Navigating SIMIT CTE FLOWNET Library Documentation and Connector Types (FLN2)

The internal mathematical functions and connector types for the SIMIT Component Type Editor (CTE) FLOWNET library are documented in the SIMIT Component Type Editor Manual and the SIMIT FLOWNET Library Reference. In SIMIT V8.1/V9.x, connector type FLN2 represents a two-phase hydrodynamic fluid connection (water and steam) transmitting a structured state vector containing pressure, specific enthalpy, mass flow, and temperature. Built-in mathematical operators like _sum(), _min(), _max(), and _limit() represent CTE preprocessor macros that compile into thermodynamic balance equations based on the international IAPWS-IF97 industrial steam formulation.

SIMIT FLOWNET Library Thermodynamic Concept

The SIMIT FLOWNET library provides rigorous hydrodynamic and thermodynamic modeling of fluid piping networks, pumps, heat exchangers, valves, and steam drums. Unlike standard signal-based simulations that transmit isolated process variables (e.g., a real value for temperature or pressure), FLOWNET calculates physical conservation laws (conservation of mass, momentum, and energy) across a connected topological grid.

Components created or edited in the Component Type Editor (CTE) interact with this network solver by defining nodal state equations and flow branch pressure-drop characteristics.

Connector Types: Scalar Signals vs Hydrodynamic Vectors (FLN1/FLN2)

The table below details SIMIT connector types and their underlying physical data structures:

Connector TypeMedium / PhaseTransmitted Thermodynamic VariablesApplication ScopeStandard Real (In/Out)Scalar DataSingle floating-point value (e.g., 4-20 mA, position 0-100%)Controller I/O signals, actuator commands.FLN1Single-Phase FluidPressure ($p$), Temperature ($T$), Mass Flow Rate ($\dot{m}$)Incompressible liquid water, hydraulic oil, compressed air networks.FLN2Two-Phase Fluid (Water/Steam)Pressure ($p$), Specific Enthalpy ($h$), Mass Flow ($\dot{m}$), Vapor Quality ($x$)Boilers, steam drums (DrumWS), evaporators, condensers, turbine steam supplies.

CTE Mathematical Functions and Syntax Reference

When implementing cyclic equations within CTE components (e.g., modifying DrumWS), SIMIT provides specialized preprocessor functions and thermodynamic state lookups:

1. Built-in Mathematical Operators

_sum(a, b, c, ...): Computes the arithmetic sum of connected branch mass flows or heat inputs.
_limit(val, min_val, max_val): Constrains a state variable within physical boundaries.
_max(a, b) / _min(a, b): Selects extreme values for direction-dependent flow models.
_sqrt(val): Square root function used in orifice and valve flow coefficient ($Cv/Kv$) formulas.

2. Thermodynamic State Functions (IAPWS-IF97)

SIMIT integrates thermodynamic properties of water and steam compliant with IAPWS-IF97:

// Example thermodynamic state queries in CTE:
T = T_ph(p, h);     // Temperature as function of pressure and enthalpy
rho = rho_ph(p, h); // Density as function of pressure and enthalpy
x = x_ph(p, h);     // Steam quality (0 = saturated liquid, 1 = dry steam)
h_liq = h_p(p);     // Boiling liquid saturation enthalpy
h_vap = h_p(p);     // Saturated vapor enthalpy

Verification

To verify custom equations and connector bindings in a modified FLOWNET component:

In CTE, open the modified component and save: confirm zero syntax errors are reported in the compiler log.
In SIMIT, create a simple test diagram containing: a pressure source, the custom DrumWS component, and a sink.
Interconnect the FLN2 terminals: verify connection lines render with the standard thick blue/red fluid net style.
Start SIMIT Simulation: observe the component diagnostic table in the property view.
Verify that pressure, mass flow, and enthalpy converge smoothly to steady-state values without numerical oscillations.

Limitations and Operational Precautions

Operational boundaries when writing FLOWNET equations:

Matrix Singularities: If writing custom branch equations, ensure pressure-flow relationships include a non-zero resistance; zero-resistance loops cause matrix solver singular errors.
Enthalpy Discontinuities: Avoid abrupt step changes in specific enthalpy ($h$); thermodynamic lookups near the critical point ($22.064\text{ MPa}$) require gradual numerical damping.
Documentation Access: Comprehensive thermodynamic function prototypes are embedded in the SIMIT CTE online help (F1) under the Thermodynamic State Functions index.

Engineer FAQ

What physical quantities does the FLN2 connector type carry in SIMIT?

FLN2 carries a four-dimensional hydrodynamic state vector: Pressure ($p$), Specific Enthalpy ($h$), Mass Flow ($\dot{m}$), and Temperature ($T$), fully modeling two-phase water/steam mixtures.

Where are SIMIT CTE mathematical functions like _sum() documented?

They are documented in the SIMIT Component Type Editor (CTE) Reference Manual and the SIMIT local help system (F1) under 'Mathematical Preprocessor Functions'.

Can standard scalar mathematical blocks be wired to FLN2 terminals?

No. FLN2 terminals can only connect to other FLN2 ports or FLOWNET boundary components (sources, sinks, nodes). Converting fluid states to scalar values requires dedicated FLOWNET measurement blocks.