Noise In Piping Systems Research Articles

Pulsation suppression in a reciprocating compressor piping system using a two-tank element

Gas pulsations excited by reciprocating compressors could introduce severe vibrations and noise in piping systems. When pulsating gas flows through the reducers, the changes in flow characteristics, such as velocity and damping coefficient, will affect the pressure pulsations. To circumvent these constraints, a two-tank element is introduced to control the gas pulsation that is still strong in the piping system with a surge tank. Installing another surge tank to form a two-tank element is more flexible and costs lower than replacing the original surge tank with a larger one. In this work, a theoretical model based on the wave theory was proposed to study the transferring mechanism of gas pulsations in the pipeline with the two-tank element. By considering the damping coefficient and the Mach number, the distributions of the pressure pulsations were predicted by the theoretical model and agreed with the three-dimensional fluid dynamics transient analysis. Three experiments were conducted to prove that the suppression capability of the two-tank element is as good as that of a single-tank element (surge tank) with the same surge volume. The volume optimization of the two-tank element is implemented by selecting the best allocations of the two tanks’ volumes to achieve larger reductions of pressure pulsations. Assuming that the total surge volume is constant, we found that the smaller the volume of the front tank (near the cylinder) is, the lower the pulsation levels are. The optimized result proves that in some conditions the two-tank element could control pulsations better than the single-tank element with the same surge volume.

A Simple Measurement Method of Pressure Pulsations Using Outer Surface Strain in Piping Systems

This study proposes a method to measure pressure pulsations in piping systems easily and directly for their accurate evaluation of occurrence location and pressure amplitude. In the proposed method, the pulsations were estimated by combining the strain measurement result on the pipe outer surface with the calculated formula result for thick-walled cylinders. The proposed method was validated experimentally using a mock-up piping system. It was demonstrated that the method could measure the amplitudes and behavior of pressure pulsations with a practical accuracy. The factors influencing the measurement accuracy of the method were also discussed. The method is expected to contribute to more efficient plant maintenance to prevent fatigue failure of piping and plant components because the pulsations that the method measures are the main cause of vibration fatigue and acoustic noise in piping systems.

Pump noise control in high rise condominiums.

Noise generated by small pumps circulating water and refrigerants in multifamily residential buildings can be significant enough to generate complaints from residents if proper precautions are not taken. This presentation highlights several multifamily residential projects where pump and piping system noise was a significant source of noise complaints, and discusses what steps were taken to resolve the situation. General guidelines that can be used to prevent these problems in future projects will also be presented.

Noise generation and propagation effects on piping system components

In power plants and petrochemical plants, the piping systems form a network that extends throughout the facility. Various components in a piping system can be major sources of in-plant and community noise, both the pipe and the contained fluid can be noise propagation paths, and noise radiation can occur from the external surface of the piping. Though the basics of these phenomena are often understood, the translation into workable predictive tools has been slow. Several possible piping system noise sources are described and the experimental test program being undertaken to generate the required non-dimensionalized spectral data is outlined. The accuracy of pressure fluctuation scaling for pressure and flow rate is also reviewed based on the equal tee test program.

Identification and prediction of piping system noise

In a power plant environment, the piping systems form a network that extends throughout the facility. Various components can be major sources of in-plant and community noise, both the pipe and the contained fluid can be propagation paths, and radiation can occur from the external surface. Though the basics of these phenomena may be understood, the translation into workable predictive tools has been slow. Too often, source, propagation, and radiation effects are treated as separate entities without allowing for the interactions that exist. The spectral characteristics of the sources will govern the type of response by the system. Pipe transmission loss models will change in pipe to duct transition areas. The status of these concepts will be reviewed with a discussion of current and possible future efforts to improve existing models.

Modeling the Wall Pressure Spectrum in Turbulent Pipe Flows

An important source of vibration and noise in piping systems is the fluctuating wall pressure produced by the turbulent boundary layer. One approach to calculating the wall pressure fluctuations is to use a stochastic model based on the Poisson pressure equation. If the model is developed in the wave-number domain, the solution to the wave-number-frequency spectrum can be expressed as an integral of the turbulent sources over the boundary layer thickness. Models based on this formulation have been reported in the literature which show good agreement with measured pressure spectra, but they have relied on adjustable “tuning” constants to account for the unknown properties of the turbulent velocity fluctuations. A variation on this approach is presented in this paper, in which only well-known “universal” constants are used to model the turbulent velocity spectrum. The resulting pressure spectrum predictions are shown to be in good agreement with canonical data sets over a wide range of Reynolds numbers.

The Effect of Seat Geometry on Gate Valve Noise

Gate valves often act as a source of tonal noise in piping systems. Occasionally, this can lead to excessive environmental noise levels. This paper presents the results of a model testing program that was conducted to determine the most cost-effective way to eliminate the noise source in one such valve. Over 300 tests were conducted on 25 different valve configurations. Testing of the original valve configuration indicated that the noise was caused by vortex shedding over the valve seat cavity coupled with an acoustic resonance across the throat of the valve. Numerous modifications to the valve seats, seat cavity, and disk were tested to determine how the vortex shedding could best be controlled. The effect of these modifications on the unsteady pressures in the valve and adjacent piping are presented and discussed. For the valve under consideration, it was concluded that the noise could best be eliminated by chamfering the upstream and downstream valve seats. Recommendations for avoiding noise problems in other valve installations are presented. [S0094-9930(00)00503-5]

Noise Reduction Using Finite-Length Flexible Segments

In this work, the reduction of acoustic noise in piping systems through the installation of finite flexible segments is explored. A mathematical model describing the relevant parameters is developed. To verify the model, experimental work is undertaken using rubber hoses as flexible segments and air as the contained fluid. The effect of the segment on propagating acoustical energy is studied in terms of its insertion loss. Both theoretical and experimental results indicate that, for light fluid loading, the flexibility of the segment is only important when significant axial shell resonances exist, or when one or both acoustical termination impedances at the ends of the segment are much larger or smaller than the characteristic impedance of the medium. Further, the model indicates that for heavier fluid loading (i.e., when the compressibility of the flexible section is significant in relation to the bulk compliance of the fluid), in addition to higher associated insertion losses, the finite length resonances become more pronounced, and performance is less sensitive to small variations in the termination impedances. [S0739-3717(00)00402-5]

Active noise control of time‐varying signals in ducts

A sound cancellation system has been developed to reduce the flow‐induced noise in piping systems under both steady‐state and transient conditions. A hybrid controller that combines both open‐loop and closed‐loop responses with adaptive digital signal processing and filtering techniques is utilized to speed up the response of the system controller for the transient condition. Autoregressive, moving average with exogenous input (ARMAX) alogrithm has been utilized in the on‐line and off‐line modeling of signal characteristics. Off‐line model data are introduced into an on‐line adaptive system model via a parameter leakage mechanism. The convergence of the resulting algorithm is improved at the expense of bias in the final system parameters. The bias depends on a weighting or leakage factor, which controls the relative amount of off‐line data to be used. A preliminary test has been conducted to demonstrate the active cancellation concept for synthesized steady‐state signals. Results showed that up to a 30‐dB reduction has been obtained for pure sinusoidal waves ranging from 100 to 500 Hz. For confined jet noise, the noise reduction is about 10 dB, and similar results have been observed for the random broad‐band noise.

Research on wave phenomena in hydraulic lines. (16th report. Pulsation reduction by branch pipe filters).

Flow pulsation often causes vibration and noise in piping systems, and therefore has been a nagging concern for fluid system engineers. As is known in acoustics, a branch pipe can act as a low-impedance element for harmonic waves of specific frequencies. The present report deals with an attempt to reduce pulsation in oil hydraulic lines using branch pipes alone. Attention in paid particularly to the effects of viscosity on their behaviors as a band-elimination filter. The availability of branch pipe filters is experimentally examined in a test to reduce prominent pulsation created by a gear pump. Finally a combination of branch pipes, which is called a 'π-shape filter', has been proved to absorb the pulsation so thoroughly that it can take the place of accumulators which are conventinally used for this purpose.

Microcomputer based data acquisition and analysis systems for graduate student research in Acoustics

The development and commercial availability of dedicated multichannel fast‐Fourier transform (FFT) analyzers have resulted in a significant advancement in productivity in research in acoustics. The capability of at least two‐channel FFT instrumentation is a must for any acoustics laboratory; however, the acquisition of a single instrument represents a major item in a research budget. Two personal‐computer‐based multichannel FFT systems will be described and demonstrated. These systems are currently being used by graduate students in theses research in internal combustion engine noise and in piping system noise. These relatively low‐cost systems were assembled with commercially available data acquisition components and software. Microphone signal conditioning preamplifiers and anti‐aliasing filters were designed by a senior electrical engineering student. Preamplifier gains and filter cutoff frequencies are controlled by the microcomputer.

Potential for valve-induced acoustic fatigue in piping systems

In recent years, as sources of noise in piping systems have become more powerful, the potential for structural fatigue induced by intense acoustic fields in such systems has increased. This paper examines the potential for such a problem in those cases where the acoustic field is produced by the passage of a gas flow through a control valve.

Acoustic Filters for Liquid Piping Systems

Acoustic filters are being developed for attenuating liquid-borne noise in piping systems. The filters investigated are analogous to RLC type electrical filters, using the series inertances of short lengths of piping together with lumped impedance shunt elements to produce low-pass filtering action. The construction of several 2- and 3-stage experimental models is shown, along with noise reduction data measured in a laboratory water pumping system using a centrifugal pump as the noise source. (This work was supported by the Bureau of Ships.)