Pressure fluctuation analysis

Motion of fluids in which local velocities and pressures fluctuate irregularly, in a random manner. Predictive maintenance technique that uses principles similar to those of vibration analysis to monitor the noise generated by plant machinery or systems to determine their actual operating condition. Ultrasonics is used to monitor the higher frequencies (i.e., ultrasound) that range between 20,000 Hertz and 100 kiloHertz. 

The qualitative analysis developed in the previous section is now complemented by examining correlations between the sound field and the flame dynamics. This is accomplished by comparing time traces of pressure fluctuation p and light emission I signals recorded during the various experiments. Results are displayed in Figures 5.2.11 and 5.2.12, respectively, for the various... 

Broadhurst, T. W., and Becker, H. A., Measurement and Spectral Analysis of Pressure Fluctuations in Slugging Beds, Fluidization Technology, Hemisphere Publishing Corporation, New York, 1 63 (1976)... 

Detector sensitivity is one of the most important properties of the detector. The problem is to distinguish between the actual component and artifact caused by the pressure fluctuation, bubble, compositional fluctuation, etc. If the peaks are fairly large, one has no problem in distinguishing them however, the smaller the peaks, the more important that the baseline be smooth, free of noise and drift. Baseline noise is the short time variation of the baseline from a straight line. Noise is normally measured "peak-to-peak" i.e., the distance from the top of one such small peak to the bottom of the next. Noise is the factor which limits detector sensitivity. In trace analysis, the operator must be able to distinguish between noise spikes and component peaks. For qualitative purposes, signal/noise ratio is limited by 3. For quantitative purposes, signal/noise ratio should be at least 10. This ensures correct quantification of the trace amounts with less than 2% variance. The baseline should deviate as little as possible from a horizontal line. It is usually measured for a specified time, e.g., 1/2 hour or one hour and called drift. Drift usually associated to the detector heat-up in the first hour after power-on. 

This paper discusses the impact of wind action on natural-draft cooling towers. The structure of the wind load may be divided into a static, a quasistatic, and a resonant part. The effect of surface roughness of the shell and of wind profile on the static load is discussed. The quasistatic load may be described by the variance of the pressure fluctuations and their circumferential and meridional correlations. The high-frequency end of the pressure spectra and of the coherence functions are used for the analysis of the resonant response. It is shown that the resonant response is small even for very high towers, however, it increases linearly with wind velocity. Equivalent static loads may be defined using appropriate gust-response factors. These loads produce an approximation of the behavior of the structure and in general are accurate. 11 refs, cited. 

The periodic response of a linear viscoelastic cooling tower to a prescribed recurring sequence of pressure fluctuations and earth accelerations are analyzed. An approximate analysis, based on the bending theory of shells, is presented. The problem is reduced to a double sequence of boundary-value problems of linear ordinary differential equations. 19 refs, cited. 

QUALITATIVE ANALYSIS FOR THE INFLUENCES OF PRESSURE FLUCTUATION AND MICROMIXING... 

Mass spectral quality is an important consideration in performing a successful GC-MS analysis. The quality of the mass spectra depends on (1) the concentration of the constituents in the sample solution, (2) the GC operating conditions used to resolve the peaks, and (3) excessive pressure fluctuation in the MS unit of the GC-MS system leading to distortion of the mass spectrum, especially an El mass spectrum, as reflected in the relative abundance of the ion peaks. The implication of (3) is that distortions of this type could lead to misinterpretation of the spectrum even though a library search is performed. 

Nowak, W., Matsuda, H., Win, K. K and Hasatani, M. Diagnosis of Multi-Solid Fluidized Beds by Power Spectrum Analysis of Pressure Fluctuations," in Circulating Fluidized Bed Technology IV (Amos A. Avidan, ed.), pp. 163-168. Somerset, Pennsylvania (1993). 

These two modes actually coexist but do not interact. Their respective traces can be found in an analysis of RMS pressure fluctuations because both acoustic and hydrod3mamic fluctuations induce pressure perturbations P profiles along the burner axis, computed both with LES and the Helmholtz solver, are presented in Fig. 9.7. The two codes give similar results in the plenum and in the exhaust, indicating the acoustic nature of the pressure fluctuations in these regions. However, in the swirler and in the first half of the chamber where the PVC is found, the pressure fluctuations given by LES are much larger than the acoustic predictions, because they also contain the effects of the PVC. 

Ellipsometry, a classical technique that is commonly employed in the study of thin films on solid supports, has long been used to investigate Langmuir monolayers. The relative ease with which such measurements can now be carried out, and their high sensitivity and high spatial resolution, has led to renewed interest in the method. Rasing et al. have recently described studies on PDA in which the phase retardation was measured as a function of the surface pressure. Fluctuations in the signal can be correlated with the texture of the monolayer, and estimates of the sizes of the domains and their character can be obtained from quantitative analysis of the data. 

Kook, H., and L. Mongeau. 2002. Analysis of the pressure fluctuations induced by flow over a cavity. J. Sound Vibration 251(5) 823-46. 

Vial, C., Camarasa, E., Poncin, S., Wild, G., Midoux, N., and Bouillard, J. (2000), Study of hydrodynamic behaviour in bubble columns and external loop airlift reactors through analysis of pressure fluctuations, Chemical Engineering Science, 55(15) 2957-2973. 

King, D.L. (1967). Analysis of random pressure fluctuations in stilling basins. Proc. 12 Z4ffl Co gre55 Fort Collins B(25) 210-217. 

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