
Once the radiator zone has been identified (in the Boundary Conditions panel), you will set all modeling inputs for the radiator in the Radiator panel (Figure 7.21.1), which is opened from the Boundary Conditions panel (as described in Section 7.1.4).
The inputs for a radiator are as follows:
Identifying the Radiator Zone
Since the radiator is considered to be infinitely thin, it must be modeled as the interface between cells, rather than a cell zone. Thus the radiator zone is a type of internal face zone (where the faces are line segments in 2D or triangles/quadrilaterals in 3D). If, when you read your grid into FLUENT, the radiator zone is identified as an interior zone, use the Boundary Conditions panel (as described in Section 7.1.3) to change the appropriate interior zone to a radiator zone.
Define Boundary Conditions...
Once the interior zone has been changed to a radiator zone, you can open the Radiator panel and specify the loss coefficient and heat flux information.
Defining the Pressure Loss Coefficient Function
To define the pressure loss coefficient you can specify a polynomial, piecewiselinear, or piecewisepolynomial function of velocity, or a constant value.
Polynomial, PiecewiseLinear, or PiecewisePolynomial Function
Follow these steps to set a polynomial, piecewiselinear, or piecewisepolynomial function for the pressure loss coefficient:
Constant Value
To define a constant loss coefficient, follow these steps:
Example: Calculating the Loss Coefficient
This example shows you how to determine the loss coefficient function. Consider the simple twodimensional duct flow of air through a watercooled radiator, shown in Figure 7.21.3.
The radiator characteristics must be known empirically. For this case, assume that the radiator to be modeled yields the test data shown in Table 7.21.1, which was taken with a waterside flow rate of 7 kg/min and an inlet water temperature of 400.0 K. To compute the loss coefficient, it is helpful to construct a table with values of the dynamic head, , as a function of pressure drop, , and the ratio of these two values, (from Equation 7.211). (The air density, defined in Figure 7.21.3, is 1.0 kg/m .) The reduced data are shown in Table 7.21.2 below.
The loss coefficient is a linear function of the velocity, decreasing as the velocity increases. The form of this relationship is
(7.219) 
where is now the absolute value of the velocity through the radiator.
Defining the Heat Flux Parameters
As mentioned in Section 7.21.1, you can either define the actual heat flux in the Heat Flux field, or set the heat transfer coefficient and radiator temperature . All inputs are in the Radiator panel.
To define the actual heat flux, specify a Temperature of 0, and set the constant Heat Flux value.
To define the radiator temperature, enter the value for in the Temperature field. To define the heat transfer coefficient, you can specify a polynomial, piecewiselinear, or piecewisepolynomial function of velocity, or a constant value.
Polynomial, PiecewiseLinear, or PiecewisePolynomial Function
Follow these steps to set a polynomial, piecewiselinear, or piecewisepolynomial function for the heat transfer coefficient:
Constant Value
To define a constant heat transfer coefficient, follow these steps:
Example: Determining the Heat Transfer Coefficient Function
This example shows you how to determine the function for the heat transfer coefficient. Consider the simple twodimensional duct flow of air through a watercooled radiator, shown in Figure 7.21.3.
The data supplied in Table 7.21.1 along with values for the air density (1.0 kg/m ) and specific heat (1000 J/kgK) can be used to obtain the following values for the heat transfer coefficient :
Velocity (m/s)  (W/m K) 
5.0  2142.9 
10.0  2903.2 
15.0  3750.0 
The heat transfer coefficient obeys a secondorder polynomial relationship (fit to the points in the table above) with the velocity, which is of the form
(7.2110) 
Note that the velocity is assumed to be the absolute value of the velocity passing through the radiator.
Defining Discrete Phase Boundary Conditions for the Radiator
If you are modeling a discrete phase of particles, you can set the fate of particle trajectories at the radiator. See Section 22.13 for details.