VacTran 3 Manual (779748), страница 19
Текст из файла (страница 19)
Note, however, that the entrance and exit loss value will also be multiplied. In most cases, a separate pipe© 2011 Professional Engineering Computations170VacTran 3entry will be appropriate for each length of pipe in the model, each with its own assessment of applicable endeffects.The Use Library tab facilitates selection of a pipe diameter from a library of standard pipe sizes. Libraries fromcommon schedule pipe are included with VacTran, and you can edit or add pipe libraries of your own.
Click on thepipe description in the selection list to change the pipe entry diameter.© 2011 Professional Engineering ComputationsSystem models171The 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.© 2011 Professional Engineering Computations172VacTran 3The 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.© 2011 Professional Engineering ComputationsSystem models173A 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 Computations174VacTran 3A 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 ComputationsSystem models175The 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 entryElliptical pipe entryMiter entryOrifice entryPipe bend entryPump station modelsRaw data conductance modelsRectangular pipe entrySlit entryTriangular pipe entry© 2011 Professional Engineering Computations176VacTran 38.13.11 Pump station modelsWhat is it?A pump station consists of one or more vacuum pumps connected by one or more conductance elements to thevacuum vessel in a system model.
Conductance elements can be pipes, elbows, bends, orifices, or constantvalues. A system model has to have at least one active pump station in order to calculate pump down time.The pump station can be built directly within a system model, or imported as a complete unit from a saved modelthat is described here.A pump station model is a stand-alone file that can besaved under a unique name and recalled for use insystem models.The conductances and pumps are entered under separatetabs as shown.The pump station model can be created and savedindependently from the system model so it can be usedas building block for several system models.How to I create one?We can create a pump station model by clicking on the following speed button:© 2011 Professional Engineering ComputationsSystem models177How do build the model?The list shown in the Conductances in series tab works exactly the same as the conductance list in the systemmodel.
The list shown in the Pumps tab also works the same as the pump list in the system model. Click in theconductance list to bring the conductance palette forward, then select conductance elements in series.© 2011 Professional Engineering Computations178VacTran 3What to do first:Click on the conductance list (initially empty) once.Add a conductance to the list in any of the following ways:Type Ctrl+A to activate the Add Conductance dialogClick on the Conductance Palette, and click on one of the conductance buttons:Click on thespeed button to activate the Add Conductance dialog.Click on a conductance icon in the conductance palette to add it to the list.© 2011 Professional Engineering ComputationsSystem models179What to do next:Click on the pump list (initially empty) once.Add a pump to the list in any of the following ways:Type Ctrl+A to activate the Open dialogClick on theyour hard disk.speed button to activate the Open dialog. Pick a pump from a folder onSave the file so it can be inserted into system models.
Note that several graphing functions are available in for thismodel such as delivered speed. They are highlighted in the Graphs menu.Where do I use the model?Right-clicking on a system model pops up the menu below, which includes options for adding a pump station froman external file.See also:Annular pipe entryCombination conductancesCone entryConstant entryElbow entryElliptical pipe entryMiter entryOrifice entryPipe bend entryPipe entryRaw data conductance modelsRectangular pipe entrySlit entryTriangular pipe entry© 2011 Professional Engineering Computations180VacTran 3© 2011 Professional Engineering ComputationsSystem models1818.13.12 Raw data conductance modelsWhat is it?A raw data conductance model is a data file of conductance versus pressure values.
The model can represent apipe, orifice, bend, valve, trap, or any other conductance element. It can be created from scratch by the user in thesame manner as a pump file or raw data gas load model. An alternative is to use the Generate raw dataconductance function from within a system model or Conductance Study.Most conductance models in VacTran are parametric; in other words, the conductance a particular pressure valuefor a pipe or elbow model is calculated on the fly during pump down calculations.
In contrast, the raw dataconductance model is a set of user defined data that defines gas load vs time as a set of data points. It is notassociated with a particular geometry.Despite the variety of conductance elements common to vacuum systems, all can be characterized by a curverepresenting total gas load vs time. In viscous flow, conductance varies significantly with pressure. A raw dataconductance model is a two dimensional array of data. It contains no information on actual physical geometry ormaterial characteristics.© 2011 Professional Engineering Computations182VacTran 3How do I use it?The user creates the model based on assumptions, published curves, measured data, or off-line calculations.VacTran provides an efficient dialog for editing the model.
This dialog works much in the same manner as thePump model and raw data gas load dialogs. For most modeling tasks, the parametric models for pipes, elbows,etc are easier to use. The need for a raw data file can come from measured conductance values for and oddgeometry, or calculated values from another software application. VacTran does not validate the data entered, otherthan ensure that it contains positive numbers.See also:Annular pipe entryCombination conductancesCone entryConstant entryElbow entryElliptical pipe entryMiter entryOrifice entryPipe bend entryPipe entryPump station modelsRectangular pipe entrySlit entryTriangular pipe entry© 2011 Professional Engineering ComputationsSystem models1838.13.13 Rectangle entry dialogDefinitionA rectaular pipe 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. Since limited data hasbeen found for entrance and exit losses associated with rectangular 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?Rectangular pipe conductance elements are used in System Models and Conductance Studies.
They are used inpumping manifolds for accelerator beam lines, load lock systems where rectangular valves are used for waferhandling systems, and other experimental applications.This dialog is a multi-tabbed interface that has several 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. 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.© 2011 Professional Engineering Computations184VacTran 3The 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.
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