Two‐Phase Flow Characterization by Automated Digital Image Analysis. Part 2: Application of PDIA for Sizing Sprays

Abstract

A series of experiments were conducted in order to assess the robustness and accuracy of a recently developed digital image analysis technique (PDIA). This paper investigates the application of the PDIA technique to the sizing of relatively small fuel droplets of diameters in the range 5 to 30 μm produced by a pressure‐swirl atomizer. The measurement performance of the PDIA system has been assessed in terms of individual object diameters and also number and volume probability density functions of diameter in comparison to phase Doppler anemometry (PDA) data obtained under identical conditions. PDIA measurements revealed good agreement with spray data obtained by PDA at a measurement location 36 diameters downstream from the nozzle orifice with differences in the arithmetic mean diameter, D10 and volume mean diameter, D30 of approximately 5 and 3% respectively. The PDIA technique was shown to detect the presence of very large, predominantly non‐spherical droplets whose diameters were in excess of 100 μm. These droplets, although few in number constitute a significant proportion of the total spray volume and would have otherwise been either erroneously measured or have passed through the probe volume undetected using PDA due to non‐sphericity. Smaller objects may also be measured correctly by both methods although sensitivity to signal‐to‐noise ratio, for both methods can generate spurious and contradictory errors.

Two‐Phase Flow Characterization by Automated Digital Image Analysis. Part 1: Fundamental Principles and Calibration of the Technique

“…Figure 3 shows a schematic diagram depicting the experimental set-up used for the calibration. The optical set-up used here remained unchanged for subsequent spray measurements which are described in the second paper [19]. Illumination was provided by an infra-red diode laser (Oxford Lasers model HSI 5000, l 808 nm) operating in single shot mode.…”

“…Although the second paper [19] is devoted to a more detailed discussion of the PDIA technique in its application to real spray measurements, initial spray results presented here provided useful test cases which helped in determining the practical limits of the PDIA technique which was necessary in order to evaluate measurement robustness and accuracy. For the optical set-up used in the present investigation, the resolving power of the objective lens and the CCD sensor characteristics limited the PDIA technique to sizing droplets or particles of diameters no smaller than 8 mm corresponding to 11 pixels.…”

Classification of two-phase flow regimes via image analysis and a neuro-wavelet approach

“…Ulbrich et al (2002) used a water-air two-component flow with visible light, and this is one of the alternatives that will also be investigated in this paper. Kashdan et al (2004b) investigated particle beam in air. Images of a flow can be produced in transparent pipes easily with visible light, but in metal pipes, needed for real two-phase flow, neither X-rays or gamma-rays are applicable.…”

Evaluation of StereoPIV Measurement of Droplet Velocity in an Effervescent Spray

“…Shadowgraph droplet analyzer is an image-based droplet analyzer which images two-dimensional projections of a droplet shadow [25,29,30]. A droplet equivalent area diameter [22] is calculated as a measure of droplet size from the area of the droplet shadow.…”