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A measurement system has been developed that can determine flow resistances quickly and accurately and can be used to complement acoustical measurements on the same samples. The use of electronic components permits measurements to be made 20–50 times faster than with the commonly used Leonard apparatus. Variable-capacitance pressure transducers are used to measure pressure differences across both the test sample and a laminar flow element with known flow resistance (these two in series): For steady nonpulsating flow, the ratio of flow resistances equals the ratio of measured pressure differences. The rate of air flow through the sample is adjusted using a mass flow controller; flows of 10−3–1 cm3 s−1 can be controlled to better than 1%. Flow resistances between 1 and 105 g cm−4 s−1 can be determined with an accuracy of better than 1.6%. The corresponding range of flow resistivities of porous materials that can be determined with the present sample holder is 1–106 cgs-rayl cm−1. Initial measurements have been made using small circular orifices and samples of porous material.
Stinson et al. (Wed,) studied this question.