What Is the Isentropic Nozzle Choking Critical Pressure Ratio Calculator?
Choked flow is a compressible fluid dynamic condition where fluid velocity at the throat reaches the speed of sound.
The critical pressure ratio defines the exact downstream pressure threshold required to trigger choking.
How Does the Isentropic Nozzle Choking Critical Pressure Ratio Calculator Work?
Evaluates the critical pressure ratio P*/P0 from the ratio of specific heats gamma.
Computes static pressure and static temperature at the sonic throat.
Calculates the local speed of sound a* at the choked throat.
Isentropic Nozzle Choking Critical Pressure Ratio Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
Critical isentropic expansion relations yielding Mach 1.0 at nozzle minimum area.
How to Use the Isentropic Nozzle Choking Critical Pressure Ratio Calculator
- Enter upstream supply stagnation pressure and temperature.
- Optionally adjust specific heat ratio gamma and gas constant R.
Step-by-Step Example Calculation
Compressed Air Discharge Nozzle
Input Values:
Understanding Your Result
For air (gamma = 1.4), the critical pressure ratio is exactly 0.5283.
If downstream pressure is below 0.5283 * P0, the nozzle is choked and throat Mach number is exactly 1.0.
Factors That Affect the Result
- Specific heat ratio: Monatomic gases (gamma=1.67) choke at P*/P0 = 0.487; triatomic gases (gamma=1.3) choke at P*/P0 = 0.546.
- Stagnation temperature: Higher temperature increases sonic throat speed but does not affect the pressure ratio.
When Should You Use This Calculator?
- Sizing rocket engine de Laval nozzles and steam turbine nozzles.
- Safety relief valve discharge capacity sizing and pipeline blowdown calculations.
Assumptions & Limitations
- Assumes steady, 1D, isentropic, ideal gas flow without boundary layer friction losses.
- Valid for converging and converging-diverging nozzle geometries.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Closed-form exact solution of the 1D Euler equations for isentropic gas dynamics.