Phase Doppler Anemometer

Figure 6.4. Schematic of optical arrangement in a phase-Doppler anemometer.

A two-color pyrometer has been used along with the phase-Doppler anemometer to simultaneously measure the local velocity and size of kerosene droplets and the temperature of burning soot mantle in a swirl burner.[648] The measurements were conducted within the flame brush that develops in the shear layer of a swirl-stabilized, gas-supported kerosene flame with a swirl number of about 0.19 and potential heat releases of 10.6 and 15.5 kW, respectively. The results showed that the maximum burning fraction of the droplets occurs adjacent to the region denoted as gas flame but the value ranges from 20 5 to 40 5% depending on the axial station, and decreases sharply across the shear layer. The flame mantle temperature was found to be independent of droplet diameter, which agrees with previous results in the literature. 

Oropharyngeal spray impaction depends on the droplet velocity and size. Both these parameters can be measured simultaneously and recorded for each droplet. With Phase Doppler Anemometer (PDA) instruments, useful results have been obtained on MDI sprays. 

Moreover, the use of extended optical systems combined with additional validation criteria, such as the dual-mode phase-Doppler anemometer (Tropea et al. 1995) may effectively reduce errors resulting from the trajectory ambiguity An overview about extended PDA-systems will be given in section 7.3.4. 

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). 

Dullenkopf, K., Willmann, M., Schone, F.,. Stieglmeier, M., Tropea, C. and Mundo, Chr. Comparative mass flux measurements in sprays using pattemator and phase-Doppler anemometers. 8th Int. Symp. on Appl. of Laser Techniques to Fluid Mechanics, Lisbon, 8.-11.7. (1996)... 

Maeda, T., Morikita, H., Hishida, K. and Maeda, M. Determination of effective measuring area in a conventional phase-Doppler anemometer. Proceedings of the Eigth International Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon, Portugal, Vol. 1, Paper 2.5 (1996 b))... 

Mignon, H., Grehan, G., Gouesbet, G., Xu, T.-H. and Tropea, C. Measurement of cylindrical particles using phase-Doppler anemometer. Applied Optics,, (1996)... 

One of the reasons the electrospray is such a useful tool is that it produces relatively small and evenly distributed droplets. Using a Phase Doppler Anemometer (PDA) system, Keqi Tang has been able to characterize the droplets of an electrospray produced from Heptane and Methanol [11]. The results of these experiments show that the spray droplets are highly mono-dispersed as they travel from the emitter tip to the ground electrode as shown in Fig. 32.11. 

Much research has, in fact, been carried out to achieve this imderstandmg [37-39]. The spray structure has been investigated using visualization techniques such as laser sheet photography [40] and laser-induced fluorescence (LIF) [36], but detailed information of droplet characteristics cannot be obtained by planar measurements. Point measurements such as phase Doppler anemometer (PDA) can provide very high temporal resolution of droplet diameter and velocity, but lacks the ability to provide information about the spatial structure of the spray. Due to incomplete information about the spray, it is still difficult to optimize the pressure swirl injector. Computational studies of spray structure have revealed details of the... 

In Figure 1 a typical phase-Doppler-anemometer (PDA) is sketched. Based on a Laser-Doppler-anemometer and supplemented by a second photo-detector, the two detectors are usually arranged symmetrically to the interference planes with equal elevation angles 0. 

Naqwi A, Ziema M (1992) Extended phase Doppler anemometer for sizing particles smaller than 10 (tm. J Aerosol Sci 23 613-621... 

The flow patterns for single phase, Newtonian and non-Newtonian liquids in tanks agitated by various types of impeller have been repotted in the literature.1 3 27 38 39) The experimental techniques which have been employed include the introduction of tracer liquids, neutrally buoyant particles or hydrogen bubbles, and measurement of local velocities by means of Pitot tubes, laser-doppler anemometers, and so on. The salient features of the flow patterns encountered with propellers and disc turbines are shown in Figures 7.9 and 7.10. 

---