What Does Convection Do?
- Convection is applied to a surface that will transfer heat to the surroundings due to the interaction of the fluid of the surroundings and the surface. A convection coefficient represents how much heat is transferred in this manner. A high convection coefficient will result in the surface transferring large amounts of heat with the surroundings. This will cause the temperature of the surface to be close to the temperature of the surroundings. A low convection coefficient will result in the surface transferring a small amount of heat with the surroundings. 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.
- To keep a surface at a certain value, it is often convenient to apply a convection load with a large convection coefficient and assign the ambient temperature to the desired fixed temperature.
- For the convection load to be applied in the analysis, you will have to assign a Convection multiplier in the Multipliers tab of the Analysis Parameters dialog. This value will be multiplied by the convection coefficient and the product will be used for the convection load in the analysis.
Apply Convection
If you have surfaces selected, you can right-click in the display area and select the Add pull-out menu. Select the Surface Convection Load command.
Convection Coefficient Section
- If the convection coefficient will be constant across the entire surface, regardless of the temperature, specify the convection coefficient in the Temperature Independent Convection Coefficient field. To calculate the convection coefficient based on the geometry and flow properties, press the Calculate button. This will access the Film/Convection Coefficient Calculator. Values for the convection coefficient can also be stored and read from the library; press the Read from Library button to access the convection library. See the page Film/Convection Coefficient Calculator: Film/Convection Library.
- If the convection coefficient will vary according to the temperature of the surface, select the Temperature Dependent Curve radio button and specify a curve number which will be used to control the convection coefficient. Press the View / Edit Curve button and specify the convection coefficient to be used at each temperature value in a tabular format. The convection coefficient values will be linearly interpolated between temperature values. This curve must include the entire temperature range that the surface will experience throughout the analysis. Linear interpolation will be used to define the convection coefficients at temperatures between the data points. For brick, tetrahedral and 2D element calculations, the temperature values at the surface integration points are used to determine the convection coefficient. For plate and rod elements, the average temperature on the element face will be used to determine the convection coefficient.
For a steady-state heat transfer analysis, the Convection Coefficient value will be multiplied by the Convection multiplier on the Multipliers tab of the Analysis Parameters dialog. If you are performing a transient heat transfer analysis, select the load curve that will be applied to the convection coefficient in the Load Curve box. The convection coefficient at any given time will equal the convection coefficient entered on the dialog multiplied by the interpolated load curve factor. Using Load Curve 0 will keep the convection coefficient constant throughout the analysis.
Ambient Temperature Section
Next, specify the temperature of the ambient conditions to which the surface is convecting 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 convection 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 there is no change through the thickness of a plate element, applying a load on both sides will be equivalent to applying twice the load on one side.