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)

    “The mother whose self-image is dependent on her children places on those children the responsibility for her own identity, and her involvement in the details of their lives can put great pressure on the children. A child suffers when everything he or she does is extremely important to a parent; this kind of over-involvement can turn even a small problem into a crisis.”
    —Grace Baruch (20th century)

    “A magazine or a newspaper is a shop. Each is an experiment and represents a new focus, a new ratio between commerce and intellect.”
    —John Jay Chapman (1862–1933)

    “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)

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

    “I candidly confess that I have ever looked on Cuba as the most interesting addition which could ever be made to our system of States. The control which, with Florida, this island would give us over the Gulf of Mexico, and the countries and isthmus bordering on it, as well as all those whose waters flow into it, would fill up the measure of our political well-being.”
    —Thomas Jefferson (1743–1826)

    “The greatest events occur without intention playing any part in them; chance makes good mistakes and undoes the most carefully planned undertaking. The world’s greatest events are not produced, they happen.”
    —G.C. (Georg Christoph)