NeqSim Input Validation Rules
Validate inputs before creating NeqSim objects or running simulations.
Each rule includes the check, the error it prevents, and the corrective action.
Thermodynamic System Inputs
Temperature
| Check |
Valid Range |
Error If Violated |
| T > 0 K (> -273.15 C) |
50-1000 K typical |
Absolute zero violation — physically impossible |
| T < 2000 K |
Engineering range |
Above 2000 K, EOS models are not validated |
| Constructor uses Kelvin |
SystemSrkEos(273.15 + T_C, P) |
Passing Celsius directly gives wrong results silently |
Corrective action: Convert Celsius to Kelvin: T_K = 273.15 + T_C
Pressure
| Check |
Valid Range |
Error If Violated |
| P > 0 bara |
0.001-2000 bara typical |
Zero/negative pressure is physically impossible |
| P < 5000 bara |
Engineering range |
Above ~2000 bara, cubic EOS accuracy degrades significantly |
Corrective action: Verify units — NeqSim uses bara (absolute), not barg (gauge) or psia.
Composition
| Check |
Rule |
Error If Violated |
| Sum of mole fractions |
Should be ~1.0 (tolerance: 0.999-1.001) |
Wrong mixture composition — all properties incorrect |
| Each fraction >= 0 |
No negative fractions |
Physically impossible |
| Each fraction <= 1 |
No fraction > 100% |
Physically impossible |
| At least 1 component |
Cannot have empty system |
NeqSim crashes on empty system |
Corrective action: Normalize fractions: x_i = x_i / sum(x). Or alert user that fractions don't sum to 1.
Component Names
Valid component names must match entries in src/main/resources/data/COMP.csv.
Common correct names:
| Correct Name |
Common Mistakes |
"methane" |
"CH4", "Methane", "c1" |
"ethane" |
"C2H6", "C2" |
"propane" |
"C3H8", "C3" |
"n-butane" |
"butane", "nC4" |
"i-butane" |
"isobutane", "iC4" |
"CO2" |
"co2", "carbon dioxide" |
"H2S" |
"h2s", "hydrogen sulfide" |
"nitrogen" |
"N2", "Nitrogen" |
"water" |
"H2O", "Water" |
"MEG" |
"meg", "ethylene glycol" |
Corrective action: Search COMP.csv for the correct component name.
Mixing Rule
| Check |
Rule |
Error If Violated |
| Mixing rule is set |
setMixingRule() must be called after addComponent() |
Flash gives wrong results or crashes |
| CPA systems use numeric rule |
setMixingRule(10) for CPA EOS |
String mixing rules don't work with CPA |
| Classic rule for cubic EOS |
setMixingRule("classic") for SRK/PR |
Wrong rule type causes errors |
Corrective action: Always call fluid.setMixingRule("classic") (or 10 for CPA) after adding all components.
Process Equipment Inputs
Stream
| Check |
Rule |
| Flow rate > 0 |
Zero flow breaks downstream equipment |
| Flow rate units specified |
setFlowRate(value, "kg/hr") — always include unit string |
| Stream has a fluid object |
new Stream("name", fluid) — fluid must not be null |
Compressor
| Check |
Rule |
| Outlet pressure > inlet pressure |
Compressor cannot decompress (use valve/expander) |
| Pressure ratio < 6 per stage |
Single-stage ratio above ~4-6 is unrealistic |
| Isentropic efficiency 0.5-0.95 |
Values outside this range are non-physical |
| Inlet stream has gas phase |
Compressor cannot handle pure liquid |
Valve / Throttle
| Check |
Rule |
| Outlet pressure < inlet pressure |
Valve reduces pressure (use compressor to increase) |
| Outlet pressure > 0 bara |
Cannot throttle to zero pressure |
Heat Exchanger / Cooler / Heater
| Check |
Rule |
| Outlet temperature set |
Must specify target temperature or duty |
| Cooler: T_out < T_in |
Cooler reduces temperature |
| Heater: T_out > T_in |
Heater increases temperature |
Temperature in Kelvin for setOutTemperature() |
Common mistake: passing Celsius to method expecting Kelvin |
Separator
| Check |
Rule |
| Inlet has 2+ phases at conditions |
Single-phase feed produces no separation |
| Use ThreePhaseSeparator for water |
Standard Separator handles gas/liquid only |
Pipeline
| Check |
Rule |
| Length > 0 meters |
Zero-length pipe has no effect |
| Diameter > 0 meters |
Must specify pipe inner diameter |
| Diameter typically 0.05-1.5 m |
Values outside range are suspect |
EOS Selection Validation
| Fluid Type |
Required EOS |
Wrong EOS Symptom |
| Hydrocarbons + water |
CPA (SystemSrkCPAstatoil) |
SRK/PR gives near-zero water solubility in HC |
| Hydrocarbons + MEG/methanol |
CPA (SystemSrkCPAstatoil) |
Wrong hydrate inhibition prediction |
| Pure hydrocarbons (no polar) |
SRK or PR |
CPA is slower with no benefit |
| Custody transfer / fiscal metering |
GERG-2008 (SystemGERG2008Eos) |
Cubic EOS not accurate enough for custody |
| Electrolyte / brine / pH |
Electrolyte CPA |
SRK/CPA ignores ionic interactions |
Corrective action: Match EOS to fluid type. When in doubt, CPA handles the widest range of systems.
Order-of-Operations Validation
These operations must happen in the correct sequence:
1. Create fluid (SystemSrkEos, etc.)
2. Add ALL components
3. Set mixing rule ← BEFORE characterization or flash
4. Characterize plus fractions (if oil) ← AFTER mixing rule
5. Create database (if needed)
6. Run flash (TPflash, etc.)
7. Call initProperties() ← AFTER flash, BEFORE reading properties
8. Read properties (density, viscosity, etc.)
Common order violations:
- Characterizing before setting mixing rule →
ArrayIndexOutOfBoundsException
- Reading properties before
initProperties() → zero values for transport properties
- Adding components after setting mixing rule → mixing rule parameters stale
Quick Validation Checklist
Use this checklist before every simulation setup:
equinor