# Gap Heat Transfer for LWRs

BC that aids with thermal contact similar to GapHeatTransfer

## Description

The GapHeatTransferLWR boundary condition differs from GapHeatTransfer in that the gap conductivity is computed based on the gases in the gap. This boundary condition can also include the effect of solid-solid conduction once the pellet and clad have come into mechanical contact with each other.

note:Gap Geometry Type Must Match Coordinate System

The parameter parameters gap geometry_type should be set to match the simulation geometry, e.g CYLINDER should be used as argument in AxisymmetricRZ simulations.

The gas in the gap may be flushed in a refabrication step. (See also PlenumPressure.)

## Example Input Syntax

GapHeatTransferLWR is a type of thermal contact boundary condition and is therefore applied within the [ThermalContact] block instead of within the usual [BCs] of the input file.


[ThermalContact]
[./thermal_contact]
type = GapHeatTransferLWR
variable = temp
master = 3
slave = 2
initial_gas_fractions = '0 0 0 1 0 0 0 0 0 0'
roughness_coef = 1.5
roughness_fuel = 1.0e-6
#min_gap = 0
emissivity_fuel = 0
tangential_tolerance = 1e-5
[../]
[]
(test/tests/gap_heat_transfer/gap_heat_transfer_catch_release.i)

## Input Parameters

• variableThe name of the variable that this boundary condition applies to

C++ Type:NonlinearVariableName

Description:The name of the variable that this boundary condition applies to

• boundaryThe list of boundary IDs from the mesh where this boundary condition applies

C++ Type:std::vector

Description:The list of boundary IDs from the mesh where this boundary condition applies

### Required Parameters

• gap_tempTemperature on the other side of the gap

C++ Type:std::vector

Description:Temperature on the other side of the gap

Default:1e-06

C++ Type:double

Description:The roughness of the cladding surface (m)

• max_gap1e+06A maximum gap size

Default:1e+06

C++ Type:double

Description:A maximum gap size

• quadratureFalseWhether or not to do Quadrature point based gap heat transfer. If this is true then gap_distance and gap_temp should NOT be provided (and will be ignored) however paired_boundary IS then required.

Default:False

C++ Type:bool

Description:Whether or not to do Quadrature point based gap heat transfer. If this is true then gap_distance and gap_temp should NOT be provided (and will be ignored) however paired_boundary IS then required.

• sphere_originOrigin for sphere geometry

C++ Type:libMesh::VectorValue

Description:Origin for sphere geometry

• roughness_fuel1e-06The roughness of the fuel surface (m)

Default:1e-06

C++ Type:double

Description:The roughness of the fuel surface (m)

• min_gap1e-06A minimum gap size

Default:1e-06

C++ Type:double

Description:A minimum gap size

Default:0

C++ Type:double

Description:The temperature jump distance for the cladding

• jumpdistance_fuel0The temperature jump distance for the fuel

Default:0

C++ Type:double

Description:The temperature jump distance for the fuel

• cylinder_axis_point_1Start point for line defining cylindrical axis

C++ Type:libMesh::VectorValue

Description:Start point for line defining cylindrical axis

• cylinder_axis_point_2End point for line defining cylindrical axis

C++ Type:libMesh::VectorValue

Description:End point for line defining cylindrical axis

• displacementsThe displacements appropriate for the simulation geometry and coordinate system

C++ Type:std::vector

Description:The displacements appropriate for the simulation geometry and coordinate system

• disp_zThe z displacement

C++ Type:std::vector

Description:The z displacement

• disp_yThe y displacement

C++ Type:std::vector

Description:The y displacement

• disp_xThe x displacement

C++ Type:std::vector

Description:The x displacement

• appended_property_nameName appended to material properties to make them unique

C++ Type:std::string

Description:Name appended to material properties to make them unique

• paired_boundaryThe boundary to be penetrated

C++ Type:BoundaryName

Description:The boundary to be penetrated

• gap_distanceDistance across the gap

C++ Type:std::vector

Description:Distance across the gap

• gap_geometry_typeGap calculation type. Choices are: PLATE CYLINDER SPHERE

C++ Type:MooseEnum

Description:Gap calculation type. Choices are: PLATE CYLINDER SPHERE

• roughness_coef1.5The coefficient for the roughness summation

Default:1.5

C++ Type:double

Description:The coefficient for the roughness summation

• warningsFalseWhether to output warning messages concerning nodes not being found

Default:False

C++ Type:bool

Description:Whether to output warning messages concerning nodes not being found

• orderFIRSTThe finite element order

Default:FIRST

C++ Type:MooseEnum

Description:The finite element order

### Optional Parameters

• enableTrueSet the enabled status of the MooseObject.

Default:True

C++ Type:bool

Description:Set the enabled status of the MooseObject.

• save_inThe name of auxiliary variables to save this BC's residual contributions to. Everything about that variable must match everything about this variable (the type, what blocks it's on, etc.)

C++ Type:std::vector

Description:The name of auxiliary variables to save this BC's residual contributions to. Everything about that variable must match everything about this variable (the type, what blocks it's on, etc.)

• use_displaced_meshFalseWhether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.

Default:False

C++ Type:bool

Description:Whether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.

• control_tagsAdds user-defined labels for accessing object parameters via control logic.

C++ Type:std::vector

Description:Adds user-defined labels for accessing object parameters via control logic.

• seed0The seed for the master random number generator

Default:0

C++ Type:unsigned int

Description:The seed for the master random number generator

• diag_save_inThe name of auxiliary variables to save this BC's diagonal jacobian contributions to. Everything about that variable must match everything about this variable (the type, what blocks it's on, etc.)

C++ Type:std::vector

Description:The name of auxiliary variables to save this BC's diagonal jacobian contributions to. Everything about that variable must match everything about this variable (the type, what blocks it's on, etc.)

• implicitTrueDetermines whether this object is calculated using an implicit or explicit form

Default:True

C++ Type:bool

Description:Determines whether this object is calculated using an implicit or explicit form

• vector_tagsnontimeThe tag for the vectors this Kernel should fill

Default:nontime

C++ Type:MultiMooseEnum

Description:The tag for the vectors this Kernel should fill

• extra_vector_tagsThe extra tags for the vectors this Kernel should fill

C++ Type:std::vector

Description:The extra tags for the vectors this Kernel should fill

• matrix_tagssystemThe tag for the matrices this Kernel should fill

Default:system

C++ Type:MultiMooseEnum

Description:The tag for the matrices this Kernel should fill

• extra_matrix_tagsThe extra tags for the matrices this Kernel should fill

C++ Type:std::vector

Description:The extra tags for the matrices this Kernel should fill