❄️

Chiller Sizing Calculator

GPSA Ch. 14

Chiller Sizing Calculator
Sizes gas chiller heat exchangers for refrigeration service in gas processing plants. Calculates required heat transfer area, log-mean temperature difference (LMTD), approach temperature, overall heat transfer coefficient (U-value), and refrigerant flow rate for propane, ethane, propylene, ammonia, or R-22 refrigerant systems per GPSA Ch. 14.
GPSA Ch. 14 TEMA Standards
Calculation Mode:
Design: Size a new chiller from process conditions and refrigerant selection.

Process Gas (Tube Side)

MMSCFD
°F
°F
psig

Refrigerant (Shell Side)

°F
psig

Exchanger Design

hr-ft²-°F/BTU
%

Typical Gas Chiller Operating Conditions

Parameter Range
Gas Inlet Temp80–120°F
Gas Outlet Temp−20–40°F
Approach Temp5–15°F
U-value (S&T)50–150 BTU/hr-ft²-°F
Fouling Factor0.001–0.003 hr-ft²-°F/BTU

Engineering Basis

Heat Duty:

Q = m · Cp · (Tin − Tout)

Where Q = heat duty (BTU/hr), m = gas mass flow rate (lb/hr), Cp = gas specific heat (BTU/lb-°F), Tin = gas inlet temperature, Tout = gas outlet temperature.

Heat Transfer Area:

A = Q / (U · LMTD · Ft)

Where A = required heat transfer area (ft²), U = overall heat transfer coefficient (BTU/hr-ft²-°F), LMTD = log-mean temperature difference (°F), Ft = LMTD correction factor for multi-pass exchangers.

Log-Mean Temperature Difference:

LMTD = (ΔT1 − ΔT2) / ln(ΔT1 / ΔT2)

For shell-side boiling refrigerant at constant temperature: ΔT1 = Tgas,in − Trefrig and ΔT2 = Tgas,out − Trefrig.

Refrigerant Flow: Determined from heat duty divided by the latent heat of vaporization of the selected refrigerant at operating pressure. Propane is the most common refrigerant in midstream gas processing.

Design Guidelines

Approach Temperature: The difference between gas outlet temperature and refrigerant temperature. Typical approach is 5–15°F; tighter approach requires more area and cost.
Propane Refrigerant: Most common in midstream gas processing. Propane systems typically operate from −40°F to +60°F evaporator temperature for hydrocarbon dewpoint control.
Fouling Considerations: Gas chiller fouling factors depend on gas composition. Higher values for sour or wet gas; lower for clean, dry gas.