Choked Flow - Minimum Pressure Ratio Required For Choked Flow To Occur

Minimum Pressure Ratio Required For Choked Flow To Occur

The minimum pressure ratios required for choked conditions to occur (when some typical industrial gases are flowing) are presented in Table 1. The ratios were obtained using the criteria that choked flow occurs when the ratio of the absolute upstream pressure to the absolute downstream pressure is equal to or greater than k/(k − 1), where k is the specific heat ratio of the gas. The minimum pressure ratio may be understood as the ratio between the upstream pressure and the pressure at the nozzle throat when the gas is traveling at Mach 1; if the upstream pressure is too low compared to the downstream pressure, sonic flow cannot occur at the throat.

Table 1
Gas k = cp/cv Minimum
Pu/Pd
required for
choked flow
Dry Air 1.400 1.893
Helium 1.660 2.049
Hydrogen 1.410 1.899
Methane 1.307 1.837
Propane 1.131 1.729
Butane 1.096 1.708
Ammonia 1.310 1.838
Chlorine 1.355 1.866
Sulfur dioxide 1.290 1.826
Carbon monoxide 1.404 1.895

Notes:

  • Pu = absolute upstream gas pressure
  • Pd = absolute downstream gas pressure
  • k values obtained from:
    1. Perry, Robert H. and Green, Don W. (1984). Perry's Chemical Engineers' Handbook, Table 2-166, (6th Edition ed.). McGraw-Hill Company. ISBN 0-07-049479-7.
    2. Phillips Petroleum Company (1962). Reference Data For Hydrocarbons And Petro-Sulfur Compounds (Second Printing ed.). Phillips Petroleum Company.

Inspection of these values leads to the inference that minimum pressure ratio is the following linear function of specific heat ratio: :Pratio = 0.6057 × k + 1.045.

Read more about this topic:  Choked Flow

Famous quotes containing the words minimum, pressure, ratio, required, choked, flow and/or occur:

    “After decades of unappreciated drudgery, American women just don’t do housework any more—that is, beyond the minimum that is required in order to clear a path from the bedroom to the front door so they can get off to work in the mourning.”
    —Barbara Ehrenreich (20th century)

    “Destiny is an absolutely definite and inexorable ruler. Physical ability and moral determination count for nothing. It is impossible to perform the simplest act when the gods say “no.” I have no idea how they bring pressure to bear on such occasions; I only know that it is irresistible.”
    —Aleister Crowley (1875–1947)

    “Official dignity tends to increase in inverse ratio to the importance of the country in which the office is held.”
    —Aldous Huxley (1894–1963)

    “The novelist is required to open his eyes on the world around him and look. If what he sees is not highly edifying, he is still required to look. Then he is required to reproduce, with words, what he sees.”
    —Flannery O’Connor (1925–1964)

    “to be choked with hate
    May well be of all evil chances chief.”
    —William Butler Yeats (1865–1939)

    “And if blood of Martyrs is to flow on the steps
    We must first build the steps;
    And if the Temple is to be cast down
    We must first build the Temple.”
    —T.S. (Thomas Stearns)

    “I defied nothing at all. I ignored the law because I didn’t know it existed. It didn’t occur to me that anyone would want to curb my inspiration.”
    —Margaret Anderson (1886–1973)