Compressor Settle-Out Pressure & Temperature Calculator
Comprehensive Settle-Out Calculator
Thermodynamic Properties
Suction Side
Discharge Side
Calculated Volumes
Suction Gas Volume (Vβ):
-
Discharge Gas Volume (Vβ):
-
Total Gas Volume:
-
Settle-Out Conditions
Settle-Out Temperature:
-
Settle-Out Pressure:
-
Methodology
1. Gas moles (n) from PV = ZΒ·nΒ·RΒ·T (ideal gas with Z-correction).
2. Total internal energy is conserved and approximated using mole-weighted temperature (same gas, constant Cv).
3. JβT cooling of discharge gas is applied based on ΞΌJT and expansion from Pβ to settle-out pressure.
4. Final P and T are solved iteratively from the combined mass & energy balance.
2. Total internal energy is conserved and approximated using mole-weighted temperature (same gas, constant Cv).
3. JβT cooling of discharge gas is applied based on ΞΌJT and expansion from Pβ to settle-out pressure.
4. Final P and T are solved iteratively from the combined mass & energy balance.
Technical Notes
Variable Definitions
- Vs, Vd: Total gas volumes (vessel gas space + connected piping) on suction and discharge sides.
- Ps, Ts, Zs: Suction-side pressure, temperature, and compressibility factor at trip time.
- Pd, Td, Zd: Discharge-side pressure, temperature, and compressibility factor at trip time.
- ΞΌJT: JouleβThomson coefficient used to approximate temperature change during pressure equalisation.
- Pso, Tso: Final settle-out (equalised) pressure and temperature after isolation and mixing.
Formulas / Logic
-
Gas moles (real-gas corrected ideal form):
n = (PΒ·V)/(ZΒ·RΒ·T), withR = 8.314462618 J/molΒ·K. -
Settle-out EOS:
Pso = (ZsoΒ·ntotΒ·RΒ·Tso)/Vtot. -
Energy balance (screening): assumes the same gas throughout
and approximately constant
Cv, soTsois computed as a mole-weighted temperature. -
JouleβThomson cooling (screening): discharge gas temperature
adjusted as
Td,eff = Td β ΞΌJTΒ·ΞP, withΞPtaken from discharge pressure down to currentPso. -
Solution method: fixed-point iteration updates
TsoandPsountil changes are small.
Assumptions / Notes
- This calculator is intended for engineering screening. For final design, use a validated EOS and system model (including real equipment volumes, elevation, and heat transfer).
-
No heat transfer is assumed during equalisation
(adiabatic/short-time settle-out). If long duration, ambient heat
exchange can shift
Tso. - Single gas composition is assumed (no phase change and no significant composition change). If condensation is possible, a rigorous flash calculation is required.
- Piping database uses a simplified internal ID table (Sch 40). For accuracy, confirm against project piping class/spec.
- References (industry practice): API 617 (centrifugal compressors) and ASME PTC 10 (compressors and exhausters) provide context for compressor system practices; settle-out evaluation is commonly performed using mass + energy balance with appropriate property methods.