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)

    “We believe that civilization has been created under the pressure of the exigencies of life at the cost of satisfaction of the instincts.”
    —Sigmund Freud (1856–1939)

    “People are lucky and unlucky not according to what they get absolutely, but according to the ratio between what they get and what they have been led to expect.”
    —Samuel Butler (1835–1902)

    “She, as a veil down to the slender waist,
    Her unadorned golden tresses wore
    Dishevelled, but in wanton ringlets waved
    As the vine curls her tendrils, which implied
    Subjection, but required with gentle sway,
    And by her yielded, by him best received,
    Yielded with coy submission, modest pride,
    And sweet, reluctant, amorous delay.
    Nor those mysterious parts were then concealed:
    Then was not guilty shame: dishonest Shame
    Of Nature’s works, Honour dishonourable.”
    —John Milton (1608–1674)

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

    “Clay answered the petition by declaring that while he looked on the institution of slavery as an evil, it was ‘nothing in comparison with the far greater evil which would inevitably flow from a sudden and indiscriminate emancipation.’”
    —State of Indiana, U.S. public relief program (1935-1943)

    “If the world is a precipitation of human nature, so to speak, then the divine world is a sublimation of the same. Both occur in one act. No precipitation without sublimation. What goes lost there in agility, is won here.”
    —Novalis [Friedrich Von Hardenberg] (1772–1801)