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.
| 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:
- 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.
- 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 dont do housework any morethat 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)
“Under the pressure of the cares and sorrows of our mortal condition, men have at all times, and in all countries, called in some physical aid to their moral consolationswine, beer, opium, brandy, or tobacco.”
—Edmund Burke (17291797)
“Official dignity tends to increase in inverse ratio to the importance of the country in which the office is held.”
—Aldous Huxley (18941963)
“Hollywood held this double lure for me, tremendous sums of money for work that required no more effort than a game of pinochle.”
—Ben Hecht (18931964)
“to be choked with hate
May well be of all evil chances chief.”
—William Butler Yeats (18651939)
“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 (17431826)
“I defied nothing at all. I ignored the law because I didnt know it existed. It didnt occur to me that anyone would want to curb my inspiration.”
—Margaret Anderson (18861973)