Turbo Pump

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  • Oleh:HERU MIRMANTOJURUSAN TEKNIK MESINFAKULTAS TEKNOLOGI INDUSTRIINSTITUT TEKNOLOGI SEPULUH NOPEMBERSURABAYA2011MESIN-MESIN TURBO

  • Reference :Dietzel Fritz. (1992),Turbin Pompa dan Kompresor Diterjemahkan oleh Ir. Dakso Sriyono, Jakarta : Penerbit Erlangga. Igor Karassik,J ( 2001) Pump Handbook. 3th, McGraw Hill, New York.Lazarkiewicz, Stephen and Troskolanski, A.T. (1965), Impeller Pump. New York, Pergamon Press.M. Khetagurov (1954), Marine Auxiliary Machinery and Systems, Peace Publishers Moscow.Robert, W Fox & Alan T. McDonald (2010),Introduction to Fluid Mechanics 7th, John Wiley & Sons, Inc, Asia. S L Dixon (1998): Fluid Mechanics, Thermodynamics of Turbo Machinery, 4th edition, Pergamon Press Ltd.Obert L. Sanks,1998,Pumping Station Design,Second Edition, Butterworth-Heinemann, Boston

  • TURBOMACHINES Aplikasi dalam kehidupan : Rumah tangga Transportasi kendaraan Industri Instalasi Pembangkit Daya Suatu pesawat yang mengkonversi energi mekanis (torsi poros yang berputar) ke atau dari energi aliran fluida sebagai akibat efek dinamik dari satu atau barisan sudu-sudu.1/3 energi USA untuk Industri, 50% digunakan untuk turbomachinery

  • Classification of Turbomachines : 1. According to Geometry of the Flow Path : Radial Flow Machines lintasan aliran fluida masuk secara aksial (sejajar poros), kemudian seiring dengan perubahan radius, aliran berubah kearah radial. Axial Flow arah aliran masuk dan keluar secara aksial (sejajar poros). Mixed Flow adalah kombinasi dari keduanya.

  • Classification of Turbomachines : Apabila fluida yang dilayani liquid atau slurry. a. Pump

  • Classification of Turbomachines : Apabila fluida yang dilayani gas atau uap dan tergantung pada kenaikan tekanan yang dihasilkan. b. Fan, Blower, Compressor

  • Classification of Turbomachines : a. Water Turbine3. Extract Energy From a Fluid Stream :b. Steam Turbinec. Gas Turbine

  • Classification of Turbomachines : 4. According to change of pressure :

  • Classification of Turbomachines : 5. According to Impeller Construction :

  • POMPAPompa adalah suatu alat/ pesawat yang digunakan untuk memindahkan fluida cair (liquid) dari suatu tempat yang berenergi rendah ke tempat lain yang yang berenergi lebih tingi melalui suatu sistem perpipaan.Definisi :

  • POMPAPrinsip Kerja Pompa :Memberikan perbedaan tekanan antara bagian suction dan bagian discharge dengan mentransfer energi mekanis dari suatu sumber energi luar (motor listrik, motor bensin/diesel ataupun turbin dll.) untuk dipindahkan ke fluida kerja yang dilayani.

  • Prinsip Kerja Pompa Centrifugal :Pompa centrifugal akan bekerja normal bila ruang di dalam casing hingga saluran suction terisi oleh cairan.Apabila impeller berputar, akibat gaya centrifugal maka cairan di antara sudu2 akan bergerak ke arah radial. Sehingga fluida pada diameter luar impeller mempunyai tekanan relatif kuat.Tekanan fluida semakin bertambah saat melalui volute chamber, dimana sebagian energi kinetik menjadi energi potential berupa kenaikan tekanan.

  • Prinsip Kerja Pompa Centrifugal :Apabila tekanan lebih besar dari tekanan discharge nya maka cairan akan kelur pompaKetika fluida meninggalkan inlet impeller, maka ruang tsb mengalami ke vacuman, sehingga cairan pada suction akan naik ke inlet akibat perbedaab tekanan.

  • Centrifugal Pumps are Classified : a. Low capacity pumps- up to 20 cu m per hb. Medium capacity pumpsfrom 20 to 60 cu m per hc. High capacity pumpsover to 60 cu m per h1. According to their capacity :a. Low pressure pumps- up to 5 kg per sq cmb. Medium pressure pumpsfrom 5 to 50 kg per sq cmc. High pressure pumpsover to 50 kg per sq cm2. According to the pressure developed :Pumps speeds are characterized by the specific rotational speed, or speed factor, of the impeller.3. According to their specific speed :

  • Specific Velocity4. Specific Velocity ns1 : a. Low speed impellerfrom 40 to 80 rpmb. Moderat speed impellerfrom 80 to 150 rpmc. High speed impellerfrom 150 to 300 rpmd. Mixed Flow impellerfrom 300 to 600 rpme. Axial Flow impellerfrom 600 to 2000 rpmSpecific velocity is a value that links together the capacity, head and power consumption of pump, all of which depend upon the principal dimensions and velocity of liquid flow in impeller.

  • a. Single admission b. Double admission6. The intake to the impeller : a. Single impeller pumpsb. Multistage pumpsc. Multi impeller pumpsd. Multi impeller Multistage pumps 5. The number of impeller and stage: a. Single casing b. Sectional pumps 7. The design of the casing :

  • a. Water pump.b. Petroleum pump, etc9. The kind of liquid handled : a. Vertical shaft pumpsb. Horizontal shaft pumps8. The disposition of the impeller axis : a. Power pump.b. Direct coupled pump11. The suction lift capacity :a. Self priming pumps.b. Non priming pump10. The method of drive :

  • The specific velocity Where :n= pump impeller speed, rpmQs= capacity of the pump, cu m per secH= head developed by the pump, mH2Og= specific weigh.Specific velocity, or specific factor, is defined as the impeller speed of a model pump which, being geometrically similar to the given pump, develops a head of one meter water column at a discharge of 75 lt/sec having a power consumption of one metric hp at highest efficiency.

  • Ref 7

  • A Selection Of The Number Of Stage RequiredCentrifugal pumps are usually designed with one impeller if the latter is sufficient to provide the required head and output. If the required head cannot be generated by a single impeller, several impeller are arrange to operate in series (multistage pumps). If the required capacity cannot be provided at the head developed by one impeller, several impellers are arranged to operate in parallel (multi-impeller pump) or double admission pumps are used.A combination of high head and high capacity may be achieved by arranging the impellers for combine series and parallel operation.

  • The specific velocity of one stage of a multistage pumpWhere :i= number of stages of pressure H1= head developed by one impeller, mH2O H= head developed by the pump, mH2O

  • The specific velocity for one impeller of a multi impeller pump Where :Qs1 = discharge through an impeller with single admission, cu m per seckk = number of admission (entries) to the impeller ofpump.On the basis of above equation the number of admission is :

  • The specific velocity of one impeller in arrangement of series and parallel operation will be :

    Where :i= number of stages of pressurekk= number of admission (entries) to the impeller of pump.

  • Contoh soal 1 :

  • Contoh soal 2 :

  • SUCTION LIFT OF CENTRIFUGAL PUMPSEnergy equation for cross section I - I to II - II : Where :Za = Distance from the free surface to the datum, mPa = Pressure on the free surface, PascalVa = Velocity of the liquid at the free surface Z = Distance from cross section II to the free surface, mPs = Pressure of the liquid at cross section II Vs = Velocity of the liquid at cross section IIHls = Loss of head in the suction pipe from strainer to cross section II

  • Assuming that velocity Va = 0

    If the inlet velocity is denote as Ce, the head at the inlet circumference of the impeller will be Where :he = Radius of the impeller inlet, mHl= Loss of head in the suction line due to hydraulic resistances, H2OAccording above equation the suction head will decrease with an increase in Zs.

  • If ps drops to the value of the vapor pressure of the liquid at the given temperature, the liquid begins to boil. Net Positive Suction Head (NPSH): The total suction head (in feet or meters) of liquid absolute at the suction nozzle less the vapor pressure absolute (in feet or meters)NPSHA NPSHR

  • So the equation will be :suction lift ThereforeGeneral cavitation begins when Ps becomes equal to the Pv. This condition corresponds to the maximum suction lift.

  • Advisable to operate pump with a permissible geodetic suction lift :Therefore Where :zsp= vertical distance from impeller axis to the free surface, m

  • Contoh soal 1 :

  • Therefore, the permissible suction lift decrease :

    With an increase in temperature of the liquid being pumped.With an increase in loss of head in the suction line.With an increase in the velocity with which the liquid approaches the inlet edge of the impeller vanes.With an increase in the distance between the inlet edge and the impeller axis.Cavitation is also promoted by sharp edges, rough passage walls, abrupt turns and other obstacles to liquid flow which force the stream away from walls.

  • Suara berisik/noise yang bertubi-tubiGetaran pompa sampai terdengarPenggunaan daya/power yang berlebihan daripada biasanya (Ampere meningkat)Debit berkurang drop secara siknifikan Tanda-tanda KavitasiErosi permukaanPermukaan impeller dan rumah keong bopeng (berlubang-lubang kecil-kecil, terkikis)Getaran strukturPenurunan efisiensiSuara berisikAkibat Kavitasi :

  • Noise generation karena kavitasiSpektrum broadband pada saat ada kavitasi, 3 5 KHz (tipikal)

  • Bagaimana menghindari Kavitasi??- Yang jelas, kavitasi hanya terkait dengan posisi suction (pipa isap pompa).Karenanya, perhatiannya hanya pada tempat ini.- Kurangi jumlah katup dan bengkokan pada pipa isap- Gunakan eccentric reducer, bukan concentric reducer- Letakkan bagian lurus dari eccentric reducer pada sisi atas dari pipa isap.- Sedapat mungkin pipa isap sangat pendek.- Pipa isap seyogyanya berdiameter sama dengan diameter inlet pompa.- Gunakan long radius elbow- Yakinkan bahwa katup kaki terbenam secara sempurna.

  • Hindari terjebaknya udara