Centrifugal Compressor Tutorial

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Centrifugal Compressor Tutorial

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    CENTRIFUGAL COMPRESSOR AERODYNAMIC

    DESIGN AND ANALYSIS USING COMPAERO

    CompAero is an aerodynamic design and analysis software system for centrifugaland axial-flow compressors for personal computers. It implements methodsdescribed in the following two books:

    Aungier, R. H., Centrifugal Compressors: A Strategyfor Aerodynamic Design and Analysis (ASME Press,New York, 2000)

    Aungier, R. H.,Axial-Flow Compressors: A Strategy forAerodynamic Design and Analysis (ASME Press, NewYork, 2003)

    Note: a users guide (CompAero.pdf) will be installed with the software to bridge the

    gap between these books and the CompAero software system.

    By Ronald H. AungierSeptember 14, 2011

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    USING THE COMPAERO MENU PROGRAM

    The Menu Program (Compaero.exe) Is Highly Recommended.

    It Simpl ifies The Navigation Among Programs Required For Design & Analysis.

    It Offers Several Taskbar Styles And Startup Options To Suit User Preferences.

    Typically, The Menu Program Is Launched From A Shortcut On Your Desktop.

    The Picture Below Shows The Balanced Rows & Columns Taskbar Style.

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    INPUT & OUTPUT UNITS FOR COMPAERO PROGRAMS

    Programs That Use Dimensional Data Offer A Wide Range Of Input/Output Units.

    A Defaul t Set Of Units (Defined By The User) Is Assumed For New Problems.

    The User Can Change The Units Used For Any Problem As Appropriate.

    Actual Units Used Are Always Saved In The Input Files For Use On Future Runs.

    Caution: Changing The Units Does Not Convert Input Data Already Loaded.

    To Set The Input/Output Units, First Select A Basic Set From The Choices Below.

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    INPUT & OUTPUT UNITS, CONTINUED

    Then, You Can Customize Individual Units From The Dropdown Lists Below.

    Note That Some Units Are Derived From Your Specif ied Units.

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    IDEAL & NON-IDEAL FLUID EQUATION-OF-STATE PACKAGE

    Available Models:

    Aungiers Modified Redlich-Kwong Equation Of State.

    Original Redlich-Kwong Equation Of State.

    Ideal (Thermally Perfect) Gas Equation Of State.

    Pseudo-Perfect Gas Equation Of State.

    Appl icable To Pure Fluids And Fluid Mixtures.

    In General, Compressor Programs Are Valid For The Vapor Phase Only. RKMODCan Handle Two-Phase Flows For Phase Checking, Liquid Knockout, Etc.

    GASDATA Contains An Initial Gas Property Database (Over 100 Compounds) ToGet Users Started. But No Gas Property Database Can Be Accurate For AllPossible Applications. Users Are Responsible For Establishing A DatabaseSuitable For Their Applications.

    Some Good Sources Of Gas Property Data For CompAero Are:

    Ried, R. C., Prausnitz, J. M., and Sherwood, T. K., The Properties Of Gases AndLiquids(McGraw-Hill, New York, 1977).

    Ried, R. C., Prausnitz, J. M. and Poling, B. E., The Properties Of Gases AndLiquids, Fourth edit ion (McGraw-Hill , New York, 1987).

    Yaws, C. L., Chemical Properties Handbook(McGraw-Hill, New York, 1999).

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    NON-IDEAL GAS EQUATION-OF-STATE ACCURACY

    Accuracy Is Quite Sufficient For Al l Aerodynamic Design And Analysis Activity.

    Aungiers Modified Redlich-Kwong Equation Of State Is The Better Choice.

    These Equations Of State Are Not Recommended For Crit ical Applications Such AsPerformance Test Data Reduction Or Low-Tolerance Performance Guarantees.

    The Figures Below Compare Predictions With Experiment For Commonly-UsedCompounds Over a Wide Range Of Pressure, Temperature And Acentric Factor.

    COMPOUND

    Ammonia 0.2550Carbon Dioxide 0.2250

    Ethylene 0.0868

    Helium -0.464

    Hydrogen -0.220

    I-Butane 0.1848

    Methane 0.0080

    N-Pentane 0.2539

    Nitrogen 0.0400

    Propane 0.1520

    Refrigerant R134a 0.3254

    Steam 0.3440

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    SELECTING COMPONENTS FOR A GAS MIXTURE

    Double-Click A Compound To Add It To The Mixture.

    Double-Click Cancel When The Mixture Definition Is Complete.

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    SPECIFYING COMPOUND MOLE FRACTIONS FOR A MIXTURE

    Enter The Mole Fraction Of Each Compound In The Mixture

    The Programs Will Let You Edit These Values Later If Needed.

    The Programs Always Normalize The Sum Of The Mole Fractions To Unity

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    SELECTING THE EQUATION OF STATE

    Select The Equation Of State To Be Used.

    Check The Box To Have The Program Form A Pseudo-Perfect Gas Model.

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    OTHER USEFUL EQUATION-OF-STATE INFORMATION

    The Various Programs Will Let You Edit An Existing Gas Model. You Can ChangeThe Equation Of State, Edit The Mole Fractions Of A Mixture, And Add Or DeleteCompounds In A Mixture.

    The Equation-Of-State Package Also Contains A Generalized Model For GasViscosity That Can Be Applied Using The Same Data Required For The Ideal AndNon-Ideal Gas Models. For The Rarely Used User-Supplied Pseudo-Perfect GasModel, You Will Have To Supply Viscosity Values At Two Temperatures As Input.

    Due To An Oversight, My Centrifugal Compressor Book Does Not Describe TheViscosity Model. It Is described In My Axial-Flow Compressor Book And In MyTurbine Aerodynamics Book (ASME Press, 2006).

    Turbine Aerodynamics Requires Treating Two-Phase (Liquid-Gas) Flows. TheModeling Of The Liquid And Vapor Saturation Lines Includes Some MinorImprovements Not Described In Either Of My Compressor Books. They AreDescribed In My Turbine Book, If You Ever Need That Information.

    When In Doubt, Use RKMOD To Estimate The Vapor Saturation Line Data To BeSure Your Compressor Inlet Conditions Are In The Vapor Phase. Remember,Except For RKMOD And The Liquid-Knockout Calculation In CENCOM, TheCompressor Programs Are Valid For Vapor Phase Flow Only.

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    STAGE PRELIMINARY AERODYNAMIC DESIGN

    Program SIZE Develops Preliminary Stage Designs From PerformanceSpecifications And Empirical Correlations, With Minimal Input By The User.

    It Also Permits the User To Modify Many Of Its Default Values To Refine The DesignTo Better Match Actual Design Requirements And Performance Predictions.

    It Can Export a Complete Input File For A Performance Analysis By ProgramCENCOM To More Accurately Assess The Stages Performance And To ProvideImproved Estimates Of The Modifiable Default Values.

    Its Stage Component Designs Are Well-Matched And Sufficiently Complete ToAssure The User That Their Detailed Design Will Be Successful.

    The Program Can Export Component Preliminary Design Geometry To The VariousCompAero Detailed Design Programs To Supply Their Initial Input Files.

    Extensive Comparison Of Its Empirical Performance Estimates For Its DefaultDesigns With CENCOM Performance Predictions Consistently Show Good

    Agreement Over A Wide Range Of Design And Operating Conditions.

    It Provides A Dramatic Reduct ion In Engineering Design Time And Improves DesignQuality By Its Ability To Rapidly Explore Many Design Alternatives Before StartingThe More Time-Consuming Detailed Aerodynamic Design Process.

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    BASIC STAGE DESIGN SPECIFICATIONS

    This Picture Shows The Basic Stage Design Specif ications Required To Define TheStage Configuration To Be Designed And The Stage Inlet conditions.

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    IMPELLER DIAMETER & SPEED SPECIFICATIONS

    There Are Several Alternative Methods To Specify Impeller Speed & Diameter.

    You Select From The Available Choices To Best Match Your Objectives.

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    STAGE HEAD & EFFICIENCY SPECIFICATIONS

    There Are Also Several Alternative Methods To Specify Head & Efficiency.

    You Select From The Available Choices To Best Match Your Objectives.

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    THE DEFAULT (RECOMMENDED) HEAD & EFFICIENCY

    The Programs Default Performance Specifications Are Based On EmpiricalCorrelations Of Polytropic Head Coefficient And Efficiency As A Function Of StageFlow Coeffic ient Developed From A Number Of Successful Development ProgramsFor Open And Covered Impellers. The Covered Impeller Correlation Is Shown Here.

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    IMPELLER TIP VELOCITY TRIANGLE SPECIFICATION

    The User Can Accept the Programs Recommended Impeller Tip Velocity Triangle OrModify It.

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    USER-MODIFIED DEFAULT PARAMETERS

    The User Can Also Modify Several Of The Programs Default Specif ications.

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    MORE USER-MODIFIED DEFAULT PARAMETERS

    The User Can Also Modify These Programs Default Specif ications.

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    SOME USEFUL HINTS ON PROGRAM SIZE

    SIZE Has Been Re