Chapter 14: Turbomachinery

1
Chapter 14 Turbomachinery

• Eric G. Paterson
• Department of Mechanical and Nuclear Engineering
• The Pennsylvania State University
• Spring 2005

2
Note to Instructors

• These slides were developed1, during the spring
  semester 2005, as a teaching aid for the
  undergraduate Fluid Mechanics course (ME33
  Fluid Flow) in the Department of Mechanical and
  Nuclear Engineering at Penn State University.
  This course had two sections, one taught by
  myself and one taught by Prof. John Cimbala.
  While we gave common homework and exams, we
  independently developed lecture notes. This was
  also the first semester that Fluid Mechanics
  Fundamentals and Applications was used at PSU.
  My section had 93 students and was held in a
  classroom with a computer, projector, and
  blackboard. While slides have been developed
  for each chapter of Fluid Mechanics
  Fundamentals and Applications, I used a
  combination of blackboard and electronic
  presentation. In the student evaluations of my
  course, there were both positive and negative
  comments on the use of electronic presentation.
  Therefore, these slides should only be integrated
  into your lectures with careful consideration of
  your teaching style and course objectives.
• Eric Paterson
• Penn State, University Park
• August 2005

1 These slides were originally prepared using the
LaTeX typesetting system (http//www.tug.org/)
and the beamer class (http//latex-beamer.sourcef
orge.net/), but were translated to PowerPoint for
wider dissemination by McGraw-Hill.
3
Objectives

• Identify various types of pumps and turbines, and
  understand how they work
• Apply dimensional analysis to design new pumps or
  turbines that are geometrically similar to
  existing pumps or turbines
• Perform basic vector analysis of the flow into
  and out of pumps and turbines
• Use specific speed for preliminary design and
  selection of pumps and turbines

4
Categories

• Pump adds energy to a fluid, resulting in an
  increase in pressure across the pump.
• Turbine extracts energy from the fluid,
  resulting in a decrease in pressure across the
  turbine.

5
Categories

• For gases, pumps are further broken down into
• Fans Low pressure gradient, High volume flow
  rate. Examples include ceiling fans and
  propellers.
• Blower Medium pressure gradient, Medium volume
  flow rate. Examples include centrifugal and
  squirrel-cage blowers found in furnaces, leaf
  blowers, and hair dryers.
• Compressor High pressure gradient, Low volume
  flow rate. Examples include air compressors for
  air tools, refrigerant compressors for
  refrigerators and air conditioners.

6
Categories

• Positive-displacement machines
• Closed volume is used to squeeze or suck fluid.
• Pump human heart
• Turbine home water meter
• Dynamic machines
• No closed volume. Instead, rotating blades
  supply or extract energy.
• Enclosed/Ducted Pumps torpedo propulsor
• Open Pumps propeller or helicopter rotor
• Enclosed Turbines hydroturbine
• Open Turbines wind turbine

7
Pump Head

• Net Head
• Water horsepower
• Brake horsepower
• Pump efficiency

8
Matching a Pump to a Piping System

• Pump-performance curves for a centrifugal pump
• BEP best efficiency point
• H, bhp, V correspond to BEP
• Shutoff head achieved by closing outlet (V0)
• Free delivery no load on system (Hrequired 0)

9
Matching a Pump to a Piping System

• Steady operating point
• Energy equation

10
Manufacturer Performance Plot
11
Pump Cavitation and NPSH

• Cavitation should be avoided due to erosion
  damage and noise.
• Cavitation occurs when P lt Pv
• Net positive suction head
• NPSHrequired curves are created through
  systematic testing over a range of flow rates V.

12
Dynamic Pumps

• Dynamic Pumps include
• centrifugal pumps fluid enters axially, and is
  discharged radially.
• mixed--flow pumps fluid enters axially, and
  leaves at an angle between radially and axially.
• axial pumps fluid enters and leaves axially.

13
Centrifugal Pumps

• Snail--shaped scroll
• Most common type of pump homes, autos, industry.

14
Centrifugal Pumps
15
Centrifugal Pumps Blade Design
16
Centrifugal Pumps Blade Design
Vector analysis of leading and trailing edges.
Side view of impeller blade.
17
Centrifugal Pumps Blade Design
Blade number affects efficiency and introduces
circulatory losses (too few blades) and passage
losses (too many blades)
18
Axial Pumps
Open vs. Ducted Axial Pumps
19
Open Axial Pumps
Propeller has radial twist to take into account
for angular velocity (?r)
Blades generate thrust like wing generates lift.
20
Ducted Axial Pumps

• Tube Axial Fan Swirl downstream
• Counter-Rotating Axial-Flow Fan swirl removed.
  Early torpedo designs
• Vane Axial-Flow Fan swirl removed. Stators can
  be either pre-swirl or post-swirl.

21
Ducted Axial Pumps Blade Design
Relative frame of reference
Absolute frame of reference
22
Dimensional Analysis

• ? analysis gives 3 new nondimensional parameters
• Head coefficient
• Capacity coefficient
• Power coefficient
• Reynolds number also appears,but in terms of
  angular rotation
• Reynolds number
• Functional relation is
• Head coefficient
• Power coefficient

23
Dimensional Analysis

• If two pumps are geometrically similar, and
• The independent ?s are similar, i.e., CQ,A
  CQ,BReA ReB?A/DA ?B/DB
• Then the dependent ?s will be the sameCH,A
  CH,BCP,A CP,B

24
Dimensional Analysis

• When plotted in nondimensional form, all curves
  of a family of geometrically similar pumps
  collapse onto one set of nondimensional pump
  performance curves
• Note Reynolds number and roughness can often be
  neglected,

25
Pump Specific Speed

• Pump Specific Speed is used to characterize the
  operation of a pump at BEP and is useful for
  preliminary pump selection.

26
Affinity Laws

• For two homologous states A and B, we can use ?
  variables to develop ratios (similarity rules,
  affinity laws, scaling laws).
• Useful to scale from model to prototype
• Useful to understand parameter changes, e.g.,
  doubling pump speed (Ex. 14-10).