# Data Entry - Kf (Equivalent length in pipe diameters)

The data entry requirement for a Kf element is shown below: Figure 1: Data Entry for a K f element. Unique Name: Allows you to enter a descriptive name for this element. It is not necessary to add any data to this field. If you do enter data here you can use this later to sort via the Lists. Status: For resistances there are 3 possible status values: On, Off, or Ignore Pressure Loss. On is the normal position and tells the application that this node is open and to calculate the flow out of the element. Off means that this component is closed to flow. You can close resistances to isolate part of a network. Ignore Pressure Loss means that the node is Open but the pressure loss calculation is skipped. Elevation: This is the height above a selected datum. You can select any datum (base line with elevation = 0) that is convenient for you. When you construct any network you need to decide on a datum. This can typically be ground level, or the centerline of a pump. In flow calculations absolute elevations are not important, only the relative elevations of the nodes are important. The elevation that you enter in this row is the elevation of the connector measured from the datum. Elevation Unit: The unit of length that defines the elevation that you have entered into the elevation row. Use K f from Database: This entry allows you to access commonly used Kf values from the FluidFlow database. The possible values are: "Yes"; "No". Selecting "Yes" allows you to select the Kf element directly from the Kf Component Name row. Selecting "No", exposes a row "K (Pressure Loss Coeff)", that allows you to directly enter any K value as shown in Figure 2. Figure 2: Direct entry of a Kf value. K f Component Name: You cannot add a name directly into this row by typing an entry. Instead when you focus on this row a button appears at the right edge. Clicking the button pops up the Set Component Dialog, which allows you to make a Kf element selection. Kf (L/D): This row allows you to directly enter a Kf value. The coefficient, Kf, is defined by the equation: Kf = ΔP / (0.5 r fT v2). Quantity: This row allows you to enter a value other than 1, in order to specify the number of Kf elements in a line section. This means that you can simplify your models that contain many Kf elements, with a quantity equal to the numbers of Kf elements in the pipe section. You should be aware that this is NOT a recommended approach to use where the fluid phase state is not liquid. This is because the pressure loss is a function of velocity2 and in gas (or two phase flow) the velocity changes with pipe position. Heat Loss Model: For a Kf element there are 3 possible entries: Ignore Heat Loss/Gain; Fixed Temperature Change; Fixed Transfer Rate. Selecting Ignore Heat Loss/Gain means that flow across the Kf element is assumed to be adiabatic. Selecting Fixed Temperature Change allows you to specify a temperature change for the fluid as it flows through the Kf element. Fixed Transfer Rate allows you to specify a fixed amount of heat to be either taken out of or added to the fluid as it flows through the Kf element. Selecting Fixed Temperature Change adds additional rows to the Input Editor as shown in Figure 2 below: Figure 3: Additional input data required for Heat Loss Model set to Fixed Temperature Change Heat Transfer Direction: This value can either be: Out of Network; or Into Network. Out of Network means that heat is lost from the fluid. This has the effect of a temperature drop in the fluid as it flows through the Kf element. Into Network means that the temperature of the fluid is increased as the fluid flows through the Kf element. Temperature Change: Use this row to specify the temperature change that occurs across the Kf element. The heat transfer direction setting determines if temperature is increased or decreased. FluidFlow adjusts fluid physical properties across the Kf element as the temperature changes and also calculates the total amount of heat that needs to be transferred for the specified temperature change to occur. You should be aware that NO check is made to determine if this temperature change is possible, i.e., can this temperature change actually occur? You can think of this mathematically as FluidFlow makes the calculation Heat Transferred = Mass Flow * Specific Heat * Temperature Change, but does not make the calculation Heat Transferred = Heat Transfer Coefficient * Heat Transfer Area * Log Mean Temperature Driving Force. If you specify a temperature that means a change of phase state you will NOT obtain accurate results unless you have the two-phase module activated, instead you will get a warning and the friction loss calculation will be made according to the upstream phase state. Temperature Unit: The unit of temperature used to specify the temperature change. Selecting Fixed Heat Transfer can be conceptualized as the converse of selecting Fixed temperature Change. As before additional rows appear in the Input Editor as shown in Figure 4 Figure 4: Additional input data required for Heat Loss Model set to Fixed Transfer Rate Heat Transferred: Allows you to specify the quantity of heat transferred to (or from) a Kf element. This row works in relation with the Heat Transfer Direction Setting to determine the direction of heat flow. FluidFlow adjusts fluid physical properties across the Kf element as the heat transfer occurs and also calculates the total temperature change that will occur. You should be aware that NO check is made to determine if this heat transfer is possible. You can think of this mathematically as FluidFlow makes the calculation Heat Transferred = Mass Flow * Specific Heat * Temperature Change, but does not make the calculation Heat Transferred = Heat Transfer Coefficient * Heat Transfer Area * Log Mean Temperature Driving Force. If you specify a heat transferred quantity that means a change of phase state occurs, you will NOT obtain accurate results unless you have the two-phase module activated, instead you will get a warning and the friction loss calculation will be made according to the upstream phase state. Heat Transfer Unit: The unit of heat transferred quantity that is used to specify the heat transferred to or from the fluid as it flows across the element. User-Defined Fields: Allows you to add "fields" to the element, for use in, for example, scripting or reporting. Clicking on the input will display the User-Defined Fields dialog to add/edit/delete fields. Properties On Flowsheet: This value can either be: Show; or Hide. The Properties on Flowsheet row is available for all components. This means that you can decide what properties you wish to show on the flowsheet and for which components. If Show is selected then additional rows appear in the Input Editor, which allow you to set text font, color, size, text position and the properties you wish to display. The additional rows are shown in Figure 5: Figure 5: Additional input data required for showing properties on the flowsheet Alignment: This row controls the alignment of the component properties on-screen. Possible values are: Top; Bottom; Left; or Right. Alignment of the displayed text is relative to the center of the component. Font: Text font properties can be set from the standard windows font dialog. Properties: Shows/hides Input and Result fields for display of properties on flowsheet. This allows for visibility of any input or calculated/result data to be controlled for each component. Individual property setting is made via the Select Element Properties dialog.