Convective Thermal Resistor
This feature models a two-port passive component of the thermal system. It connects two nodes, by creating a difference in the temperatures of its two connecting ports. It models heat loss by convection in a fluid of temperature Tp2 over a solid wall of temperature Tp1.
It adds equations for the heat rates Pp1 and Pp2 and the temperatures Tp1 and Tp2 at the connecting ports p1 and p2 of the component, and defines the following relation between the heat rate P and the temperature difference ΔT:
where Rconv (SI unit: K/W) is the thermal resistance, which is defined from the surface Area A and the Heat transfer coefficient h as
Model Input
This section contains fields and values that are inputs for expressions defining material properties. If such user-defined property groups are added, the model inputs appear here.
By default the Temperature is User defined and set to the port p1 temperature, Tvar = Tp1.
Identifier
Enter a Component name for the convective thermal resistor. The prefix is CR.
Node Connections
Set the two Node names for the nodes connected by the convective thermal resistor. Note that the ports p1 and p2 correspond respectively to the solid wall and fluid regarding the evaluation of the temperature.
Component Parameters
Set the Area A of the surface of the convective heat rate and define the Heat transfer coefficient h used to express the convective thermal resistance. The default option is to enter a User defined value for the Heat transfer coefficient h.
In addition, the following options are also available to control the type of convective heat rate to model: External natural convection, Internal natural convection, External forced convection, or Internal forced convection.
For all options except User defined, select a Fluid: Air (default), Transformer oil, Water, Moist air, or From material.
When From material is selected, choose a material available from the Materials list.
Depending of the selected option, different parameters are needed. You can refer to the Sketch section to get an illustration of the configuration.
See the Fluid feature for more details on the settings related to each correlation.
The external conditions should be set.
Set the Absolute pressure, pA. For User Defined, enter a value or expression. Else, select an Ambient absolute pressure defined in an Ambient Properties node under Definitions. The pressure is used to evaluate the Fluid material properties and this setting is not available for the Transformer oil and Water options.
Finally, when the Fluid is Moist air, also set the External relative humidity, ϕw,ext, and the Surface relative humidity, ϕw,s, used to evaluate the material properties.
For the external temperature, the temperature Tp2 at the connecting port p2 is used.
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This feature is the two-port component equivalent of the Heat Rate node with Convective heat rate option.
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The detailed definition of the predefined heat transfer coefficients is given in Convective Heat Transfer Correlations.
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For a thorough introduction about how to calculate heat transfer coefficients, see Incropera and DeWitt in Ref. 21.
Initial Values
Set user defined values or expressions for the Initial temperature at node 1, T1,init, and the Initial temperature at node 2, T2,init, to be used at initialization, in particular to evaluate the heat transfer coefficient.
Results
Select appropriate options in the Add the following to default results in order to include the following global variables (space-independent) in the default plots:
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 Heat rate
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 Temperature at node 1
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 Temperature at node 2
Location in User Interface
Context Menus
Lumped Thermal System > Convective Thermal Resistor
Ribbon
Physics tab with Lumped Thermal System selected:
Global > Convective Thermal Resistor