SKKK2043 Chapter 4 Latest

7/27/2019 SKKK2043 Chapter 4 Latest

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Losses in internal flowLosses in internal flow

systemssystems

CHAPTER 4

-- Friction and minorFriction and minorlosses in pipes networklosses in pipes network

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Internal flows through pipes, elbows,

tees, valves, etc., as in this oil refinery,

are found in nearly every industry.


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LAMINAR AND TURBULENT FLOWS

The behavior of

colored fluid

injected into the

flow in laminar

Laminar: Smooth streamlines and highly ordered motion.Turbulent: Velocity fluctuations and highly disordered motion.

Transition: The flow fluctuates between laminar and turbulent

flows.

Most flows encountered in practice are turbulent.

Laminar flow is encountered when highly viscous fluids such

as oils flow in small pipes or narrow passages.

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Laminar and

turbulent flow

regimes of candle

smoke plume.

an tur u ent

flows in a pipe.


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REYNOLDS NUMBER (Re No.)

-Flows with low Re No. appear

slow and smooth and are called

laminar flow.

-Flows with high Re No. appear

fast and rough and are called

.

-Friction losses occur as the fluid

flows along straight lengths of

pipe and tubing.

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REYNOLDS NUMBER (Re No.)

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GENERAL ENERGY EQUATION

2

2

22

1

2

11

22z

g

v

g

Phhhz

g

v

g

PLRA ++=+++

where;

Energy added to the fluid with a mechanical device such

as pump,

Energy removed from the liquid by a mechanical device

such as fluid motor,

Energy losses from the system due to friction (a.k.a

head loss or pressure drop) in pipes or minor losesdue to valves and fittings.


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Head Loss, hL

22

2

22

1

11

22 zg

v

ghhhzg

v

gLRA ++=+++

Total head loss (general)


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DARCYS EQUATION

Based on;

(to be used for laminar and turbulent flows)

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HAGEN-POISEUILLE EQUATION FOR LAMINAR FLOW

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REMEMBER! SOME BOOKS USE DIFFERENT f,

where;

PLEASE SEE CAREFULLY THE MOODYS DIAGRAM

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MOODY DIAGRAM TO FIND THE FRICTION FACTOR, f

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The Moody Chart

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EXPLANATION OF MOODYS DIAGRAM

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In calculations, we shouldmake sure that we use the

actual internal diameter

of the pipe, which may be

different than the nominal

diameter.

At very large Reynoldsnumbers, the friction factor

curves on the Moody chart are

nearly horizontal, and thus the

friction factors are independent

of the Reynolds number.


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MINOR LOSSES

The fluid in a typical piping

system passes through various

fittings, valves, bends,elbows, tees, inlets, exits,expansions, and contractionsin addition to the pipes.

These components interrupt the

smooth flow of the fluid and

cause additional losses

because of the flow separation

and mixing they induce.

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n a typ ca system w t ong

pipes, these losses are minorcompared to the total head loss

in the pipes (the major losses)and are called minor losses.

Minor losses are usually

expressed in terms of the loss

coefficientK

L.

For a constant-diameter section of a pipe with a minor loss

component, the loss coefficient of the component (such as

the gate valve shown) is determined by measuring the

additional pressure loss it causes and dividing it by the

dynamic pressure in the pipe.


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MINOR LOSSES

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1) SUDDEN ENLARGEMENT

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2) EXIT LOSS

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3) GRADUAL ENLARGEMENT

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4) SUDDEN CONTRACTION

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5) GRADUAL CONTRACTION

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6) ENTRANCE LOSS

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The head loss at the inlet of a pipe is

almost negligible for well-rounded inlets

(KL

= 0.03 for r/D > 0.2) but increases to

about 0.50 for sharp-edged inlets.


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B) MINOR LOSSES DUE TO VALVES AND FITTINGS

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SKKK2043 Chapter 4 Latest