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13.2.4 Postprocessing Heat Transfer Quantities



Available Variables for Postprocessing


FLUENT provides reporting options for simulations involving heat transfer. You can generate graphical plots or reports of the following variables/functions:

The first 12 variables listed above are contained in the Temperature... category of the variable selection drop-down list that appears in postprocessing panels, and the remaining variables are in the Wall Fluxes... category. See Chapter  30 for their definitions.



Definition of Enthalpy and Energy in Reports and Displays


The definitions of the reported values of enthalpy and energy will be different depending on whether the flow is compressible or incompressible.



Reporting Heat Transfer Through Boundaries


You can use the Flux Reports panel to compute the heat transfer through each boundary of the domain, or to sum the heat transfer through all boundaries to check the heat balance.

Report $\rightarrow$ Fluxes...

It is recommended that you perform a heat balance check to ensure that your solution is truly converged.



Reporting Heat Transfer Through a Surface


You can use the Surface Integrals panel to compute the heat transfer through any boundary or any surface created using the methods described in Chapter  27.

Report $\rightarrow$ Surface Integrals...

To report the mass flow rate of enthalpy


 Q = \int {H \rho \vec{v} \cdot d \vec{A} } (13.2-13)

choose Flow Rate for the Report Type in the Surface Integrals panel, select Enthalpy (in the Temperature... category) as the Field Variable, and select the surface(s) on which to integrate.



Reporting Averaged Heat Transfer Coefficients


The Surface Integrals panel can also be used to generate a report of averaged heat transfer coefficient $h$ on a surface ( $\frac{1}{A}\int{h \; dA}$).

Report $\rightarrow$ Surface Integrals...

In the Surface Integrals panel, choose Area-Weighted Average for Report Type, select Surface Heat Transfer Coef. (in the Wall Fluxes... category) as the Field Variable, and select the surface.



Exporting Heat Flux Data


It is possible to export heat flux data on wall zones (including radiation) to a generic file that you can examine or use in an external program. To save a heat flux file, you will use the custom-heat-flux text command.

file $\rightarrow$ export $\rightarrow$ custom-heat-flux

Heat transfer data will be exported in the following free format for each face zone that you select for export:

zone-name nfaces
x_f  y_f  z_f  A  Q  T_w  T_c  HTC
.
.
.

Each block of data starts with the name of the face zone ( zone-name) and the number of faces in the zone ( nfaces). Next there is a line for each face (i.e., nfaces lines), each containing the components of the face centroid ( x_f, y_f, and, in 3D, z_f), the face area ( A), the heat transfer rate ( Q), the face temperature ( T_w), the adjacent cell temperature ( T_c), and the heat transfer coefficient ( HTC). If the heat transfer coefficient is calculated based on wall function (Equation  30.4-33), then $Q$ is the convective heat transfer rate. Otherwise, $Q$ will be the total heat transfer rate, including radiation heat transfer.


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