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Dynamics of Viscous Fluid Flow in Closed Pipe: Darcy-Weisbach equation for flow in pipes. Major and minor losses in pipe lines. Dr. Mohsin Siddique Assistant Professor 1 FLUID MECHANICS

Dr. MohsinSiddique Assistant Professor · 2018. 7. 11. · to mean velocity of flow (V) as long as the flow in laminar. i.e., But with increasing velocity, as the flow become turbulent

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  • Dynamics of Viscous Fluid Flow in

    Closed Pipe: Darcy-Weisbach equation for flow in pipes. Major and minor losses in pipe

    lines.

    Dr. Mohsin Siddique

    Assistant Professor

    1

    FLUID MECHANICS

  • Steady Flow Through Pipes

    2

    � Laminar Flow:

    flow in layers

    Re4000 (pipe flow)

  • Steady Flow Through Pipes

    3

    � Reynold’s Number(R or Re): It is ratio of inertial forces (Fi) to viscous forces (Fv) of flowing fluid

    � For laminar flow: Re

  • Steady Flow Through Pipes

    4

    � Hydraulic Radius (Rh) or Hydraulic Diameter: It is the ratio of area of flow to wetted perimeter of a channel or pipe

    P

    A

    perimeterwetted

    AreaRh ==

    For Circular Pipe

    ( )( )

    h

    h

    RD

    D

    D

    D

    P

    AR

    4

    4

    4/ 2

    =

    ===π

    π

    For Rectangular pipe

    DB

    BD

    P

    ARh

    2+==

    B

    D

    Note: hydraulic Radius gives us indication for most economical section. More the Rh more economical will be the section.

    ννh

    h

    VRVDR

    4==

    By replacing D with Rh, Reynolds’ number formulae can be used for non-circular sections as well.

  • Head Loss in Pipes

    5

    � Total Head Loss=Major Losses+ Minor Losses

    � Major Loss: Due to pipe friction

    � Minor Loss: Due to pipe fittings, bents and valves etc

  • Head Loss in Pipes due to Friction

    6

    The head loss due to friction in a given length of pipe is proportional to mean velocity of flow (V) as long as the flow in laminar. i.e.,

    But with increasing velocity, as the flow become turbulent the head loss also varies and become proportion to Vn

    Where n ranges from 1.75 to 2

    Log-log plot for flow in uniform pipe (n=2.0 for rough wall pipe; n=1.75 for smooth wall pipe

    VH f ∝

    n

    f VH ∝

  • Frictional Head Loss in Conduits of Constant

    Cross-Section

    7

    � Consider stead flow in a conduit of uniform cross-section A. The pressure at section 1 & 2 are P1 & P2 respectively. The distance between the section is L. For equilibrium in stead flow,

    ∑ == 0maF

    Figure: Schematic diagram of conduit

    0sin 21 =−−− APPLWAP oτα

    P= perimeter of conduit= Avg. shear stress

    between pipe boundary and liquid

    01221 =−

    −−− PL

    L

    zzALAPAP oτγ

    αsin12 =

    L

    zz

  • Frictional Head Loss in Conduits of Constant

    cross-section

    8

    01221 =−

    −−− PL

    L

    zzALAPAP oτγ

    Dividing the equation by Aγ

    ( ) 01221 =−−−−A

    PLzz

    PP o

    γ

    τ

    γγ

    fLo hhA

    PLPz

    Pz ===

    +−

    +

    γ

    τ

    γγ2

    21

    1

    Therefore, head loss due to friction hf can be written as

    h

    oof

    R

    L

    A

    PLh

    γ

    τ

    γ

    τ==

    Lhg

    vz

    P

    g

    vz

    P+++=++

    22

    2

    22

    2

    2

    11

    1

    γγ

    Remember !! For pipe flow

    For stead flow in pipe of uniform diameter v1=v2

    LhzP

    zP

    =

    +−

    + 2

    21

    1

    γγ

    This is general equation and can be applied to any shape conduit having either Laminar or turbulent flow.

    P

    ARh =Q

  • Determining Shear Stress

    9

    � For smooth-walled pipes/conduits, the average shear stress at the wall is

    � Using Rayleigh's Theorem of dimensional analysis, the above relation can be written as;

    � Rewriting above equation in terms of dimension (FLT), we get

    ( ),,,, VRf ho ρµτ =

    ( )

    =

    ncb

    a

    T

    L

    L

    FT

    L

    FTLK

    L

    F4

    2

    22

    ( )ncbaho VRk ... ρµτ =

    LlengthR

    L

    Fareaforce

    h

    o

    ==

    ==2

    ( )22

    4233

    /.

    ////

    /

    −==

    ===

    =

    FTLmsN

    LFTLaFLM

    TLV

    µ

    ρ( ) ( ) ( ) ( )( )ncba TLLFTFTLLKFL /4222 −−− =

  • Determining Shear Stress

    10

    � According to dimensional homogeneity, the dimension must be equal on either side of the equation, i.e.,

    ( ) ( ) ( ) ( )( )ncba TLLFTFTLLKFL /4222 −−− =

    )(20:

    )(422:

    )(1:

    iiincbT

    iincbaL

    icbF

    →−+=

    →+−−=−

    →+=Solving three equations, we get

    1;2;2 −=−=−= ncnbna

    � Substituting values back in above equation

    ( ) ( ) 22

    122 ...... VVR

    kVRkVRk

    n

    hnnnn

    h

    ncba

    ho ρµ

    ρρµρµτ

    −−−

    ===

    ( ) 22 VRk neo ρτ−

    =

    � Setting = we get

    2

    2V

    C fo ρτ = Where, Cf is coefficient of friction

    ( ) 2−neRk 2/fC

  • Determining Shear Stress

    11

    � Now substituting the equation of avg. shear stress in equation of head loss,

    � For circular pipe flows, Rh=D/4

    � Where, f is a friction factor. i.e.,

    � The above equation is known as pipe friction equation and as Darcy-Weisbach equation.

    � It is used for calculation of pipe-friction head loss for circular pipes flowing full (laminar or turbulent)

    2/2VC fo ρτ =

    h

    of

    R

    Lh

    γ

    τ=

    h

    f

    h

    f

    fgR

    LVC

    R

    LVCh

    22

    22

    ==γ

    ρ

    g

    V

    D

    Lf

    g

    V

    D

    LC

    Dg

    LVCh f

    f

    f22

    442

    4 222

    ===

    ( )Re4 fCf f ==

  • Friction Factor for Laminar and

    Turbulent Flows in Circular Pipes

    12

    � Smooth and Rough Pipe

    � Mathematically;

    � Smooth Pipe

    � Rough Pipe

    � Transitional mode

    Turbulent flow near boundary

    =

    =

    v

    e

    δ

    Roughness height

    Thickness of viscous sub-layer

    Smooth pipe

    Rough pipe

    f

    D

    fVv

    Re

    14.1414.14==

    νδ

    ve δ<

    ve δ>

    ve δ<

    ve δ14>

    vv e δδ 14≤≤

  • Friction Factor for Laminar and Turbulent Flows in

    Circular Pipes

    13

    � For laminar flow

    � For turbulent flow

    Re

    64=f2000Re <

    51.2

    Relog2

    1 f

    f=

    9.6

    Relog8.1

    1=

    f

    25.0Re

    316.0=f

    7/1

    max

    =

    or

    y

    u

    u

    Def /

    7.3log2

    1=

    +−=

    f

    De

    f Re

    51.2

    7.3

    /log2

    1

    +

    −=

    Re

    9.6

    7.3

    /log8.1

    111.1

    De

    f

    Colebrook Eq. for turbulent flow in all pipes

    Halaand Eq. For turbulent flow in all pipes

    Von-karman Eq. for fully rough flow

    Blacius Eq. for smooth pipe flow

    Seventh-root law

    510Re3000 ≤≤

    From Nikuradse experiments

    Colebrook Eq. for smooth pipe flow

    for smooth pipe flow

    4000Re >

  • Friction Factor for Laminar and Turbulent Flows

    in Circular Pipes

    14

    � The Moody chart or Moody diagram is a graph in non-dimensional form that relates the Darcy-Weisbach friction factor, Reynoldsnumber and relative roughness for fully developed flow in a circular pipe.

    � The Moody chart is universally valid for all steady, fully developed,incompressible pipe flows.

  • Friction Factor for Laminar and Turbulent Flows

    in Circular Pipes

    15

    � For laminar flow For non-laminar flow

    eRf

    64=

    +−=

    f

    De

    f Re

    51.2

    7.3

    /log2

    1 Colebrook eq.

  • Friction Factor for Laminar and

    Turbulent Flows in Circular Pipes

    16

    � The friction factor can be determined by its Reynolds number (Re) and the Relative roughness (e/D) of the Pipe.( where: e = absolute roughness and D = diameter of pipe)

  • 17

  • Problem Types

    18

    � Type 1: Determine f and hf,

    � Type 2: Determine Q

    � Type 3: Determine D

  • Problem

    19

    � Find friction factor for the following pipe

    � e=0.002 ft

    � D=1ft

    � Kinematic Viscosity, ν=14.1x10-6ft2/s

    � Velocity of flow, V=0.141ft/s

    � Solution:

    � e/D=0.002/1=0.002

    � R=VD/ ν =1x0.141/(14.1x10-6)=10000

    � From Moody’s Diagram; f=0.034___________

    Re

    51.2

    7.3

    /log2

    1

    =

    +−=

    f

    f

    De

    f

  • Problem-Type 1

    20

    � Pipe dia= 3 inch & L=100m

    � Re=50,000 ʋ=1.059x10-5ft2/s

    � (a): Laminar flow:

    � f=64/Re=64/50,000=0.00128

    ftgD

    fLVH Lf 0357.0

    )12/3)(2.32(2

    )12.2)(100(00128.0

    2

    22

    ===

    sftVVVD

    /12.210059.1

    )12/3(50000Re

    5=⇒

    ×=⇒=

    −ν

  • Problem-Type 1

    21

    � Pipe dia= 3 inch & L=100m

    � Re=50,000 ʋ=1.059x10-5ft2/s

    � (b): Turbulent flow in smooth pipe: i.e.: e=0

    0209.0

    50000

    51.2

    7.3

    0log2

    Re

    51.2

    7.3

    /log2

    1

    =

    +−=

    +−=

    f

    ff

    De

    f

    ftgD

    fLVH Lf 582.0

    )12/3)(2.32(2

    )12.2)(100(0209.0

    2

    22

    ===

  • Problem-Type 1

    22

    � Pipe dia= 3 inch & L=100m

    � Re=50,000 ʋ=1.059x10-5ft2/s

    � (c): Turbulent flow in rough pipe: i.e.: e/D=0.05

    0720.0

    50000

    51.2

    7.3

    05.0log2

    Re

    51.2

    7.3

    /log2

    1

    =

    +−=

    +−=

    f

    ff

    De

    f

    ftgD

    fLVH Lf 01.2

    )12/3)(2.32(2

    )12.2)(100(0720.0

    2

    22

    ===

  • Problem-Type 1

    23

    hL=?

    memDmL 0005.0;25.0;1000 ===

    smsmQ /10306.1;/051.0 263 −×== ν

    ( ) ( )002.025.0/0005.0/

    10210306.1/25.0039.1/ 56

    ==

    ×=××== −

    De

    VDR ν

    0.0245f

    Diagram sMoody' From

    =

    mgD

    fLVhL 39.5

    2

    2

    ==

    smAQV /039.1/ ==Q

  • Problem-Type 2

    24

    gDfLVhL 2/2=

  • Problem-Type 2

    25

    � For laminar flow For non-laminar flow

    eRf

    64=

    +−=

    f

    De

    f Re

    51.2

    7.3

    /log2

    1 Colebrook eq.

  • Problem-Type 3

    26

  • Problem

    27

    gD

    flVh

    f

    De

    f

    Lf2

    Re

    51.2

    7.3

    /log2

    1

    2

    =

    +−=

  • Problem

    28

  • Problem

    29

  • MINOR LOSSES

    30

    � Each type of loss can be quantified using a loss coefficient (K). Losses are proportional to velocity of flow and geometry of device.

    � Where, Hm is minor loss and K is minor loss coefficient. The value of K is typically provided for various types/devices

    � NOTE: If L > 1000D minor losses become significantly less than that of major losses and hence can be neglected.

    g

    VKHm

    2

    2

    =

  • Minor Losses

    31

    � These can be categorized as

    � 1. Head loss due to contraction in pipe

    � 1.1 Sudden Contraction

    � 1.2 Gradual Contraction

    � 2. Entrance loss

    � 3. Head loss due to enlargement of pipe

    � 3.1 Sudden Enlargement

    � 3.2 Gradual Enlargement

    � 4. Exit loss

    � 5. Head loss due to pipe fittings

    � 6. Head loss due to bends and elbows

  • Minor Losses

    32

    � Head loss due to contraction of pipe (Sudden contraction)

    � A sudden contraction (Figure) in pipe usually causes a marked drop in pressure in the pipe because of both the increase in velocity and the loss of energy of turbulence.

    g

    VKH cm

    2

    2

    2=

    Head loss due to sudden contraction is

    Where, kc is sudden contraction coefficient and it value depends up ratio of D2/D1 and velocity (V2) in smaller pipe

  • Minor Losses

    33

    � Head loss due to enlargement of pipe (Gradual Contraction)

    � Head loss from pipe contraction may be greatly reduced by introducing a gradual pipe transition known as a confusor as shown Figure.

    g

    VKH cm

    2'

    2

    2=

    Head loss due to gradual contraction is

    Where, kc’ is gradual contraction

    coefficient and it value depends up ratio of D2/D1 and velocity (V2) in smaller pipe

  • Minor Losses

    34

    � Entrance loss

    � The general equation for an entrance head loss is also expressed in terms of velocity head of the pipe:

    � The approximate values for the entrance loss coefficient (Ke) for different entrance conditions are given below

    g

    VKH em

    2

    2

    =

  • Minor Losses

    35

    � head loss due to enlargement of pipe (Sudden Enlargement)

    � The behavior of the energy grade line and the hydraulic grade line in the vicinity of a sudden pipe expansion is shown in Figure

    The magnitude of the head loss may be expressed as

    ( )g

    VVHm

    2

    2

    21 −=

  • Minor Losses

    36

    � head loss due to enlargement of pipe (Gradual Enlargement)

    � The head loss resulting from pipe expansions may be greatly reduced by introducing a gradual pipe transition known as a diffusor

    The magnitude of the head loss may be expressed as

    ( )g

    VVKH em

    2

    2

    21 −=

    The values of Ke’ vary with the diffuser angle (α).

  • Minor Losses

    37

    � Exit Loss

    � A submerged pipe discharging into a large reservoir (Figure ) is a special case of head loss from expansion.

    ( )g

    VKH dm

    2

    2

    =

    Exit (discharge) head loss is expressed as

    where the exit (discharge) loss coefficient Kd=1.0.

  • Minor Losses

    38

    � Head loss due to fittings valves

    � Fittings are installed in pipelines to control flow. As with other losses in pipes, the head loss through fittings may also be expressed in terms of velocity head in the pipe:

    g

    VKH fm

    2

    2

    =

  • Minor Losses

    39

    � Head loss due to bends

    � The head loss produced at a bend was found to be dependent of the ratio the radius of curvature of the bend (R) to the diameter of the pipe (D). The loss of head due to a bend may be expressed in terms of the velocity head as

    � For smooth pipe bend of 900, the values of Kb for various values of R/D are listed in following table.

    g

    VKH bm

    2

    2

    =

  • Minor Losses

    40

  • Numerical Problems

    41

  • Numerical Problems

    42

  • Thank you

    � Questions….

    � Feel free to contact:

    43

  • Fluid Dynamics:

    (ii) Hydrodynamics: Different forms of energy in a flowing

    liquid, head, Bernoulli's equation and its application, Energy

    line and Hydraulic Gradient Line, and Energy Equation

    Dr. Mohsin Siddique

    Assistant Professor

    1

    Fluid Mechanics

  • Forms of Energy

    2

    � (1). Kinetic Energy: Energy due to motion of body. A body of mass, m, when moving with velocity, V, posses kinetic energy,

    � (2). Potential Energy: Energy due to elevation of body above an arbitrary datum

    � (3). Pressure Energy: Energy due to pressure above datum, most usually its pressure above atmospheric

    2

    2

    1mVKE =

    mgZPE =

    m andV are mass and velocity of body

    Z is elevation of body from arbitrary datumm is the mass of body

    hγ=PrE !!!

  • Forms of Energy

    3

    � (4). Internal Energy: It is the energy that is associated with the molecular, or internal state of matter; it may be stored in many forms, including thermal, nuclear, chemical and electrostatic.

  • HEAD

    4

    � Head: Energy per unit weight is called head

    � Kinetic head: Kinetic energy per unit weight

    � Potential head: Potential energy per unit weigh

    � Pressure head: Pressure energy per unit weight

    g

    VmgmV

    Weight

    KE

    2/

    2

    1head Kinetic

    22 =

    == mgWeight =Q

    ( ) ZmgmgZWeight

    PE=== /head Potential

    γ

    P

    Weight==

    PrEhead Pressure

  • TOTAL HEAD

    5

    � TOTAL HEAD

    = Kinetic Head + Potential Head + Pressure Head

    g

    VPZ

    2HHead Total

    2

    ++==γ

    g

    V

    2

    2

    γ

    PZ

  • Bernoulli’s Equation

    6

    � It states that the sum of kinetic, potential and pressure heads of a fluid particle is constant along a streamline during steady flow when compressibility and frictional effects are negligible.

    � i.e. , For an ideal fluid, Total head of fluid particle remains constant during a steady-incompressible flow.

    � Or total head along a streamline is constant during steady flow when compressibility and frictional effects are negligible.

    21

    22

    22

    12

    11

    2

    22

    2Head Total

    HH

    g

    VPZ

    g

    VPZ

    consttg

    VPZ

    =

    ++=++

    =++=

    γγ

    γ

    1

    2

    Pipe

  • Derivation of Bernoulli’s Equation

    7

    � Consider motion of flow fluid particle in steady flow field as shown in fig.

    � Applying Newton’s 2nd Law in s-direction on a particle moving along a streamline give

    � Where F is resultant force in s-direction, m is the mass and as is the acceleration along s-direction.

    ss maF =

    Assumption:Fluid is ideal and incompressibleFlow is steadyFlow is along streamlineVelocity is uniform across the section and is equal to mean velocityOnly gravity and pressure forces are acting

    ds

    dVV

    dtds

    dsdV

    dsdt

    dsdV

    dt

    dVas ====

    Eq(1)

    Eq(2)

    Fig. Forces acting on particle along streamline

  • Derivation of Bernoulli’s Equation

    8

    W=weight of fluidWsin( )= component acting along s-directiondA= Area of flowds=length between sections along pipe

    θ

    ( ) θsinWdAdpPPdAFs −+−=

    Substituting values from Eq(2) and Eq(3) to Eq(1)

    Eq(3)

    ( )ds

    dVmVWdAdpPPdA =−+− θsin

    ds

    dVdAdsV

    ds

    dzgdAdsdpdA ρρ =−−

    ( )gdAdsmgW ρ==

    ds

    dz=θsin

    Cancelling dA and simplifying

    VdVgdzdp ρρ =−−

    Note that 2

    2

    1dVVdV =

    2

    2

    1dVgdzdp ρρ =−−

    Eq(4)

    Eq(5)

    Fig. Forces acting on particle along streamline

  • Derivation of Bernoulli’s Equation

    9

    � Dividing eq (5) by

    � Integrating

    � Assuming incompressible and steady flow

    � Dividing each equation by g

    ρ

    02

    1 2 =++ dVgdzdp

    ρ

    conttdVgdzdp

    =

    ++∫

    2

    2

    1

    ρ

    conttVgzP

    =++ 2

    2

    1

    ρ

    conttg

    Vz

    g

    P=++

    2

    2

    ρ

    � Hence Eq (9) for stead-incompressible fluid assuming no frictional losses can be written as

    Eq (6)

    Eq (7)

    Eq (8)

    Eq (9)

    ( ) ( )21

    22

    22

    12

    11

    Head TotalHead Total

    22

    =

    ++=++g

    VPZ

    g

    VPZ

    γγ

    Above Eq(10) is general form of Bernoulli’s Equation

    Eq (10)

  • Energy Line and Hydraulic Grade line

    10

    � Static Pressure :

    � Dynamic pressure :

    � Hydrostatic Pressure:

    � Stagnation Pressure: Static pressure + dynamic Pressure

    Hg

    Vz

    P=++

    2

    2

    γ

    Head TotalheadVelocity headElevation head Pressure =++

    P

    gZρ

    2/2Vρ

    conttV

    gzP =++2

    2

    ρρ

    Multiplying with unit weight,γ,

    stagPV

    P =+2

    2

    ρ

  • Energy Line and Hydraulic Grade line

    11

    � Measurement of Heads

    � Piezometer: It measures pressure head ( ).

    � Pitot tube: It measures sum of pressure and velocity heads i.e.,

    g

    VP

    2

    2

    γ/P

    What about measurement of elevation head !!

  • Energy Line and Hydraulic Grade line

    12

    � Energy line: It is line joining the total heads along a pipe line.

    � HGL: It is line joining pressure head along a pipe line.

  • Energy Line and Hydraulic Grade line

    13

  • Energy Equation for steady flow of any fluid

    14

    � Let’s consider the energy of system (Es) and energy of control volume(Ecv) defined within a stream tube as shown in figure. Therefore,

    � Because the flow is steady, conditions within the control volume does not change so

    � Hence

    in

    CV

    out

    CVCVs EEEE ∆−∆+∆=∆

    in

    CV

    out

    CVs EEE ∆−∆=∆

    0=∆ CVE

    Eq(1)

    Eq(2)

    Figure: Forces/energies in fluid flowing in streamt ube

  • Energy Equation for steady flow of any

    fluid

    15

    � Now, let’s apply the first law of thermodynamics to the fluid system which states ” For steady flow, the external work done on any system plus the thermal energy transferred into or out of the system is equal to the change of energy of system”

    ( )

    ( ) inCVout

    CV

    s

    EEshaftworklowwork

    Eshaftworklowwork

    ∆−∆=++

    ∆=++

    =+

    ferredheat transf

    ferredheat transf

    energy of changeferredheat transdone work External

    � Flow work: When the pressure forces acting on the boundaries move, in present case when p1A1 and p2A2 at the end sections move

    through ∆s1 and ∆s2, external work is done. It is referred to as flow work.

    msAsApp

    mg

    sAp

    sAp

    sApsAp

    ∆=∆=∆

    −∆=

    ∆−∆=∆−∆=

    222111

    2

    2

    1

    1

    222

    2

    2111

    1

    1111111

    workFlow

    workFlow

    ρργγ

    γγ

    γγ

    Q Steady flow

    Eq(3)

    Eq(4)

    Eq(5)

  • Energy Equation for steady flow of any

    fluid

    16

    � Shaft work: Work done by machine, if any, between section 1 and 2

    ( ) ( ) mm

    m

    hmghsA

    thdt

    dsAtime

    weight

    energy

    time

    weight

    ∆=∆=

    ==

    111

    111

    Shaft work

    Shaft work

    γ

    γ

    � Where, hm is the energy added to the flow by the machine per unit weight of flowing fluid. Note: if the machine is pump, which adds energy to the fluid, hm is positive and if the machine is turbine, which remove energy from fluid, hm is -ve

    � HeatTransferred: The heat transferred from an external source

    into the fluid system over time interval ∆t is

    ( ) ( ) HH

    H

    QmgQsA

    tQdt

    dsA

    ∆=∆=

    =

    111

    111

    ferredHeat trans

    ferredHeat trans

    γ

    γ

    � Where, QH is the amount of energy put into the flow by the external heat source per unit weight of flowing fluid. If the heat flow is out of the fluid, the value QH is –ve and vice versa

    Eq(6)

    Eq(7)

  • Energy Equation for steady flow of any

    fluid

    17

    � Change in Energy: For steady flow during time interval ∆t, the weight of fluid entering the control volume at section 1 and leaving at section 2 are both equal to g∆m . Thus the energy (Potential+Kinetic+Internal) carried by g∆m is;

    ( )

    ( )

    ++∆=∆

    ++=∆

    ++

    =∆

    ++∆=∆

    ++=∆

    ++

    =∆

    2

    2

    22

    2

    2

    222222

    2

    22

    222

    1

    2

    11

    1

    2

    111111

    2

    11

    111

    2

    22

    2

    22

    Ig

    VzmgE

    Ig

    VzdsAtI

    g

    Vz

    dt

    dsAE

    Ig

    VzmgE

    Ig

    VzdsAtI

    g

    Vz

    dt

    dsAE

    out

    CV

    out

    CV

    in

    CV

    in

    CV

    α

    αγαγ

    α

    αγαγ

    α is kinetic energy correction factor and ~ 1

    Eq(8)

    Eq(9)

  • Energy Equation for steady flow of any

    fluid

    18

    � Substituting all values from Eqs. (5),(6), (7), (8), & (9) in Eq(4)

    ( ) inCVout

    CV EEshaftworklowwork ∆−∆=++ ferredheat transf

    ( ) ( )

    ++∆−

    ++∆=∆+∆+

    −∆ 1

    2

    112

    2

    22

    2

    2

    1

    1

    22I

    g

    VzmgI

    g

    VzmgQmghmg

    ppmg Hm αα

    γγ

    ++−

    ++=++

    − 1

    2

    112

    2

    22

    2

    2

    1

    1

    22I

    g

    VzI

    g

    VzQh

    ppHm αα

    γγ

    +++=++

    ++− 2

    2

    22

    2

    21

    2

    11

    1

    1

    22I

    g

    Vz

    pQhI

    g

    Vz

    pHm α

    γα

    γ

    This is general form of energy equation, which applies to liquids, gases, vapors and to ideal fluids as well as real fluids with friction, both incompressible and compressible. The only restriction is that its for steady flow.

    Eq(10)

  • Energy Equation for steady flow of

    incompressible fluid

    19

    � For incompressible fluids

    � Substituting in Eq(10), we get

    ( )122

    22

    2

    2

    11

    1

    22II

    g

    Vz

    pQh

    g

    Vz

    pHm −+

    ++=++

    +−

    γγ

    γγγ == 21

    ( ) Hm QIIg

    Vz

    ph

    g

    Vz

    p−−+

    ++=+

    +− 12

    2

    22

    2

    2

    11

    1

    22 γγ

    Lm hg

    Vz

    ph

    g

    Vz

    p+

    ++=+

    +−

    22

    2

    22

    2

    2

    11

    1

    γγ Eq(11)

    ( ) HL QIIh −−= 12Q

    � Where hL=(I2-I1)-QH= head loss. It equal to is gain in internal energy minus any heat added by external source.

    � Hm is head removed/added by machines. It can also be referred to head loss due to pipe fitting, contraction, expansion and bends etc in pipes.

  • Energy Equation for steady flow of

    incompressible fluid

    20

    � In the absence of machine, pipe fitting etc, Eq(11) can be written as

    � When the head loss is caused only by wall or pipe friction, hLbecomes hf, where hf is head loss due to friction

    Lhg

    Vz

    p

    g

    Vz

    p+

    ++=

    ++

    22

    22

    22

    21

    11

    γγEq(12)

  • Power

    21

    � Rate of work done is termed as power

    Power=Energy/time

    Power=(Energy/weight)(weight/time)

    � If H is total head=total energy/weight and γQ is the weight flow ratethen above equation can be written as

    Power=(H)(γQ)= γQH

    In BG:

    Power in (horsepower)=(H)(γQ)/550

    In SI:

    Power in (Kilowatts)=(H)(γQ)/1000

    1 horsepower=550ft.lb/s

  • Reading Assignment

    22

    � Kinetic energy correction factor

    � Limitation of Bernoulli’s Equation

    � Application of hydraulic grade line and energy line

  • NUMERICALS

    23

    � 5.2.1

  • 24

    � 5.2.3

  • 25

    � 5.3.2

  • 26

    � 5.3.4

  • 27

    � 5.3.6

  • 28

    � 5.9.6

  • Momentum and Forces in Fluid Flow

    29

    � We have all seen moving fluids exerting forces. The lift force on an aircraft is exerted by the air moving over the wing. A jet of water from a hose exerts a force on whatever it hits.

    � In fluid mechanics the analysis of motion is performed in the same way as in solid mechanics - by use of Newton’s laws of motion.

    � i.e., F = ma which is used in the analysis of solid mechanics to relate applied force to acceleration.

    � In fluid mechanics it is not clear what mass of moving fluid we should use so we use a different form of the equation.

    ( )dt

    mdma s

    VF ==∑

  • Momentum and Forces in Fluid Flow

    30

    � Newton’s 2nd Law can be written:

    � The Rate of change of momentum of a body is equal to the resultant force acting on the body, and takes place in the direction of the force.

    � The symbols F and V represent vectors and so the change in momentum must be in the same direction as force.

    It is also termed as impulse momentum principle

    ( )dt

    md sVF =∑

    =

    =∑

    mV

    F Sum of all external forces on a body of fluid or system s

    Momentum of fluid body in direction s

    ( )smddt VF =∑

  • Impact of a Jet on a Plane

    31

  • Impact of a Jet on a Plane

    32

  • Thank you

    � Questions….

    � Feel free to contact:

    33

    Unit 4 Fluid Dyanamics.pdf (p.1-43)unit 4 part 2fluiddynamics.pdf (p.44-76)