Doppler burst

Figure 6.3. Schematic of interference fringe region, measurement volume, Doppler burst signals, and effects of particle size on signal modulation.

In order to demonstrate the performance of the Doppler-burst envelope integral value method for the estimation of the instantaneous particle velocity vector and the particle mass flux or concentration, measurements were performed in a liquid spray issuing from a hollow cone pressure atomizer (cone angle 60°) and a swirling flow which exhibits complex particle trajectories (Sommerfeld and Qiu 1993). All the measurements were conducted using the one-component phase-Doppler anemometer. The integration of the mass flux profiles provided the dispersed phase mass flow rate which agreed to 10 % with independent measurements of the mass flow rate (Sommerfeld and Qiu 1995). 

Figure 8.2. Yanta s equipment for size measurements using Doppler shifts, a) Arrangement of Yanta s equipment, b) Fringes created in the interrogation zone by interference of the two laser beams, c) Typical Doppler burst formed by a fineparticle passing through the interrogation...

However, there are difficulties for this use of the overall size of the Doppler burst. Note that the part of the signal which is modified by the oscillation is referred to as the pedestal of the Doppler burst [4]. 

Figure 8.3. The Doppler burst produced by a fineparticle passing through the interrogation zone depends on both the size of the fineparticle with respect to the fringes, and the position with respect to the zone, a) Interrogation zone of a laser Doppler system, b) Bursts produced (i) by a fineparticle on centre (ii) by a fineparticle larger than the spacing of the fringes (iii) by a fineparticle passing the zone off-centre.

Figure 4-43 Typical single- and multiple-particle Doppler bursts.

Use dead-time mode. The dead time is a specified period of time after each detected Doppler burst, during which further bmsts will be ignored. Setting the dead time equal to two times the integral time scale will ensure statistically independent samples, while the integral time scale itself can be estimated from a previous series of velocity samples, recorded with the dead-time feature switched off. 

Mathematically, the phase of a Doppler burst received at detector i can be expressed as... 

Handling the 2n Ambiguity. Figure 4-52 shows the phase difference for three different particles of increasing size. While the phase difference for the first two particles is within 2n = 360°), the third particle falls beyond this range. Thus, from measuring the phase difference between the Doppler bursts... 

The receiving aperture of the PDPA is partitioned into three areas. Figure 2. The light from each of these areas is collected and delivered to three separate photodetectors located within the receiver behind a single aperture. Each photodetector outputs a Doppler burst similar to the output of an LDV system. However, the phase differences, r i2 and t]i3 of the detector outputs may be utilized to determine the size of a particle moving thorough the measurement volume. 

The time difference, measurable as a phase difference between the Doppler bursts at the first and the second photodetector, is simply related to the... 

The frequency information and phase difference of the bandpass-filtered Doppler-bursts were obtained by using a FFT-processor ... 

Pig. 13.5 Determination of particle size in Phase Doppler Anemometry (PDA). The phase difference between two Doppler bursts is computed from A4> = 2 K(AtlT). The figure is drawn based on a sinular sketch from Manasse et al. [126]... 

The phase difference (shift) between a pair of Doppler burst signals in the PDA optical arrangement (°)... 

Pressure drop through the solids flow control devices (Pa) Differential energy transfer to the thermodynamic system (kJ). The 6 symbol is used to indicate that the integration of 6Q which is not a state function is dependent on the path Time difference between Doppler bursts in PDA (s)... 

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