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)

    “The area [of toilet training] is one where a child really does possess the power to defy. Strong pressure leads to a powerful struggle. The issue then is not toilet training but who holds the reins—mother or child? And the child has most of the ammunition!”
    —Dorothy Corkville Briggs (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)

    “After I have said what is required by my vanity and my morality, I may find a moment for Truth.”
    —Mason Cooley (b. 1927)

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

    “Water doesn’t flow if it’s level, and people won’t complain if you treat them on the level.”
    —Chinese proverb.

    “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)