For more information, see the following sections:
The material properties you specify for the fibers are used for all fibers defined in your model. You cannot consider fibers consisting of different fiber materials in one simulation.
The continuous fiber model makes use of Ansys Fluent’s material concept for the Material Type of the fluid. Because not all properties are available in Ansys Fluent’s Create/Edit Materials dialog box for this material type, some additional property information can be provided through the Fiber Model dialog box (Figure 34.1: The Fiber Model Dialog Box). The procedure to define the material properties for the fibers in your simulation is as follows:
In the Create/Edit Materials dialog box, set the Material Type as fluid. This fluid will be used as the polymer or solvent in the fiber.
Enter all data for this material.
You can use all profiles available in the Create/Edit Materials dialog box to define the properties as functions of temperature. In order to invoke user-defined fiber properties, you need to use the UDF template file (see User-Defined Functions (UDFs) for the Continuous Fiber Model for details). UDF access is available for viscosity, density, specific heat capacity, thermal conductivity and solvent liquid-vapor equilibrium pressure.
Select the Polymer in the Materials group box of the Fiber Model dialog box.
For dry spinning simulations, you also have to select Solvent and the gas phase species that represents the Solvent Vapor.
Enter any additional data needed for the fiber material in the Fiber Model dialog box.
The properties that appear in the Fiber Model dialog box vary depending on the fiber model type.
The following list describes the properties you may need for a fiber material. For every property listed, the dialog box name is provided where the property can be defined.
- Blending Interval
(Fiber Model dialog box) is the temperature interval used to compute an average of the fiber viscosities in liquid and solid state of Melt Spun Fibers. This option is only available when the Melt Spun Fibers option is selected. See Fiber Viscosity for details about how the Blending Interval is applied to the fiber viscosity.
- Cp
(Create/Edit Materials dialog box) is the specific heat,
, of the fiber in units of energy per mass and temperature. In the
case of dry spun fibers, a mass average is computed based on the values entered for
Polymer and its Solvent. You can use any
of the functions available to define temperature dependency. If you want to use a
user-defined function profile, you need to modify the UDF template provided by
Ansys Fluent. See User-Defined Functions (UDFs) for the Continuous Fiber Model for details.- Density
(Create/Edit Materials dialog box) is the density,
, of the fiber in units of mass per unit volume. This density is
the mass density and not the volume density. In the case of dry spun fibers, a mass
average is computed based on the values entered for Polymer and
its Solvent. You can use any of the functions available to
define temperature dependency. If you want to use a user-defined function profile,
you need to modify the UDF template provided by Ansys Fluent. See User-Defined Functions (UDFs) for the Continuous Fiber Model for details.- Emissivity
(Fiber Model dialog box) is the emissivity of fibers in your model,
, used to compute radiation heat transfer to the fibers (Equation 22–13, Equation 22–14, Equation 22–24 and Equation 22–25) when the P-1 or
discrete ordinates radiation model is active. Note that you must enable radiation to
fiber, using the Fiber Radiation Interaction option in the
Fiber Model dialog box.- Flory Huggins
(Fiber Model dialog box) can be enabled to apply Equation 22–3 to compute the vapor-liquid equilibrium at the fiber surface. When it is enabled, you have to specify an appropriate value for the dimensionless Flory Huggins parameter,
. This option is only visible when Dry Spun
Fibers has been chosen.- Latent Heat
(Fiber Model dialog box) is the latent heat of vaporization of the Solvent when evaporated from a dry spun fiber. Note that you have to enter the vaporization or reference temperature,
, where the specified value of the latent heat has been measured.
This vaporization temperature is used to automatically consider the change of latent
heat with temperature. See Equation 22–16 and Equation 22–39 for more information on how this is achieved.
These options are only visible when Dry Spun Fibers has been
chosen.- Solidification Temperature
(Fiber Model dialog box) is the temperature below which the fiber polymer of a Melt Spun Fiber will solidify. It will be used when computing the viscosity of Melt Spun Fibers. This option is only visible when Melt Spun Fibers has been chosen.
- Solvent Vapor Pressure
(Fiber Model dialog box) is the vapor pressure of the solvent evaporating from the fiber surface in dry spinning. You have to enter coefficients for an Antoine-type equation (Equation 22–38). Note that the coefficients must be entered in such units that the outcome of the Antoine-type equation is in Pascal. In addition to the coefficients of the Antoine equation, you have to enter the range of validity for the vapor pressure. Below the minimal temperature the vapor pressure at the minimal temperature will be used. Above the maximal temperature, the vapor pressure at the maximal temperature is used.
- Thermal Conductivity
(Create/Edit Materials dialog box) is the thermal conductivity,
, of the fiber in units of power per length and temperature. In the
case of dry spun fibers, a mass average is computed based on the values entered for
Polymer and its Solvent. You can use any
of the functions available to define temperature dependency. If you want to use a
user-defined function profile, you need to modify the UDF template provided by
Ansys Fluent. See User-Defined Functions (UDFs) for the Continuous Fiber Model for details.- Zero Shear Viscosity
(Create/Edit Materials dialog box and/or the Fiber Model dialog box, depending on the chosen fiber model) is the fiber viscosity,
, at zero shear rate. It is not the elongational or Trouton
viscosity. For Melt Spun Fibers, you have to enter the viscosity of the fiber in solid state in the Create/Edit Materials dialog box for the fluid you have selected as the fiber polymer. Typically this value will be very high compared to the liquid fiber viscosity to represent the fibers as solids. For the solid fiber viscosity you can make use of any temperature-dependent function available in the Create/Edit Materials dialog box. If you want to use a user-defined function profile, you need to modify the UDF template provided by Ansys Fluent. See User-Defined Functions (UDFs) for the Continuous Fiber Model for details.
In the Fiber Model dialog box, you have to enter the coefficients for the fiber viscosity in liquid state (Equation 22–35). To define viscosity as a function of fiber velocity gradient, set
to a value different than 1. In the case of Melt Spun
Fibers, you also have to enter data for the Solidification
Temperature and the Blending Interval. The blending
of the viscosities in liquid and solid state will be computed based on Equation 22–36.For Dry Spun Fibers you only have to enter the coefficients for Equation 22–37 in the Fiber Model dialog box. To specify fiber viscosity as a function of fiber velocity gradient, set
to a value different than 1. Any value entered in the
Create/Edit Materials dialog box for viscosities of the fluids
used as fiber polymer and fiber solvent will not be considered.Note: Note that depending on fiber velocity gradient, the numerical behavior of the Fiber Model equations may become unstable in combination with fiber viscosity.