Characterization of spatial particle distributions in a spray-forming process using digital holography

Abstract

An application of digital inline holography to a metal spray-forming process is presented. In contrast to conventional 2D techniques such as particle image velocimetry (PIV) it is possible to capture the 3D particle distribution at once. From the reconstructed hologram the size of the particles can also be extracted. A plane wave passes the particle stream and the diffracted wave is recorded by a CCD sensor using a lens to image the sample volume closer to the sensor. The reconstruction of the particle distribution is performed numerically in the computer and provides direct access to the intensity and the phase of the recorded wavefront. A brief introduction to digital holography will be given and the process of spray forming will be described. An intensity-based algorithm is applied to detect the particles. Recent measurements of the spray-forming process are presented and the suitability of this technique for industrial applications is demonstrated.

Optical Particle Characterization in Flows

“…Particle sizing using holography is not new (Thomson 1974, Jones et al 1978, Shimizu et al 1982, but the technique became significantly more attractive with the advent of digital holography (Schnars & Jüptner 2002, Kühn et al 2008 and digital in-line holography (Müller et al 2004, Garcia-Sucerquia et al 2006, Sheng et al 2006, the latter simplifying the optical arrangement greatly. For in-line holography, an expanded laser beam is passed through the measurement volume (e.g., a spray).…”

Advanced particle-based velocimetry techniques for microscale flows

“…The FFT of diffraction kernel function can be analytically obtained by adopting the Fresnel approximation (Schnars and Jüptner 1994) or the angular spectrum analysis (Goodman 1996). Finally, the 3D position information of the whole tracer particles located inside the measurement volume can be extracted from the reconstructed flow field (Müller et al 2004;Sheng et al 2006;Garcia-Sucerquia et al 2006;Sheng et al 2008).…”

Snapshot 3D reconstruction of liquid surfaces

“…This is a challenging task where only a few examples of succesful techniques can be found in the literature. For example, various optical techniques have been used for 3D reconstruction of the position of large and isolated drops including tomographic shadowgraphy [14], in-line holography [15][16][17] and plenoptic imaging [16]. Plenoptic imaging has also been used to produce snapshot 3D reconstructions of sprays where bulk features such as spray angle could be estimated [18].…”