# Data Entry - Shell and Tube Exchanger

The data entry requirement for flow through a shell and tube heat exchanger is shown below, In this version of FluidFlow you can only consider either the shell side or the tubeside. Figure 1: Data Entry for flow through a shell and tube heat exchanger. 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 heat exchangers 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. Pressure Loss Model: FluidFlow allows the user to choose from three available pressure loss models: 1) Standard Relationships, 2) Manufacturer Loss Data & 3) Fixed Value (Pressure Loss Constant). Standard Relationships: Allows you to enter the geometric characteristics of the heat exchanger in which case, FluidFlow will solve the equations noted in Shell and Tube Exchanger | Calculation Method. Manufacturer Loss Data: Exposes a series of rows on the Input inspector allowing you to enter sufficient data to define the pressure loss relationship as a function of flow (similar to the Kv node). When you define the flow, pressure loss and reference density for a heat exchanger, FluidFlow will automatically scale up or down depending on the actual flow experienced in the system. Fixed Value: Exposes a series of rows on the Input inspector allowing you to define a constant pressure loss for the heat exchanger irrespective of the flow. Number of Tubes: The total number of tubes in the heat exchanger, irrespective of the total number of passes. Figure 2- Schematic of a two tube pass shell and tube heat exchanger. Number of Tubes: The total number of tubes in the tube bundle, irrespective of the total number of passes. Number of Tube Passes: The number of times the fluid passes through the tube bundle. In Figure 2 there are 2 tube passes. Tube Diameter: This is the internal diameter of the exchanger tubes. Diameter Unit: The unit of length used to define the tube diameter. Tube Length: The length of the exchanger from tube sheet to tube sheet. Length Unit: The unit of length used to define the tube length. Tube Pitch Type: This entry refers to the layout of the tubes in the tube sheet. The value can be either "In-line" or "Staggered". Tube Pitch Distance: This is the distance between the tubes in the tube sheet. Figure 3: Tube pitch staggered arrangement. Tube Outside Diameter: This is the outside diameter of the tube. Note, care should be taken when defining the tube outside diameter to ensure that the combined radius of adjacent tubes is less than the available tube pitch distance. If the tube outside diameter is defined as being greater than the available pitch distance (which is a physical impossibility), the calculated pressure loss will be displayed as zero. A design input must therefore be changed to obtain useful results. Tube Size Unit: The unit of length used to define the tube pitch and tube outside diameter. Number of Baffles: The number of baffle plates in the exchanger shell. Distance between Baffles: The distance between each shell baffle. Shell Inside Diameter: The inside diameter of the exchanger shell. Distance/Diameter Unit: The unit of length used to define the shell inside diameter and baffle spacing. Heat Loss Model: For a heat exchanger 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 heat exchanger is assumed to be adiabatic. Selecting Fixed Temperature Change allows you to specify a temperature change for the fluid as it flows through the heat exchanger. 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 heat exchanger. Selecting Fixed Temperature Change adds additional rows to the Input Editor as shown in Figure 4 below: Figure 4: 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 heat exchanger. Into Network means that the temperature of the fluid is increased as the fluid flows through the heat exchanger. Temperature Change: Use this row to specify the temperature change that occurs across the heat exchanger. The heat transfer direction setting determines if temperature is increased or decreased. FluidFlow adjusts fluid physical properties across the heat exchanger 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 5. Figure 5: Additional input data required for Heat Loss Model set to Fixed Transfer Rate. Note, when selecting the Fixed Heat Transfer model, take care to ensure the amount of heat energy, heat transfer direction and heat transfer units are set correctly. When we use this approach, the temperature of the fluid at the inlet of the element is known from upstream conditions and the software calculates the resultant fluid outlet temperature based on the fixed amount of heat transfer defined by the user. During the solution routines, the software makes an initial estimate for flow through the various pipe nodes in a network and determines the resultant pressure and fluid physical properties throughout the system. The software begins with a low estimated flow rate through each sub-network in the system and through each iteration step, increases the flow rate until the model reaches convergence. In the specific case where a system experiences a very low flow rate through an element and a user has defined a high quantity of heat transfer Into the Network at this element, this high level of heat input may result in a corresponding high outlet temperature of the fluid. Depending on system operating conditions, the fluid phase state may change between the inlet and outlet of the element (perhaps from liquid to gas phase). If the fluid condition at the outlet of the element is for example, in gas phase instead of liquid phase, this can result in higher pressure losses and as such, through the subsequent iterations, the fluid may continue to solve in vapor phase. In the unlikely event of this rare phenomenon occurring, you can counteract the condition by swapping the heat transfer selection from Fixed Heat Transfer to Fixed Temperature Change. The fluid temperature at the inlet of the element will be known from upstream conditions and the resultant fluid outlet temperature calculated based on the temperature change defined by the user. The amount of heat energy transferred is also calculated and displayed in the results table for the element. Heat Transferred: Allows you to specify the quantity of heat transferred to (or from) a heat exchanger. 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 heat exchanger 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 6: Figure 6: 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.