Acoustic performance tests and parameters for fluid piping system components: A critical evaluation of the state of the art: Part 2

Abstract

This paper, which has been published in two parts, presents a critical evaluation of the state of the art relating to the measurement and characterisation of the acoustic performance of fluid system components, in particular of pumps and acoustic filters for liquid piping systems. The first part reviewed, in non-mathematical terms, the analysis techniques which can be used for acoustic circuits, and pointed out that the effect of any component (such as a filter) cannot be predicted accurately without making a complete circuit analysis. Various performance measurements and analytical parameters for acoustic filters were described, the theoretical relationships between ‘measured attenuation’ and ‘transmission loss’ were demonstrated, and causes for discrepancies between theoretical and measured filter performance discussed. Approaches toward acoustic characterisation of pumps and other noise sources were examined, and this lead to the conclusion that the difficulties therein have only begun to be recognised, and are far from solved. Some new suggestions for experimental approaches were presented. This second part deals more directly with practical considerations in the design of acoustic test loops for liquid piping system components. After a review of the general requirements, more detailed consideration is given to the measurement of standing waves, to entrained and entrapped air problems, to the design of practicable acoustic ‘terminations’, and to the advantages and disadvantages of plastic pipes for loop piping and filter models. Slightly more mathematical appendices deal with the acoustic impedance and acoustic velocity in fluid-filled elastic pipes, and the measurement of acoustic power flow.