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FAKULTAS TEKNIK MESIN
UNIVERSITAS SULTAN AGENG TIRTAYASA BANTEN
BAB II
RECIPROCATING COMPRESSOR
OLEH : SANTOSO BUDI
santoso budi,fak teknik mesin UNTIRTA,HP 08129589918 ,
Email [email protected]
SISTEM COMPRESSOR
FILTER
INTERCOOLER
TABEL UDARA- MOISTURE
Gambar 6.7B
CONTOH SOAL :
KANDUNGAN MOISTURE DALAM UDARA
REGULATOR
REGULATOR
TIPE ABSORPTIVE DRYER
TIPE REGENERATIP ADSORPTIVE DRYER
CHECK VALVE
BALL CHECK VALVE
PILOT OPERATED CHECK VALVE
PENGGUNAAN CHECK VALVE
SUTTLE VALVE
RELIEF VALVE
RANGKAIAN PILOT OPERATED VALVE
DAPAT DIGERAKAN DENGAN REMOTE C
PENGOPERASIAN
PILOT –OPERATED VALVE
CONTOH
RELIEF VALVE
CONTOH KOMPRESSOR JENIS PISTON
TUNGGAL
LANJUTAN
ACCUMULATOR
BLADDER ACC DIAPRAGMA ACC DIAPRAGMA ACC
CENTRIFUGAL COMPRESSOR
SINGLE STAGE
HORIZONTAL
MULTI STAGE
VERTICAL
RESISTENSI ALIRAN DAN TEKANAN
PADA KOMPRESOR SENTRIFUGAL DAN AXIAL
AXIAL COMPRESSOR
VANE ROTARY COMPRESSOR
Total Energy Balance
cWm
QHgZ
u ˆ2
2
adiabatic
compression
Note that Ŵc in TEB includes efficiency while Ŵ in
MEB does not include efficiency
12ˆ TTCHW pc
ISO THERMAL COMPRESSOR
POLYTROPIC COMPRESSOR
Isentropic Work of Compression As a first approximation, a compressor without any internal
cooling can be assumed to be adiabatic. If the process is
also assumed to be reversible, it will be isentropic.
.1
1 constpp
Solve for , substitute into MEB, and integrate
Isentropic Work of Compression Upon Integration
This is the isentropic (adiabatic) work of compression.
The quantity p2/p1 is the compression ratio.
11
ˆ
1
1
2
1
10
p
ppW S
Compressor Work Compression is not reversible, however. Deviations from
ideal behavior must be accounted for by introducing an
isentropic compressor efficiency such that the true work
of compression is given by.
ad
Sc
WW
0
ˆˆ
How can ad be found?
12ˆ TTCW pc
Isothermal Compression If sufficient cooling is provided to make the compression
process isothermal, the work of compression is simply:
1
210 lnˆ
p
p
M
RTW T
For a given compression ratio and suction condition, the
work requirement in isothermal compression is less than
that for adiabatic compression. This is one reason that
cooling is useful in compressors.
Polytropic Compression In actuality the S = 0 path assumed in writing the
expression p/ const. is not the true thermodynamic path
followed by gases in most large compressors and the
compression is neither adiabatic not isothermal. A polytropic
path is a better representation for which:
.1
1 constpp
nn
Here n depends on the nature of the gas and details of the
compression process.
Polytropic Compression
11
ˆ
1
1
2
1
1n
n
pp
p
n
npW
where Ŵp is the work for polytropic compression
Again the actual work of compression is larger than the
calculated work and:
p
p
c
WW
ˆˆ
Polytropic Compression The polytropic efficiency p is often the efficiency quoted
by manufacturers. From this efficiency useful relations can
be stated to convert from polytropic to adiabatic results:
To get n the polytropic exponent:
p
pn
1p
n
n
11
or
To get relationships between T or and compression ratio
simply replace with n. n
n
p
p
T
Tge
1
1
2
1
2..
Multistage Compression Consider a two stage compression process p1→p2→p3
with perfect intercooling (temperature reduced to T1 after
each compression)
11
11
ˆ
1
2
31
1
1
210
p
pRT
p
pRTW S
Now find p2 which will minimize work, differentiate wrt p2
312 pppopt
Multistage Compression 2
1
1
3
2
3
1
2
p
p
p
p
p
p
So the compression ratio that minimizes total work is such that each
stage has an identical ratio.
This can be generalized for n stages as:
n
n
p
p
p
p
p
p1
1
1
2
3
1
2
.
1
1 constp
pT
i
ii
When T is not cooled to T1:
i
ii
p
pT 1
Multistage Compression P-H Chart Method Example
Natural Gas (methane)
P = 100 psia
P = 300 psia P = 900 psia
Isentropic Compression
“Real” Compression
HIdeal HActual