# Fluid model

Enabling the fluid solver and specifying fluid model options. The following inputs must be preceded by the given to the fluid solver e.g., “fluid.”

| Description | Type | Default
--- | --- | --- | ---
solve | Specify the names of the fluids or None to disable the fluid solver. The name assigned to the fluid solver is used to specify fluids inputs. | String | None
molecular_weight | Value of constant fluid molecular weight | Real | 0
viscosity | Specify which viscosity model to use for fluid [required]. Available options include: ‘constant’ for constant viscosity model | String | None
viscosity.constant | Value of constant fluid viscosity [required if viscosity_model=’constant’]. | Real | 0
specific_heat | Specify which specific heat model to use for fluid [required if advect_enthalpy]. Available options include: ‘constant’ for constant specific heat model ‘mixture’ required when fluid is a mixture of species | String | None
specific_heat.constant | Value of constant fluid specific heat [required if specific_heat_model=’constant’]. | Real | 0
thermal_conductivity | Specify which thermal conductivity model to use for fluid [required if advect_enthalpy=1]. available options include: ‘constant’ for constant thermal conductivity model | String | None
thermal_conductivity.constant | Value of constant fluid thermal conductivity [required if thermal_conductivity_model=’constant’]. | Real | 0
thermodynamic_pressure | Value of the thermodynamic pressure [required if the constraint type is IdealGasClosedSystem] | Real | 0
reference_temperature | Value of the reference temperature used for specific enthalpy | Real Real | 0 0
species | Specify which species can constitute the fluid phase [defined species must be a subset of the species.solve arguments] | String | None
newton_solver.absolute_tol | Define absolute tolerance for Damped-Newton solver | Real | 1.e-8
newton_solver.relative_tol | Define relative tolerance for Damped-Newton solver | Real | 1.e-8
newton_solver.max_iterations | Define max number of iterations for Damped-Newton solver | int | 500

Below is an example for specifying fluid solver model options.

    fluid.solve = my_fluid

    fluid.viscosity = constant
    fluid.viscosity.constant = 1.8e-5

    fluid.reference_temperature = 298.15

    fluid.thermal_conductivity = constant
    fluid.thermal_conductivity.constant = 0.024

    fluid.specific_heat = mixture

    fluid.species =  O2  CO  CO2