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The performance of two digital holographic techniques (digital in-line holography and Digital Image Plane Holography) is compared in the study of the droplets generated by a micro-dispensing device. This device provides droplets whose diameter can be changed by varying the pressure applied to the reservoir containing the substance to be atomized.Digital in-line holograms of the droplets were recorded at four different pressures (10, 15, 20 and 25 psi). The obtained size distribution is quite similar for the four pressures. Although is true that the mean droplet diameter increases with the pressure, also increases the dispersion in the measured values. While for P= 10 and 15 psi the droplet sizes are quite uniform (mean diameter = 159,63 ± 17.1 µm and 163.24±21.8 µm respectively) for the higher pressures the dispersion is three times bigger. The mean diameter measured for 20 psi is 174.2 ± 56.03 µm and for 25 psi is 155,42 ± 34.4 µm.The droplets generated at pressures of 10 and 20 psi were also analyzed with Digital Image Plane Holography. As expected, we found basically the same results as when in-line holography was applied. The mean diameter increases as the pressures increases and so does the dispersion. In this case the average droplet size is 176.78 ± 21.9 µm and 184.71±40.56 µm for 10 and 20 psi respectively.The results obtained with both techniques agree reasonably well. Digital in-line holography can be a very good option for particle characterization in systems with low particle density and relatively big sizes. The great attractiveness of the in-line holographic set-up is that it requires minimum optical equipment and laser coherence length. On the other hand Digital Image Plane Holography need a slightly complicated optical setup but it can be easily adapted for any droplet size by choosing the appropriated magnification on each case. Also, it can be used when the particle density is high, as individual particles in the illuminated plane can be easily isolated.

The gun-type burner is an oil burner frequently used for industrial and domestic applications. The oil droplets are mixed with air and the flow generated is extremely complex and requires the combination of different techniques for its complete description. Here, for the first time, the full three-dimensional velocity vector map has been measured for different droplet sizes in non-reacting conditions using stereoscopic PIV together with a technique called multi-intensity layer, that allows size discrimination by accounting for differences in the scattered light intensity. Different spatial structures are detected depending on the droplet size: droplets under 30 µm in diameter follow the incoming airflow and entrain the recirculation zones while droplets bigger than 50 µm penetrate due to their large momentum. Differences are also found for the swirl component near the baffle plate, measuring stronger swirl for droplets smaller than 30 µm.

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