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From Atmospheric Dispersion Modelling
BIRD, STEWART AND LIGHTFOOT MODEL
RAZOULI AND WILLIAMS MODEL
RAMSKILL'S EQUATION FOR NON-CHOKED GAS FLOW
Ramskill's equation for the non-choked flow of an ideal gas is shown below as Equation (1):
ρA in Ramskill's equation is the ideal gas density at the downstream conditions of temperature and pressure and it is defined in Equation (2) using the ideal Gas Law:
Since the downstream temperature TA is not known, the adiabatic expansion Equation (3) below is used to determine TA in terms of the known upstream temperature T:
Combining Equations (2) and (3) results in Equation (4) which defines ρA in terms of the known upstream temperature T:
Using Equations (1) and (4) to determine non-choked mass flow rates for ideal gases gives identical results to the results obtained using equation (5)
below:
Reference for Equation (1):
Gierer, Conrad and Hyatt, Nigel,"Using Source Term Analysis Software for Calculating
Fluid Flow Release Rates", Dyadem International Ltd., CACHE Newsletter No.48, Spring 1999,Austin, Texas (www.che.utexas.edu/cache/newsletters/Spr_99.pdf)
Ramskill, P.K., "Discharge Rate Calculation Methods
for Use In Plant Safety Assessments", Safety and Reliability Directory, 1986, United Kingdom Atomic Energy Authority
References for Equation (5):
Handbook of Chemical Hazard Analysis Procedures" Appendix B, Federal Emergency Management Agency, U.S. Dept. of Transportation, and U.S. Environmental Protection Agency, 1989.
"Risk Management Program Guidance For Offsite Consequence Analysis", U.S. EPA publication EPA-550-B-99-009, April 1999.
"Methods For The Calculation Of Physical Effects Due To Releases Of Hazardous Substances (Liquids and Gases)", PGS2 CPR 14E, Chapter 2, Section 2.5.2.3, The Netherlands Organization Of Applied Scientific Research, The Hague, 2005.
COMPLETE GAUSSIAN EQUATION
