14.3.5 Specifying the Auxiliary Fluid Properties and Conditions

To define the auxiliary fluid properties and conditions, you will specify the Auxiliary Fluid Flow Rate ( $\dot{m}$) in the Auxiliary Fluid tab. The properties of the auxiliary fluid can be specified using the Auxiliary Fluid Properties Method drop-down list. You can choose a constant-specific-heat ( $c_p$) and set the value in the Auxiliary Fluid Specific Heat field below, or as a user-defined function for the enthalpy using the user-defined-enthalpy option and selecting the corresponding UDF from the Auxiliary Fluid Enthalpy UDF drop-down list.

The function should return a single value depending on the index:

• Enthalpy for given values of temperature, pressure, and quality.

• Temperature for given values of enthalpy and pressure

• Specific heat for given values of temperature and pressure

The user-defined function should be of type

DEFINE_SOURCE(udf_name, cell_t c, Thread *t, real d[n], int index).

where n in the expression d[n] would be 0 for temperature, 1 for pressure, or 2 for quality. The variable index is 0 for enthalpy, 1 for temperature, or 2 for specific heat. This user-defined function should return

real value; /* (temperature or enthalpy or Cp depending on index). */

• If you want ANSYS FLUENT to compute the auxiliary fluid inlet temperature for a specified heat rejection, follow the steps below:

  1.   Enable the Fixed Heat Rejection option in the Model Data tab.

  2.   Specify the Heat Rejection ( $q_{\rm total}$ in this equation in the separate Theory Guide) in the Auxiliary Fluid tab.

  3.   Specify the Initial Temperature, which will be used by ANSYS FLUENT as an initial guess for the inlet temperature ( $T_{\rm in}$ in this equation in the separate Theory Guide and this equation in the separate Theory Guide).

• If you want ANSYS FLUENT to compute the total heat rejection of the core for a given inlet auxiliary fluid temperature, follow the steps below:

  1.   Enable the Fixed Inlet Temperature option in the Model Data tab.

  2.   Specify the Inlet Temperature ( $T_{\rm in}$ in this equation in the separate Theory Guide and this equation in the separate Theory Guide) in the Auxiliary Fluid tab.

• If you enable the User Defined Enthalpy option under the Auxiliary Fluid Properties Method, you must also specify the Inlet Pressure ( $p_{\rm in}$ in this equation in the separate Theory Guide) and Inlet Quality ( $x$ in this equation in the separate Theory Guide).