The Boundary Conditions are listed within a group located under the HEAT solver, in the object tree. It allows the user to define thermal boundary conditions in the simulation region and assign values to them.
You can add a new boundary condition by selecting one from the Boundary Conditions section of the HEAT tab. Each boundary condition can be edited, renamed, deleted in the same way as any simulation object.
NOTE: The sweep option of the thermal boundary conditions is not available when they are used as part of an electrothermal simulation ('coupled' mode). If the thermal boundary is set to sweep mode then the solver will ignore the boundary condition and will generate a warning message in the log file. 
Temperature
NAME: Name of the BC
General tab
BC MODE: Steady state
Sweep Type: Can be 'single' value or a parameter sweep.
 TEMPERATURE: Temperature at the boundary in Kelvin.
 THERMAL IMPEDANCE(OPTIONAL): Applies a thermal insulance at the boundary with units of m2K/W.
BC MODE: Transient
Can be a 'Single' constant value or a timedependent 'Transient' value.
 T (us): Time step.
 TEMPERATURE (K): Temperature at the boundary, at the specified time step, in Kelvin.
 THERMAL IMPEDANCE(OPTIONAL): Applies a thermal insulance at the boundary with units of m2K/W.
Geometry tab
The geometry option defines where the boundary condition can be applied.
Note: A list of domains will be available under the SIMULATION REGION object once the simulation region is partitioned. A list of solids (primitives) are available under the GEOMETRY Container Group. 
Volume, surface, line and point in 3D and 2D:

Volume 
Surface 
Point 

3D 
Volume 
Surface or Line 
Point 
2D 
Surface 
Line 
Point 
Surface Type
 DOMAIN:EXTERIOR : Select the target domain. The reference geometry is the common surface(s) shared by the uttermost surface(s) of the selected domain and the simulation region. The selected domain has to have at least a surface that is shared with one of the simulation region surfaces.
 DOMAIN:DOMAIN : Select the target domains. The reference geometry is the common surface(s) shared by the two selected domains.
 DOMAIN : Select the target domain. The reference geometry is the surfaces of the selected domain.
 SOLID : Select the target solid. The reference geometry is the surfaces that enclose the selected volume if the solid is a 3D shape, or the surface if the solid is a 2D plane.
 SIMULATION REGION : Select one or more simulation region boundaries. The reference geometry is the selected boundaries.
 SOLID:SIMULATION REGION : Select one or more simulation region boundaries and the target solid. The reference geometry is the common surface(s) shared by the simulation region and the target solid.
 MATERIAL:MATERIAL : Select the target materials. The reference geometry is the surface(s) that is shared by the two selected materials. This is only available in some boundary conditions.
 SURFACE : Type the identifier of the partition surface. If the target partition surface is SURFACE 3, type 3. If the target partition surfaces are SURFACE 3 and SURFACE 5, enter 3,5.
Power
NAME: Name of the BC
General tab
BC MODE: Steady state
Sweep Type: Can be 'single' value or a parameter sweep.
 POWER (W): Absolute power (heat) flow at the boundary in units of W. A positive value indicates heating (heat going into the simulation volume) and a negative value indicates cooling (heat being removed from the simulation volume).
BC MODE: Transient
Can be a 'Single' constant value or a timedependent 'Transient' value.
 T (us): Time step.
 POWER (W): Absolute power (heat) flow at the boundary in units of W. A positive value indicates heating (heat going into the simulation volume) and a negative value indicates cooling (heat being removed from the simulation volume).
Geometry tab
See the "Geometry tab" of the "Temperature" boundary condition.
Heat flux
NAME: Name of the BC
General tab
HEAT FLUX: This sets the heat flux at the interface between two materials. This option can be used to define a cooling (or heating) boundary condition at the surface of an object in the simulation region.
 HEAT FLUX (W/m2): Sets the heat flux through the interface.
Geometry tab
See the "Geometry tab" of the "Temperature" boundary condition.
Convection
NAME: Name of the BC
General tab
 AMBIENT TEMPERATURE (K): Sets the temperature of the fluid.
 MODEL: There are 5 different convection models available.
Model 
Definition 
Input parameters 

Constant 
Simple model using a constant convective heat transfer coefficient 
h (W/m^2.K): Sets a constant value for the convective heat transfer coefficient 
Natural convection (vertical) 
Analytic model applicable to convective heat transfer between a vertical plate and surrounding fluid at rest 
length scale (m): Characteristics length dependent on the height of the vertical plane 
Natural convection (top plate) 
Analytic model applicable to convective heat transfer between the top surface of a horizontal plane and surrounding fluid at rest 
length scale (m): Characteristics length dependent on the diameter (area/perimeter) of the horizontal plane 
Natural convection (bottom plate) 
Analytic model applicable to convective heat transfer between the bottom surface of a horizontal plane and surrounding fluid at rest 
length scale (m): Characteristics length dependent on the diameter (area/perimeter) of the horizontal plane 
Forced convection 
Analytic model applicable to convective heat transfer between a surface and surrounding fluid flowing at a certain velocity 
length scale (m): Characteristics length dependent on the length of the plane along the direction of the fluid flow fluid velocity (m/s): Velocity of the surrounding fluid due to external influence 
Geometry tab
See the "Geometry tab" of the "Temperature" boundary condition.
For details about the convective boundary conditions see the following subsection on convective heat transfer.
Convective heat transfer
The amount of heat transfer at the surface of a material (solid) due to convection can be calculated using the following equation,
$$q=Ah(T_{surf}T_{fluid})................................(1)$$
where, q is the amount of heat transferred (lost) due to convection, A is the surface area of the solid, h is the convective heat transfer coefficient which depends on the surface type and fluid properties, Tsurf is the temperature at the solid surface, and Tfluid is the nominal temperature of the fluid. The convection boundary condition at the material interfaces either uses a constant value for the convective heat transfer coefficient (h) or calculates its value from the fluid properties and the surface properties (length, orientation, etc.) using analytic equations [1]. In the case of the analytic equations, all the material data are evaluated at temperature (Tsurf + Tfluid) / 2.
Constant: When the "constant" model is chosen, the solver uses a constant value for the convective heat transfer coefficient and calculates the amount of heat transfer due to convection using eq. (1).
Natural convection (vertical): This analytic model is used in cases where convective heat transfer takes place at the surface of a vertical plate immersed in a fluid (e.g. air) that has no external force acting on it. The motion of the fluid that creates the convective heat transfer arises solely from temperature gradient in the fluid adjacent to the solid surface and from gravitational pull. The analytic equation used by this model is given by,
$$h=\frac{k}{L}(0.68+\frac{0.670Ra_L^{1/6}}{[1+(\frac{0.492k}{\mu C_p})^{9/16}]^{4/9}})................................(2)$$
and
$$h=\frac{k}{L}(0.825+\frac{0.387Ra_L^{1/6}}{[1+(\frac{0.492k}{\mu C_p})^{9/16}]^{4/9}})................................(3)$$
where, k is the heat transfer coefficient of the fluid, L is the characteristics length defined by the height of the vertical plate, μ is the dynamic viscosity of the fluid, Cp is the specific heat of the fluid, and RaL is the Rayleigh number for length L. Eq. (2) is used for laminar flow (RaL≤109) and eq. (3) is used for turbulent flow (109≤RaL≤1013). The value of the Rayleigh number for a vertical wall of height L is given by,
$$Ra_L=\frac{g\beta \rho^2C_p(T_{surf}T_{fluid})L^3}{\mu k}................................(4)$$
where, g is the gravitational acceleration and β is the thermal expansivity of the fluid.
Natural convection (top plate): This analytic model is used in cases where convective heat transfer takes place at the top surface of a horizontal plate immersed in a fluid (e.g. air) that has no external force acting on it. The motion of the fluid that creates the convective heat transfer arises solely from temperature gradient in the fluid adjacent to the solid surface and from gravitational pull. There are two analytic equations in this model. For a hot plate (Tsurf > Tfluid), the convective coefficient is given by,
$$h=\frac{k}{L}0.54Ra_L^{1/4}...............................(5)$$
and
$$h=\frac{k}{L}0.15Ra_L^{1/3}...............................(6)$$
where, the Rayleigh number is given by eq. (4). Eq. (5) is used for laminar flow (104≤RaL≤107) and eq. (6) is used for turbulent flow (107≤RaL≤1011). For a cold plate (Tsurf < Tfluid), the convective coefficient is given by,
$$h=\frac{k}{L}0.27Ra_L^{1/4}................................(7)$$
where, the Rayleigh number is again given by eq. (4). This model is valid for both laminar and turbulent flows (105≤RaL≤1010).
Natural convection (bottom plate): This analytic model is used in cases where convective heat transfer takes place at the bottom surface of a horizontal plate immersed in a fluid (e.g. air) that has no external force acting on it. The motion of the fluid that creates the convective heat transfer arises solely from temperature gradient in the fluid adjacent to the solid surface and from gravitational pull. The equations used in this model are similar to the ones used for natural convection on the top surface of a horizontal plate with the difference that for a hot plate (Tsurf > Tfluid), the convective coefficient is given by eq. (7) and for a cold plate (Tsurf < Tfluid), it is given by eqs. (5) and (6).
Forced convection: This analytic model is used for convection on a solid surface immersed in fluid (e.g. air) where the fluid is flowing due to an external force. For example, the fluid flow can be forced by a fan or a pump. The average convective heat transfer coefficient for a plate length of L is give by,
$$h=\frac{2k}{L}(\frac{0.3387Pr^{1/3}Re_L^{1/2}}{[1+(\frac{0.0468k}{\mu C_p})^{2/3}]^{1/4}})................................(8)$$
and
$$h=\frac{2k}{L}Pr^{1/3}(0.037Re_L^{4/5}871)................................(9)$$
where, ReL is the Reynolds number given by
$$Re_L=\frac{\rho\nu_{fluid}L}{\mu}................................(10)$$
where vfluid is the velocity of the fluid. Eq. (8) is used for the case of laminar flow (ReL ≤ 5.105) and eq. (9) is used for the case of mixed flow (laminar + turbulent) in the range ReL > 5.105.
Radiation
NAME: Name of the BC.
General tab
 AMBIANT TEMPERATURE (K): Sets the temperature of the surrounding environment.
 EMISSIVITY (A.U.): 1 for blackbody radiation and <1 for graybody radiation.
Heat transfer due to radiation is calculated using the StefanBoltzmann law given by,
$$q=A\varepsilon\sigma(T_{surf}T_{env})^4$$
where, q is the heat loss due to radiation, A is the surface area, ε is the emissivity of the solid, σ is the StefanBoltzmann constant, Tsurf is surface temperature and Tenv is the temperature of the surrounding environment.
Geometry tab
See the "Geometry tab" of the "Temperature" boundary condition.
Insulating
NAME: Name of the BC.
Geometry tab
See the "Geometry tab" of the "Temperature" boundary condition.
Voltage
NAME: Name of the BC
General tab
BC MODE: Steady state
Sweep Type: can be a 'Single' voltage or a voltage 'Sweep'.
Single
 VOLTAGE: Single voltage value in units of Volt.
Sweep
 RANGE: A range of values can be defined by the START, STOP, and INTERVAL or NUMBER OF POINTS.
 VALUE: A set of voltage values can be defined by the user in a table
BC MODE: Transient
In the transient mode, the bias assigned to each contact can either be fixed at a value ( this is the same as the fixed bias in DC mode) or transient, swept over a range of time dependant values. In the transient case, the values for each voltage point as well as the time point can be entered in a table. If only one point is specified in the table, then a constant value is assumed for that element. The values for the voltage will be linearly interpolated in time for consistency.
NOTE: This boundary condition is not available in an electrothermal simulation ('coupled' mode) 
Geometry tab
See the "Geometry tab" of the "Temperature" boundary condition.