# Working Fluid

This Panel Consists of settings related to working fluid of the flow circuit.

Parameter | Description |
---|---|

Transition Reynolds Number (REYTRAN) |
Transition value for Reynolds Number used in all tube elements. For values of Reynolds Numbers within 5% of REYTRAN, the flow is assumed to be in transition. In the transition region a transition factor (between 0 and 1) is calculated as the ratio of (Reynolds Number minus 95% of REYTRAN) to (10% of REYTRAN). This transition factor is then used to linearly scale the values of friction factor, heat transfer coefficient, and adiabatic wall temperature between the fully laminar and the fully turbulent values. For values of Reynolds Number above REYTRAN, turbulent flow values are used. For values of Reynolds Number below REYTRAN, laminar flow values are used. (Default value = 2300 providing a transition range from 2185 to 2415.) |

Supersonic Chamber Mode (ISUPER) |
Flag used to specify whether or not supersonic Mach numbers (Mach >
1.0) will be permitted in momentum chambers. Suggested input is either 0
or 2 depending on whether supersonic flow should be allowed. < 2.0 Mach number to be limited to 1.0. (0-Supersonic Momentum Chambers Disallowed). ≥ 2.0 Supersonic Mach numbers are permitted. (2-Supersonic Momentum Chambers Allowed). In inertial chambers, supersonic values are always permissible and ISUPER has no effect. (Default value = 0. Supersonic flow in momentum chambers not allowed). |

Fluid Properties Option (PROPS) |
Identifies working fluid(s). This is not a required input. Fluids are
usually identified by boundary chambers and not this input. 0: Fluid 1 is Ideal Air; Fluid 2 is Steam (default). 1-11: Not supported in standard Flow Simulator. 12: Fluid 1 is Ideal Air; Fluid 2 is a Real Gas. 13: Fluids 1 and 2 are distinct Real Gases. 17: Fluid 1 is CEA air; Fluid 2 is a CEA fuel. 18: Fluid 1 is Ideal Air; Fluid 2 is a CEA fuel. (Default value = 0). If PROPS is set to 17 or 18, Flow Simulator looks for either a fuel source component or a name list in the model database that identifies the type(s) of CEA fuel used. PROPS = 17 uses CEA definition of air properties for working fluid 1 instead of using the Flow Simulator definition of air (types 0, 12, 18). |

Chamber Gas Handling Flag (CH_FLUID_MODE) |
Flag that specifies how Flow Simulator
models should handle incompressible/compressible gas mixtures at
chambers. The values for the flag are: 0: All gas chambers - compressible 1: All gas chambers - incompressible 3: Treat chambers as compressible if at least one neighboring element is compressible. 4: Treat chambers as incompressible if at least one neighboring element is incompressible. |

Energy Balance Option (TMIX) |
Chamber energy balance calculation procedure. Options one and two use
fluid specific heat times fluid temperature, while option three uses
enthalpy. Options one and two use different methods for calculating the
specific heat of the streams entering a chamber. 0: Default (Traditional Energy Balance). 1: Traditional Flow Simulator Energy Balance. 2: Second Order Energy Balance → Use second order T mixing, which works well when mixing different species with different specific heats. 3: Enthalpy based energy balance → Requires Coolprop fluids. |

Call NASA CEA T Change Limit (CHCO_T_LIM) |
Percentage temperature change between iterations. Only above this cut off are the Fluid Properties updated. Automatically adjusted inside the solver. Only an initial guess from the user. (Only visible if PROPS = 17 or 18). |

Call NASA CEA P Change Limit (CHCO_P_LIM) |
Percentage pressure change between iterations. Only above this cut off are the Fluid Properties updated. Automatically adjusted inside the solver. Only an initial guess from the user. (Only visible if PROPS = 17 or 18). |

Coolprop Method (CP_METHOD) |
Coolprop fluid property retrieval method. Only try option two if
option one is not working. 0: Automatic (uses the Fast, Low Level method) 1: Fast, Low Level method. 2: Slow, High Level method. |

Check Limits Option (PROP_LIMIT_OPT) |
Option for temperature and pressure limit checking when retrieving
fluid properties. This was implemented to help Coolprop run early in
iterations when T and P may fall outside of limits. The automatic limit
check option uses Coolprop’s minimum and maximum T and P, but these may
not be accurate for some fluids (CO2 in particular). 0: Automatic limit checks. 1: Use Fluid Chamber P and T limits. 2: No limit checking. |

Converge Limits Option (PROP_CONV_OPT) |
This option controls convergence behaviour if the T and P are found
to be outside of the limits established with PROP_LIMIT_OPT. 0: Do not converge if the outside the limit (default). 1: Ignore limits for convergence. 2: Ignore limits after a percentage of maximum iteration. |

Percentage Of Maximum Number Iterations
(PROP_CHECK_PCT) |
The percentage of the maximum iteration used if PROP_CONV_OPT=2. |

Limit NASA CEA Products (CEA_ONLY_OPT) |
Controls how NASA CEA calculates fluid properties for chambers and
all elements except combustion elements. This control limits the species
considered in the CEA equilibrium calculation. If the Limit Products
option is used, CEA only considers the species received. For example, if
pure NH3 is sent to NASA CEA, it only considers NH3 when calculating
properties. With the No Limit option, CEA returns the properties for a
mixture of NH3, H2, and N2. 0: No limit. 1: Limit products. |