# General Resistances

FluidFlow contains a database of General Resistance elements which can be used to represent any fitting or device when building a network. The user can also supplement this database by adding new resistance elements and values. There are five categories of general resistance elements: 1) Inline Filter; 2) K [Pressure Loss Coefficient]; 3) Kf [Eq len in pipe diameters]; 4) Kv [Flow Coefficient]; and 5) User Defined Generic. To access the General Resistances database, select: Database | General Resistances. This opens the Database Editor - General Resistances dialog as shown in Figure 1. Figure 1 outlines the data entry for a round wire screen filter. Figure 1: General Resistances Database. Name: Allows you to enter a descriptive name for the element. Max Operating Pressure: If there is a maximum pressure rating for the general resistance element you should enter this value here. Leaving the value at 0 means that FluidFlow will not make an overpressure check. Pressure Unit: The pressure units used when defining the Max Operating Pressure. Curve Data: The valve curve coordinates can be defined in this field. Simply enter the coordinates as provided by the manufacturer in the columns on the left hand side. FluidFlow will automatically create the curve-fit once a minimum of three coordinates have been defined. Figure 2 provides an overview of the data entry for the round wire screen filter curve-fit. Figure 2: Inline Filter Curve-Fit Data Entry. Curve Fit Type: You can select the most accurate curve-fit from the top left corner of the dialog. There are three choices available: 1) Polynomial, 2) Log Log and 3) Log Polynomial. K [Pressure Loss Coefficient] Figure 3 provides an overview of the data entry for a K [Pressure Loss Coefficient] element. Figure 3: K [Pressure Loss Coefficient]. Name: Allows you to enter a descriptive name for the element. Max Operating Pressure: If there is a maximum pressure rating for the general resistance element you should enter this value here. Leaving the value at 0 means that FluidFlow will not make an overpressure check. Pressure Unit: The pressure units used when defining the Max Operating Pressure. K Value: Product manufacturer's often provide a single K value for a given pipe fitting (valve, nozzle, etc.). You can enter this value here. Kf [Eq len in pipe diameters] Figure 4 provides an overview of the data entry for a Kf [Eq len in pipe diameters] element. Figure 4: Kf [Eq len in pipe diameters]. Name: Allows you to enter a descriptive name for the element. Max Operating Pressure: If there is a maximum pressure rating for the general resistance element you should enter this value here. Leaving the value at 0 means that FluidFlow will not make an overpressure check. Pressure Unit: The pressure units used when defining the Max Operating Pressure. Kf Value: Product manufacturer's often provide a single Kf value for a given pipe fitting (valve, nozzle, etc.). You can enter this value here. Kv [Flow Coefficient] Figure 5 provides an overview of the data entry for a Kv [Flow Coefficient] element. Figure 5: Kv [Flow Coefficient]. Name: Allows you to enter a descriptive name for the element. Max Operating Pressure: If there is a maximum pressure rating for the general resistance element you should enter this value here. Leaving the value at 0 means that FluidFlow will not make an overpressure check. Pressure Unit: The pressure units used when defining the Max Operating Pressure. Flow: The flow used to define the pressure loss data for a Kv element. This flow corresponds with the pressure loss at this flow. Flow Unit: The flow unit that defines the flow data. You can use mass or volumetric flow units. Pressure Drop: The pressure loss that exists at the flow specified above. Pressure Drop Unit: The pressure loss unit that defines the pressure loss. You can use pressure or head loss units. Reference Density: The density of the fluid was used to obtain the flow and pressure loss data. Density Unit: The units of density of the reference or test fluid. Exponent: This is the exponent used to scale the reference pressure drop and flow. Normally the pressure loss is a function of flow squared and so this exponent is 2. For some complex/specialized equipment this may be slightly different from 2. If you have two pressure loss and flow readings you can adjust this exponent so that the curve passes exactly through your experimental data. Design Notes: If you have a full pressure loss curve relationship for your fitting, a sensible reference coordinate for the Kv node would be a midpoint coordinate on the Flow vs. Pressure loss curve. FluidFlow will then automatically scale up or down depending on the actual flow experienced in the system. Equipment data sheets are also usually provided with details of the reference fluid density (typically water or air depending on the fitting). This therefore allows us to define all required parameters for the Kv element. User Defined Generic Element Note, the information for the User Defined Generic element is defined directly on the Input Inspector on the Data Palette and as such, a database for this specific element is not required. FluidFlow allows users to model Non-Standard pipe or duct fittings using the "User Defined Generic" node which is available from the "General Resistances" tab on the Component Palette. This node tends to be more accurate than the Kv node as when using this node we need to define the manufacturer's curve relationship for the fitting. The Kv node by comparison, only requires a single point on the curve. FluidFlow then scales up or down accordingly based on the actual system flow rate. This section will demonstrate how to develop the full curve relationship for a flame arrester using the User Defined Generic node and model the pressure loss relationship in a network. Details of the flame arrester pressure loss are set out in Figure 6. Figure 6: Flame Arrester Model DN 150 / 6". The first step is to define a number of coordinates from the relevant curve (Flame Arrester Model DN 150 / 6") into a table in MS Excel. From this table, create a graph plot of the curve (Insert | Scatter | Scatter with only markers). Right mouse-click on the coordinates and select Add Trendline. A new dialog will appear titled Format Trendline. Click through each of the trendline/curve-fit options taking care to select the curve which best reflects the coordinate positions. Place a check mark in the option for Display the Equation on the chart. Finally, select OK. It is important that the user gives careful consideration to selecting the appropriate curve fit in Excel, in this case, the Power Law curve fit has been selected. Figure 7 provides details of this data entry. Figure 7: Excel Graph Plot for Flame Arrester Model DN 150 / 6". The variables derived from the excel equation are those which may now be defined in FluidFlow (see Figure 3). Note, ensure the flow and pressure loss units are set to m3/h and mbar as per the manufacturer's curve data. Figure 8: Data Entry for User Defined Generic Node. Now the User Defined node has been fully defined, we can build a few sample models using different flow rates to test the accuracy. Figure 9 provides details of the test models. We can see that the calculated friction loss values compare well with those set out in the manufacturer's datasheet illustrated in Figure 1. Figure 9: Test Models using different design flow rates. Add: This button allows you to add a new general resistance component to the database. Delete: This button allows you to delete a general resistance component record from the database. Load: You can load a ".comp" file to the "DATA" Folder stored on your local PC or network if another user has saved (see step described below) and shared their general resistance component data with you. Save: This option allows you to save a general resistance component ("clone") as a ".comp" file type. This means if you have created a new general resistance component in your local database (stored on your "DATA" Folder), you can save the general resistance component file and share with another user. The user can then save the .comp file to their local PC, select the "Load" button which will load-in the new general resistance component file data to their local database. If any of the above is unclear or you require any further information, please contact us at: support@fluidflowinfo.com.