In gas handling there are two types of flow. The most common one is non-expanding flow as the normal condition in most operating process lines. Generally, the flow is isenthalpic. The impact of a velocity change is minimal and assumed to be constant throughout the length of the pipeline. Any pressure decrease is attributed to frictional losses in the line. If the total pressure drop is less than about 10 % of inlet pressure, the unmodified Darcy equation can be applied to calculate the flowrate with reasonable accuracy. By comparison, expanding flow is the engineer's headache. TRhis worrisome occurrence starts from an abnormal flow condition, which manifests itself by a very high pressure drop. Flowrate calculations have to account for the effects of adiabatic expansion and friction losses at high velocities. Such abnormal situations are: At the tailpipe of high-pressure blowdown systems during shutdown or depressurization, seen particularly on offshore petroleum and gas production platforms; accidental gas-blowby as a result of inadvertent opening a drain valve of a prwessurized vessel, or stuck-open failure of level-control valves; rupture of heat exchanger tubes; bursting of a rupture disc; opening of a pressure safety valve. This article provides an Excel speadsheet to put on the computer, address expanding-flow conditions, and determine flowrates without hours of research. The author focuses upon expanding flow through constant diameter pipes. A detailed overview to the thermodynamic situation including the equations is given. Energy balance as well as the frictionless thermodynamic ratios and the critical expansion factor are described and explained in details including the mathematical and thermodynamic equations.
Spreadsheet calculates critical flow
Tabellenkalkulation der kritischen Durchflussmenge
Chemical Engineering, New York ; 109 , 11 ; 62-67
2002
6 Seiten, 2 Bilder, 7 Quellen
Aufsatz (Zeitschrift)
Englisch
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