[FXC-1512]: Add natural convection BC

tidy3d/__init__.py

@@ -1,395 +1,396 @@
 """Tidy3d package imports"""
 
 from __future__ import annotations
 
 from tidy3d.components.material.multi_physics import MultiPhysicsMedium
 from tidy3d.components.material.tcad.charge import (
     ChargeConductorMedium,
     ChargeInsulatorMedium,
     SemiconductorMedium,
 )
 from tidy3d.components.material.tcad.heat import (
     FluidMedium,
     FluidSpec,
     SolidMedium,
     SolidSpec,
 )
 from tidy3d.components.microwave.data.monitor_data import (
     AntennaMetricsData,
 )
 from tidy3d.components.spice.analysis.dc import (
     ChargeToleranceSpec,
     IsothermalSteadyChargeDCAnalysis,
 )
 from tidy3d.components.spice.sources.dc import DCCurrentSource, DCVoltageSource
 from tidy3d.components.spice.sources.types import VoltageSourceType
 from tidy3d.components.tcad.analysis.heat_simulation_type import UnsteadyHeatAnalysis, UnsteadySpec
 from tidy3d.components.tcad.boundary.specification import (
     HeatBoundarySpec,
     HeatChargeBoundarySpec,
 )
 from tidy3d.components.tcad.data.monitor_data.mesh import VolumeMeshData
 from tidy3d.components.tcad.data.sim_data import (
     DeviceCharacteristics,
     HeatChargeSimulationData,
     HeatSimulationData,
     VolumeMesherData,
 )
 from tidy3d.components.tcad.data.types import (
     SteadyCapacitanceData,
     SteadyElectricFieldData,
     SteadyEnergyBandData,
     SteadyFreeCarrierData,
     SteadyPotentialData,
     TemperatureData,
 )
 from tidy3d.components.tcad.doping import ConstantDoping, GaussianDoping
 from tidy3d.components.tcad.generation_recombination import FossumCarrierLifetime
 from tidy3d.components.tcad.grid import (
     DistanceUnstructuredGrid,
     GridRefinementLine,
     GridRefinementRegion,
     UniformUnstructuredGrid,
 )
 from tidy3d.components.tcad.mesher import VolumeMesher
 from tidy3d.components.tcad.monitors.charge import (
     SteadyCapacitanceMonitor,
     SteadyElectricFieldMonitor,
     SteadyEnergyBandMonitor,
     SteadyFreeCarrierMonitor,
     SteadyPotentialMonitor,
 )
 from tidy3d.components.tcad.monitors.heat import TemperatureMonitor
 from tidy3d.components.tcad.monitors.mesh import VolumeMeshMonitor
 from tidy3d.components.tcad.simulation.heat import HeatSimulation
 from tidy3d.components.tcad.simulation.heat_charge import HeatChargeSimulation
 from tidy3d.components.tcad.types import (
     AugerRecombination,
     CaugheyThomasMobility,
     ConstantMobilityModel,
     ConvectionBC,
+    NaturalConvectionVerticalSpec,
     CurrentBC,
     HeatFluxBC,
     HeatFromElectricSource,
     HeatSource,
     InsulatingBC,
     RadiativeRecombination,
     ShockleyReedHallRecombination,
     SlotboomBandGapNarrowing,
     TemperatureBC,
     UniformHeatSource,
     VoltageBC,
 )
 
 from .components.apodization import ApodizationSpec
 
 # boundary placement for other solvers
 # boundary placement for other solvers
 from .components.bc_placement import (
     MediumMediumInterface,
     SimulationBoundary,
     StructureBoundary,
     StructureSimulationBoundary,
     StructureStructureInterface,
 )
 
 # analytic beams
 from .components.beam import (
     AstigmaticGaussianBeamProfile,
     GaussianBeamProfile,
     PlaneWaveBeamProfile,
 )
 
 # boundary
 from .components.boundary import (
     PML,
     Absorber,
     AbsorberParams,
     BlochBoundary,
     Boundary,
     BoundaryEdge,
     BoundaryEdgeType,
     BoundarySpec,
     DefaultAbsorberParameters,
     DefaultPMLParameters,
     DefaultStablePMLParameters,
     PECBoundary,
     Periodic,
     PMCBoundary,
     PMLParams,
     PMLTypes,
     StablePML,
 )
 
 # data
 from .components.data.data_array import (
     CellDataArray,
     ChargeDataArray,
     DiffractionDataArray,
     EMECoefficientDataArray,
     EMEModeIndexDataArray,
     EMEScalarFieldDataArray,
     EMEScalarModeFieldDataArray,
     EMESMatrixDataArray,
     FieldProjectionAngleDataArray,
     FieldProjectionCartesianDataArray,
     FieldProjectionKSpaceDataArray,
     FluxDataArray,
     FluxTimeDataArray,
     HeatDataArray,
     IndexedDataArray,
     IndexedFieldVoltageDataArray,
     IndexedTimeDataArray,
     IndexedVoltageDataArray,
     ModeAmpsDataArray,
     ModeIndexDataArray,
     PointDataArray,
     ScalarFieldDataArray,
     ScalarFieldTimeDataArray,
     ScalarModeFieldCylindricalDataArray,
     ScalarModeFieldDataArray,
     SpatialDataArray,
     SpatialVoltageDataArray,
     SteadyVoltageDataArray,
 )
 from .components.data.dataset import (
     FieldDataset,
     FieldTimeDataset,
     ModeSolverDataset,
     PermittivityDataset,
 )
 from .components.data.monitor_data import (
     AbstractFieldProjectionData,
     DiffractionData,
     DirectivityData,
     FieldData,
     FieldProjectionAngleData,
     FieldProjectionCartesianData,
     FieldProjectionKSpaceData,
     FieldTimeData,
     FluxData,
     FluxTimeData,
     ModeData,
     ModeSolverData,
     PermittivityData,
 )
 from .components.data.sim_data import DATA_TYPE_MAP, SimulationData
 from .components.data.utils import (
     TetrahedralGridDataset,
     TriangularGridDataset,
 )
 from .components.eme.data.dataset import (
     EMECoefficientDataset,
     EMEFieldDataset,
     EMEModeSolverDataset,
     EMESMatrixDataset,
 )
 from .components.eme.data.monitor_data import EMECoefficientData, EMEFieldData, EMEModeSolverData
 from .components.eme.data.sim_data import EMESimulationData
 from .components.eme.grid import (
     EMECompositeGrid,
     EMEExplicitGrid,
     EMEGrid,
     EMEModeSpec,
     EMEUniformGrid,
 )
 from .components.eme.monitor import (
     EMECoefficientMonitor,
     EMEFieldMonitor,
     EMEModeSolverMonitor,
     EMEMonitor,
 )
 
 # EME
 from .components.eme.simulation import EMESimulation
 from .components.eme.sweep import EMEFreqSweep, EMELengthSweep, EMEModeSweep, EMEPeriodicitySweep
 
 # field projection
 from .components.field_projection import FieldProjector
 
 # frequency conversion utilities
 from .components.frequencies import FreqRange, frequencies, wavelengths
 
 # geometry
 from .components.geometry.base import Box, ClipOperation, Geometry, GeometryGroup, Transformed
 from .components.geometry.mesh import TriangleMesh
 from .components.geometry.polyslab import PolySlab
 from .components.geometry.primitives import Cylinder, Sphere
 from .components.grid.corner_finder import CornerFinderSpec
 from .components.grid.grid import Coords, Coords1D, FieldGrid, Grid, YeeGrid
 from .components.grid.grid_spec import (
     AutoGrid,
     CustomGrid,
     CustomGridBoundaries,
     GridRefinement,
     GridSpec,
     LayerRefinementSpec,
     QuasiUniformGrid,
     UniformGrid,
 )
 
 # lumped elements
 from .components.lumped_element import (
     AdmittanceNetwork,
     CoaxialLumpedResistor,
     LinearLumpedElement,
     LumpedElement,
     LumpedResistor,
     RectangularLumpedElement,
     RLCNetwork,
 )
 
 # medium
 # for docs
 from .components.medium import (
     PEC,
     PEC2D,
     PMC,
     AbstractMedium,
     AnisotropicMedium,
     CustomAnisotropicMedium,
     CustomDebye,
     CustomDrude,
     CustomLorentz,
     CustomMedium,
     CustomPoleResidue,
     CustomSellmeier,
     Debye,
     Drude,
     FullyAnisotropicMedium,
     HammerstadSurfaceRoughness,
     HuraySurfaceRoughness,
     KerrNonlinearity,
     Lorentz,
     LossyMetalMedium,
     Medium,
     Medium2D,
     NonlinearModel,
     NonlinearSpec,
     NonlinearSusceptibility,
     PECMedium,
     PerturbationMedium,
     PerturbationPoleResidue,
     PMCMedium,
     PoleResidue,
     Sellmeier,
     SurfaceImpedanceFitterParam,
     TwoPhotonAbsorption,
     medium_from_nk,
 )
 from .components.mode.data.sim_data import ModeSimulationData
 
 # Mode
 from .components.mode.simulation import ModeSimulation
 
 # modes
 from .components.mode_spec import ModeSpec
 
 # monitors
 from .components.monitor import (
     AuxFieldTimeMonitor,
     DiffractionMonitor,
     DirectivityMonitor,
     FieldMonitor,
     FieldProjectionAngleMonitor,
     FieldProjectionCartesianMonitor,
     FieldProjectionKSpaceMonitor,
     FieldProjectionSurface,
     FieldTimeMonitor,
     FluxMonitor,
     FluxTimeMonitor,
     ModeMonitor,
     ModeSolverMonitor,
     Monitor,
     PermittivityMonitor,
 )
 from .components.parameter_perturbation import (
     CustomChargePerturbation,
     CustomHeatPerturbation,
     IndexPerturbation,
     LinearChargePerturbation,
     LinearHeatPerturbation,
     NedeljkovicSorefMashanovich,
     ParameterPerturbation,
     PermittivityPerturbation,
 )
 
 # run time spec
 from .components.run_time_spec import RunTimeSpec
 
 # scene
 # scene
 from .components.scene import Scene
 
 # simulation
 from .components.simulation import Simulation
 from .components.source.base import Source
 from .components.source.current import (
     CustomCurrentSource,
     PointDipole,
     UniformCurrentSource,
 )
 from .components.source.field import (
     TFSF,
     AstigmaticGaussianBeam,
     CustomFieldSource,
     FixedAngleSpec,
     FixedInPlaneKSpec,
     GaussianBeam,
     ModeSource,
     PlaneWave,
 )
 
 # sources
 from .components.source.time import (
     ContinuousWave,
     CustomSourceTime,
     GaussianPulse,
     SourceTime,
 )
 
 # structures
 from .components.structure import MeshOverrideStructure, Structure
 
 # subpixel
 from .components.subpixel_spec import (
     ContourPathAveraging,
     HeuristicPECStaircasing,
     PECConformal,
     PolarizedAveraging,
     Staircasing,
     SubpixelSpec,
     SurfaceImpedance,
     VolumetricAveraging,
 )
 
 # time modulation
 from .components.time_modulation import (
     ContinuousWaveTimeModulation,
     ModulationSpec,
     SpaceModulation,
     SpaceTimeModulation,
 )
 from .components.transformation import RotationAroundAxis
 from .components.viz import VisualizationSpec, restore_matplotlib_rcparams
 
 # config
 from .config import config
 
 # constants imported as `C_0 = td.C_0` or `td.constants.C_0`
 from .constants import C_0, EPSILON_0, ETA_0, HBAR, K_B, MU_0, Q_e, inf
 from .log import log, set_logging_console, set_logging_file
 
 # material library dict imported as `from tidy3d import material_library`
 # get material `mat` and variant `var` as `material_library[mat][var]`
 from .material_library.material_library import material_library
 from .material_library.parametric_materials import Graphene
 
 # updater
 from .updater import Updater
 
 # version
 from .version import __version__
 
 
 def set_logging_level(level: str) -> None:
@@ -405,312 +406,314 @@
 Transformed.update_forward_refs()
 ClipOperation.update_forward_refs()
 GeometryGroup.update_forward_refs()
+ConvectionBC.update_forward_refs()
 
 __all__ = [
     "C_0",
     "DATA_TYPE_MAP",
     "EPSILON_0",
     "ETA_0",
     "HBAR",
     "K_B",
     "MU_0",
     "PEC",
     "PEC2D",
     "PMC",
     "PML",
     "TFSF",
     "Absorber",
     "AbsorberParams",
     "AbstractFieldProjectionData",
     "AbstractMedium",
     "AdmittanceNetwork",
     "AnisotropicMedium",
     "AntennaMetricsData",
     "ApodizationSpec",
     "AstigmaticGaussianBeam",
     "AstigmaticGaussianBeamProfile",
     "AugerRecombination",
     "AutoGrid",
     "AuxFieldTimeData",
     "AuxFieldTimeMonitor",
     "BlochBoundary",
     "Boundary",
     "BoundaryEdge",
     "BoundaryEdgeType",
     "BoundarySpec",
     "Box",
     "CaugheyThomasMobility",
     "CellDataArray",
     "ChargeConductorMedium",
     "ChargeDataArray",
     "ChargeInsulatorMedium",
     "ChargeToleranceSpec",
     "ClipOperation",
     "CoaxialLumpedResistor",
     "ConstantDoping",
     "ConstantMobilityModel",
     "ContinuousWave",
     "ContinuousWaveTimeModulation",
     "ContourPathAveraging",
     "ConvectionBC",
     "Coords",
     "Coords1D",
     "CornerFinderSpec",
     "CurrentBC",
     "CustomAnisotropicMedium",
     "CustomChargePerturbation",
     "CustomCurrentSource",
     "CustomDebye",
     "CustomDrude",
     "CustomFieldSource",
     "CustomGrid",
     "CustomGridBoundaries",
     "CustomHeatPerturbation",
     "CustomLorentz",
     "CustomMedium",
     "CustomPoleResidue",
     "CustomSellmeier",
     "CustomSourceTime",
     "Cylinder",
     "DCCurrentSource",
     "DCVoltageSource",
     "Debye",
     "DefaultAbsorberParameters",
     "DefaultPMLParameters",
     "DefaultStablePMLParameters",
     "DeviceCharacteristics",
     "DiffractionData",
     "DiffractionDataArray",
     "DiffractionMonitor",
     "DirectivityData",
     "DirectivityMonitor",
     "DistanceUnstructuredGrid",
     "Drude",
     "EMECoefficientData",
     "EMECoefficientDataArray",
     "EMECoefficientDataset",
     "EMECoefficientMonitor",
     "EMECompositeGrid",
     "EMEExplicitGrid",
     "EMEFieldData",
     "EMEFieldDataset",
     "EMEFieldMonitor",
     "EMEFreqSweep",
     "EMEGrid",
     "EMELengthSweep",
     "EMEModeIndexDataArray",
     "EMEModeSolverData",
     "EMEModeSolverDataset",
     "EMEModeSolverMonitor",
     "EMEModeSpec",
     "EMEModeSweep",
     "EMEMonitor",
     "EMEPeriodicitySweep",
     "EMESMatrixDataArray",
     "EMESMatrixDataset",
     "EMEScalarFieldDataArray",
     "EMEScalarModeFieldDataArray",
     "EMESimulation",
     "EMESimulationData",
     "EMESweepSpec",
     "EMEUniformGrid",
     "FieldData",
     "FieldDataset",
     "FieldGrid",
     "FieldMonitor",
     "FieldProjectionAngleData",
     "FieldProjectionAngleDataArray",
     "FieldProjectionAngleMonitor",
     "FieldProjectionCartesianData",
     "FieldProjectionCartesianDataArray",
     "FieldProjectionCartesianMonitor",
     "FieldProjectionKSpaceData",
     "FieldProjectionKSpaceDataArray",
     "FieldProjectionKSpaceMonitor",
     "FieldProjectionSurface",
     "FieldProjector",
     "FieldTimeData",
     "FieldTimeDataset",
     "FieldTimeMonitor",
     "FixedAngleSpec",
     "FixedInPlaneKSpec",
     "FluidMedium",
     "FluidSpec",
     "FluxData",
     "FluxDataArray",
     "FluxMonitor",
     "FluxTimeData",
     "FluxTimeDataArray",
     "FluxTimeMonitor",
     "FossumCarrierLifetime",
     "FreqRange",
     "FullyAnisotropicMedium",
     "GaussianBeam",
     "GaussianBeamProfile",
     "GaussianDoping",
     "GaussianPulse",
     "Geometry",
     "GeometryGroup",
     "Graphene",
     "Grid",
     "GridRefinement",
     "GridRefinementLine",
     "GridRefinementRegion",
     "GridSpec",
     "HammerstadSurfaceRoughness",
     "HeatBoundarySpec",
     "HeatChargeBoundarySpec",
     "HeatChargeSimulation",
     "HeatChargeSimulationData",
     "HeatDataArray",
     "HeatFluxBC",
     "HeatFromElectricSource",
     "HeatSimulation",
     "HeatSimulationData",
     "HeatSource",
     "HeuristicPECStaircasing",
     "HuraySurfaceRoughness",
     "IndexPerturbation",
     "IndexedDataArray",
     "IndexedFieldVoltageDataArray",
     "IndexedTimeDataArray",
     "IndexedVoltageDataArray",
     "InsulatingBC",
     "IsothermalSteadyChargeDCAnalysis",
     "KerrNonlinearity",
     "LayerRefinementSpec",
     "LinearChargePerturbation",
     "LinearHeatPerturbation",
     "LinearLumpedElement",
     "Lorentz",
     "LossyMetalMedium",
     "LumpedElement",
     "LumpedResistor",
     "Medium",
     "Medium2D",
     "MediumMediumInterface",
     "MeshOverrideStructure",
     "ModeAmpsDataArray",
     "ModeData",
     "ModeIndexDataArray",
     "ModeMonitor",
     "ModeSimulation",
     "ModeSimulationData",
     "ModeSolverData",
     "ModeSolverDataset",
     "ModeSolverMonitor",
     "ModeSource",
     "ModeSpec",
     "ModulationSpec",
     "Monitor",
     "MultiPhysicsMedium",
     "NedeljkovicSorefMashanovich",
     "NonlinearModel",
     "NonlinearSpec",
     "NonlinearSusceptibility",
     "PECBoundary",
     "PECConformal",
     "PECMedium",
     "PMCBoundary",
     "PMCMedium",
     "PMLParams",
     "PMLTypes",
     "ParameterPerturbation",
     "Periodic",
     "PermittivityData",
     "PermittivityDataset",
     "PermittivityMonitor",
     "PermittivityPerturbation",
     "PerturbationMedium",
     "PerturbationPoleResidue",
     "PlaneWave",
     "PlaneWaveBeamProfile",
     "PointDataArray",
     "PointDipole",
     "PolarizedAveraging",
     "PoleResidue",
     "PolySlab",
     "Q_e",
     "QuasiUniformGrid",
     "RLCNetwork",
     "RadiativeRecombination",
     "RectangularLumpedElement",
     "RotationAroundAxis",
     "RunTimeSpec",
     "ScalarFieldDataArray",
     "ScalarFieldTimeDataArray",
     "ScalarModeFieldCylindricalDataArray",
     "ScalarModeFieldDataArray",
     "Scene",
     "Sellmeier",
     "SemiconductorMedium",
     "ShockleyReedHallRecombination",
     "Simulation",
     "SimulationBoundary",
     "SimulationData",
     "SlotboomBandGapNarrowing",
     "SolidMedium",
     "SolidSpec",
     "Source",
     "SourceTime",
     "SpaceModulation",
     "SpaceTimeModulation",
     "SpatialDataArray",
     "SpatialVoltageDataArray",
     "Sphere",
     "StablePML",
     "Staircasing",
     "SteadyCapacitanceData",
     "SteadyCapacitanceMonitor",
     "SteadyElectricFieldData",
     "SteadyElectricFieldMonitor",
     "SteadyEnergyBandData",
     "SteadyEnergyBandMonitor",
     "SteadyFreeCarrierData",
     "SteadyFreeCarrierMonitor",
     "SteadyPotentialData",
     "SteadyPotentialMonitor",
     "SteadyVoltageDataArray",
     "Structure",
     "StructureBoundary",
     "StructureSimulationBoundary",
     "StructureStructureInterface",
     "SubpixelSpec",
     "SurfaceImpedance",
     "SurfaceImpedanceFitterParam",
     "TemperatureBC",
     "TemperatureData",
     "TemperatureMonitor",
     "TetrahedralGridDataset",
     "Transformed",
     "TriangleMesh",
     "TriangularGridDataset",
     "TwoPhotonAbsorption",
     "UniformCurrentSource",
     "UniformGrid",
     "UniformHeatSource",
     "UniformUnstructuredGrid",
     "UnsteadyHeatAnalysis",
     "UnsteadySpec",
     "Updater",
     "VisualizationSpec",
     "VoltageBC",
     "VoltageSourceType",
     "VolumeMeshData",
     "VolumeMeshMonitor",
     "VolumeMesher",
     "VolumeMesherData",
     "VolumetricAveraging",
     "YeeGrid",
     "__version__",
     "config",
     "frequencies",
     "inf",
     "log",
     "material_library",
     "medium_from_nk",
     "restore_matplotlib_rcparams",
     "set_logging_console",
     "set_logging_file",
     "wavelengths",
+    "NaturalConvectionVerticalSpec",
 ]

tidy3d/components/tcad/boundary/heat.py

@@ -1,11 +1,12 @@
 """Defines heat material specifications"""
 
 from __future__ import annotations
 
 import pydantic.v1 as pd
 
+from typing import Union
 from tidy3d.components.tcad.boundary.abstract import HeatChargeBC
 from tidy3d.constants import HEAT_FLUX, HEAT_TRANSFER_COEFF, KELVIN
 
 
 class TemperatureBC(HeatChargeBC):
@@ -39,6 +40,100 @@
         units=HEAT_FLUX,
     )
 
+#TODO Should I adapt to Tidy3D units (e.g. micrometers), or keep the original ones?
+THERMAL_CONDUCTIVITY_UNITS = "W/(m*K)"
+DYNAMIC_VISCOSITY_UNITS = "Pa*s"
+SPECIFIC_HEAT_UNITS = "J/(kg*K)"
+DENSITY_UNITS = "kg/m**3"
+THERMAL_EXPANSIVITY_UNITS = "1/K"
+LENGTH_UNITS = "m"
+ACCELERATION_UNITS = "m/s**2"
+
+class NaturalConvectionVerticalSpec(HeatChargeBC):
+    """
+    Specification for natural convection from a vertical plate.
+
+    This class calculates the heat transfer coefficient (h) based on fluid
+    properties and an expected temperature difference, then provides these
+    values as 'base' and 'exponent' for a generalized heat flux equation
+    q = base * (T_surf - T_fluid)^exponent.
+    """
+    # --- Input Parameters ---
+    fluid_k: pd.NonNegativeFloat = pd.Field(
+        title="Fluid Thermal Conductivity",
+        description="Thermal conductivity (k) of the fluid.",
+        units=THERMAL_CONDUCTIVITY_UNITS,
+    )
+    fluid_mu: pd.NonNegativeFloat = pd.Field(
+        title="Fluid Dynamic Viscosity",
+        description="Dynamic viscosity (μ) of the fluid.",
+        units=DYNAMIC_VISCOSITY_UNITS,
+    )
+    fluid_Cp: pd.NonNegativeFloat = pd.Field(
+        title="Fluid Specific Heat",
+        description="Specific heat capacity (Cp) of the fluid at constant pressure.",
+        units=SPECIFIC_HEAT_UNITS,
+    )
+    fluid_rho: pd.NonNegativeFloat = pd.Field(
+        title="Fluid Density",
+        description="Density (ρ) of the fluid.",
+        units=DENSITY_UNITS,
+    )
+    fluid_beta: pd.NonNegativeFloat = pd.Field(
+        title="Fluid Thermal Expansivity",
+        description="Thermal expansion coefficient (β) of the fluid.",
+        units=THERMAL_EXPANSIVITY_UNITS,
+    )
+    plate_L: pd.NonNegativeFloat = pd.Field(
+        title="Plate Characteristic Length",
+        description="Characteristic length (L), defined as the height of the vertical plate.",
+        units=LENGTH_UNITS,
+    )
+
+    gravity: pd.NonNegativeFloat = pd.Field(
+        default=9.80665,
+        title="Gravitational Acceleration",
+        description="Gravitational acceleration (g).",
+        units=ACCELERATION_UNITS,
+    )
+
+    def _compute_parameters(self):
+
+        # Calculate the Rayleigh Number (Ra_L)
+        rayleigh_numerator_notemp = (
+                self.gravity
+                * self.fluid_beta
+                * self.fluid_rho ** 2
+                * self.fluid_Cp
+                * self.plate_L ** 3
+        )
+        rayleigh_denominator = self.fluid_mu * self.fluid_k
+        Ra_L = rayleigh_numerator_notemp / rayleigh_denominator
+
+        # Calculate the denominator term from the Nusselt number correlation
+        # This term is related to the Prandtl Number (Pr = mu * Cp / k)
+        pr_term_inner_num = 0.492 * self.fluid_k
+        pr_term_inner_den = self.fluid_mu * self.fluid_Cp
+
+        pr_term_inner = pr_term_inner_num / pr_term_inner_den
+        pr_denominator = (1 + pr_term_inner ** (9 / 16)) ** (4 / 9)
+
+        # Select formula based on flow regime (determined by Ra_L)
+        if Ra_L <= 1e9:
+            # Laminar Flow
+            h_factor_linear = 0.68
+            h_factor_non_linear =  (0.670 * Ra_L ** (1 / 6)) / pr_denominator
+        elif 1e9 < Ra_L <= 1e13:
+            # Turbulent Flow
+            h_factor_linear = 0.825
+            h_factor_non_linear = (0.387 * Ra_L ** (1 / 6)) / pr_denominator
+        else:
+            raise ValueError(f"Ra_l={Ra_L} should be smaller than 1e13 for NaturalConvectionVerticalSpec")
+
+        h = (self.fluid_k / self.plate_L) * h_factor_linear
+        h_nonlinear = (self.fluid_k / self.plate_L) * h_factor_non_linear
+        exponent = 1 + 1/6
+        return h, h_nonlinear, exponent
 
 class ConvectionBC(HeatChargeBC):
     """Convective thermal boundary conditions.
@@ -55,8 +150,12 @@
         units=KELVIN,
     )
 
-    transfer_coeff: pd.NonNegativeFloat = pd.Field(
+    transfer_coeff: Union[pd.NonNegativeFloat, NaturalConvectionVerticalSpec] = pd.Field(
         title="Heat Transfer Coefficient",
         description=f"Heat flux value in units of {HEAT_TRANSFER_COEFF}.",
         units=HEAT_TRANSFER_COEFF,
     )
+
+#TODO Maybe I should find a better place for these lines.
+NaturalConvectionVerticalSpec.update_forward_refs()
+ConvectionBC.update_forward_refs()

tidy3d/components/tcad/types.py

@@ -1,10 +1,10 @@
 """File containing classes required for the setup of a DEVSIM case."""
 
 from __future__ import annotations
 
 from tidy3d.components.tcad.bandgap import SlotboomBandGapNarrowing
 from tidy3d.components.tcad.boundary.charge import CurrentBC, InsulatingBC, VoltageBC
-from tidy3d.components.tcad.boundary.heat import ConvectionBC, HeatFluxBC, TemperatureBC
+from tidy3d.components.tcad.boundary.heat import ConvectionBC, HeatFluxBC, TemperatureBC, NaturalConvectionVerticalSpec
 from tidy3d.components.tcad.generation_recombination import (
     AugerRecombination,
     RadiativeRecombination,