Heat Pipe
This feature models a two-port passive component of the thermal system used to take into account heat loss in a heat pipe. It connects two nodes, by creating a difference in the temperatures of its two connecting ports, corresponding to the evaporator and condenser sides of the heat pipe.
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 R (SI unit: K/W) is the total thermal resistance, accounting for the relevant heat transfer processes present in the heat pipe. It may be defined either directly or as the sum of the resistances related to conduction through the solid wall and porous wick of the heat pipe, depending on the available data for the thermal and geometric properties.
Note that ΔT =Tcondenser -Tevaporator and is meant to be negative in the classical operating mode of the heat pipe. The heat rate P is set to 0 when this condition does not hold.
See Theory for the Heat Pipe Component for more details on the underlying theory.
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 the average of the two port temperatures, Tave = 0.5*(Tp1+Tp2), is set.
Identifier
Enter a Component name for the heat pipe. The prefix is HP.
Node Connections
Set the two Node names for the nodes connected by the heat pipe. Note that the ports p1 and p2 correspond respectively to the evaporator and condenser sides of the heat pipe.
Component Parameters
Select an option from the Model list for the expression of the total thermal resistance R:
when Total resistance is selected, set a value or expression for the Total thermal resistance, R.
when Multiple inputs (default) is selected, the total thermal resistance is the sum of the thermal resistances due to conduction in the wall and the wick of the heat pipe, on the evaporator and condenser sides, and further settings are required.
When Input quantity is set to Thermal resistances, enter values or expressions for the Thermal resistance, evaporator wall, Rwall,e, the Thermal resistance, evaporator wick, Rwick,e, the Thermal resistance, condenser wick, Rwick,c, and the Thermal resistance, condenser wall, Rwall,c.
In the network representation of heat transfer in the heat pipe, these thermal resistances are connected in a serial way, and the total thermal resistance R is thus defined as:
The thermal resistances due to transport of vapor in the channel and transport of liquid in the porous wick are neglected in this network representation, see Theory for the Heat Pipe Component for details.
Alternatively, set Input quantity to Configuration and thermal properties to calculate the thermal resistances from the geometric dimensions and thermal properties of the wick and wall of the heat pipe. This option is available for a flat or cylindrical heat pipe. Further settings display underneath to define the geometric configuration. You can refer to the Sketch section to get an illustration of the configuration.
Cylindrical
Set values or expressions for the geometric dimensions used to calculate the wick and wall thermal resistances on the evaporator and condenser sides: Outer radius, ro, Wall thickness, dwall, Wick thickness, dwick, Evaporator length, Le, and Condenser length, Lc.
Flat
Set values or expressions for the geometric dimensions used to calculate the wick and wall thermal resistances on the evaporator and condenser sides: Depth, D, Height, H, Wall thickness, dwall, Wick thickness, dwick, Evaporator length, Le, and Condenser length, Lc.
Heat Conduction, Wall
The thermal conductivity ks of the wall should be set in this section when Input quantity is set to Configuration and thermal properties in the Component Parameters section.
Select any material from the Material list to define the Thermal conductivity k From material. Alternatively, choose among Copper and Aluminum for a predefined material. For User defined enter a value or expression.
Heat Conduction, Wick
The thermal conductivity keff of the wick should be set in this section when Input quantity is set to Configuration and thermal properties in the Component Parameters section.
The wick is a porous medium. When Input quantity is set to Structure model, its effective thermal conductivity is expressed as a function of its porosity and the thermal conductivities of the immobile solid and the liquid parts.
Select any material from the Material list to define the Thermal conductivity, liquid kl From material. Alternatively, choose among Water and Mercury for a predefined material. For User defined enter a value or expression.
Select any material from the Material list to define the Thermal conductivity, immobile kw From material. Alternatively, choose among Copper and Aluminum for a predefined material. For User defined enter a value or expression.
Then, set a value or expression for the Porosity, ε, and select an option from the Structure list to calculate the effective conductivity. See Theory for the Heat Pipe Component for details.
Alternatively, set Input quantity to User defined to set directly the Effective thermal conductivity of the wick, keff.
Operating Maximum Power
Finally, select the Specify operating maximum power check box to curb the heat pipe when the operating maximum power Pmax is known. Set a value or expression for Pmax.
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 material properties of the heat pipe.
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:
Heat rate
Temperature at node 1
Temperature at node 2
Location in User Interface
Context Menus
Ribbon
Physics tab with Lumped Thermal System selected: