Two techniques for measurement of flow resistance

The accurate measurement of flow resistance has many applications in acoustics. In our laboratory, it is particularly important for the characterization of materials used as regenerators in thermoacoustic refrigerators and for the quantification of leakage paths in complex assemblies. This presentation will describe two techniques for flow resistance measurements made at sufficiently low Reynolds numbers that the resistances measured for unidirectional flow are relevant to acoustic flows. One technique uses a “constant current generator” configuration to characterize stacked stainless steel screens and the other uses an Airpot® graphite piston in a glass cylinder to produce a constant pressure difference and accurate flow rate. Both techniques use air at atmospheric pressure as the test fluid. The constant current technique produces results that are consistent to ±3% for stacks of stainless steel screens that vary in thickness from 10 to 50 screens. The Airpot® technique can produce similar accuracy for flow resistances as large as 1010 Pa-sec/m3. [Work supported by the Applied Research Laboratory and the U.S. Department of Energy.]