chapter 7-fluid machinery.ppt -...

1

Chapter 7

Introduction to Fluid Machinery

2

Classification of Fluid Machines– Positive diplacement machines (static type)– Turbomachines (dynamic type)

• Turbines: extract energy to the flow :the fluid does work on them

• Pumps: add energy to the flow = do work to the fluid

• Pumps• Fans• Blowers• Compressor

3

Positive diplacement machinesforce a fluid into or out of a

chamber by changing the volume of the chamber.

Typical positive displacement pumps:(a) tire pump,(b) human heart, (c) gear pump,(d) Peristaltic pump.

From fundamentals of fluid mechanichs Monson (5th edition) Young Okiishi Wiley(d)

4

Turbomachines• Machines for Doing Work on a Fluid

– Pumps– Fans– Blowers– Compressors

• Machines for Extracting Work (Power) from a Fluid– Hydraulic Turbines – Gas Turbines – Wind-Power Machines

5

Machines for Doing Work on a Fluid

Centrifugal Blower Centrifugal Pump

left ventricular assist devices

Fan

http://www.youtube.com/watch?v=V3aPHmZ97yM

6

Figure 12.7 (p. 694)(a) Open impeller, (b) enclosed or shrouded impeller. (Courtesy of Ingersoll-Dresser Pump Company).

From fundamentals of fluid mechanichs Monson (5th edition) Young Okiishi Wiley

7

Machines for Extracting Work

Very simple impulse turbine Impulse turbine

Propeller turbine:Kaplan type

Windmill

8

Turbomachinery AnalysisBlade speed U = ω rr : radial distance from the axis of the fan. ω:angular velocity

Relative velocity W(that seen by a person riding on the fan blade)

Absolute fluid velocity V = W + U(that seen by a person sitting stationary at the

table on which the fan rests)

Fan = pump = do work

9

Turbomachinery Analysis• Blade speed U = ω rr : radial distance from the axis of the fan. ω:angular velocity

Relative velocity W

Absolute fluid velocity V = W + U

Windmill = turbine = extracting work Here we are looking for U

Home work: coloring

10

Pump or Turbine?• the tangential component of the force of

the blade on the fluid is ►in the direction of the blade motion : PUMPS► in the opposite direction of the blade motion : TURBINE

V=U+WPUMP

W

U

TURBINE

W

U

V=U+W

11

Angular momentum principle

Sum of external torques

Net rate of flow of moment-of-momentumThrough the surfae control

Shaft torque :Torque that the shaft applies to the rotor

Torque of the gravity force

Torque of surface forces

Time rate of change of the moment-of-momentum in the volume

12

Euler turbomachine equation• Volume controle enclosing the

rotor• Steady flow• Force due to the surface force

may be ignored• Gravity may be ignored

CV

shaft dAVVrT

Notes:

: flow rate m = ρQ = ρVS

Vt > 0 if Vt and U are in the same dircetion

m

13

Pump or Turbine?• if the shaft torque and the rotation of the rotor are in the same direction:

► the energy is transferred from the shaft to the rotor and from the rotor to the fluid

►the machine is a pump

• if the torque exerted by the shaft on the rotor is opposite to the direction of rotation:

►the energy transfer is from the fluid to the rotor►the machine is a turbine.

So if we choose Vt > 0 if Vt and U are in the same directionTshaft > 0 for PUMPSTshaft < 0 for TURBINE

14

Pump or Turbine?

VV

Vr

V

Vt

Vn

r

PUMP TURBINE

ω

VVt Vn

r

ω

15

Mechanical Power orShaft Power

shaftm TW

0mW

Using U = r ω and

0mWPUMP TURBINE

16

Theoretical Head:

Note: Mechanical Power and Theoretical Head come from angular-moment equation for a control volume then it if for:-Steady flow-Uniform flow at each section

Hydraulic head is a specific measurement of total energy per unit weight

It is usually measured as a water surface elevation :

msm

sm

sm

2

1

H

http://www.youtube.com/watch?v=473XQrJjDZE&list=TLoxakqLv6wIM

17

– Negligible torque due to surface forces (viscous and pressure).

– Steady flow– Inlet and exit flow tangent to blades.– Uniform flow at inlet and exit.– Zero inlet tangential velocity = purely radial– Incompressible flow

Example: Idealized Centrifugal Pump

18

• Governing equation:

CV

shaft dAVVrT Euler turbomachine equation : from momentum

Continuity

CSCV

AdVVdt

0Steady

R1

R2

VW

U = R2ω

Given: Q , WFind: b2, Tshaft, Wm

ω

b2

Idealized Centrifugal Pump…

19

Idealized Centrifugal Pump…

222 2 rW

Qb

Then from continuity: 02 2222

11 brWrV

r1

r2

W

U = r2ω

Given: Q , WFind: b2, Tshaft, Wm

ω

b2

or the mass flow rate:

then

222 2 brWQm

20

Idealized Centrifugal Pump…

r1

r2

W

U = r2ω

Given: Q , WFind: b2, Tshaft, Wm

ω

b2

mrTshaft 22U = r2ω = Vt2

V=U+W

W = Vn2

21

Idealized Centrifugal Pump…(case: W normal)

shaftm TW

r1

r2

W

U = r2ω

Given: Q , WFind: b2, Tshaft, Wm

ω

b2

U = r2ω = Vt2

V=U+W

W = Vt2222 mRWm

1 0tV

22 2 2 2 2 2 2 2 2

2

cos cos cotsin

nt n

VV U W U U V

Vt2

case: W with a angle β2

b2

2nV2tV

2V

nVt2

23

2222 nVbrQ so, 22

2 2 brQVn

H become :

2

2 2 22 2 2 22 2 2 2

cotcot 2nt

QU UU U VU V r bH

g g g

222

22 cot

2

brgQ

gUH

Ideal head developed by a pump with Q flow rate

2 2shaft tW U VHmg g

http://www.youtube.com/watch?v=IiE8skW8btE

b2

2nV2tV

2V

24

Torque: Power:

2 2 1 11 ( )shaft

t t

WH U V U V

mg g

Theoretical head :

SUMMARY

b2

tt

tt

t tt

t

25

Performance characteristicsFor design a pump or a turbine we must know:-Head-Torque-Power requirement-Efficiency

Note: The idealized analyses presented previously is useful to predict approximate the performances : It is a stat point for design….

But to determined the real performance we must perform measurement of

-Head or pressures-Speed -Input torque-PowerFor different flow rate

26

Head as function of flow rateEffect of losses on the pump head-flowrate curve.

From fundamentals of fluid mechanichs Monson (5th edition) Young Okiishi Wiley

1. Recirculation in the impeler (At low flow rate)

2. Fiction loss (increase with the flow rate)

3. Leakage (increase with the flow rate)

4. « shock loss » mismatch between relative velocity direction and the tangent to impeller blade at the inlet (largest at low and hight flow rate, decrease around the optimum operating condition )

PUMP

27

Performance characteristics

Pump head:

Hydraulic Power:

Pump Efficiency:

Note: in term of horse power550

hWePowerWatterHors

For machine doing work on a fluid: Hp is rate of the mechanical energy input to the fluid

For machine doing work on a fluid

28

Typical performance characteristics for a centrifugal pump of a given size operating at a constant impeller speed.

From fundamentals of fluid mechanichs Monson (5th edition) Young Okiishi Wiley

PUMP

29

• To vary pump capacity, we could change the impeller size:

Performance curves for a two-stage centrifugal pump operating at 3500 rpm. Data given for three different impeller diameters.

From fundamentals of fluid mechanichs Monson (5th edition) Young Okiishi Wiley

Bhp: brake horse power

NPSH: Net positive suction head

Best efficiency point

PUMP

30

NPSH: Net positive suction head

• On the suction side of a pump: low pressures ►possibility of cavitations( liquid pressure to small ► bubbles ; liquid boil)

►loss in efficiency or pump damage

NPSH = total Head on the suction side (inlet) – liquid vapor pressure

To avoid cavitations NPSH have to be maintained or exceeded.

gPv

gVs

gPsNPSH

2

2

PUMP

31

NPSH: Net positive suction head

• NPSH could be determined experimentally• Calculate with known parameters:

Lsss hzg

Vg

Pzg

Vg

P22

2

1

211

Energy equation:

Lssatm hg

Vg

Pzg

P2

2

1 atms PPzV 100;1

Lh Head loss between free surface and pump intlet

Latmss hzg

Pg

Vg

P1

2

2 So,

Then :

gPvhz

gP

gPv

gVs

gPsNPSH L

atm

1

2

2def

PUMP

32

Dimensional Analysis

Flow Coefficient:

Head Coefficient:

Performance may be defined by curves head/flow rate for different values of speed, different flow properties etc…But, This would be difficult to represent all the data on a single chart!

Power Coefficient:

Torque Coefficient:DEMO

33

Typical performance data for a centrifugal pump: (a) characteristic curves for a 12-in. centrifugal pump operating at 1000 rpm, (b) dimensionless characteristic curves. (Data from Ref. 8, used by permission.)

Power Coefficient

Head Coefficient

Flow Coefficient

From fundamentals of fluid mechanichs Monson (5th edition) Young Okiishi Wiley

34

Similarity RulesTo achieve dynamic similarity requires geometric and

kinetic similarity:

Head

Power

Flow

35

Similarity Rules

For the same pump (same dimension) working a different speed:

21

22

1

2

hh

1

2

1

2

QQ

Head

Power

Flow

31

32

1

2

36

Specific Speed

Specific Speed:(dimensionless)

Specific Speed(Customary Units US):

By combining of Flow and Head coefficient, and eliminating the machine size :

4/3

2/1

SN

ScuS NN 46.43

37

Specific Speed

Holding specific speed constant describes all operating conditions of geometrically similar machines with similar condition:

Variation in specific speed with type of pump. (adapted from Ref. 10, used with permission.)From fundamentals of fluid mechanichs Monson (5th edition) Young Okiishi Wiley

38

Applications to Fluid SystemsSystem equation

• Application of equation enegy to a control volume consisting af a pump-pipe system:

Due to the frictionAt the

inlet of the system

At the outlet of the system

Head due to the pump only

flp HHzg

Vg

pzg

Vg

p

1

21

11

2

22

22

22

α : Correction factor=2 for laminar flow close to 1 for hight reynolds number.Cf chap 8 of the text book

39

flp HzzH 12

For pipes flows the losses 2KQH fl

212 KQzzH p

flp HHzg

Vg

pzg

Vg

p

1

21

11

2

22

22

22

Applications to Fluid SystemsSystem equation : typical fluid system

Flow loss

40http://www.pipeflow.co.uk

41

Applications to Fluid SystemsSystem curve : typical fluid system

Utilization of the system curve and the pump performance curve to obtain the operating point for the system.

System curve :system equation & pump performance

Intersection represent the operating point

If you change the system equation -Change pipe friction (fouling)-Change the watter elevation►You will change the operating point

Idealy: opreating point close the best efficiency

http://www.youtube.com/watch?annotation_id=annotation_261560&feature=iv&src_vid=IiE8skW8btE&v=pWSyrxFJmt4

42

– Pump Wear

Applications to Fluid Systems

43

-Pumps in Series

Applications to Fluid Systems

44

Applications to Fluid Systems

– Pumps in Parallel

45

Centrifugal blood pumpExtracorporeal blood pump for cardiac surgery

• Specific requierements: Avoid hemolysis

http://www.medtronic.com/cardsurgery/arrested_heart/centrifugal_pump.html

46

Positive diplacement pumpsforce a fluid into or out of a

chamber by changing the volume of the chamber.

Typical positive displacement pumps:(a) tire pump,(b) human heart, (c) gear pump,(d) Peristaltic pump.

From fundamentals of fluid mechanichs Monson (5th edition) Young Okiishi Wiley(d)

47

Positive-Displacement Pumps• Fluid with higth viscosity can not be moved with standard

centrifugal pump : viscosity above 850 cP (loss efficiency)

• PD is better! it can work with viscosity changing in a same batch from 1 over 100,000 cP!

• The majority of problems, both centrifugal and PD start at the suction, There must be a minimum amount of absolute pressure avaible to suplly fluid pum suction. PD pumps generally requiere less absolute pressure than centrifugal pumps.

48

PD : EfficencyVolumetric efficency = actual volumetric delivery / pump displacement

As pressure is raised or pumps speed reduced

Overall efficency = power delivred to the fluid / power input to the pump

Tends to rise as pump speed increase

49

Peristaltic pump

50

Syringe-pump

Modern medical infusion pump

Blood pumps

Exemples

CHAP. 7- Fluid Machinery…

http://www.youtube.com/watch?v=YqvTKrRJIl8

Jarvik 7 CardioWest TAH• The CardioWest TAH replaces each ventricle with a separate

diaphragm-type pump– Each pump is divided into two chambers by a flexible diaphragm with

blood on one side and air on the other• As air is forced into the device, the diaphragm deforms into the blood

chamber causing blood ejection (systole)• As air is evacuated from the device, the diaphragm deforms into the air

chamber causing blood the enter the device (diastole)– This device is driven pneumatically by an external console attached

to the device by two drivelines that go through the skin– The maximum stroke volume in this device is 70 mL with a flow rate

of 6 to 8 L/min under normal conditions

• This device is currently being used in patients under 67 years old who suffer from biventricular failure and are candidates for transplantation

Nikkiso

• The Nikkiso HPM-15 (Nikkiso Co., Ltd., Tokyo, Japan) is an extracorporeal centrifugal blood pump currently in use in Japan for CPB

– This pump has an impeller with 6 blades

• Extensive simulations of flow and hemolysis have been performed on this device

• According to their website, Nikkiso is presently developing an implantable centrifugal pump

Nikkiso HPM-15 (from Takiura et al., 1998).

HeartQuest VAD

• This device makes use of MagLev technology to magnetically suspend the pump impeller

• Currently, this device has a wearable external battery and controller– Future versions will

make use of TET technology

Upper housing

Outflow cannula

Lower housingImpeller

Figure 5-14. HeartQuest VAD (from Song et al., 2004).

Impella Recover• The Impella Recover (Impella

CardioSystems GmbH, Aachen, Germany) is a catheter-based pump offering short term uni- or biventricular support

– This device is the smallest mechanical circulatory support device in the world

– The Impella Recover can be inserted via the femoral artery or directly into the left ventricle and provides circulatory support for up to 7 days

– A portable console is use to drive and control the pump, thus allowing for easy patient transport

– This device is in use in Europe

Impella Recover Pump (from www.impella.com/bilder/produkte/pumpe_a.jpg).