VacTran 3 Manual (779748), страница 28
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If more data is in the list than can fit in the window, use the scroll bar to move up and down thelist. Clicking on one row of the list will update the input fields at the top of the dialog. To change the value of thisdata, click in each input field and edit the number as you would with a word processor.The number you edit in the input field will not change the list values below until you either add it to the list using theAdd command, or replace the selected list value with the Replace command.Buttons on the bottom left of the dialog are provided for the basic editing functions.
These Add, Replace, andDelete commands are also available under the Model menu.© 2011 Professional Engineering Computations26215.4VacTran 3Dialog commandsAdd (Ctrl+A): Adds the data in the input fields to the list. Since this is the default command, pressing the Returnkey has the same effect as clicking on Add.The Replace and Delete commands are available only if there is data in the list.Replace (Ctrl-R): Replace the currently highlighted list selection with the data in the input fields.resorted according to the current sort option. This option will be dimmed if the model is empty.The list isDelete (Ctrl-D): Delete the currently highlighted list selection.
This option will be dimmed if the model is empty.© 2011 Professional Engineering ComputationsPipe libraries15.5263Opening Existing Pipe LibrariesTo open an existing Pipe Library: Under the File menu, select the Open... command, or click on the icon asshown:In the Open Document dialog that appears, select Pipe Library and click on OK.(click to expand)You will then be presented with a file selection dialog from which you can choose the directory and name of thePipe library.© 2011 Professional Engineering Computations26415.6VacTran 3Pipe library file formatThe pipe library file is stored as a text file, and can be edited with most word processors.
So if you prefer to use aword processor to enter all the data, save the file as "TEXT". VacTran will not read word processor files in theirnative formats, but will read text files. Change the extension of the file from "TXT" to "VTPIP". When editing yourown files outside VacTran, be sure to follow the formatting guide for pipe libraries or VacTran will report an errorreading the file. A badly corrupted o-ring library file may cause unpredictable results.The following format is required for pipe libraries. Diameter is the inside diameter of the pipe, measured incentimeters.[ Gener al ]Tot al =3[ 0]Des c r i pt i on= 1 c m pi peDi amet er =1[ 1]Des c r i pt i on= 4 i nc h pi peDi amet er =10.
16[ 2]Des c r i pt i on= 1 i nc h pi peDi amet er =2. 54© 2011 Professional Engineering ComputationsGas Models16265Gas ModelsVacuum system performance is directly affected by the properties of the gas being pumped. For example, gasesconsisting of large molecules (large molecular diameter) will have a smaller mean free path than smaller molecules.Simply put, tiny marbles are less likely to run into each other than basketballs. This means that viscous flow willbe present at lower pressures for large molecules. It is important to use realistic values when modeling the gas.(click to expand)A gas model is a file that contains data for a single gas. Each gas is stored in a separate file on disk.Dynamic viscosity is used in viscous flow calculations.Molecular weight is used in molecular flow calculations.Molecular diameter is used to determine flow regime.Temperature is used in molecular flow calculations.Ratio of specific heats (Cp/Cv or Gamma) is used in orifice sonic flow calculations.CAUTIONUse caution in making significant changes to the temperature value without checking if the selected gas parametersare valid.
For example, dynamic viscosity of a gas will change significantly with temperature. VacTran does notautomatically calculate this change, because there is no general formula that is valid for all possible gas types.Therefore, when changing the temperature value, be sure to change the selected gas properties as well.See also:Creating gas modelsDialog descriptionHow gas variables affect calculations© 2011 Professional Engineering ComputationsCalculating Mean Free Path vs. PressureOpening existing gas modelsFormat for gas model files26616.1VacTran 3Creating gas modelsTo create a new gas model: Under the File menu, select the New...
command, or click on the icon as shown:In the New Document dialog that appears, select Gas Model and click on OK.(click to expand)© 2011 Professional Engineering ComputationsGas ModelsThe following dialog allows gas model data entry and editing:© 2011 Professional Engineering Computations26726816.2VacTran 3Dialog descriptionThe gas dialog contains entry fields that describe a gas for VacTran calculations.
The units can be modified usingpull down menus. All entries must be real numbers greater than zero.To save changes to the gas model, select the Save command under the File menu. To save changes to a new filewith a different name, select the Save As...
command under the File menu.To change the default gas model for all subsequent VacTran calculations, choose the Gas Model: command underthe Model menu.© 2011 Professional Engineering ComputationsGas Models16.3How gas variables affect calculationsGas variables have a large effect on vacuum calculations.Viscous flow conductance is inversely proportional to Dynamic Viscosity.Molecular flow conductance is proportional to the square root of Temperature divided by Molecular weight.Mean free path is inversely proportional to Molecular Diameter.Sonic flow is affected by the Ratio of Specific Heats© 2011 Professional Engineering Computations26927016.4VacTran 3Calculating Mean Free Path vs.
PressureMean free path of a gas will vary with pressure. During conductance calculations, different equations applydepending on whether the pressure regime is viscous, molecular, or transition flow. If the mean free path is muchgreater than the pipe diameter, we have molecular flow. If the mean free path is much less than the pipe diameter,we have viscous flow.Under the Model menu, select Mean free path vs. Pressure to display a graph for the currently selected gas.This curve is useful for making judging what flow regimes are to be expected during pump down.
For example, thegraph below is for air at 273 degrees Kelvin. We can see from the graph that down to about 10-1 torr, flow will beviscous for most applications because most pipes are greater than 1 cm in diameter. Conversely, below 10-4 torrmost pumping systems would be in molecular flow because the mean free path is calculated to be greater than 100cm.© 2011 Professional Engineering ComputationsGas Models16.5271Opening existing gas modelsTo create a new gas model: Under the File menu, select the Open... command, or click on the icon as shown:In the Open Existing Document dialog that appears, select Gas Model and click on OK.You will then be presented with a file selection dialog from which you can choose the directory and name of the gasmodel file.© 2011 Professional Engineering Computations27216.6VacTran 3Format for gas model filesThe gas library file is stored as a text file, and can be edited with a word processor.
If a word processor is thepreferred tool to enter the data, save the file as text with a “VTGAS” extension. VacTran will not read wordprocessor files in their native formats, but will read text files in the following format. Units: Dynamic viscosity(poise), Molecular diameter (cm), Temperature (Kelvin)Example:[Properties]Name=Neon.VTGASCvCpRatio=1.4Viscosity=0.0002973MDiameter=2.590038E-8MWeight=20.183Temperature=273.15© 2011 Professional Engineering ComputationsDefault Settings17273Default SettingsVacTran manages an extensive number of custom settings that are saved after you exit VacTran. These includecurrent environment, file directories, units of measure and graph controls.
Most data entry dialogs retain the mostrecent data from session to session.See also:Graph Controls dialogPreset StylesGalleryBackground colorsTitlesAxis typeUpdatesLine styleFontsGrid StyleLog ScalesPointsBorderLegendUnits of measureEnvironment dialog - globalEnvironment dialog - system© 2011 Professional Engineering Computations27417.1VacTran 3Graph Controls dialogWhat is it?The Graph Controls dialog is used to alter the appearance of graphs, including fonts, colors, axis settings, andtitles.How to open the dialog:To access this dialog, click on the Graph Controls speed button as shown below or select Graph Controls from theDefaults Menu.Another way to access Graph Controls is from the Graph Window, using the Controls button below:Click to expand graphic© 2011 Professional Engineering ComputationsDefault SettingsThe graph controls dialog is shown below:See also:Export GraphPreset StylesGalleryBackground colorsTitlesAxis typeUpdatesLine styleFontsGrid StyleLog ScalesPointsBorderLegend© 2011 Professional Engineering Computations275276VacTran 317.1.1 Graph controls helpClick on one of the tabs in the Graph controls dialog below to get help on aspecific topic.See also:Graph controls dialogBackground colorsLine stylePointsExport GraphTitlesFontsBorderPreset StylesAxis typeGrid StyleLegendGalleryUpdatesLog ScalesShadows© 2011 Professional Engineering ComputationsDefault Settings27717.1.2 Preset StylesVacTran comes preconfigured with 12 styles in addition to the many other customized looks available to the user.To use them, select the “Use Predefined Background Style” check box first.
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