Investigation method of pressure fluctuation

The most important characteristics involved in pressure fluctuation are the frequency and the amplitude and must therefore be the major focus of investigation into pressure fluctuation. In addition, it is necessary to understand the distributions of the frequency and the amplitude of fluctuation over the space inside the reactor and the influences of some factors on them. 

The amplitude mentioned above indicates the extent of the pressure fluctuation actually it characterizes the intensity of the fluctuation. For convenience, the term fluctuation intensity is also used in this chapter as it means the same as amplitude . 

In principle, pressure fluctuation signals can be determined directly by suitable probes. However, the device used for the measurement must meet two essential requirements (1) the frequency response of the instrumentation, including the probes and recorder etc., must match the range of signals to be measured, and (2) the influence of the probes on the flow field in the space to be detected must be minimized as possible. Otherwise, reality or even a near reality cannot be achieved. 

Two methods were employed for the substantial studies mentioned above, as described below. 

The instantaneous pressure at a certain point in the reactor can be considered as the sum of the average pressure and the pulsant one. To describe the intensity of fluctuation, the standard deviation of the instantaneous pressure, PsD, is used as the index. Higher PSD suggests stronger pulsant. It is calculated by 

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