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Publication Citation: Relaxation Effects in Small Critical Nozzles

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Author(s): Aaron N. Johnson; C L. Merkle; Michael R. Moldover; John D. Wright;
Title: Relaxation Effects in Small Critical Nozzles
Published: January 01, 2006
Abstract: We computed the flow of four gases (He, N2, CO2, and SF6) through a critical nozzle by augmenting traditional computational fluid dynamics (CFD) with a rate equation that accounts for τrelax, a species-dependent relaxation time that characterizes the equilibration of the vibrational degrees of freedom with the translational and rotational degrees of freedom. Conventional CFD (τrelax = 0) under-predicts the flow through a small nozzle (throat diameter d = 0.593 mm) by up to 2.3 % for CO2 and by up to 1.2 % for SF6. When we used values of τrelax from the acoustics literature, the augmented CFD under-predicted the flow for SF6 by only 0.3 %, in the worst case. The augmented predictions for CO2 were within the scatter of previously published experimental data ({plus or minus}0.1 %). As expected, both conventional and augmented CFD agree with experiments for He and N2. Thus, augmented CFD enables one to calibrate a small nozzle with one gas (e.g., N2) and then to use it as a flow standard with any other gas (e.g., CO2) for which reliable values of τrelax and the relaxing heat capacity are available.
Citation: Journal of Fluids Engineering-Transactions of the ASME
Volume: 128
Issue: 1/1/06
Pages: pp. 170 - 176
Keywords: flow standard
Research Areas: Measurement Standards, Flow, Flow, Chemical Engineering & Processing, Calibrations (Mechanical), Manufacturing, Chemistry, Metrology
PDF version: PDF Document Click here to retrieve PDF version of paper (140KB)