u2 r2
Speed [rpm]
n 100000
10000
u2 m / s
200 320 500
1000
10
100
1000
Diameter [mm] D2
Michael Casey
Version: August 2015 Compressors C_4_Selection Page 5
C_4.1.4
Selection diagram for industrial compressor types
• Standard types from MAN Turbo
Discharge Pressure (bara)
600 400 200 100 60 40 20 10 6,0 4,0 2,0 0,4 1,0 2,0 4,0 10 20 40 60 100 200 400
– A non-dimensional enthalpy rise and flow for a certain impeller size and tip speed: V hs t1 2t1 s 2 • Head rise Flow D2 u2 u2 coefficient coefficient – A non-dimensional angular velocity or size for a given volume flow and head 1 1 rise: 2 4 Vt1 h s • Specific Specific s Ds D2 3 1 speed diameter h 4 2
pt 3 pt1 1 ( 1)M

2 n /( n 1) u2

• Radial compressor with air at 20°C and tip speed Mach number of 1.0
Gas : Air, M 28.97, R 8314.4 / 28.97 287.1 J/kg/K
Compressors (C) C_4: Compressor selection
Prof. Michael Casey MA, DPhil, FIMechE, CEng, FASME
Retired Professor of Thermal Turbomachinery in the University of Stuttgart


s


V
t1

Michael Casey
Version: August 2015
Compressors
C_4_Selection
Page 3
C_4.1.2
Other influences on the design
• Compression tasks can often be met with different designs. • The technical choice of design and type is influenced not only by the non-dimensional coefficients but also influenced by
• Pressure ratio depends on blade speed and speed of sound
– For fixed speed we get • More pressure ratio on a cold day
at1 RTt1
• (see chapter C_3 for derivation of the equation above) Michael Casey
pt 3 pt1 1 ( 1)M
2 n /( n 1) u2
• Hydrogen compressor – low molecular weight gas
Gas : H 2 , M 2, R 8314.4 / 2 4157.2 J/kg/K
1.4, ( 1) 3.5, p 0.857, 0.65, M u 2 1.0
Standard Compressor Types
R – Radial A – Axial AV - Axial mit verstellbaren Leitschaufeln B - Barrel Z - Cooling S – Sidestream RIK – Radial with integrated cooler
– Gas properties • Molecular weight / Toxicity – Available design experience – International standards – Available driver (motor, gas turbine, steam turbine, turbocharger turbine) – Economics: initial cost, energy costs and operating costs – Size – Available materials – Maximum allowable operating speed – Requirements on the performance map (operating range, efficiency) – Application (for example, low frontal area and weight in jet engines)
• Refrigeration applications not limited by mechanical properties
– At 340 m/s a very high pressure rise
M u 2 2.143,
pt 3 pt1 (1 0.216 * 0.65 * 2.1432 ) 4,82 11.0
Michael Casey
Version: August 2015
Compressors
C_4_Selection
Page 4
C_4.1.3
Effect of radial compressor speed and size

Microcompressors Small turbocharger compressors n 60u2 / D2 Large turbocharger compressors Classical process compressors 1000000
n /(n 1) 3.5 * 0.857 3, pt 3 pt1 (1 0.4 * 0.65 *1.0 2 ) 3 2.000 Tt1 20 C 293.1 K , at1 RTt1 1306.1 m/s, u 2 1306.1 m/s !!!
• Limited by mechanical properties
Compressors
C_4_Selection
Page 2
C_4.1.1
Influence of design data
• Four key items of data are needed to specify a single-stage compressor application:
– – – – The pressure rise, or isentropic enthalpy rise, hs The inlet volume flow rate, V t1 The rotor casing diameter at impeller outlet, D2 The rotor angular velocity, or blade tip-speed
Version: August 2015 Compressors C_4_Selection Page 7
C_4.1.6
Pressure ratio with high molecular weight gas
pt 3 pt1 1 ( 1)M
2 n /( n 1) u2
• Refrigeration compressor – high molecular weight gas
Gas : CH 2 FClF3 , M 102.0, R 8314.4 / 102 81.5 J/kg/K
1.216, ( 1) 5.63, p 0.857, 0.65, M u 2 1.0
n /(n 1) 5.63 * 0.857 4.82, pt 3 pt1 (1 0.216 * 0.65 *1.0 2 ) 4.82 1.88 Tt1 20 C 293.1 K , at1 160.1 m/s, u 2 160.1 m/s
0.65, M u 2 1.0, 1.4, ( 1) 3.5 p 6 / 7 0.857, n /(n 1) 3.5 * 0.857 3.0
pt 3 pt1 (1 0.4 * 0.65 *1.0 2 ) 3 2.000 Tt1 20 C 293.1 K, at1 RTt1 343.2 m/s, u2 343.2 m/s
An educational course on compressors based on lectures given by the author in the University of Stuttgart
Michael Casey
Version: August 2015
Compressors C_4_Selection
Page 1
C_4: Compressor selection
C_4.1 Influences on the design C_4.2 Cordier or Balje diagram C_4.3 Effect of gas properties