FEM ConstraintHeatflux

Description

Defines a heat flux load on a surface. The following heat flux types are supported:

• regular surface heat flux load ${\displaystyle q}$
• convective heat flux load on a surface at a temperature ${\displaystyle T}$ with a film coefficient ${\displaystyle h}$ and with the environment (sink/ambient) temperature ${\displaystyle T_0}$. The convective heat flux ${\displaystyle q}$ will satisfy: ${\displaystyle q=h(T-T_0)}$.
• introduced in 1.0: radiation heat flux on a surface. It satisfies: ${\displaystyle q=ϵ\sigma (T^4-T_0^4)}$ where ${\displaystyle ϵ}$ is the surface emissivity and ${\displaystyle \sigma }$ is the Stefan-Boltzmann constant.

Heat sink with convective heat flux load on the surfaces exposed to air

Usage

1. There are several ways to invoke the command:
   • Press the Heat Flux Load button.
   • Select the Model → Thermal Boundary Conditions and Loads → Heat Flux Load option from the menu.
2. Click the Add button. In the 3D view select the face(s) (introduced in 1.1: or edge(s) in 2D models) on which the heat flux load should be applied. Optionally, click the Remove button to remove the selected faces/edges from the selection list.
3. Choose the heat flux type and specify its parameters:
   • DFlux - general heat flux, enter the Surface Heat Flux in Watts per surface area (W/m^2)
   • Convection (default) - convective heat flux, enter the desired Film Coefficient and Ambient Temperature
   • introduced in 1.0: Radiation - radiation heat flux, enter the surface Emissivity and Ambient Temperature

Properties

• DataAmbient Temp: Ambient temperature (for Convection and Radiation modes).
• DataFilm Coef: Film coefficient (for Convection mode).
• DataEmissivity: Emissivity (for Radiation mode).
• DataDFlux: Distributed heat flux (for DFlux mode).
• DataConstraint Type: Type of heat flux load: DFlux, Convection or Radiation.
• DataCavity Radiation - introduced in 1.1: Enable cavity (surface-to-surface) radiation (for Radiation mode).
• DataCavity Name - introduced in 1.1: Name of the cavity definition to which the heat flux constraint belongs (for Radiation mode).
• DataEnable Amplitude - introduced in 1.1: Enables the use of CalculiX's amplitude for time variation of the heat flux load. At a given time, magnitude of the load is multiplied by the amplitude value corresponding to that time. Linear interpolation is used between the specified values. Constant values are used outside of the specified range.
• DataAmplitude Values - introduced in 1.1: Amplitude table in the following format:

time_1, amplitude_value_1
...

Default is linear increase from 0% at t=0 to 100% at t=1:

0, 0
1, 1

Notes

• The heat flux load uses the following CalculiX cards depending on the selected mode:
  • *FILM for Convection
  • introduced in 1.0: *RADIATE for Radiation
  • *DFLUX for DFlux