1. Creating a User-Defined Condenser in THERMOFLEX
Thermoflow Inc.
Creating a User-Defined Condenser in THERMOFLEX
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2. Introduction
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THERMOFLEX contains 300 components. These can be used to cover virtually any application.
However, in case the need arises, the framework exists to create your own THERMOFLEX component.

3. Imagine the following scenario….
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You wish to model a vendor’s condenser in THERMOFLEX.
The vendor has supplied you with performance curves, relating condenser pressure to condenser duty at six different cooling water inlet temperatures.

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To edit User-Defined Components, start THERMOFLEX and select this menu item. The User-Defined Component option will be enabled in any of THERMOFLEX’s modes of operation. However, the user must have the UDC program enabled on their key. Otherwise this selection will be grayed out at all times.

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These tabs allow you to navigate the User-Defined Component creation process. We will start with Icon & Connections, then address Isolated Inputs and Isolated Outputs.

6. Choose a name for your component here.
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Choose a name for your component here.
Right-click on this gray area to select a custom visage for your component. Picture must be in .WMF format.

7. Choose the dimensions of the icon on the sheet.
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Choose the dimensions of the icon on the sheet.
Right-click on the node slots where you wish to create a node, and select Add Inlet Stream or Add Outlet Stream. We will put inlets on the green nodes and outlets on the orange nodes.

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Stream name: Inlet Steam
Stream type: Water/Steam
Mass flow: propagates through component
Conjugate node: Outlet Condensate
Pressure: set by component
Priority: high priority pressure dictator
Stream name: Outlet CW
Stream type: Water/Steam
Mass flow: propagates through component
Conjugate node: Inlet CW
Pressure: propagates through component
Stream name: Outlet Condensate
Stream type: Water/Steam
Mass flow: propagates through component
Conjugate node: Inlet Steam
Pressure: set by component
Priority: high priority pressure dictator
Stream name: Inlet CW
Stream type: Water/Steam
Mass flow: propagates through component
Conjugate node: Outlet CW
Pressure: propagates through component

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Choose the number of isolated inputs here.
Isolated Inputs are component parameters that you will set in Edit Inputs mode. Each input has an associated set of units which you will select.
Enter a name for the input in the Input column. Select a default numerical value for the parameter in the Value column. Right click on the Units Selection column to choose the units the parameter is measured in.
We choose:
Water Head to Condensate Outlet, to calculate pressure rise on condensing side that is due to hydrostatic pressure.
Working/Out of Service, a switch to take the condenser off-line for maintenance.

10. Isolated Outputs are results that your component calculates.
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Choose the number of isolated outputs here.
Isolated Outputs are results that your component calculates.
Enter a name for the output in the Output column. Select a default numerical value for the parameter in the Value column. Right click on the Units Selection column to choose the units the parameter is measured in.
We choose:
Condenser Duty.
Condenser Surface Area, which was provided to us by the vendor.
Cooling Water Side Pressure Drop, which we calculate from vendor’s reference value scaled with the square of CW flow rate.

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You may embed the calculations for your component in either an Excel workbook or in an executable. We will demonstrate how to do it using Excel.
Click here to create an Excel workbook containing the code for the condenser.

12. The Calculation Workbook
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When you create a THERMOFLEX calculation workbook, it contains a sheet called TF Data Transfer that interacts with the model. Data in this sheet is organized in a standard format.

13. Structure of an Excel Calculation Workbook
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Based on your definitions when you defined your icon, THERMOFLEX will populate the first 8 columns of the active worksheet with the following information:
There will be a column with the name of the parameter, and a column containing its default value.
Interrelated Inputs
Interrelated Outputs
Isolated Inputs
Isolated Outputs
Global inputs passed from TFX to the component. Examples are ambient conditions and grid frequency. Do not change these values.
Outputs from your component which are passed to and used by the rest of the TFX model. These are in addition to any stream parameters determined by the component and passed to the TFX network via its nodes.
Inputs specific to your component.
Outputs from your component to display on its own outputs, but not passed to the rest of the TFX model.

14. The anatomy of a UDC calculation workbook:
Isolated and interrelated inputs and outputs.
Isolated Outputs
Isolated Inputs
Interrelated Outputs
Interrelated Inputs

15. Structure of an Excel Calculation Workbook
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Additionally, the TF data transfer sheet will automatically create a pair of columns for each node, with the first column of this pair showing the stream descriptors, and the second column showing corresponding numerical values.
You may have up to 40 nodes for your component. Excel has columns for all 40 and will hide the empty ones you do not use.
Node #1
Node #2
Node #3
Node #4
In our model, this is the Steam Inlet.
In our model, this is the Condensate Outlet.
In our model, this is the CW Inlet.
In our model, this is the CW Outlet.
The cells underneath each node describe its conditions and behavior.

16. The anatomy of a UDC calculation workbook:
Four sets of node data are highlighted, with a standard format.
Node #1
Node #4
Node #2
Node #3

17. The format of node data in Calculation workbook:
Actual flow dictator flag for current model.
0 = network determines flow
-1 = inlet node dictates outlet node flow
+1 = outlet node dictates inlet node flow
2 = component determines flow directly
1 = the node is an outlet
0 = the node is empty
-1 = the node is an inlet
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Node Fluid Type:
1 = Gas/Air, 2 = Water/Steam, 3 = Fuel,
4 = Refrigerant, 6 = Brine, 7 = Heat Transfer Fluid
Component definition for flow dictator flag.
0 = network determines flow
1 = flow propagates to/from a pair of inlet/outlet nodes
2 = component determines flow directly
Actual pressure dictator flag for current model.
0 = network determines pressure
-1 = inlet node dictates outlet node pressure
+1 = outlet node dictates inlet node pressure
2 = component determines pressure directly
Node to which current node’s flow propagates if Component Definition for Flow Dictator Flag is 1.
Flow priority between 1 and 100 if component determines flow. Lower is higher priority.
Component definition for pressure dictator flag.
0 = network determines pressure
1 = pressure propagates to/from a pair of inlet/outlet nodes
2 = component determines pressure directly
The format of node data in Calculation workbook:
This is a breakdown of the cells that represent a node in the worksheet. This is Node #3 in our workbook.
Node to which current node’s pressure propagates if Component Definition for Pressure Dictator Flag is 1.
Pressure priority between 1 and 100 if component determines pressure. Lower is higher priority.
Thermodynamic properties at node

18. Calculation model
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To model the condenser we will maintain two spreadsheets:
The TF Data Transfer sheet which interacts with THERMOFLEX.
Separate calculation sheet which takes stream data, determines the condenser pressure, and returns it to the TF Data Transfer sheet. To solve for condenser pressure we will also need to define two relationships:
Enthalpy of Saturated Liquid as a function of pressure.
Mathematical expression for the vendor-supplied curves which relate condenser pressure to duty and inlet CW temperature.

19. Enthalpy of Saturated Liquid
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We derived a curve fit via Excel for enthalpy of saturated water as a function of pressure within the range of parameters of interest:
Function A (listed as fn_A):
Where:
𝑃 𝑐𝑜𝑛𝑑 is in psia
𝐻 𝑓 𝐵𝑇𝑈 𝑙𝑏 = ln 𝑃 𝑐𝑜𝑛𝑑

20. Relationship between condenser pressure and duty
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To model this relationship we first produce quadratic fits relating pressure and duty at each cooling water temperature.
Pcond= A*Qcond2 + B*Qcond + C
Where the constants equal…
CW Temp A B C 65
1.00E-05
0.007
0.4962 70
2.00E-05
0.0056
0.7463 75
4.00E-05
0.004
0.9959 80
5.00E-05
0.0029
1.1971 85
0.0047
1.3981 90
0.0069
1.5987

21. Relationship between condenser pressure and duty
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We find that the coefficients in our five quadratic fits (the lines shown to the left) can be approximated as a function of inlet cooling water temperature, as follows:
A = A1*Tcw2 + A2*Tcw + A3
B = B1*Tcw2 + B2*Tcw + B3
C = C1*Tcw2 + C2*Tcw + C3

22. Relationship between condenser pressure and duty
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Combining these elements, we produce a single equation that represents condenser pressure as a function of condenser duty and cooling water inlet temperature:
Function B (listed as fn_B):
Where:
𝑇 𝑐𝑤 is in degrees Fahrenheit
𝑄 𝑐𝑜𝑛𝑑 is in MMBTU per hour
𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑖𝑛 𝐻𝑔 = − 1∗10 −7 𝑇 𝑐𝑤 ∗10 −5 𝑇 𝑐𝑤 − 𝑄 𝑐𝑜𝑛𝑑 ∗10 −5 𝑇 𝑐𝑤 2 − 𝑇 𝑐𝑤 𝑄 𝑐𝑜𝑛𝑑 + − 𝑇 𝑐𝑤 𝑇 𝑐𝑤 −4.1971

23. To solve for condenser pressure, we use an iterative approach embedded in a different Excel sheet. Starting with an assumed pressure, we first find the duty from the inlet steam enthalpy (imposed by the TFX network) and exit condensate enthalpy (which we calculate from saturation pressure), then we enter the vendor’s curves (which we expressed as an equation) with this duty and find the corresponding pressure, then repeat. This converges quickly as shown below. We repeat this correction five times, to ensure convergence. .
Where…
Fn_A is the function for the enthalpy of saturated liquid (derived from NIST data).
Fn_B is the function for condenser pressure as a function of duty that we received from the vendor.
Different sheet

24. These values are the taken from the node data in the TF Data Transfer sheet. Because our relationship between cooling water inlet temperature, pressure, and duty is valid for temperatures from 65°F to 90°F, we insert a logical statement that cuts this value off at 65 if too low or 90 if too high.

25. With the condenser pressure and duty determined on the other sheet, the TF Data Transfer sheet extracts their values. IF statements tests to determine if condenser is online.
Condenser duty: grabbed from other sheet
=IF(F5=1, Sheet3!A12*0.0036, 0)
Condenser pressure: grabbed from other sheet
=Sheet3!A13/2.032

26. Condenser Surface Area is 17,868 ft2 according to vendor, so this is entered directly into the output field.

27. Additionally, we calculate the pressure drop on the cooling-water side as a function of cooling water mass flow, based on the following relationship:
∆𝑃= 𝑃 𝑟𝑒𝑓 𝑚 𝑐𝑤 𝑚 𝑟𝑒𝑓 2
Formula entered for cooling water side pressure drop:
=6.67*(P26/1870)*(P26/1870)

28. With the condenser duty solved for, we calculate the states of the outlet streams.
Formula entered for CW outlet enthalpy:
=P27+(L27-N27)*L26/R26
Or, the sum of the inlet enthalpy plus the change in enthalpy.
Formula entered for Outlet Condensate enthalpy:
=Sheet3!A14
Grabbed from other sheet.

29. To fully specify the outlet states we indicate the pressures of the outlet streams based on the physical information provided, and define the inlet steam pressure.
Formula entered for CW outlet pressure:
=P24-H5
Formula entered for Inlet and Outlet Condensate pressures:
=Sheet3!A13

30. Close Excel and return to THERMOFLEX to model the component.

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After changing the calculation workbook in Excel, be sure to update the workbook by selecting this option.

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When you are done defining your component, save it as a .myc file in the C:\TFLOW24\MyComponents directory to start using it.

33. Using your UDC in models
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Now we can use the user-defined condenser in a THERMOFLEX model.

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Choose My Components in the icon navigator to access your new condenser.

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Here is the component in the context of a simple model, with inlet sources and sinks, in Edit Inputs mode.

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After computing, we find the model shows the isolated outputs on the component’s output view to the left.

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This is a model showing the User-Defined Condenser connected to a steam turbine in off-design mode.

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Likewise, the model produces outlet conditions based on the cooling water temperature, and inlet states and mass flows.

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Alternative Component Modeling Approach: Instead of using Excel, a user can embed the component calculation in an .exe, provided the calculation routine stores data in appropriately named structures. Contact us if you would like further information about this process.

40. Questions?
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Contact us at if you have any questions about the user defined component.