Kuliah 2 - Basic Principles of Airflow

7/25/2019 Kuliah 2 - Basic Principles of Airflow

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Basic Principles of Airflow

Rini Novrianti Sutardjo Tui


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Introduction on Basic Fluids Mechanics

Liquidtakes shapeof vessel but does notnecessarily fill it.

FluidsFree to move about

with respect to each other

Gastakes shape of

vessel and fills it.


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Basic Principles

Conservation of EnergyWithin a system, energy is neither created nor destroyed but

may be converted from one form to another.

Newtons 2ndLawThe acceleration aof an object is proportional to the forceFacting on it and inversely proportional to its mass m.


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Pressure

Definition

Fluid Pressure isthe equalandopposite forceapplied by thevessel as themoleculerebounds fromthe boundary.

Variationsanddifferences inpressurebetweentwo points areimportant in mineventilationsurveys.

Here absolutepressure is notusually considered,rather thegaugepressure is used.

Absolute pressure= atmosphericpressure + gaugepressure

Importance Types of Pressure


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Pressure Measurement Mercury Column Barometer

The height of the columnin the sealed tube,against a vacuum, is equal to the pressurepushing on that column


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Pressure Measurement Aneroid Barometer


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Pressure Measurement U-Tube Manometer


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Pressure Measurement Diaphragm Type Gauge

Directly read pressure, reactquickly to temperature, donot require precise leveling,and are available in a widevariety of ranges and scales

Require routine calibration.Usually on an annual basis, orprior to a major survey.


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Bernoullis Equation

Bernoullis Equation is useful to define different types of energy contained in

a given mass of fluids.

vis the fluid flow speed at a certain point in a streamline

zis the height of the point over a reference planegis the gravitypis the pressure at the pointis the density of the fluid

02

22

21

21

21

vvgzz

pp


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Bernoullis Equation

lHzgvpz

gvp

2

2

22

1

2

11

22

Based on the principle of conservation of energy

Total Energy1= Total Energy2+ Energy Loss

Headstatic

HeadlossHeadvelocity

Headpotential


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Mine Head

Mine Static Head(Mine Hs)

Energy which is used toovercome all head loss ofthe flow. It includes all headloss that happens betweeninput and output points ofthe system.

Mine VelocityHead (Mine Hv)

Function of the weightofthe air contents andvelocityof the air flow.

Mine head is difference of pressurewhich isneeded in order to provide certain amount of air

into the mine


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Principal of Airflow

Flow of fluids happens since there is different pressure occurredbetween two points in a system. Energy given to have steady flow, is used to

emerge the difference of pressure and to overcome the head loss.

FrictionLoss illustratesthe head loss inlinear flow through

channel withconstant diameter

Shock Loss isthe loss resultedfrom change offlow or channels

diameter


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Friction Loss

Dimensionof the

opening

AirflowVelocity Coarseness

of theopening

Configuration of

theopening

Characteristics of theopening

Friction Loss

g

V

D

LfHl

2

.

2

3

2

A

KPLQHf


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Shock Loss

Shock lossoccurs as a result of changein direction of the flow, or in cross-section of the channel. It is an addition to friction loss and is about 10% to

30% of head loss.

Direct CalculationDerived from velocity head,

Equivalent Length MethodEvery loss is considered as an equivalent length of a straightairflow channel.

vx XHH

gK

XwRL h

e 2


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Friction Factor, K

Type ofAirway

Irregularities of

Surfaces,Areas, andAligment

Values of K x 10-10

Straight Sinuous or Curved

Clean(basic

value)

SlightlyObstruc

ted

Moderately

Obstructed

Slightly Moderately High Degree

CleanSlightly

Obstructed

Moderately

Obstructed

CleanSlightly

Obstructed

Moderately

Obstructed

CleanSlightlyObstruc

ted

Moderately

Obstructed

Smoothlined

MinimumAverageMaximum

101520

152025

253035

202530

253035

354045

253035

303540

404550

354045

404550

505560

Sedimentary rock


305570

356075

457085

406580

457085

558095

457085

507595

6085

100

558095

6085

100

7095110

Timbered

(5ftcenters)


8095105

85100110

95110120

90105115

95110120

105120130

95110120

100115125

110125135

105120130

110125135

120135145

Igneousrock MinimumAverageMaximum

90145195

95150200

105160210

100155205

105160210

115165220

105160210

110165215

120175225

115170220

120175225

130195235

K is based on standard air density (w = 0.075 lb/ft3). To convert K to

SI units (kg/m3

), multiple table values by 1.855 x 106

.

Source: McElroy (1935)


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Formula to Determine Shock Loss Factor, X


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Kuliah 2 - Basic Principles of Airflow

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