1. Pumps, Compressors, Fans, Ejectors and Expanders
Chapter 20
ChEN 4253 Design I
Terry A. Ring

2. Pumps Moves Liquid, Creates Pressure Pump Types
Vapor bubbles
Causes Cavitations
Erodes Impeller
Solids Erode Impeller
Pump Types
Centrifugal
Positive Displacement
Piston
diaphragm
Pump Power = Q*ΔP = brake (delivered) (horse) power from motor

3. Centrifugal Pumps
Two Basic Requirements for Trouble-Free Operation of Centrifugal Pumps
no cavitation of the pump occurs throughout the broad operating range
a certain minimum continuous flow is always maintained during operation
Pump around loops

4. Reduced Flows
Unfavorable conditions which may occur separately or simultaneously when the pump is operated at reduced flows
Cases of heavy leakages from the casing, seal, and stuffing box
Deflection and shearing of shafts
Seizure of pump internals
Close tolerances erosion
Separation cavitation
Product quality degradation
Excessive hydraulic thrust
Premature bearing failures

5. Centrifugal Pump
Electric Motor

6. Centrifugal Pump
Electric
Motor

7. Centrifugal Pump
Converts kinetic energy to pressure energy

8. Impellers

9. Converts Kinetic Energy to Pressure Energy

10. Different Types of Pump Head
Total Static Head -  Total head when the pump is not running
Total Dynamic Head (Total System Head) - Total head when the pump is running
Static Suction Head - Head on the suction side, with pump off, if the head is higher than the pump impeller
Static Suction Lift - Head on the suction side, with pump off, if the head is lower than the pump impeller
Static Discharge Head - Head on discharge side of pump with the pump off
Dynamic Suction Head/Lift - Head on suction side of pump with pump on
Dynamic Discharge Head - Head on discharge side of pump with pump on

11. Pump Head The head of a pump can be expressed in metric units as:
head = (p2 - p1)/(ρg) + (v22- v12)/(2g) + (z2-z1)      
where
h = total head developed (m) 
p2 = pressure at outlet (N/m2)
p1 = pressure at inlet (N/m2)
ρ =   density of liquid (kg/m3)
g = acceleration of gravity (9.81)  m/s2
v2 = velocity at the outlet (m/s)

12. Pump Efficiency
Centrifugal Pump

13. Pump Performance Curves
Resistance

14. Pump Design Scaling Pump Flow rate Pump Head Pump Brake Horse Power
Q2 = Q1 x [(D2xN2)/(D1xN1)]
Pump Head
H2 = H1 x [(D2xN2)/(D1xN1)]2
Pump Brake Horse Power
BHP2 = BHP1 x [(D2xN2)/(D1xN1)]3
D = Impeller Diameter
N = specific speed

15. Net Positive Suction Head-NPSH
Pumps can not pump vapors!
The satisfactory operation of a pump requires that vaporization of the liquid being pumped does not occur at any condition of operation.

16. Net Positive Suction Head Required, NPSHR
As the liquid passes from the pump suction to the eye of the impeller, the velocity increases and the pressure decreases. There are also pressure losses due to shock and turbulence as the liquid strikes the impeller. The centrifugal force of the impeller vanes further increases the velocity and decreases the pressure of the liquid. The NPSH required is the positive head (absolute pressure) required at the pump suction to overcome these pressure drops in the pump and maintain the liquid above its vapor pressure.

17. Net Positive Suction Head Available, NPSHA
Net Positive Suction Head Available is a function of the system in which the
pump operates. It is the excess pressure of the liquid in feet absolute over its vapor
pressure as it arrives at the pump suction, to be sure that the pump selected does not cavitate.
Head to Feed Pump Subcooling before Pump
To overcome suction head HX
Head
Designed into Installation
Cool a few Degrees
To overcome suction head

18. Piston Pumps

19. Gear Pumps

20. Lobe Pumps
food applications, because they handle solids without damaging the pump.
Particle size pumped can be much larger in these pumps than in other PD types

21. Screw Pump

22. Centrifugal Pump

23. Positive Displacement Pumps
Piston Pumps
Gear Pumps
Lobe Pumps
Diaphragm Pumps
The lower the speed of a PD pump, the lower the NPSHR.

24. Pump Costs Cost based upon Size Factor Must cost Electric Motor also
Centrifugal Pump
S=QH1/2
Gear Pump
S=Q
Piston Pump
S= Power (brake)
Must cost Electric Motor also
S=Pc=PB/ηM

25. Compressors Types Centrifugal Others
Piston
Lobed
Screw
Methods of Calculation in Simulators
Polytropic, PVk-1/k= constant,
Polytropic - This model takes into account both a rise in temperature in the gas as well as some loss of energy (heat) to the compressor's components. This assumes that heat may enter or leave the system, and that input shaft work can appear as both increased pressure (usually useful work) and increased temperature above adiabatic (usually losses due to cycle efficiency). Compression efficiency is then the ratio of temperature rise at theoretical 100 percent (adiabatic) vs. actual (polytropic). (k-1)/k = polytropic coefficient
Isentropic, s(T1,P1)=s(T2,isentropic,P2)
Theoretical Power
Powerisentropic= FlowRate*(h2,isentropic-h1)
Efficiency ηs =Powerisentropic/Powerbrake
ηs = (h2,isentropic-h1)/(h2-h1)
Cost of Compressors
Size Factor is Compressor Power

26. Positive Displacement Compressor

27. Positive Displacement Compressor

28. Centrifugal Compressors
Rotors
Stators
Jet Engine Design

29. Piston Compressor

30. Expander Reverse of Compressor Let flow produce shaft work Types
Centrifugal
Positive Displacement
Piston
Lobed
Screw
Methods of Calculation in Simulators
Polytropic, PVk-1/k= constant,
Isentropic, s(T1,P1)=s(T2,isentropic,P2)
Theoretical Power
Powerisentropic= f*(h2,isentropic-h1)
Efficiency ηs=Powerbrake/Powerisentropic= (h2-h1) /(h2,isentropic-h1)
Cost
Size factor = Power

31. Fans and Blowers Types Cost of Fans and Blowers
Centrifugal ( acfm, P=1-40 in H2O)
Backward Curved
Straight radial
Vane Axial
Tube Axial
Cost of Fans and Blowers
Size factor = Volumetric Flow Rate
Motor

32. Choice to Increase Pressure
Heuristic 34
Use a Fan
Atm to 1.47 psig
Use a Blower
< 30 psig
Compressor (or staged system)
> 30 psig
Heuristic 34 - Number of Stages
Up to a Compression ratio 4 for each stage
With intercooler between stages (ΔP=2 psi)
Equal Hp for each stage (equal compression ratio)

33. Producing Vacuum Steam Ejector

34. Producing Vacuum Types Design for Cost
Ejector - advantage = large volumetric flow rate
Multi-Stage with interstage condensers
Liquid (Oil) Ring Vacuum Pump
Dry Vacuum Pump (rotary screw, lobe) (advantage =low pressure) Designs similar to Expanders
Design for
Flow Rate at suction plus
Air Leakage Rate
Function of pressure and Volume of vessel
Cost
Size factor = Flow Rate at suction
Motor for pumps

35. Ejector Produces Vacuum
Provides Low Pressures for Distillation Columns
Fluid (P ≥ Psat)
Steam
for suction pressure below 100 mbar absolute, more than one ejector will be used, with condensors between the ejector stages
Air
Water
Collects Particles in Gas Stream
Venturi Scrubber