Use of transport delay to avoid compensatory effects in sonic orifice‐based gas concentration probes
作者:
Thomas D. Radcliff,
J. Roger Parsons,
W. Stan Johnson,
Arthur E. Ruggles,
期刊:
Review of Scientific Instruments
(AIP Available online 1996)
卷期:
Volume 67,
issue 8
页码: 2837-2842
ISSN:0034-6748
年代: 1996
DOI:10.1063/1.1147114
出版商: AIP
数据来源: AIP
摘要:
As part of a mixing test, an instrument to measure transient concentration of several different binary gas mixtures was required. A combination sonic nozzle/hot film instrument was selected for this measurement, but for certain gas mixtures the output from this device was unexpectedly small. A study of the dynamics of the instrument reveals that this is caused by the compensatory nature of the two principal contributors to convection: change in constant velocity convection coefficient and change in sonic velocity. The problem is addressed by introducing a physical delay line between the hot film element and the sonic nozzle. Results show that a finite interval of constant velocity thermal convection data can be taken before sonic velocity effects are introduced. A second variation is proposed where the hot film sensor is replaced by a simple orifice flowmeter. Orifice pressure drop and sonic velocity effects, normally strongly compensatory, are also separated by a delay line such that nearly constant velocity orifice discharge coefficient data can be taken over a finite time interval. Results show that this instrument design has higher sensitivity and lower cost than the hot film variant, albeit with slower time response. ©1996 American Institute of Physics.
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