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:

    “There are ... two minimum conditions necessary and sufficient for the existence of a legal system. On the one hand those rules of behavior which are valid according to the system’s ultimate criteria of validity must be generally obeyed, and on the other hand, its rules of recognition specifying the criteria of legal validity and its rules of change and adjudication must be effectively accepted as common public standards of official behavior by its officials.”
    —H.L.A. (Herbert Lionel Adolphus)

    “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)

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

    “Someday soon, we hope that all middle and high school will have required courses in child rearing for girls and boys to help prepare them for one of the most important and rewarding tasks of their adulthood: being a parent. Most of us become parents in our lifetime and it is not acceptable for young people to be steeped in ignorance or questionable folklore when they begin their critical journey as mothers and fathers.”
    —James P. Comer (20th century)

    “Night is a dead monotonous period under a roof; but in the open world it passes lightly, with its stars and dews and perfumes, and the hours are marked by changes in the face of Nature. What seems a kind of temporal death to people choked between walls and curtains, is only a light and living slumber to the man who sleeps afield.”
    —Robert Louis Stevenson (1850–1894)

    “Opinionated writing is always the most difficult ... simply because it involves retaining in the cold morning-after crystal of the printed word the burning flow of molten feeling.”
    —Gavin Lyall (b. 1932)

    “The great epochs of our lives occur when we gain the courage to rechristen what is evil in us as what is best.”
    —Friedrich Nietzsche (1844–1900)