3.5.2 Description of Fiber Properties

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 Section  2.9.1 for details about how the Blending Interval is applied to the fiber viscosity.

Cp   ( Create/Edit Materials dialog box) is the specific heat, $C_{p,f}$, 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, except user-defined functions.

Density   ( Create/Edit Materials dialog box) is the density, $\rho_f$, 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, except user-defined functions.

Emissivity   ( Fiber Model dialog box) is the emissivity of fibers in your model, $\epsilon_f$, used to compute radiation heat transfer to the fibers (Equations  2.2-13, 2.2-14, 2.6-4 and 2.6-5) 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  2.2-3 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, $\chi$. 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, $T_{vap}$, 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 Equations  2.2-16 and 2.9-5 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  2.9-4). 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, $\lambda_f$, 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, except user-defined functions.

Zero Shear Viscosity   is the fiber viscosity, $\mu_f$, at zero shear rate. It is not the elongational or Trouton viscosity. Depending on the chosen fiber model, you have to enter values in the Create/Edit Materials dialog box and/or in the Fiber Model dialog box.

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 except user-defined functions.

In the Fiber Model dialog box, you have to enter the coefficients for the fiber viscosity in liquid state. 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  2.9-2.

For Dry Spun Fibers you only have to enter the coefficients in the Fiber Model dialog box. 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.