What Does Radiation Do?
- Radiation is applied to a surface that will transfer heat to the surroundings without physical interaction. The transfer in this case will be to the ambient. Radiation can also occur between two objects. In this instance, body-to-body radiation must be used.
- The amount of heat that is transferred due to radiation is controlled by the radiation function. A high radiation function will result in the surface transferring large amounts of heat with the ambient. This will cause the temperature of the surface to be close to the temperature of the surroundings. A low radiation function will result in the surface transferring a small amount of heat with the ambient. This will create a significant difference between the surface temperature and the ambient temperature.
- The ambient temperature is the average temperature of the surroundings with which the surface is transferring heat.
- For the radiation load to be applied in the analysis, you will have to assign a Radiation multiplier in the Multipliers tab of the Analysis Parameters dialog. This value will be multiplied by the radiation function and the product will be used for the radiation load in the analysis.
- The radiation function must follow a load curve during the analysis. If you assign this to load curve 0, the value will remain constant at the value input for the duration of the analysis. You can vary the values by creating a load curve in the Load Curves dialog. For a radiation function, the factor will be multiplied by the radiation function at each time step and also by the value in the Radiation multiplier field in the Multipliers tab of the Analysis Parameters dialog. The product of these three values will be used for the radiation function at that time step.
Apply Radiation
If you have surfaces selected, you can right-click in the display area and select the Add pull-out menu. Select the Surface Radiation Load command.
Radiation Section
Specify the radiation function in the Function field. F rad , adjusts the amount of heat transferred by radiation to account for emissivity (e) and the view factor (V m-s ) between the model (m) and the surroundings s. The view factor is dependent on the geometry between the model and the surroundings and can be looked up in heat transfer textbooks. The radiation function is defined as
F rad = e * Vm-s
For a steady-state heat transfer analysis, the Function value will be multiplied by the Radiation multiplier on the Multipliers tab of the Analysis Parameters dialog. For a transient heat transfer analysis, select the load curve that will be applied to the function in the Load Curve box. The function at any given time will equal the function entered on the dialog multiplied by the interpolated load curve factor. Using Load Curve 0 will keep the function constant throughout the analysis.
Ambient Temperature Section
Specify the temperature of the ambient conditions to which the surface is radiating in the Temperature field.
For a steady-state heat transfer analysis, the ambient temperature is simply the value you enter. If you are performing a transient heat transfer analysis, select the load curve that will be applied to the ambient temperature in the Load Curve box. The Temperature value is added to the factor entered in the load curve. To maintain dimensional consistency, enter a Load Curve Magnitude value on the dialog. This value is multiplied by the interpolated load curve factor and then added to the Temperature value.
Temperature at time t = Temperature + Load Curve Magnitude * load curve factor interpolated at time t
Using Load Curve 0 will keep the ambient temperature constant throughout the analysis.
For either load curve, press the View / Edit Load Curve button to define a load curve in the Load Curve Editor, or use the Setup 
Model Setup Parameters Analysis Parameters dialog box.
Plate Options Section
If the radiation load is being applied to plate elements, and you want it to be applied to both sides, activate the Apply load to both sides check box. Since the plate element is assumed to have the same temperature on each face, applying a load on both sides will be equivalent to applying twice the load on one side.