Fluid Mechanics

FLUID MECHANICS

Manila Review Institute Chemical Engineering Reviewfor the November, 2012 Board Examination

[email protected] CP No. 09185663419Dr. Servillano Olao, Jr.

Join the yahoo groups: mrii_che_2012Group homepage: http://groups.yahoo.com/group/mrii_che_2012Group email: [email protected]

Fluid Mechanics Fluid mechanics

Branch of engineering science that has to do with the behavior of fluids (liquids, gases and vapors)

Branches of Fluid Mechanics1. Fluid Statics

Fluids in equilibrium state of no shear stress2. Fluid Dynamics

Portions of the fluid are in motion relative to the other parts

6/18/2012 2S. Olano, Jr. MRII

Nature of FluidsA fluid is a substance that does not permanently resist distortion.

Some physical properties of fluids:a) Density or relative densityb) Viscosityc) Surface tension


Fluid Mechanics

Types of Fluids1. Incompressible

Density is not affected by changes in temperature and pressure

2. Compressible Density varies appreciably with

temperature and pressure Pressure Concept

For a static fluid, the pressure at any point is independent of direction.


Fluid Mechanics

English SILength, L ft., inch meter (m)Mass, M lbm, slugs KgTime, T seconds (s), hr sForce, F lbf newton (N)Density, lbm/ft3, slug/ft3 Kg/m3

Systems of Units

Relationship between Force and Mass: F=ma

2

2

32.16ENGLISH:

32.16c

ftg lbfsF m lbm lbm lbflbm ftg lbm

lbf s

= = =

2 2SI: 9.806 ( )m mF mg kg kg newton Ns s

= = = 6/18/2012 5S. Olano, Jr. MRII

Fluid Mechanics

A. Fluid Statics and Applications

Hydrostatic EquilibriumForce balance:

- ( ) - 0

0

c

c

gp S p dp S Sdzg

gdp dzg

+ =

+ =


Fluid Statics and Applications

2 11 2

constant

( )c

c

p gz

gp p g

z zg

+ =

=

Hydrostatic Equilibrium, for constant density (most liquids)

0

0

c

c

pM gdp dzRT g

dp gM dzp g RT

+ =

+ =

Barometric EquationFor an ideal gas, = (pM/RT).

Substituting,


Integrating between levels 1 and 2:

( )( )

22 1

1

2 12

1

ln

exp

c

c

p gMz z

p g R T

gM z zpp g R T

=

=

(Called the barometric equation)



2. Simple ManometersPressure balance at level 0:

zggH

ggpp

ggH

gg

agg

zpgg

aggHp

c

mm

c

c

mm

cccc

m

+=

+++=++

)(21

21

Simplifying gives:



Two-fluid U-tube ManometerPressure balance at point 0:

=

=

+=

++=++

AaHh

hAaHbutghgHpp

gHhpgHhp

m

m

ABBmm

mmBBmA

)()()()(

21

21




Other Liquid Column Manometers

Viscous forces in a fluid

Rheological Properties of Fluids



B. Fluid Dynamics (Flow of Fluids)

Evaluation of Fanning friction factorFluid Dynamics and Applications


Evaluation of surface roughness factor


Flow of Incompressible Fluids3. Turbulent flow in pipes and closed channels

(correlation equations for f )


Blassius Formula: (for smooth tubes)

Colebrook Equation:

Churchill Equation:


Non-Circular Pipes


Friction due to Pipe Fittings

Evaluation of Ff (for fittings and valves)


Entrance and Exit Effects in a Pipe

Entrance Effects for fully developed velocity profile:for laminar flow:

for turbulent flow:

Le


Exit Effects:


Design Charts for Adiabatic Flow of Gases Fig. 6-21, Perry 8/ed


Momentum Equation

dtmvd

dtdv

mmaF )(=== (Change in momentum)

Coverage Chart


Classification of Pumps


Examples of PumpsA. Centrifugal pumps

Dynamic pumpsB. Reciprocal pumps

Positive displacement pumpsC. Gear pumpsD. Axial flow pumps



Examples of Pumps

Characteristic Curves


Characteristic Curves of Centrifugal Pumps


Guide in the selection of Pumps


System head vs Available head


Net Positive Suction Head (NPSH) Head available at the pump inlet to keep the

liquid from cavitating or boiling

Where: ps = pressure at suction pointpv = vapor pressure of the liquid

If NPSH

==== 1HH mmv


Pitot Tube


Pitot Tube

For Compressible Fluids:


Flow Metersc) Head Meters (Orifices, venturi meters,

nozzles)


Head MetersEvaluation of Y: f (type of fluid)

For liquids, Y = 1.0For gases, see Fig. 10-16, Perry


Evaluation of C (discharge coefficient)Types of Taps:



Friction Loss Due to Flowmeters

Rotameters


Flow in Open Channels and Weirs1. Rectangular Weir

(Modified Francis Weir Formula))2)(2.0(415.0 5.1 ghhLq oo=


==== tang2h31.0

q5.2

o

2. Triangular Weir Notch

Note: Both equations apply only for water


Discussion of ProblemsNEXT



Solution

Solution to Problems


Solution



Solution


hp 622.065.0/550

min/60/48.7/4.62min/4040

550'

=

=

=

hpslbftscuftgal

cuftlbgalftBHP

wWBHPp


Solution


m/s 456.2

100060

4

3600/252 =

==

piSqV


Solution


mba

abRD HH 18.25.12425.144

2244 =

+

=

+==


Solution



Solution


KWKWPower 478.054.2124.621445.05001072.2)( 5 =

=


Solution


Thank You!!

Manila Review Institute Chemical Engineering Reviewfor the November, 2012 Board Examination

[email protected] CP No. 09185663419

Dr. Servillano Olao, Jr.

Yahoo group: mrii_che_2012Group homepage: http://groups.yahoo.com/group/mrii_che_2012Group email: [email protected]

Fluid Mechanics Lecture Notes 2012Fluid Mechanics Problems

Fluid Mechanics

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