14.4 Using the Grouped Macro Heat Exchanger Model

To define a single heat exchanger that uses multiple fluid zones, or to connect the auxiliary fluid flow path among multiple heat exchangers, you can use heat exchanger groups. To use heat exchanger groups, perform the following steps:

1.   Enable the calculation of energy in the Energy dialog box.

Models Energy Edit...

2.   Enable the Macro Model Group option and click the Define... button in the Heat Exchanger Model dialog box to access the Macro Heat Exchanger Group dialog box.

Models Heat Exchanger Edit...

3.   Specify the inputs to the heat exchanger group in the Macro Heat Exchanger Group dialog box (Figure  14.4.1).

Figure 14.4.1: The Macro Heat Exchanger Group Dialog Box

(a)   Enter the Name of the heat exchanger group.

(b)   Under Fluid Zones, select the fluid zones that you want to define in the heat exchanger group (Section  14.4.1).

(c)   Click the Model Data tab.

i.   Under Primary Fluid Flow Direction, specify the primary fluid flow direction as either Width, Height, or Depth.

ii.   Under Connectivity, select the Upstream heat exchanger group if such a connection exists (see Section  14.4.2).

iii.   In the Heat Transfer Model drop-down list, choose either the ntu-model or the simple-effectiveness-model (see Section  14.3.2).

iv.   From the Core Porosity Model drop-down list, specify the core model that should be used to calculate the porous media parameters for the zones in the group. More information is available in Section  14.3.6.

v.   Provide the Heat Exchanger Performance Data according to the chosen model.

(d)   Click the Geometry tab (Figure  14.4.2).

Figure 14.4.2: The Macro Heat Exchanger Group Dialog Box - Geometry Tab

i.   Define the macro mesh by specifying the Number of Passes, the Number of Rows/Pass, and the Number of Columns/Pass. More information is available in Sections  14.3.3 and 14.3.4.

ii.   Specify the Auxiliary Fluid Inlet Direction and Pass-to-Pass Direction (see Section  14.4.3).

(e)   Click the Auxiliary Fluid tab (Figure  14.4.3) to specify the auxiliary fluid operating conditions.

Figure 14.4.3: The Macro Heat Exchanger Group Dialog Box - Auxiliary Fluid Tab

i.   Specify the Specific Heat as either a constant-specific-heat or as a user-defined-enthalpy.

ii.    Auxiliary Fluid Flow Rate, Initial Temperature, and Inlet Pressure can be provided as a constant, polynomial or piecewise-linear profile that is a function of time (see Section  14.3.5).

(f)   If a supplementary auxiliary stream is to be modeled, click the Supplementary Auxiliary Fluid Stream tab.

Figure 14.4.4: The Macro Heat Exchanger Group Dialog Box - Supplementary Auxiliary Fluid Stream Tab

i.   You can specify the Supplementary Mass Flow Rate as a constant, polynomial or piecewise-linear profile that is a function of time.

ii.   You can specify the Supplementary Flow Temperature as a constant, polynomial or piecewise-linear profile that is a function of time.

(g)   Click Create or Replace in the Macro Heat Exchanger Group dialog box to save all the settings. Replace changes the parameters of the already existing group that is selected in the HX Groups list.

Creating or replacing any heat exchanger group initializes any previously calculated values for temperature and enthalpy for all macros.

4.   If a heat exchanger group comprises multiple fluid zones and you wish to override any of the inputs defined in the previous steps, click the Set... button to open the Ungrouped Macro Heat Exchanger dialog box (Figure  14.3.2). Select the particular fluid zone as usual. Notice that the individual heat exchanger inherits the properties of the group by default. You may override any of the following:

• Number of Passes, Number of Rows/Pass, and Number of Columns/Pass

• Auxiliary Fluid Inlet Direction and the Pass-to-Pass Direction

• Core Porosity Model