PROBLEM
PROBLEM
State the pipe selection for
Shaft Seal
Brake and Jake Device
Governor
Head Cover
Relationship of
Surface Area (pipe dia.) vs Air Flow Rate
Surface Area (pipe dia.) vs Velocity of Air
DATA
PnID of Pressure Air by BTU
A. Variable of Each Service
ServiceP (bar)Flow rate (ltr/min)DINSch
Shaft Seal 7421520
Governor6.325202080
Brake 'n Jack775.61520
Head Cover
B. Description of Services
DESIGN CALCULATION
COMPRESSED AIR CONSUMPTION, AIR RECEIVER & AIR
COMPRESSOR
1Air consumption when governor is working maximum (per unit)
>Piston working volume of one servomotor:20L
>Piston working volume of two servomotors:40L
>Oil working pressure:63barG
>Air working pressure equal to oil pressure:63barG
>Air consumption :2520NL/second(normal litre)
2Air receiver for generator brake (per unit)
2.1Brake
>Piston volume of each brake:1.8L
>Number of brake pad (per unit):6
>Brake working pressure7barG
>Air required for once brake (per unit):75.6NL/second
2.2Seal Belt
>Air consumption for service seal belt:6L/second
>Seal belt working pressure:7barG(4~8 barG)
>Air required for once service seal belt (per
unit):42NL/second
>Total air consumption for once brake and seal belt (per
unit):117.6NL/second
>Air receiver pressure before brake and seal are
working:7.5barG(assumed)
>Air receiver pressure during brake and seal are
working:7barG
>Air receiver volume required :235.2L
>Air receiver volume designed:250L
3Main Air Receiver (MAR)
Each MAR supplies compressed air to 4 units of Turbine.
>Total air consumption (for4 units) :10550.4NL/time
>MAR pressure before governor, brake, & seal
work:75barG(assumed)
>MAR pressure during governor, brake, & seal are
working:68barG
>Air receiver volume required :1507.2L
Safety factor for Air receiver volume design:3
>Air receiver volume required :4521.6L
Air receiver design for prepare 4 turbine Consumption5000L
4Total time to supply air pressure consumption :7.5Min
THEORY
Compressible Flow
.. ( 1 )
Property Relation for Isentropic Flow of Ideal GasesNext we
develop relations between the static properties and stagnation
properties of an ideal gas in terms of the specific heat ratio k
and the Mach Number Ma. We assume the flow is isentropic and the
gas has constant specific heat.
.. ( 2 )
.. ( 3 )
By setting Ma=1
.. ( 4 )
.. ( 5 )
.. ( 6 )
.. ( 7 )
General Equation-
.. ( 8 )-
.. ( 9 )-
.. ( 10 )-
.. ( 11 ) Choked Flow. Means decrease of surface area, when
critical pressure ratio the mass flow rate reaches its maximum
value and the flow is said to be choked. By using the equations for
quasi-one-dimensional flow and the isentropic flow condition, we
can derive a relation for the area ratio that is needed to
accelerate or decelerate the gas to sonic conditions. Under
isentropic conditions,
.. ( 12 )
.. ( 13 )
ASSUMPTION
The flow through is under :
Isentropic condition on a choked flow
Adiabatic condition on a same size pipe
Constant temperature along the pipe system
No heat input
No friction, so that pressure kept constant except required.
SOLUTION
1. Main Air Receiver (MAR) Small Vessel Main Pipe of MAR to
parallel pipeline.
In case to determine the surface area of narrow area, it is
represented whether diameter of pipe from the system vessel is DN40
Sch80 (d=41.2 mm). It means equal to 0.0412 m. It also defined the
Mach Number which describe the air velocity. Stagnation condition
on vessel kept constant by compressor, pressure (Po) and
temperature (To). By using the table A.13 of Fluid Mechanics
(Author: Cengel). . By interpolate it depend on value above, it is
determined the derived value of . As derive diameter is decreased
into A*= 6.75E-4. So that it is known the diameter of smaller part
is 29.34 mm. The pressure flow in the piping system is 0.75 Mpa
maximum, so that the pipe is DN32 Sch80 (Inside diameter = 32.9
mm).
Parallel pipeline
The pipe from the small vessel flow through to the both service
unit, seal belt and brake device. By using the same diameter of
pipe, and the required air flow rate, it is able to determined the
velocity of each service by using the equation ( 8 ).
Unit Seal Belt and Brake Device each unit
2. Small Vessel Brake and Shaft Seal Device Unit
Main Pipe of smaller vessel to parallel pipeline.
In case to determine the surface area of narrow area, it is
represented whether diameter of pipe from the system vessel is DN20
Sch40 (d=19.4 mm). It means equal to 0.0194 m. It also defined the
Mach Number which describe the air velocity. Stagnation condition
on vessel kept constant by compressor, pressure (Po) and
temperature (To). By using the table A.13 of Fluid Mechanics
(Author: Cengel). . By interpolate it depend on value above, it is
determined the derived value of . As derive diameter is decreased
into A*= 1.498E-4. So that it is known the diameter of smaller part
is 13.8 mm. The pressure flow in the piping system is 0.75 Mpa
maximum, so that the pipe is DN15 Sch40 (Inside diameter = 16.1
mm).
Parallel pipeline
The pipe from the small vessel flow through to the both service
unit, seal belt and brake device. By using the same diameter of
pipe, and the required air flow rate, it is able to determined the
velocity of each service by using the equation ( 8 ).
Unit Seal Belt
Unit Brake Device
3. Main Air Receiver (MAR) Governor Unit
4. Main Air Receiver (MAR) Head Cover Unit
EMBED Equation.3
Graphic 3. Variation value of velocity to inside diameter of
pipe from small vessel to parallel pipeline.
Graphic 4. Variation value of velocity to inside diameter of
pipe to seal belt unit
Graphic 5. Variation value of velocity to inside diameter of
pipe to brake device unit
Graphic 1. Variation value of velocity to inside diameter of
pipe from Main Air Receiver (MAR) to parallel pipeline.
Graphic 2. Variation value of velocity to inside diameter of
pipe from Main Air Receiver (MAR) to small vessel.
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