a system modelling approach to roots-claw pump...
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A System Modelling Approach to Roots-Claw Pump Performance Prediction
M. A. Galtry, N. Turner
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The content of this presentation is confidential and should not be distributed to a third party without prior authorization from BOC Edwards2
Contents
HistoryTransCalc Network Solution ToolSteady-state ModelsTransient ModelsFuture Development
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The content of this presentation is confidential and should not be distributed to a third party without prior authorization from BOC Edwards3
Volumetric Performance Modelling - History
Roots mechanism successfully modelled withinEdwards over last 15 yearsClaw mechanism is more challenging• More complex geometry• Koss et al. achieved limited success in continuum flow
with full thermodynamic treatment.• JVST A 13, 3, May 1995, pp.536-539
Pump developers require easy to use and rapidcode to speed up design process
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The content of this presentation is confidential and should not be distributed to a third party without prior authorization from BOC Edwards4
TransCalc Network Solution Tool
Developed for modelling of complex vacuumsystems• Network based: no a priori knowledge of system layout• Transient and steady-state solutions• Isothermal modelling
Widely applicable• Enables use for modelling in-pump behaviour as well as
system wide behaviour• Based on Edwards’GasFlow routines for flow in ducts.
• Across all flow regimes
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The content of this presentation is confidential and should not be distributed to a third party without prior authorization from BOC Edwards5
TransCalc Network Solution Tool
Largerange oftool types
Drag & Drop interface for rapid model creation
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The content of this presentation is confidential and should not be distributed to a third party without prior authorization from BOC Edwards6
Steady-State Models
Perform a steady calculation on a simple network• Swept volume and carry over modelled as constant speed pumps in
opposing directions• All leakages/ports modelled as ducts.
• Geometry of openings must be “averaged over a cycle”
Simple model• Quick and easy to set up• Can be easily combined to give multiple stages
• Interstage leakage down shaft modelled
Gave acceptable predictions for speed• Issues over accuracy of averaging, filling efficiency at high rotational
speedsPoor prediction of powers• Doesn’t predict over-compression during and after port closing
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The content of this presentation is confidential and should not be distributed to a third party without prior authorization from BOC Edwards7
Steady-state Model Network
B
C
A
E
F
D
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The content of this presentation is confidential and should not be distributed to a third party without prior authorization from BOC Edwards8
Steady-State Model Results - Speed
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The content of this presentation is confidential and should not be distributed to a third party without prior authorization from BOC Edwards9
Steady-State Model Results - Power
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The content of this presentation is confidential and should not be distributed to a third party without prior authorization from BOC Edwards10
Transient Modelling
TransCalc modified to allow volumes, ducts etc to changewith time.System modelled dynamically over a number of revolutions.More complex model to set up• Full pump model is very large• More economic to model stage by stage
• Interstage leakages reduced to leakage back to inlet• Real case has leakage to inlet of previous stage
Still gives results in acceptable timesGood agreement for speed and power• Model extracted into specific model for pump performance• Speed and power curves for multi-stage pumps calculated in ~15
minutes on a PC
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The content of this presentation is confidential and should not be distributed to a third party without prior authorization from BOC Edwards11
Transient Stage Model Network –Single Stage
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Transient Model Results –Single Stage
Zero Flow Compression CurvesMeasured Compression Ratio Predicted Compression Ratio Predicted Power Measured Power
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Transient Model Results –Single Stage
Effect of Rotational Speed on Roughing PerformancePredicted Flow Measured Flow Predicted Power Measured Power
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Transient Model Results –Multistage Pump
Measured Speed Predicted Speed Measured Power Predicted Power
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The content of this presentation is confidential and should not be distributed to a third party without prior authorization from BOC Edwards15
Future Development
Thermal Modelling• Similar lumped-parameter network approach takes power
and pressure data from isothermal modeller• Good agreement with measured pump temperatures• Future integration to calculate clearances dynamically
Gas Mixtures• Pumping of light gases strongly affected by N2 purge• Need to handle changing mixture composition through
pump
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The content of this presentation is confidential and should not be distributed to a third party without prior authorization from BOC Edwards16
Conclusions
Isothermal models capable of giving good speedand power predictionsSystem modelling tools allowed rapid developmentof complex model• Approx 1 man month
Pump modelling tool used for new pumpdevelopment• Significantly shortening NPI process