VacTran 3 Manual (779748), страница 18
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Depending on downstream geometry, it may or may not have an exit loss.The user must determine whether to select the exit loss option, based on whether there will be a significantpressure drop at the interface with the next conductance element. Guidance is provided at Choosing entrance andexit loss options.Where is it used?Elbow conductance elements are used in System Models and Conductance Studies.© 2011 Professional Engineering Computations158VacTran 3See also:Annular pipe entryCombination conductancesCone entryConstant entryElliptical pipe entryMiter entryOrifice entryPipe bend entryPipe entryPump station modelsRaw data conductance modelsRectangular pipe entrySlit entryTriangular pipe entry© 2011 Professional Engineering ComputationsSystem models1598.13.6 Ellipse entry dialogDefinitionAn ellipse (elliptical pipe) is a conductance element having an elliptical cross section (two diameters) and non-zerolength.Entrance and exit lossesDepending on upstream and downstream geometry relative to the pipe, it can have an entrance loss, and exit loss,or both.
The user must determine whether to select the entrance loss or exit loss options. Since limited data hasbeen found for entrance and exit losses associated with elliptical pipe, circular pipe formulas are used for endeffects. This will introduce some level of error that has not been quantified. Use the entrance and exit functions forestimating purposes.Where is it used?Elliptical conductance elements are used in System Models and Conductance Studies.This dialog is a multi-tabbed interface that has several functions.© 2011 Professional Engineering Computations160VacTran 3The Data Entry tab contains the basic information needed to create a pipe. You need not go any further than thistab if you know the dimensions, and end effects.
Quantities greater than one will be calculated as conductances inseries. Note, however, that the entrance and exit loss value will also be multiplied. In most cases, a separate pipeentry will be appropriate for each length of pipe in the model, each with its own assessment of applicable endeffects.The Use Recent Entry tab allows selection of a previous conductance element that was entered, with the mostrecent entry shown at the top of the list. This function is intended to be a time saver for frequently used geometries.The Entrance Detail tab contains more detail on the type of entrance present, and applies to the pipe calculationsonly if the entrance loss option is selected. The three images below show the three different types of entrancesapplicable to pipe.
Note that K factor and r/d ratios will only apply to viscous flow calculations, and not molecularflow calculations.A projecting pipe is assumed to be square-edged, with no entrance radius.A radius-edge entrance tends to minimize turbulance. For an edge radius r and pipe diameter d, the r/d ratio isused to determine the loss factor. At r/d >0.15, there is no significant improvement in flow loss.© 2011 Professional Engineering ComputationsSystem models161A sharp edge entrance has a radius of zero, and maximizes the turbulent entrance loss effect in viscous flow. Formany designs where a pipe is welded into a vessel at a machined port location, sharp edged entrances arecommon.© 2011 Professional Engineering Computations162VacTran 3The Summary tab contains calculation information for this conductance element.
The text in this section can behighlighted, copied, and pasted into another application. The information is intended to provide significantly moredetail than can otherwise be gained from looking at conductance curves, and serves to allow the user additionalscrutiny into the basis for flow calculations.See also:Annular pipe entryCombination conductancesCone entryConstant entryElbow entryMiter entryOrifice entryPipe bend entryPipe entryPump station modelsRaw data conductance modelsRectangular pipe entrySlit entryTriangular pipe entry© 2011 Professional Engineering ComputationsSystem models1638.13.7 Miter entry dialogDefinitionA miter is a conductance element having a circular cross section a single abrupt bend created by the geometricintersection of two pipes, and a short length of pipe at the entrance and exit.Entrance and exit lossesA miter is considered a randomizing element that disrupts fully developed flow coming from upstream piping.Therefore, no option for an entrance loss is provided because the randomizing affect of the entrance is alreadyimplicitly included in the miter formula.
Depending on downstream geometry, it may or may not have an exit loss.The user must determine whether to select the exit loss option, based on whether there will be a significantpressure drop at the interface with the next conductance element. Guidance is provided at Choosing entrance andexit loss options.Where is it used?Miter conductance elements are used in System Models and Conductance Studies.© 2011 Professional Engineering Computations164VacTran 3See also:Annular pipe entryCombination conductancesCone entryConstant entryElbow entryElliptical pipe entryOrifice entryPipe bend entryPipe entryPump station modelsRaw data conductance modelsRectangular pipe entrySlit entryTriangular pipe entry© 2011 Professional Engineering ComputationsSystem models1658.13.8 Orifice entry dialogDefinitionAn orifice is a conductance element having a circular cross section and essentially zero length.
An orifice can havean entrance corner radius, which by geometry creates a finite length, but this additional length is not included theorifice calculations. The radius of the edge is used only in viscous and sonic flow calculations. Generally speaking,a sharp edge (zero radius) will have a lower viscous flow conductance than a finite radius.Entrance and exit lossesEntrance and exit losses are not added to orifices, which are essentially an entrance or exit depending on thecontext.
In some text books, for example, a pipe exiting to a larger volume is modeled as a pipe and and samediameter orifice in series.Where is it used?Orifice conductance elements are often used flow limiters and metering devices in systems where a known flow rateis required.© 2011 Professional Engineering Computations166VacTran 3See also:Annular pipe entryCombination conductancesCone entryConstant entryElbow entryElliptical pipe entryMiter entryPipe bend entryPipe entryPump station modelsRaw data conductance modelsRectangular pipe entrySlit entryTriangular pipe entry© 2011 Professional Engineering ComputationsSystem models1678.13.9 Pipe bend entry dialogDefinitionA bend is a conductance element having a circular cross section a constant radius bend angle.Entrance and exit lossesA bend is considered a randomizing element that disrupts fully developed flow in upstream piping.
Therefore, nooption for an entrance loss is provided because the randomizing affect of the entrance is already implicitly includedin the bend formula. Depending on downstream geometry, it may or may not have an exit loss.The user must determine whether to select the exit loss option. Guidance is provided at Choosing entrance andexit loss options.© 2011 Professional Engineering Computations168VacTran 3Where is it used?Bend conductance elements are used in System Models and Conductance Studies. Generally, a bend is a pipethat turns at a constant rate, while an elbow is a fitting between pipes that turns abruptly, usually between 45 and90 degrees.See also:Annular pipe entryCombination conductancesCone entryConstant entryElbow entryElliptical pipe entryMiter entryOrifice entryPipe entryPump station modelsRaw data conductance modelsRectangular pipe entrySlit entryTriangular pipe entry© 2011 Professional Engineering ComputationsSystem models1698.13.10 Pipe entry dialogDefinitionA pipe is a conductance element having a circular cross section and non-zero length.Entrance and exit lossesDepending on upstream and downstream geometry relative to the pipe, it can have an entrance loss, and exit loss,or both.
The user must determine whether to select the entrance loss or exit loss options.Where is it used?Pipe conductance elements are used in System Models and Conductance Studies.This dialog is a multi-tabbed interface that has several convenience functions.The Data Entry tab contains the basic information needed to create a pipe. You need not go any further than thistab if you know the dimensions, and end effects. Quantities greater than one will be calculated as conductances inseries.
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