Particle Concentration and Mass Flux Measurements by PDA

This implies that for accurate particle concentration measurements one has to 

The validation rate is the number of validated samples normalized by the total number of analyzed samples. The validation criteria are mainly applied to insure that the signal information, such as signal frequency and phase, received from two or more channels or two pairs of channels are within certain limits in order to ensure that the signals come from the same particle or that the particle is spherical. Especially in complex flows, e.g. for high particle concentration, the 

The particle trajectory angle can be determined from the different instantaneous particle velocity components with  

The particle size-dependent radius of the measurement volume r(Di) may be determined in-situ by using the burst length method (Saffman 1987 b)) or the so-called logarithmic mean amplitude method (Qiu and Sommerfeld 1992). The latter is more reliable for noisy signals, i.e. low signal to noise ratio as demonstrated by Qiu and Sommerfeld (1992). 

The above discussion reveals that in complex two-phase flows with random particle trajectories through the measurement volume, a three-component PDA-system is required for accurate concentration measurements. For a spectrum of particle sizes the local particle number concentration is then evaluated from  

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