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Chapter 14: Turbomachinery
Eric G. PatersonDepartment of Mechanical and Nuclear Engineering
The Pennsylvania State University
Spring 2005
Chapter 14: TurbomachineryME33 : Fluid Flow 2
Note to InstructorsThese 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 PatersonPenn State, University ParkAugust 2005
1 These slides were originally prepared using the LaTeX typesetting system (http://www.tug.org/) and the beamer class (http://latex-beamer.sourceforge.net/), but were translated to PowerPoint for wider dissemination by McGraw-Hill.
Chapter 14: TurbomachineryME33 : Fluid Flow 3
Objectives
Identify various types of pumps and turbines, and understand how they workApply dimensional analysis to design new pumps or turbines that are geometrically similar to existing pumps or turbinesPerform basic vector analysis of the flow into and out of pumps and turbinesUse specific speed for preliminary design and selection of pumps and turbines
Chapter 14: TurbomachineryME33 : Fluid Flow 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.
Chapter 14: TurbomachineryME33 : Fluid Flow 5
Categories
For gases, pumps are further broken down intoFans: 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.
Chapter 14: TurbomachineryME33 : Fluid Flow 6
Categories
Positive-displacement machinesClosed volume is used to squeeze or suck fluid. Pump: human heartTurbine: home water meter
Dynamic machinesNo closed volume. Instead, rotating blades supply or extract energy.Enclosed/Ducted Pumps: torpedo propulsor Open Pumps: propeller or helicopter rotorEnclosed Turbines: hydroturbineOpen Turbines: wind turbine
Chapter 14: TurbomachineryME33 : Fluid Flow 7
Pump Head
Net Head
Water horsepower
Brake horsepower
Pump efficiency
Chapter 14: TurbomachineryME33 : Fluid Flow 8
Matching a Pump to a Piping System
Pump-performance curves for a centrifugal pumpBEP: best efficiency pointH*, bhp*, V* correspond to BEPShutoff head: achieved by closing outlet (V=0)$Free delivery: no load on system (Hrequired = 0)
Chapter 14: TurbomachineryME33 : Fluid Flow 9
Matching a Pump to a Piping System
Steady operating point:
Energy equation:
Chapter 14: TurbomachineryME33 : Fluid Flow 10
Manufacturer Performance Plot
Chapter 14: TurbomachineryME33 : Fluid Flow 11
Pump Cavitation and NPSH
Cavitation should be avoided due to erosion damage and noise.
Cavitation occurs when P < Pv
Net positive suction head
NPSHrequired curves are created through systematic testing over a range of flow rates V.
Chapter 14: TurbomachineryME33 : Fluid Flow 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.
Chapter 14: TurbomachineryME33 : Fluid Flow 13
Centrifugal Pumps
Snail--shaped scroll
Most common type of pump: homes, autos, industry.
Chapter 14: TurbomachineryME33 : Fluid Flow 14
Centrifugal Pumps
Chapter 14: TurbomachineryME33 : Fluid Flow 15
Centrifugal Pumps: Blade Design
Chapter 14: TurbomachineryME33 : Fluid Flow 16
Centrifugal Pumps: Blade Design
Side view of impeller blade. Vector analysis of leading and trailing edges.
Chapter 14: TurbomachineryME33 : Fluid Flow 17
Centrifugal Pumps: Blade Design
Blade number affects efficiency and introduces circulatory losses (too few blades) and passage losses (too many blades)
Chapter 14: TurbomachineryME33 : Fluid Flow 18
Axial Pumps
Open vs. Ducted Axial Pumps
Chapter 14: TurbomachineryME33 : Fluid Flow 19
Open Axial Pumps
Propeller has radial twist to take into account for angular velocity (=r)
Blades generate thrust like wing generates lift.
Chapter 14: TurbomachineryME33 : Fluid Flow 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.
Chapter 14: TurbomachineryME33 : Fluid Flow 21
Ducted Axial Pumps: Blade Design
Absolute frame of reference Relative frame of reference
Chapter 14: TurbomachineryME33 : Fluid Flow 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
Chapter 14: TurbomachineryME33 : Fluid Flow 23
Dimensional Analysis
If two pumps are geometrically similar, and
The independent ’s are similar, i.e., CQ,A = CQ,B
ReA = ReB
A/DA = B/DB
Then the dependent ’s will be the sameCH,A = CH,B
CP,A = CP,B
Chapter 14: TurbomachineryME33 : Fluid Flow 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,
Chapter 14: TurbomachineryME33 : Fluid Flow 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.
Chapter 14: TurbomachineryME33 : Fluid Flow 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 prototypeUseful to understand parameter changes, e.g., doubling pump speed (Ex. 14-10).