous droplets

Working Principle and Experimental Results for a Differential Phase-Doppler Technique

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