ventilasi - week 7

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VENTILASI TAMBANG

21 Oktober 2014 – Hendra Harisman, S.T., M.Eng.S

JTP 505 – 2 SKS



FRICTION, DISCONTINUITY & OBSTRUC

Flow separation occurring at discontinuities leads toconcept of:

• Shock loss

• Shock loss factor

Shock Loss due to Circuit Discontinuities




Shock losses occur due to:• flow separation

• Impact due to changes

in direction of airflow





The shock loss is in addition to surface frictional loss.

The static pressure loss due to flow separation depe

• Air velocity

• Relative magnitude of the change in velocity

• Degree to which flow separation occurs





The static pressure loss due to shock (Pa) is gdetermined asa function of velocity pressure:


ρ = density(kg/m3)

X = shock loss factor

V = Velocity(m/s)

V




•

The shock loss factors have been determineddiscontinuities encountered, by:

• empirical method

• Scale models

• Computational fluid dynamic program





Shock Loss due to CircuitDiscontinuities

• In practice, shock loss factors are

obtain from design charts specific

to particular component geometry.





For example:

• A 90 degree bend in rectangular

duct hasan X factor=?

1.5




Example:

• 8 m3/s udara mengalir dalam pipa 610 mm

yang melengkung 45o. Massa jenis udara

adalah 1.16 kg/m3, dan static pressure di

titik A adalah -1250 Pa gauge.

• Berapakah velocity pressure, static pressure

dan total pressure di titik A dan B?





Pressure losses due to obstructions are determined b• Shape of obstruction

• Amount of that obstacles fill the airway

• Velocity pressure impacting on the obstruction

Shock Loss due to Airway Obstruction




Airway obstructions comprise:• Longitudinal objects, mis: pipa

• Transverse objects, mis: support/cribs






ρ = density(kg/m3)

Cd = drag coefficient

V = Velocity(m/s)

Ao = Frontal area (m2)

A = Area of airway which it is placed (m2)

Cf= Coefficient of fill

FRICTION DISCONTINUITY & OBSTRUC





ρ = density(kg/m3)

Cd = drag coefficient

Q = Quantity(m3/s)

Cf = Coefficient of fill

A = Area of airway which it is placed (m2)

V = Q/A






The base case drag coefficient must be corrected for aspratio Cd’




FRICTION, DISCONTINUITY & OBSTRUCShock Loss due to Airway Obstruction





Example: Terowongan di sebuah tambang

batubara sepanjang 2.5 km akan di-support dengan pipa concrete. Pipatsb mempunyai 800 mm diameterberjarak 4 m satu sama lain,sepanjang 500 m di dekat ujungterowongan. Terowongan tersebut

mempunyai tinggi 2.5 m dan lebar 5.4m. Quantity udara di terowongan tsb45 m3/s, dan density udaranyaadalah 1.2 kg/m3.Hitung pressure lost akibatpemasangan pipa2 support tsb.

ventilasi - week 7

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