Chapter 10 Power and Refrigeration Systems Gaseous …home.sogang.ac.kr/.../menu4/Lists/b8/Attachments/38/Chapter10.pdf · 10.1 Air-standard power cycles Chapter 10. Power and Refrigeration

Fundamentals of Thermodynamics

Chapter 10

Power and Refrigeration Systems

Gaseous Working Fluids

Thermal Engineering Lab. 2

10.1 Air-standard power cycles

Chapter 10. Power and Refrigeration Systems – Gaseous Working Fluids

- Working fluid : Fixed mass of air

- Combustion process : replaced by heat transfer from external

source

- Exhaust & intake process : replaced by heat transfer to the

surrounding

- Internally reversible

- Constant specific heat

Internal Combustion Engine – Otto, Diesel, gas-turbine

External Combustion Engine – Steam, Stirling


10.2 The Brayton cycle


2

2

P const

S const

개의

개의 process를구성

working fluid : gas single phase

1 L

H

Q

Q th



4 1 1 4 1

3 2 2 3 2

/ 11 1 1

/ 1

pL

H p

C T T T T TQ

Q C T T T T T

th

H,avg

H,avg L,avg

3 : T

: T & T

1- 2 - - 4 -1

1- 2 - 3 - 4 -1

1 13 3 32 2 2

4 1 1 1 4 4

3 3 32 4 4

4 1 2 1 2 1

1

1 1

1

2 22 1

,

1 1

11 1 1

/

k k

k k

k

k

th k

k

P P TP P T

P P P T P T

T T TT T T

T T T T T T

T P

T PP P



kPv const

Pv RT

kRTv const

v

1kTv const

k

RTp const

p

1 k kp T const

1 k

kT P const

1 1

2 1 2

1 2 1

k k

k kT P P

T P P



cycle실제

compressor 40 ~ 80% 가 차지

2 1

2 1

3 4

3 4

scomp

turb

s

h h

h h

h h

h h


Ex. 10.1 In an air-standard Brayton cycle, the air enters the compressor at 0.1 Mpa

and 15℃. The pressure leaving the compressor is 1.0 MPa, and the

maximum temperature in the cycle is 1100℃. Determine

1. The pressure and temperature at each point in the cycle.

2. The compressor work, turbine work, and cycle efficiency.



Ex. 10.2 Consider a gas turbine with air entering the compressor under the same

conditions as in Example 10.1 and leaving at a pressure of 1.0 Mpa. The

maximum temperature is 1100℃. Assume a compressor efficiency of

80 %, a turbine efficiency of 85 %, and a pressure drop between the

compressor and turbine of 15 kPa. Determine the compressor work,

turbine work, and cycle efficiency.



10.3 The simple gas-turbine cycle with a regenerator




net t cth

H H

w w w

q q

3H p xq C T T

3 4t pw C T T

x 4 H tIdeal case: T =T q =w

1 1p

H c cth

H t

Cq w w

q w

2 1

p

T T

C

3 4T T1

2 2

1 11 1

1

3 341

32

1 1

1 1

11

k

k

k

k

T PT PT T

T TTP

TP

1

1 1

21 2

1

3 11

2

1

1

1

k

kk

k

k

k

PPT P

T PP

P

1

1 2 2

3 1 3

1 1

k

kT P T

T P T



regenerator efficiency

2

' 2

xreg

x

h h

h h

2

' 2

if .xreg p

x

T TC const

T T


Ex. 10.3 If an ideal regenerator is incorporated into the cycle of Example 10.1,

determine the thermal efficiency of the cycle.



10.4 Gas-turbine power cycle configurations


Ericsson Cycle2 const. T

2 const. P

개의

개의


Ex. 10.4 An air-standard power cycle has the same states given in Example 10.1.

In this cycle, however, the compressor and turbine are both reversible,

isothermal processes. Calculate the compressor work and the turbine

work, and compare the results with those of Example 10.1.





10.5 The air-standard cycle for jet propulsion



Ex. 10.5 Consider an ideal jet propulsion cycle in which air enters the compressor

at 0.1 Mpa and 15℃. The pressure leaving the compressor is 1.0 Mpa,

and the maximum temperature is 1100℃. The air expands in the turbine

to a pressure at which the turbine work is just equal to the compressor

work. On leaving the turbine, the air expands in a nozzle to 0.1 Mpa. The

process is reversible and adiabatic. Determine the velocity of the air

leaving the nozzle.



10.6 The air-standard refrigeration cycle


1 41 4

2 1 3 4 2 1 3 4

PL L

net C E P P

C T Tq q h hCOP

w w w h h h h C T T C T T



/ 1 / 1

3 32 2

1 1 4 4

1 4

3 2 222 1 3 4

11 4 1

1 /

1 1

1 /1

1 /

1

k k k k

k k

p

P TP T

P T P T

T T

T T TTT T T T

TT T T

r




Ex. 10.6


Consider the simple air-standard refrigeration cycle of Fig. 10.12. Air

enters the compressor at 0.1 MPa and -20℃ and leaves at 0.5 MPa. Air

enters the expander at 15℃. Determine

1. The COP for this cycle.

2. The rate at which air must enter the compressor to provide 1 kW of

refrigeration.


10.7 Reciprocating engine power cycles


max min

max min

max min

: 2

:

: /

:

:60 60

crank

displ cyl cyl cyl

v

net net meff

cyl net meff disp

Stroke S R

Displacement V N V V N A S

Compression ratio r V V

Net work per cylinder W mw P V V

RPM RPMPower W N mw P V


10.8 The Otto cycle


2

2

S const

V const

개의


Thermal Engineering Lab.


4 1

th

3 2

1 1vH L L

H H v

mC T TQ Q Q

Q Q mC T T

4 1

1 11 1 1

132 2 2

2

11

1 1 1 1 1

1

k

k

v k

v

TTT T v

rTT T v r

T

kPv const

Pv RT

1 1 1

2 2 2

Pv RT

P v RT

R

1

1 1

kT v R 1

2 2

kT v

11

2 1 4

1 2 3

kk

T v v

T v v

3

4

T

T



tetraethyl lead knocking 방지

옥탄가

8 18 7 16iso - octan C H n - heptan C H과 의질량비로결정



*

1.

2.

3.

4.

5.

v

Deviation

C T

Incomplete Combustion

Work

Heat Loss

Irreversibilities

배기흡기를위한


Ex. 10.7


The compression ratio in an air-standard Otto cycle is 10. At the

beginning of the compression stoke, the pressure is 0.1 MPa and the

temperature is 15℃. The heat transfer to the air per cycle is 1800 kJ/kg air.

Determine

1. The pressure and temperature at the end of each process of the cycle.

2. The thermal efficiency.

3. The mean effective pressure.


10.9 The Diesel cycle


1 L

th

H

Q

Q

4 1

3 2

1v

P

T TC

C T T

1 4 1

2 3 2

( 1)1

( 1)

/

/

T T T

kT T T

Effect

) 1 2 3 4 1i

) 1 2 3 4 1ii Otto

) 1 2 3 4 1iii Otto

1

3 3

2 2

111

1

: cutoff ratio

k

th k

vr k

v T

v T

Diesel Otto 최고온도를제한했을때에는



p

p P

v

v v

T S

v const

Tds dh vdP C dT

T T

S C

Tds du Pdv C dT

T T

S C

P const

선도상에서 등압곡선과등적곡선의기울기


Ex. 10.8


An air-standard diesel cycle has a compression ratio of 20, and the heat

transferred to the working fluid per cycle is 1800 kJ/kg. At the beginning

of the compression process, the pressure is 0.1 MPa and the temperature is

15℃. Determine

1. The pressure and temperature at each point in the cycle.

2. The thermal efficiency.

3. The mean effective pressure.


10.10 The Stirling cycle


2

2

T const

V const

개의



10.11 The Atkinson and Miller cycles


1 1

32 1 4

1 2 3 4

For the compression amd expansion processes(s=const),

,

k k

vT v T

T v T v

Higher expansion ratio than compression ratio



44 1 4 1

1

4 1

3 2

4 1 4 1

3 2 3 2

The heat rejection process gives

: ,

The efficiency of the cycle becomes

1 1

1 1

L

H L L

H H

p

v

vP C T T q h h

v

q q q h h

q q u u

C T T T Tk

C T T T T



1 1 3

4 3

1 42 1 1 4 1 1

1 1

1 1

3 4 1 1

1 1

1

The smaller compression ratio : /

The expansion ratio : /

,

The efficiency of the cycle becomes

1

1

k

kk k

k

CR v v

CR v v

v CRT T CR T T T

v CR

CR CRT T CR T CR T

CR CR

CR

CRk

CR

1

1 11

1

1k k

k

CR CRk

CR CRCR

CR



Cycle in between the Otto cycle and Atkinson cycle


10.12 Combined-cycle power and refrigeration systems






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Chapter 10 Power and Refrigeration Systems Gaseous …home.sogang.ac.kr/.../menu4/Lists/b8/Attachments/38/Chapter10.pdf · 10.1 Air-standard power cycles Chapter 10. Power and Refrigeration