2.Materi Bab II Reciprocating & Sistem Compressor

FAKULTAS TEKNIK MESIN

UNIVERSITAS SULTAN AGENG TIRTAYASA BANTEN

BAB II

RECIPROCATING COMPRESSOR

OLEH : SANTOSO BUDI

santoso budi,fak teknik mesin UNTIRTA,HP 08129589918 ,

Email santosobud@yahoo.com

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