Critical Flow of Dense Gases - Modeling and Experimental Validation

Abstract

The critical mass flow of dense gases strongly depends on real gas effects. In the present work the detailed assessment of the critical flow conditions and the limiting mass velocity in the flow of refrigerants has been experimentally verified. Critical flow function C* data for R-410A and R-507A have been predicted based on Martin–Hou equation of state. The computational study was assured by implementation of theoretical model [1] for one dimensional (1D) and non-linear gas dynamic problems. This model, with the corrections for the boundary layer (BL) displacement thickness, gives a better prediction of the critical flow function than classical approach. Appropriate sonic flow conditions have been executed in the pressurized closed loop system by using ISO 9300 critical Venturi nozzle. Measurements of critical mass flow for dense superheated vapour of R-410A and R-507A carried out on laboratory test stand have confirmed the accuracy of the model and its physical significance. A main result of the investigations is a set of graphs C*(T₀, p₀) and tables for an assumed range of stagnation temperature T₀ and pressure p₀ at the upstream flow.

Keywords

• Thermodynamics; refrigeration; Venturi flow

References

1. Annon, DuPont™, Suva refrigerants, www2.dupont.com/Refrigerants/en_US/products/Suva/i ndex.html.
2. Annon, 1997, Sonic Nozzles for Mass Flow Measurement and Reference Nozzles for Thrust Verification, AGARD-AR- 321, ISBN 92-836-1056-3.
3. Bober W., and Chow W.L., 1977, Nonideal Isentropic Flow Through Converging-Diverging Nozzles, ASME J. Fluids Eng., 112(4), pp. 455 -460.
4. Geropp, D., 1971, Laminare Grenzschichten in ebenen und Rotationssymmetrischen Lavalduesen, Deutsche Luft- und Raumfahrt Forschungsbericht, pp.71-90.
5. Górski, J., 1997, Modeling of Real Gas Properties and its Thermal-Flow Processes, (in Polish). Rzeszow, Oficyna Wyd. PRz.
6. Johnson, R.C., 1971, Real Gas Effects in the Flow of Methane and Natural Gas Through Critical Flow Nozzles. NASA-TM-X-52994.
7. Johnson, A.N., 2000, Numerical Characteri-zation of the Discharge Coefficient in Critical Nozzles, Ph.D. Dissertation, Pennsylvania State University, College Station, PA.
8. Leung J.C., and Epstein M., 1988, A Generalized Critical Flow Model for Nonideal Gases, AIChE J., 34 (9), pp. 1568-1572.

9. Rabczak, S., 2007, Thermal Equations of State in the Flow Analysis of New Refrigerants, (in Polish), PhD Dissertation, Faculty of Environmental Engineering, Warsaw University of Technology.
10. Shumann, S.P., 1990, Real Gas Critical Flow Factors for R12, R22 and R502, ASHRAE Transactions, 96(2), pp. 329-336.
11. Span,R., 2000, Multiparameter Equations of State: An Accurate Source of Thermodynamic Property Data. Springer Verlag, Berlin.
12. Standard ISO 9300:2005, Measurement of Gas Flow by Means of Critical Flow Venturi Nozzles.
13. Thompson P.A., and Sullivan D.A., 1977, Simple Predictions for the Sonic Conditions in a Real Gas, ASME Jour. Fluids Eng.; 99(1), pp. 217-225.