| 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: |
 Click here to retrieve PDF version of paper (136KB) |
