VacTran 3 Manual (779748), страница 15
Текст из файла (страница 15)
All three pump station valves will change at once. The arrows in the open gatevalves indicate the direction of gas flow.In bypass mode, the pumps in the pump list will be connected directly to the vacuum vessel, with noconductance loss calculated during pump down. This may be useful to compare the results of an ideal case tothe particular conductance path being considered.Gas load gate valve: Click on the gas load gate valve to change the connection setting between the gas load listand the vacuum vessel. The arrow in the open gate valve indicates the direction of gas flow during pump down.With the gas valve closed, pump down calculations will be performed without a gas load included.Clicking on the gate valve ...toggles its setting.© 2011 Professional Engineering ComputationsSystem models8.7133Pump, conductance, and gas load listsThree scrolling lists contain the system configurations for conductances, pumps, and gas loads.
In a new model,these lists are empty. The conductance list and the pump list are associated with the current pump station. Thegas load list is associated with the vacuum vessel and independent of the pump stations.Conductance list: This list contains a brief description of each conductance element in the current pump station.Conductance elements in the list are added in series. The following commands are applicable to the conductancelist only if it is focused. Click on the conductance list once to activate it. Double-click on a conductance element inthe list to edit it.Add (Ctrl+A): Adds a conductance element to the list.
You can also use the Conductance palette orbutton orbutton.The Delete, and Get Info commands are available only if there is data in the list.Delete (Ctrl-D): Deletes the highlighted element from the list.Get Info (Ctrl-I): Displays an information box describing the conductance element in detail.Pump list: This list will show the name of each pump model in the current pump station. Pumps are added in© 2011 Professional Engineering Computations134VacTran 3parallel. The following commands are applicable to the pump list if it is focused. Click on the pump list once toactivate it.
Double-click on a pump in the list to edit it.Add (Ctrl+A): Adds a pump model to the list, or you can also use thebutton orbutton.. System models save only the name and disk location of the pumps ineach pump station. When reopened, the system model will search for the pump models on disk, and loadthe data into each pump station.The Delete, and Get Info commands are available only if there is data in the list.Delete (Ctrl-D): Deletes the highlighted pump model from the list.Get Info (Ctrl-I): Displays an information box describing the pump model.Gas load list:A gas load is defined as a source of gas other than the initial vessel volume that must be removed by the pumpstation.
Unlike the initial volume in the vessel, the gas load is a dynamic entity, which can add gas to the systemat a continuously changing rate. Common gas load sources include out gassing, permeation, and leaks. An o-ringis a special case of a permeation source.This list will display the gas loads in the System model. The list shows a brief description of each gas load, and itis independent of the pump stations. The ordering of the list does not affect calculations, and the elements areadditive. The following commands are applicable to the gas load list only if it is active.
Click on the gas load listonce to make it focused. Double-click on a gas load element in the list to edit it. The following commands areapplicable to the gas load list if it is focused.Add (Ctrl+A): Adds a gas load element to the list. You can also use the Gas load palette or thebutton orbutton.The Delete, and Get Info commands are available only if there is data in the list.Delete (Ctrl-D): Deletes the highlighted element from the list.Get Info (Ctrl-I): Displays an information box describing the gas load element in detail.© 2011 Professional Engineering ComputationsSystem models8.8135Dialog check boxesStation Active check box:Even if you have loaded pumps and conductances into a pump station, you may want to temporarilydeactivate that station if you are doing trade studies, so that it is not included in the next calculation.Click on the check box to toggle its state.Add cond volume:Adding the conductance volume to the model will include that volume in all pump down calculations.
Itis equivalent to placing a valve between the pump and the conductance path, so that when the pump isturned on, it is evacuating both the conductance path and the vacuum vessel from the same startpressure.If Add cond volume is unchecked, calculations will assume that the valve is at the interface between thevessel and the conductance path. In this case, the pump down calculations will assume that theconductance path is at the base pressure of the pump before the pump down starts.© 2011 Professional Engineering Computations1368.9VacTran 3Vacuum vesselThe vacuum vessel icon represents the volume to be pumped by the vacuum system. Associated with the vacuumvessel are other global parameters, such as the type of gas to be pumped, the vessel volume, and the start andtarget pressure.
The start pressure is pressure at which pumping begins. Many system models will use a startpressure of 760 torr, or 1 atmosphere, because pumping is simulated from the condition of the vessel "up to air".The target pressure is the desired pressure we wish to achieve with the pumping system.
For some simple dryingprocesses, a rough vacuum target pressure of 10 torr may be all that is required. An inertial confinement fusiontarget chamber imposes more challenging pumping requirements, which may need a target pressure of 10e-6 torr orless. To change these parameters on the system model, simply click on the vacuum vessel icon shown in thesystem model dialog.Clicking on the vessel icon...will invert black and white...and activate the Environment dialog. Alternatively, select any of the global vessel parameters under the Modelmenu.© 2011 Professional Engineering ComputationsSystem models8.10137Working with environment settingsTo open Environment settings, click on the system model vacuum vessel icon...All of the parameters associated with the system model vacuum vessel are accessible here. Parameters have pulldown menus for changing units of measure where applicable. Units will change globally.Gas loads are not associated with the vacuum vessel icon.System start pressure: This is defined as the pressure at which pump down analysis starts, measured at thevacuum chamber.
This can be any value greater than the target pressure. For pump down calculations, the startpressure must be within the pumping capacity of at least one of the pump stations. For example, the start pressurecannot be selected as 760 torr with the highest operating pressure in any pump station at 10-2 torr,.System target pressure: The ending pressure for the pump down analysis, measured at the vacuum chamber.This must be less than the start pressure and greater than zero. For pump down calculations, the target pressuremust be within the defined range of at least one of the pumping stations.Calculation increments: This is number of steps to divide a calculation.
For a sequential set of calculations suchas pump down time, this is the number of increments of pressure between the start and target. A higher increment© 2011 Professional Engineering Computations138VacTran 3value usually results in a more accurate calculation, but also requires more time to perform. Generally, no morethan 500 increments are required to get an adequately smooth curve, and 100 is often acceptable.Gas load decay time: The classical out gas formula approaches infinite gas load as time approaches zero.
Realworld systems do not behave this way. Use the decay time to ignore the theoretical gas load curve values at earlierstart times. For example, for a decay time of 10 seconds, the calculated gas load curve will be based on an initialtime of 10 seconds. The curve will then be applied to the system model at the Gas load start time.Gas load start time: Start time delays the addition of gas loads to the system during pump down calculations.
Forexample, if gas load start time is one hour, the calculated gas load curve will start being applied to the system afterone hour.Gas load stop time: The allotted time to which all gas load calculations will be made. This time limit should beset by the user to be greater than the maximum pump down time for the system.
If stop time is excessively high,the temporal resolution of the gas load calculations will be reduced. If the stop time is less than the pump downtime for the system, it will shut off the gas load before a complete pump down curve can be generated.Vessel volume: Total volume of the chamber to be evacuated, not including the conductance elements connectingto the vacuum pumps. The volume of the conductance elements can be added to the vessel volume using the AddCond Volume check box, as explained later.Change gas model: Activates a dialog that displays all available gas files in the current folder.
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