Minimum pressure ratio required for choked flow to occur

The minimum burden ratios appropriate for afraid altitude to action (when some archetypal automated gases are flowing) are presented in Table 1. The ratios were acquired application the belief that afraid breeze occurs if the arrangement of the complete upstream burden to the complete after burden is according to or greater than  (k+1) / 2 k/(k−1) , area k is the specific calefaction arrangement of the gas. The minimum burden arrangement may be accepted as the arrangement amid the upstream burden and the burden at the bill throat if the gas is traveling at Mach 1; if the upstream burden is too low compared to the after pressure, sonic breeze cannot action at the throat.

Table 1

Gas k = cp/cv Minimum

Pu/Pd

required for

choked flow

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 = complete upstream gas pressure

Pd = complete after gas pressure

k ethics acquired 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 ethics leads to the inference that minimum burden arrangement is the afterward beeline action of specific calefaction ratio: P_ratio = 0.6057 * k + 1.045.

editVacuum Conditions

In the case of upstream air burden at ambient atmospheric burden and exhaustion altitude down beck of an orifice, both the air acceleration and the accumulation breeze amount becomes afraid or bound if sonic acceleration is accomplished through the orifice.