Settings for the Heat Transfer Interface
The Label is the default physics interface name.
The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.
The default Name (for the first physics interface in the model) is ht.
Physical Model
In 2D and 1D axisymmetric components, set the Thickness dz, which is the thickness of the domain in the out-of-plane direction. The default value is 1 m.
In 1D components, set the Cross sectional area Ac and the Cross sectional perimeter Pc of the domain. Default values are 1 m2 and 1 m, respectively.
Some check boxes are also present in this section with certain COMSOL products.
For a detailed overview of the functionality available in each product, visit http://www.comsol.com/products/specifications/
Click to select any of the following check boxes to activate the versions of the ht interface as described in Benefits of the Different Heat Transfer Interfaces:
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Select the Surface-to-surface radiation check box to enable surface-to-surface radiation features as described in The Heat Transfer with Surface-to-Surface Radiation Interface.
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Select the Radiation in participating media check box to enable radiation in participating media features. See The Heat Transfer with Radiation in Participating Media Interface.
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Select the Heat transfer in biological tissue check box to enable the Biological Tissue feature.
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Selecting Isothermal domain provides support for isothermal domain modeling. See Isothermal Domain Interface and Isothermal Domain.
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Select the Heat Transfer in Porous Media check box to enable the Porous Medium, Fracture, and Building Material features. See The Heat Transfer in Porous Media Interface and The Heat Transfer in Building Materials Interface.
Ambient Settings
In this section, you can define ambient variables to be available as inputs from several features: the temperature Tamb, the absolute pressure pamb, the relative humidity φamb, the wind velocity vamb, and the direct and diffuse solar irradiances Isn,amb and Ish,amb.
See Heat Flux, Diffuse Surface, Temperature, Initial Values, or External Radiation Source for examples of features of the Heat Transfer interface that have ambient variables available as inputs.
See Initial Values, Moisture Content, or Moisture Flux for examples of features of the Moisture Transport interface that have ambient variables available as inputs.
Two options are available for the definition of the Ambient data:
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When User defined (the default) is selected, the Ambient temperature Tamb, the Ambient absolute pressure pamb, the Ambient relative humidity φamb, the Wind velocity vamb, the Clear sky noon beam normal irradiance Isn,amb, and the Clear sky noon diffuse horizontal irradiance Ish,amb should be specified directly.
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When Meteorological data (ASHRAE 2013) is selected, the ambient variables are computed from monthly and hourly averaged measurements, made over several years at weather stations worldwide. See Using Ambient Data for more information. Further settings for the choice of the location, time, and ambient conditions are needed; and additional input fields are displayed underneath.
Location
In this section you can set the location by choosing among more than 6000 weather stations worldwide. Two options are available for the selection of the Weather station:
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When From list is selected, additional lists display underneath for the selection of a Region, a Country, and a Station. The Country list is refreshed for each selection in the Region list, and the Station list is refreshed for each selection in the Country list.
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It is also possible to select a station From reference by entering the corresponding World Meteorological Organization reference, which is a 6-digit number.
A single country may be available for more than one region selection if it has stations spread over different regions. For example, United States of America is available in the Country list when either North America, Eurasia, or Oceania is selected in the Region list.
When a station is selected From list, its World Meteorological Organization (WMO) reference is displayed below the Station list. The WMO references can also be retrieved from maps offered by third parties like the one available as of this product release on http://ashrae-meteo.info/.
Time
The Date and Local time should be set by entering values or expressions in the Day, Month, Hour, Minute, and Second fields of the two tables.
If the Specify year check box is selected, a value or expression for the Year should also be set. As the data are given as averages over several past years, this input is only used for the detection of leap years, in order to interpolate the data over the months.
For temporal studies, these inputs define the starting time of the simulation. By default, the Update time from solver check box is selected, and the time is then automatically updated with the time from the solver to evaluate the variables by interpolation of the measured data. Unselect this check box to manually set the time update.
See Ambient Data Interpolation for more information about the interpolation of data over months and hours.
See Processing of ASHRAE Data for more information about the data.
A time unit suitable for simulations over a day or a year may be set in the Study Settings section of the Time Dependent node, by using for example h for hour, d for day, or a for a year. See Using Units in the COMSOL Multiphysics Reference Manual for more details.
Ambient conditions
Based on the measured data, several conditions are available for the Temperature, the Dew point temperature, and the Wind speed. The formula for each condition is recalled in Table 5-5, Table 5-6, and Table 5-7. The Average conditions correspond to weighted means of the measured data, whereas the other conditions are obtained by applying standard or modified deviations (Low, High, and User defined coefficient for deviation conditions), user defined corrections, or wind correlations to the average conditions; or by taking the minimum or maximum of the measured data (Lowest and Highest conditions). More information about these definitions can be found in Ambient Variables and Conditions.
Table 5-5: Temperature Conditions
Condition
Definition
Average
Low
High
Lowest
Highest
User defined coefficient for deviation
User defined correction
Heating wind correlation(1)
Cooling wind correlation(1)
 (1)These correlations are not related to the wind speed conditions described in Table 5-7.
Table 5-6: Dew Point Temperature Conditions
Condition
Definition
Average
Low
High
Lowest
Highest
Table 5-7: Wind Speed Conditions
Condition
Definition
Average
Low
High
Lowest
Highest
The conditions set for Temperature and Dew point temperature should be consistent in order to keep the temperature larger than the dew point temperature. However, all settings combinations are available, and the relative humidity is majored by 1 when necessary.
The sum of the Clear sky noon beam normal irradiance and the Clear sky noon diffuse horizontal irradiance is available through the post-processing variable ht.Is_amb, defined as the Ambient solar irradiance.
For an example of the use of user-defined ambient data, see:
Temperature Field in a Cooling Flange: Application Library path Heat_Transfer_Module/Thermal_Processing/cooling_flange
For an example of the use of meteorological ambient data, see:
Condensation Detection in an Electronic Device with Transport and Diffusion: Application Library path Heat_Transfer_Module/Power_Electronics_and_Electronic_Cooling/condensation_electronic_device_transport_diffusion
Condensation Detection in an Electronic Device: Application Library path Heat_Transfer_Module/Power_Electronics_and_Electronic_Cooling/condensation_electronic_device
Consistent Stabilization
The Streamline diffusion check box is selected by default and should remain selected for optimal performance for heat transfer in fluids or other applications that include a convective or translational term. Crosswind diffusion provides extra diffusion in regions with sharp gradients. The added diffusion is orthogonal to the streamlines, so streamline diffusion and crosswind diffusion can be used simultaneously. The Crosswind diffusion check box is also selected by default.
Inconsistent Stabilization
The Isotropic diffusion check box is not selected by default.
Heat Transfer Consistent and Inconsistent Stabilization Methods
Advanced Settings
Add both a Heat Transfer (ht) and a Moving Mesh (ale) interface (found under the Mathematics>Deformed Mesh branch when adding a physics interface) then click the Show button () and select Advanced Physics Options to display this section.
When the component contains a moving mesh, the Enable conversions between material and spatial frame check box is selected by default. This option has no effect when the component does not contain a moving frame because the material and spatial frames are identical in such cases. With a moving mesh, and when this option is active, the heat transfer features automatically account for deformation effects on heat transfer properties. In particular the effects of volume changes on the density are considered. Rotation effects on the thermal conductivity of an anisotropic material and, more generally, deformation effects on an arbitrary thermal conductivity, are also covered. When the Enable conversions between material and spatial frame check box is not selected, the feature inputs (for example, Heat Source, Heat Flux, Boundary Heat Source, and Line Heat Source) are not converted and are instead defined on the Spatial frame.
Discretization
To display this section, click the Show button () and select Discretization.
In the Heat Transfer interfaces you can choose not only the order of the discretization, but also the type of shape functions: Lagrange or serendipity. For highly distorted elements, Lagrange shape functions provide better accuracy than serendipity shape functions of the same order. The serendipity shape functions will however give significant reductions of the model size for a given mesh containing hexahedral, prism, or quadrilateral elements. At first order, Lagrange and serendipity shape functions are the same.
The default shape functions used for the temperature are Quadratic Lagrange for the modeling of heat transfer in solids, and Linear for the modeling of heat transfer in fluids. See the description of each version of the physics interface for more details.
Dependent Variables
The Heat Transfer interfaces have the dependent variable Temperature T. The dependent variable names can be changed. Editing the name of a scalar dependent variable changes both its field name and the dependent variable name. If a new field name coincides with the name of another field of the same type, the fields share degrees of freedom and dependent variable names. A new field name must not coincide with the name of a field of another type or with a component name belonging to some other field.